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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
21

The effect of garlic extracts on the control of postharvest pathogens and postharvest decay of apples

Daniel, Chanel Karousha 04 1900 (has links)
Thesis (MSc)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Apples are an important export commodity for the South African market, and postharvest losses that occur as a result of decay due to infection with pathogenic fungi such as Botrytis cinerea Pers., Penicillium expansum (Link) Thom. and Neofabraea alba (E.J. Guthrie) are of major concern for all parties concerned with fruit production and distribution. Decay control of these fungi is primarily managed through the use of synthetic fungicides; however, pathogen development of resistance to these fungicides and recent worldwide concern over healthier living and a greener environment has called for the discriminate use of synthetic chemicals. This has opened up an avenue for the development of safer and more environmentally friendly alternatives to control postharvest decays. The use of plant extracts and essential oils are favoured as natural sources of antimicrobials whilst still being safe for human consumption and having no negative impact on the environment. Allium sativum (garlic) is one such plant species that is well documented for its value in improving human health and is readily available for consumption not just as a flavour component of food but also to be taken as a daily herbal diet supplement. Given the antimicrobial effectiveness of garlic against human pathogens and ailments, its value as an antifungal agent against postharvest pathogens causing grey mould, blue mould and bull’s eye rot of apples was investigated in vitro and in vivo within this study. Furthermore, an attempt was made to elucidate the chemical components of garlic extracts by gas chromatography-mass spectrometry (GC-MS). All experiments in this study were carried out with garlic extracts prepared from fresh garlic bulbs. For the in vitro experiments, two extract preparations of garlic, one containing ethanol (Extract 1) and one where ethanol had been removed by evaporation (Extract 2), was tested for antifungal action within an amended media experimental design. Both extract preparations were each subjected to two dilution series (0-80% garlic extract) with water and ethanol as diluents. Both extract preparations were successful at retarding pathogen mycelial growth and spore germination; however, concentrations of Extract 2 (ethanol evaporated) and diluted with distilled water provided markedly better inhibition of B. cinerea and P. expansum than the ethanolic dilutions of extract 2. Both extract preparations yielded similar inhibitory results when tested against N. alba. Due to the results achieved in the amended media experiments, the use of a crude garlic extract without ethanol and diluted in water was considered to be the best option for further tests throughout the remainder of the study. In vitro volatile effects of crude garlic extracts at concentrations between 0 and 40% garlic extract were subsequently tested. Garlic volatiles were effective in inhibiting pathogen mycelial growth and spore germination of all three pathogens, at lower concentrations compared to the amended media experiments. In vitro volatile exposure with garlic extracts was more effective at inhibiting N. alba than direct application of the extracts. Curative and protective application of garlic extracts and clove oil for increased fungal inhibition through synergism was tested by direct and volatile exposure to the pathogens in vivo on three economically important apple cultivars; ‘Granny Smith’, ‘Golden Delicious’, and ‘Pink Lady’. Direct exposure of artificially wounded and inoculated fruit to the garlic extract and clove oil revealed that garlic extracts applied curatively but not protectively effectively controlled decay caused by B. cinerea and P. expansum on all apple cultivars. Both curative and protective applications were ineffective in controlling N. alba. In vivo volatile exposure to the garlic extracts and clove oil did not inhibit decay on any of the cultivars and was not effective against any of the three pathogens investigated. A full chemical profile analysis was done by GC-MS analysis of garlic extract samples. The compounds diallyl disulphide, allyl methyl trisulphide, allyl methyl disulphide and dimethyl trisulphide were detected in relatively high amounts. This result suggests that the abundance of sulphur and sulphur related compounds detected may be responsible for the antifungal action noted in the experimental studies. In conclusion, garlic was shown to have antifungal activity against B. cinerea, P. expansum and N. alba. The pathogens used in this study were not compared with each other, but undoubtedly each pathogens reacts differently to exposure to the garlic extracts. It would therefore be advisable to investigate the effects of the extracts on each of the pathogens in a more in-depth study. More investigations into the application of the garlic extracts is required before it may be recommended for use; however, results for the use of garlic extracts against these postharvest pathogens and the postharvest decay they cause are promising. / AFRIKAANSE OPSOMMING: Appels is ‘n belangrike uitvoerproduk vir die Suid-Afrikaanse vrugtebedryf, maar noemenswaardige na-oes verliese word weens bederf deur patogeniese swamme soos Botrytis cinerea Pers., Penicillium expansum (Link) Thom. en Neofabraea alba (E.J. Guthrie) ervaar. Dit raak alle partye betrokke met die produksie en verspreiding van hierdie vrugsoort. Hierdie swamme word hoofsaaklik met behulp van kunsmatige swamdoders beheer, alhoewel weerstand-ontwikkeling en wêreldwye bewusmaking van ‘n gesonder leefstyl en omgewing die gebruik van kunsmatige middels streng aanspreek en die ontwikkeling van veiliger en meer omgewingsvriendelike alternatiewe middels verlang. Plant-ekstrakte en essensiële olies kan dien as sulke middels en is natuurlike bronne van anti-mikrobiese aktiwiteit, is veilig vir menslike verbruik en het ook geen negatiewe invloed op die omgewing nie. Allium sativum (knoffel) is so ‘n plantspesie wat as alternatiewe middel gebruik kan word. Dit is bekend vir sy waarde in die verbetering van menslike gesondheid, is maklik bekombaar en word nie net as ‘n geurmiddel vir voedsel gebruik nie, maar ook as ‘n daaglikse krui-aanvulling. Gegewe die anti-mikrobiese doeltreffendheid van knoffel teenoor menslike patogene en kwale, is die werking (in vitro en in vivo) teen na-oes patogene wat grys skimmel, blou skimmel en teikenvrot in appels veroorsaak, in hierdie studie ondersoek. Bepaling van die chemiese samestelling van die knoffel-ekstrak is ook met behulp van gaschromatografie massa spektrometrie (GK-MS) onderneem.Vars knoffelbolle is vir elke eksperiment in hierdie studie gebruik met die voorbereiding van die knoffel-ekstrak. Vir die in vitro eksperiment is twee knoffel-ekstrakte voorberei, naamlik: ‘n ekstrak wat etanol bevat (Ekstrak 1) en een waarvan die etanol verwyder is met verdamping (Ekstrak 2). Die ekstrakte is getoets vir werking teen fungi in kultuur-medium.. Albei ekstrakte is verdun tot twee konsentrasie reekse (0-80%) met water en etanol as verdunningsmiddels. Albei ekstrakte het suksesvolle werking getoon teenoor die patogene ten opsigte van vertraging van miseliumgroei en spoor-ontkieming, alhoewel konsentrasies van Ekstrak 2, verdun met gesuiwerede water, patogene B. cinerea en P. expansum beter onderdruk het as Ekstrak 2 verdunnings met etanol.. Beide ekstrakte en hul afsonderlike verdunnings met etanol en water het soortgelyke resultate gelewer met onderdrukking van N. alba. Volgens resultate wat verkry is van die kultuur-medium eksperimente, is Ekstrak 2 verdun met gesuiwerde water beskou as die geskikste vir verdere toetse in hierdie studie. Die vlugtige effek van Ekstrak 2 is in vitro getoets by konsentrasies tussen 0 tot 40%. Die vlugtige stowwe van knoffel het al drie patogene se groei en spoor-ontkieming effektief onderdrukby laer konsentrasies as wat gebruik is in die kultuur-medium eksperiment. Dus is in vitro blootstelling van N. alba aan die vlugtige stowwe meer effektief as direkte toediening van die ekstrakte. Die voorkomende en beskermende effek van die knoffel-ekstrak, asook naeltjie-olie, is in vivo ondersoek om te bepaal of die stowwe saam sterker onderdrukking van die patogene kon bewerkstellig. Direkte en vlugtige blootstelling is op drie ekonomies-belangrike appel-kultivars getoets, naamlik: ‘Granny Smith’, ‘Golden Delicious’ en ‘Pink Lady’. Direkte blootstelling met die knoffel-ekstrak en naeltjie-olie aan gewonde en ge-inokuleerde vrugte het aangedui dat B. cinerea- en P. Expansum-bederf net beheer kon word indien knoffel voorkomend toegedien is vir al die ondersoekte appel-variëteite. Voorkomende en beskermende toediening was onsuksesvolle om N. alba te beheer. In vivo blootstelling van die drie patogene aan die knoffel-ekstrak en naeltjie-olie se vlugtige stowwe kon nie enige van die patogene effektief onderdruk nie en was onsuksesvol in bederf-beheer. ‘n Volledige chemiese profiel is saamgestel deur GK-MS ontleding van die knoffelekstrakte. Hoë vlakke van verbindings dialliel disulfied, alliel-metiel-tri-sulfied, alliel-metieldisulfied en dimetiel-trisulfied is bespeur. Die aantal vrye sulfied en sulfied-verwante verbindings in die ekstrak kan moontlik ‘n verduideliking bied vir die anti-swam werking waargeneem gedurende hierdie studie. Ten slotte: knoffel toon ‘n anti-swam werking teenoor B. cinerea, P. expansum en N. alba. Die patogene in hierdie studie is nie met mekaar vergelyk nie, omdat elkeen uniek en uiteenlopend op knoffel reageer het. Alhoewel die huidige studie alreeds belowende resultate gelewer het, moet die ekstrak se effek op elke patogeen onderskeidelik nog in diepte ondersoek word, asook die wyse van die toediening in die na-oes praktyk voordat hierdie middel aanbeveel kan word vir gebruik.
22

Characterisation of Cylindrocarpon spp. associated with black foot disease of grapevine

Halleen, Francois 12 1900 (has links)
Dissertation (PhD (Agric))--University of Stellenbosch, 2005. / ENGLISH ABSTRACT: During the past few years a drastic reduction has been noted in the survival rate of grafted grapevines in nurseries, as well as in young vineyards in the Western Cape Province of South Africa. Circumstantial evidence suggested that Cylindrocarpon spp., which cause black foot disease of grapevine, were associated with this decline. Black foot disease of grapevine is a relatively new, and as yet poorly known disease affecting vines in various countries where grapevines are cultivated. Primary aims of this research have been (1) to conduct nursery surveys in order to determine which fungi are involved in the decline phenomenon, with special reference to the involvement of Cylindrocarpon spp., (2) to identify and characterise the organisms believed to be the causal organisms of black foot disease, and (3) the development of control and/or management strategies to prevent or eradicate Cylindrocarpon infections. Nursery grapevines were sampled at different stages from three commercial nurseries in the Wellington area of the Western Cape Province and were investigated during the 19992000 season by means of destructive sampling. The first samples were taken in September from callused cuttings prior to planting in nurseries. After planting, asymptomatic rooted cuttings were selected from nurseries after 3, 6 and 9 months. Isolation studies clearly demonstrated that different “Cylindrocarpon spp.” infected cuttings from nursery soils. These species rarely occurred in rootstock propagation material prior to planting. At the time of planting, the susceptible basal ends (especially the pith area) of most of the nursery cuttings are partly or even fully exposed. Callus roots also break during the planting process, resulting in small wounds susceptible to infection by soilborne pathogens. The isolation studies revealed that the first infections occurred in the roots, followed by infections of the rootstocks. These infections increased progressively during the course of the growing season. Substantial variation in cultural and morphological characters was observed among the Cylindrocarpon isolates obtained from the nursery survey, as well as from isolations that were made from diseased grapevines. Morphological and phylogenetic studies were conducted to identify these “Cylindrocarpon spp.” and to establish their association with black foot disease. Sequences of the partial nuclear large subunit ribosomal DNA (LSU rDNA), internal transcribed spacers 1 and 2 of the rDNA including the 5.8S rDNA gene (ITS), and partial β-tubulin gene introns and exons were used for phylogenetic inference. Phylogenetic analyses confirmed the diversity observed among the isolates and four Cylindrocarpon-like species were identified. One of these species was initially identified as Cylindrocarpon destructans. However, further research revealed C. destructans to represent a species complex. Grapevine isolates of “C. destructans” proved to be identical to the ex-type strain of Cylindrocarpon liriodendri, which also produced a teleomorph, Neonectria liriodendri in culture. A second species was newly described in this study as Cylindrocarpon macrodidymum (Neonectria macrodidyma). The two remaining Cylindrocarpon-like species were placed in a new genus, Campylocarpon. The two species were named Campylocarpon fasciculare and Campylocarpon pseudofasciculare. Pathogenicity studies confirmed that all four species were able to reduce root and shoot mass significantly. Knowledge obtained pertaining to the disease cycle of black foot disease suggest that suitable management strategies should focus on prevention of primary infection in nurseries. However, at present, no fungicides are registered for control of this disease in South African vineyards or nurseries. Thirteen fungicides were screened in vitro for mycelial inhibition of these pathogens. Prochloraz manganese chloride, benomyl, flusilazole and imazalil were the most effective fungicides tested, and were subsequently included in semi-commercial field trials. Basal ends of grafted cuttings were dipped (1 min) in various chemical and biological treatments prior to planting in open-rooted nurseries. Black foot pathogens were not isolated from grafted cuttings prior to planting in nurseries. Additional treatments involved soil amendments with Trichoderma formulations and hot water treatment (50°C for 30 min) of dormant nursery grapevines. Field trials were evaluated after a growing season of eight months. The incidence of black foot pathogens was not significantly and/or consistently reduced by the majority of chemical or biological treatments. However, these pathogens were not isolated from uprooted plants that were subjected to hot water treatment. It is therefore recommended that hot water treatment of dormant nursery plants be included in an integrated strategy for the proactive management of black foot disease in grapevine nurseries. / AFRIKAANSE OPSOMMING: Gedurende die afgelope paar jaar is ‘n drastiese afname waargeneem in die sukses van geënte wingerdplante in kwekerye, sowel as jong wingerde van die Wes-Kaap. Omstandigheidsgetuienis dui daarop dat Cylindrocarpon spp., wat die wingerdsiekte swartvoet veroorsaak, geassosieer word met hierdie agteruitgang. Swartvoet is ‘n relatiewe nuwe siekte waarvan daar baie min inligting bekend is, alhoewel dit voorkom in verskeie lande waar wingerd verbou word. Die primêre doel van navorsing was (1) om opnames in wingerdkwekerye uit voer om te bepaal watter swamme betrokke is by die verskynsel van agteruitgang, met spesiale verwysing na die betrokkenheid van Cylindrocarpon spp., (2) om die organismes te identifiseer en te karakteriseer wat daarvan verdink word dat hulle die siekte swartvoet veroorsaak, en (3) om beheer en/of bestuurspraktyke te ontwikkel om Cylindrocarpon infeksies te voorkom of uit te wis. Kwekeryplantjies in drie kommersiële kwekerye in die Wellington omgewing van die Wes-Kaap is gedurende verskillende tye gedurende die groeiseisoen gemonitor. Die opnames het plaasgevind gedurende die 19992000 seisoen deur middel van destruktiewe monsterneming. Die eerste monsters is geneem in September nadat die stokkies geënt en gekallus is en voordat dit in die kwekery geplant is. Na plant is asimptomatiese, gewortelde plante vanuit die kwekerye na 3, 6 en 9 maande uitgehaal. Isolasiestudies dui duidelik daarop dat verskillende “Cylindrocarpon spp.” plante vanuit die kwekerygrond geïnfekteer het. Hierdie spesies het selde voorgekom in onderstok-voortplantingsmateriaal voor plant. Tydens plant is die vatbare basale gedeelte, veral die pit, van die meeste geënte stokkies gedeeltelik of selfs volledig blootgestel. Kalluswortels breek ook tydens plant wat wonde laat vir infeksie deur grondgedraagde siektes. Die isolasiestudies dui ook daarop dat die eerste infeksies in die wortels plaasgevind het, gevolg deur infeksies van die onderstokke. Hierdie infeksies het toenemend voorgekom gedurende die verloop van die groeiseisoen. Substansiële variasie in kultuur- en morfologiese eienskappe is waargeneem in die Cylindrocarpon isolate wat tydens die kwekeryopnames versamel is, sowel as van isolasies wat gemaak is uit siek plante. Morfologiese en filogenetiese studies is uitgevoer om hierdie “Cylindrocarpon spp.” te identifiseer en hul betrokkenheid by die siekte swartvoet uit te klaar. Gedeeltelike DNS volgordes van die groot ribosomale subeenheid (“LSU rDNA”), interne getranskribeerde spasiëerderarea (“ITS1, “ITS2”), insluitend die 5.8S rRNS geen, en gedeeltelike β-tubilien geen introns and eksons is gebruik vir filogenetiese analise. Filogenetiese analises het die diversiteit wat waargeneem is tussen die verskillende isolate bevestig deurdat vier Cylindrocarpon-agtige spesies geïdentifiseer is. Een van hierdie spesies is aanvanklik geïdentifiseer as Cylindrocarpon destructans. Verdere navorsing het egter daarop gedui dat C. destructans ‘n spesie-kompleks verteenwoordig. “C. destructans” afkomstig van wingerd blyk identies te wees aan die ex-tipe isolaat van Cylindrocarpon liriodendri, wat ook ’n teleomorf, Neonectria liriodendri in kultuur vorm. ’n Tweede spesie is nuut beskryf in hierdie studie as Cylindrocarpon macrodidymum (Neonectria macrodidyma). Die twee oorblywende Cylindrocarpon-agtige spesies is geplaas in ‘n nuwe genus, Campylocarpon. Die twee spesies staan bekend as Campylocarpon fasciculare en Campylocarpon pseudofasciculare. Patogenisiteitstudies het bevestig dat al vier spesies die vermoë het om wortel- en lootmassa van wingerdplant drasties te verlaag. Kennis wat opgedoen is rakende die lewensiklus van swartvoet dui daarop dat bestuurspraktyke daarop moet fokus om primêre infeksies in wingerdkwekerye te voorkom. Op die oomblik is daar egter geen fungisiedes geregistreer vir die beheer van die siekte in Suid- Afrikaanse wingerde of kwekerye nie. Dertien fungisiedes is in vitro geëvalueer om te bepaal of dit miseliumgroei van hierdie swamme kan inhibeer. Prochloraz mangaan chloried, benomyl, flusilasool en imazalil was die effektiefste fungisiedes wat ondersoek is, en is gevolglik ingesluit in semi-kommersiële veldproewe. Die basale gedeelte van geënte stokkies is gedoop (1 min) in verskeie chemies en biologiese behandelings voordat dit geplant is in die kwekerye. Patogene wat geassosieer word met swartvoet is nie vanuit geënte stokkies geïsoleer voordat dit in die kwekerye geplant is nie. Addisionele behandelings het bestaan uit grondtoevoegings met Trichoderma formulasies, sowel as warmwaterbehandeling (50°C vir 30 min) van dormante kwekeryplante. Die veldproewe is geëvalueer na ‘n groeiseisoen van 8 maande. Die voorkoms van swartvoet patogene is nie betekenisvol/konstant verlaag deur die meeste chemies en biologiese behandelings nie. Hierdie patogene is egter nie vanuit plante geïsoleer wat na uithaal aan warmwaterbehandeling blootgestel is nie. Dit word dus aanbeveel dat warmwaterbehandeling van dormante kwekeryplante deel word van ‘n geïntegreerde strategie vir die pro-aktiewe beheer van swartvoet in wingerdkwekerye.
23

Optimisation of fungicide spray coverage on grapevine and the incidence of Botrytis cinerea

Brink, Johannes Cornelius (Jan-Cor) 03 1900 (has links)
Thesis (PhD(Agric))--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Despite adherence to fungicide spray schedules and label recommendations, table and wine grape producers invariably suffer crop losses when environmental conditions are conducive to fruit and foliar pathogens. Registered fungicides are effective and poor control is often attributed to: 1) improper spray timing, 2) reduced sensitivity to fungicides in the pathogen populations, and 3) poor spray deposition. Spray timing, management of fungicide resistance and the epidemiology of Botrytis cinerea have been thoroughly researched under South African conditions on grape crops. However, limited research regarding spray deposition exists in South Africa, probably due to a lack of proper spray deposition assessment protocols. To determine minimum spray deposition quantity and quality levels needed for effective B. cinerea control, bunches and leaves of table (Waltham Cross) and wine grapes (Chenin blanc) were sprayed at various stages using different volumes with a precision spray gun. A deposition assessment protocol using fluorometry, photomicrography and digital image analyses was improved. Deposition values correlated favourably with Botrytis infection. Increasing spray volume increased spray deposition; however, at a certain point, deposition quality remained constant and B. cinerea infections did not decrease significantly with increasing spray volume, indicating the importance of both spray deposition quantity and quality. Fluorescent pigment area that effected 75% control of B. cinerea infection (FPC75 values) was calculated for leaves, pedicels and receptacles at different growth stages. The FPC75 values obtained in this study can be used as benchmarks to evaluate future spray application. In order to study the optimisation of spray deposition with existing application technology (air blast and air shear sprayers) in commercial vineyards, spray deposition quantity and quality values were assessed from leaves and structural bunch parts of wine (Chenin blanc) and table grapes (Waltham Cross) and compared with FPC75 values. Spray trials were conducted at different growth stages at current best-practice recommendations, and with a range of spray volumes but with spray mixture concentration amended accordingly (i.e. fixed dosage per hectare). Spray trails indicated that deposition levels following current best-practice spray application were sub-optimal to control B. cinerea infections on bunches and leaves. Deposition values between air blast and air shear sprayers were generally similar. The air blast sprayer resulted in higher deposition levels with diluted spraying and increased spray volume; however, when dosage per hectare was kept constant, no significant differences were calculated between spray volumes (250-1000 L/ha), indicating that this sprayer can as effectively but more efficiently be used at lower spray volume. The air shear were not as efficient at higher spray volumes (>500 L/ha), but was superior at low volume concentrate application (≈250 L/ha at 4× concentration). This study clearly demonstrated the efficacy and cost-saving potential in optimising spray application with respect to application technology. / AFRIKAANSE OPSOMMING: Wingerdprodusente kan oesverliese ondervind indien omgewingstoestande bevorderlik is vir swampatogene. Siektes word onvoldoende beheer ten spyte van die nakoming van korrekte swamdoder aanbevelings. Geregistreerde swamdoders is effektief, mits die vatbare plantdele voldoende spuitbedekking ontvang. Onvoldoende siekte beheer kan gewoonlik toegeskryf word aan: 1) verkeerde spuit tydsberekening, 2) vermindere sensitiwiteit in patogeen-populasies teen swamdoders, en 3) swak spuitbedekking. Spuit tydsberekening, die bestuur van weerstand teen swamdoders en die epidemiologie van Botrytis cinerea is deeglik onder Suid-Afrikaanse toestande nagevors. Nietemin is daar beperkte navorsing oor spuitbedekking, waarskynlik weens 'n gebrek aan behoorlike spuitbedekking assesseringsprotokol. Om te bepaal hoeveel spuitbedekking (% area bedek deur fluoresserende pigment) nodig is om 75% van B. cinerea infeksies (FPC75 waardes) op vatbare wingerddele te beheer, is druiwetrosse en blare van tafel- en wyndruiwe (Waltham Cross en Chenin blanc, onderskeidelik) op verskillende groei stadiums en spuitvolumes in die laboratorium gespuit. ‘n Assesseringsprotokol van spuitbedekking op vatbare druifdele en blare is ontwikkel deur gebruik te maak van fluorometrie, fotomikrografie en digitale beeldanalise. Spuitbedekking het goed met Botrytis infeksies gekorreleer. Toenemende spuitvolume het bedekking laat toeneem, maar egter net tot 'n sekere punt, waar die kwantiteit van die bedekking nog toegeneem het, maar die kwaliteit van bedekking en B. cinerea infeksies nie beduidend toegeneem het nie. Dit is ‘n aanduiding van die belangrikheid van beide die kwantiteit en kwaliteit van spuitbedekking. Die FPC75 waardes wat in hierdie studie verkry is, kan as drempelwaardes om toekomstige spuittoediening te evalueer, gebruik word. Ten einde spuitbedekking met bestaande tegnologie (druk en waaierpomp spuitmasjiene) te optimiseer, is kommersiële wyn- en tafeldruiwe (Chenin blanc en Waltham Cross, onderskeidelik), volgens huidige spuit aanbevelings vir wingerde tydens verskillende groeistadiums en met ‘n reeks van verskillende spuitvolumes gespuit. Die konsentrasie van die spuitmengsel is dienooreenkomstig gewysig, i.t.v. ‘n vaste dosis per hektaar ongeag die spuitvolume. Bedekkingswaardes is met FPC75 waardes vergelyk en het aangedui dat kommersiële spuit aanbevelings aan produsente sal lei tot sub-optimale beheer van B. cinerea op beide blare en druiwetrosse. In die algemeen was bedekkingswaardes vir beide druk- en waaierpomp spuitmasjiene soortgelyk. Vir die waaierpomp teen verskillende spuitvolumes en aanbevole konsentrasie het ‘n toename in spuitvolumes tot hoër beddekingswaardes gelei, maar indien die dosis per hektaar van die spuitmengsel konstant behou is, is geen betekenisvolle verskille tussen spuitvolumes (250-1000 L/ha) voorspel nie. Hierdie dui aan dat die waaierpomp net so doeltreffend, maar meer effektief teen laer spuitvolumes gebruik kan word. Die drukpomp was nie so doeltreffend teen hoër spuitvolumes (> 500 L/ha) nie, maar was aansienlik beter by lae volume konsentraat toediening (≈ 250 L/ha op 4 × konsentrasie). Die studie toon duidelik die doeltreffendheid en moontlike kostebesparing moontlikhede deur bespuiting relatief tot bespuitingstegnologie te optimiseer. / Department of Plant Pathology, National Research Foundation, THRIP, Deciduous Fruit Producers’ Trust, Winetech, Bayer, BASF, Dow Agrosciences, DuPont, Syngenta, Nexus, Terason, UAP and Wenkem for financial assistance
24

Imazalil and wax coating application in citrus packhouses to control green mould and preserve fruit quality

Njombolwana, Ncumisa Shelly 03 1900 (has links)
Thesis (MScAgric)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Green mould is a major citrus postharvest disease caused by a wound pathogen called Penicillium digitatum. Imazalil (IMZ) is the most important postharvest fungicide that is currently registered against green mould and blue mould, given its good protective and curative control and sporulation inhibition. Imazalil can be applied in drench, dip, spray and wax coating applications. Wax coatings improve the quality of the fruit during shelf life by limiting moisture loss and providing a shiny appearance. The primary objective of this study was to investigate the application of imazalil in wax coatings in citrus packhouses to control green mould and preserve fruit quality. The first aim of this study was to evaluate the protective and curative control and sporulation inhibition of IMZ sensitive and resistant isolates of P. digitatum following single IMZ application in wax coating and IMZ application in aqueous dip as well as wax coating. For single application, Valencia orange fruit was curatively or protectively treated with a carnauba-based coating into which IMZ at 3000 μg.mL-1 was mixed. For curative treatments, fruit was treated after 24 hour's incubation. Coating was applied at 0.6, 1.2 and 1.8 L.ton-1 of fruit on a commercial coating applicator. Untreated control and fruit treated with coating only showed up to 80% infection for both sensitive and resistant isolates. Imazalil in coating proved to have better protective than curative action against the sensitive isolate, while control of the resistant isolate was poor. Imazalil residue levels increased with increasing coating load (0.85 to 1.75 μg.g-1). For double application, clementine, satsuma, navel and Valencia orange fruit were used. Curative and protective control following dip only treatment (IMZ sulphate at 500 μg.mL-1 for 45 s and 90 s) was compared with coating only treatment (IMZ at 3000 μg.mL-1 at 1.8 L.ton-1), and double application comprising dip (45 s in IMZ sulphate at 500 μg.mL-1) followed by 2000 μg.mL-1 IMZ in coating at 0.6, 1.2 and 1.8 L.ton-1. Double application resulted in improved residue loading (0.85 to 2.06 μg.g-1) compared to dip only treatments (≈ 0.49 μg.g-1). Coating only resulted in the highest residue levels (1.82 to 7.09 μg.g-1), often exceeding the maximum residue limit of 5 μg.g-1. In all treatments, poor curative and protective control of the resistant isolate (<46% and <55%, respectively) and generally no sporulation inhibition was observed. For the sensitive isolate, dip only treatments resulted in better curative control (≈ 77%) than protective control (≈ 38%). Double application showed increased protective control with increasing wax load (≈ 69%) as well as good curative control (≈ 83%). Wax coating only treatment resulted in poor curative control (≈ 26%), but good protective control (≈ 80%). Sporulation inhibition of the sensitive isolate was generally improved in treatments that included IMZ application in the wax coating. This study successfully showed the additive benefits of double application of IMZ in the wax coating following an aqueous dip application. However, despite improved control of the sensitive isolate, the resistant isolate could not be controlled. The second objective of the study was to evaluate green mould control and quality preservation following IMZ application using different coating and brush types. The inoculation and treatment procedure was similar to the single application of wax coating described above but only the sensitive isolate of P. digitatum was used. Carnauba- or polyethylene-based wax coatings, including IMZ at 3000 μg.mL-1, was applied at a dosage of 0.6, 1.2 and 1.8 L.ton-1 using commercial horsehair or synthetic brushes. Fruit was either incubated for 4 days prior to wound infection ratings or stored at -0.5oC for 26 days and 7 days shelf life. Imazalil residues on fruit increased with increasing coating loads on navel oranges (1.31 to 3.32 μg.g-1) and Valencia oranges (3.22 to 6.00 μg.g-1). Better protective (≈ 58%) than curative control (≈ 14%) was observed, with horsehair brushes resulting in lower sporulation levels (≈ 59%) than synthetic brushes (≈ 64%). Fruit weight loss and firmness loss ratios relative to uncoated control fruit were significantly higher in fruit treated with polyethylene coating compared with carnauba coating treated fruit. However, polyethylene coating resulted in shinier fruit before and after storage, whereas carnauba coating resulted in lower shine ratios. Gaseous (CO2) exchange ratios remained similar for both coatings, but higher polyethylene coating loads (1.8 L.ton-1) resulted in off-tastes similar to the uncoated control fruit and higher than the ratings for carnauba. Scanning electron micrographs revealed an amorphous crystallised natural wax layer with uncovered stomatal pores on the surface of uncoated fruit. The thickness of the applied coating layer increased with increasing coating load. Coating layers following application with synthetic brushes at 1.2 L.ton-1 appeared to be thicker than when applied using horsehair brushes. This study indicated the effects of brush type on the distribution and polishing of the wax coating on the surface of the fruit and also the importance of cautious application of coating as under or over application may lead to poor results in terms of bio-efficacy, residue loading and fruit quality. / AFRIKAANSE OPSOMMING: Groenskimmel is 'n belangrike sitrus na-oessiekte, veroorsaak deur 'n wondpatogeen, genaamd Penicillium digitatum. Imazalil (IMZ) is die belangrikste na-oesfungisied wat tans teen groenskimmel geregistreer is, gegewe sy goeie beskermende en genesende beheer en sporulasie-inhibisie. Imazalil kan in bad-, doop-, spuit- en wakslaagbehandelings toegedien word. Wakslae behou die kwaliteit van die vrugte gedurende raklewe deur vogverlies te beperk en 'n glansvoorkoms te verskaf. Die primêre doel van hierdie studie was om die toediening van imazalil in wakslaagbehandelings in sitruspakhuise vir groenskimmel en vrugkwaliteit beheer te ondersoek. Die eerste doelwit van hierdie studie was om die beskermende en genesende beheer en sporulasie-inhibisie van IMZ sensitiewe en weerstandbiedende isolate van P. digitatum, gevolg deur enkel IMZ toediening in 'n wakslaagbehandeling, en IMZ toediening in 'n doop-, asook wakslaagbehandeling, te evalueer. Vir enkelltoediening is Valencia lemoenvrugte genesend of beskermend met 'n carnauba-gebaseerde wakslaag behandel, waarin IMZ teen 3000 μg.mL-1 gemeng is. Vir genesende behandelings is vrugte ná 24 uur inkubasie behandel. Wakslaagbehandeling is teen 0.6, 1.2 en 1.8 L.ton-1 vrugte op 'n semi-kommersiële paklyn toegedien. Onbehandelde kontrole en vrugte met waks behandel, het slegs tot 80% infeksie vir beide sensitiewe en weerstandbiedende isolate getoon. Imazalil in waks het beter beskermende as genesende aksie teen die sensitiewe isolaat getoon, terwyl beheer van die weerstandbiedende isolaat swak was. Imazalil residuvlakke het met toename in wakslading toegeneem (0.85 tot 1.75 μg.g-1). Vir dubbeltoediening is clementine, satsuma, navel en Valencia lemoenvrugte gebruik. Genesende en beskermende beheer van IMZ na enkel doopbehandeling (IMZ sulfaat teen 500 μg.mL-1 vir 45 s en 90 s), is met enkel waksbehandeling (IMZ teen 3000 μg.mL-1 teen 1.8 L.ton-1) vergelyk, asook dubbeltoediening bestaande uit doop (45 s in IMZ sulfaat teen 500 μg.mL-1), gevolg deur 2000 μg.mL-1 IMZ in waksbehandeling teen 0.6, 1.2 en 1.8 L.ton-1. Dubbeltoediening het verbeterde residulading (0.85 tot 2.06 μg.g-1) tot gevolg gehad, in vergelyking met enkel doopbehandelings (≈ 0.49 μg.g-1). Enkel waksbehandeling het die hoogste residuvlakke (1.82 tot 7.09 μg.g-1) tot gevolg gehad, wat dikwels die maksimum residu-limiet van 5 μg.g-1 oorskry het. In alle behandelings is swak genesende en beskermende beheer van die weerstandbiedende isolaat (<46% en <55%, onderskeidelik), en oor die algemeen, geen sporulasie-inhibisie, waargeneem. Vir die sensitiewe isolaat, het die enkel doopbehandelings beter genesende beheer (≈ 77%) in vergelyking met die beskermende beheer (≈ 38%) tot gevolg gehad. Dubbeltoediening het verhoogde beskermende beheer met toenemende wakslading (≈ 69%) getoon, asook goeie genesende beheer (≈ 83%). Enkel wakslaagbehandeling het swak genesende beheer (≈ 26%) tot gevolg gehad, maar goeie beskermende beheer (≈ 80%). Sporulasie-inhibisie van die sensitiewe isolaat was oor die algemeen beter in behandelings wat IMZ toediening in die wakslaag ingesluit het. Hierdie studie het suksesvol die toegevoegde voordele van dubbeltoediening van IMZ in doopbehandeling en wakslaag getoon. Ten spyte van die verbeterde beheer van die sensitiewe isolaat, kon die weerstandbiedende isolaat egter nie beheer word nie. Die tweede doelwit was om groenskimmelbeheer en behoud van kwaliteit te evalueer, volgende op IMZ toediening deur gebruik van verskillende waks- en borseltipes. Inokulasie- en behandelingsprosedure was soortgelyk aan die enkeltoediening van wakslaagbehandeling soos bo beskryf, maar slegs die sensitiewe isolaat van P. digitatum is gebruik. Carnauba- of poli-etileen-gebaseerde wakslae, insluitende IMZ teen 3000 μg.mL-1, is teen 'n dosis van 0.6, 1.2 en 1.8 L.ton-1 toegedien, deur die gebruik van kommersiële perdehaar of sintetiese borsels. Vrugte is óf vir 4 dae vóór wond-infeksie evaluering geïnkubeer, óf teen -0.5oC vir 26 dae en 7 dae raklewe gestoor. Imazalil residuvlakke op vrugte het met toenemende waksladings op navellemoene (1.31 tot 3.32 μg.g-1) en Valencia lemoene (3.22 tot 6.00 μg.g-1) toegeneem. Beter beskermende (≈ 58%) as genesende beheer (≈ 14%) is waargeneem, met perdehaar borsels wat laer sporulasievlakke (≈ 59%) tot gevolg gehad het, in vergelyking met sintetiese borsels (≈ 64%). Vruggewig- en fermheidsverlies verhoudings, relatief tot onbedekte kontrole vrugte, was betekenisvol hoër in vrugte wat met 'n poli-etileenwaks behandel is, in vergelyking met carnauba-waks behandelde vrugte. Poli-etileen waksbehandeling het egter blinker vrugte vóór en ná opberging tot gevolg gehad, terwyl canauba waksbehandeling laer blink verhoudings tot gevolg gehad het. Gas (CO2) uitruilverhoudings het dieselfde vir beide waksbehandelings gebly, maar hoër poli-etileen waksladings (1.8 L.ton-1) het tot afsmake soortgelyk aan die onbedekte kontrole vrugte gelei, en hoër as die evaluerings vir carnauba. Skandeer-elektronmikrograwe het 'n amorfe gekristalliseerde natuurlike wakslaag met onbedekte stomata op die oppervlak van onbedekte vrugte getoon. Die dikte van die toegediende waks het met toename in wakslading toegeneem. Wakslae na toediening met sintetiese borsels teen 1.2 L.ton-1 het dikker vertoon in vergelyking met perdehaar borsels. Hierdie studie het die effekte van borseltipe op die verspreiding en polering van die wakslaag op die oppervlak van vrugte getoon, en versigtige toediening van wakslae onderskryf, aangesien ónder- of óórtoediening swak resultate, in terme van bio-effektiwiteit, residu-lading en vrugkwaliteit, tot gevolg kan hê. / National Research Foundation, THRIP, Citrus Academy & Citrus Research International for bursary and research funding.
25

Population structure of Phytophthora infestans in selected central, Eastern and Southern African countries

Pule, Boitumelo Bronwen 12 1900 (has links)
Thesis (MSc)--Stellenbosch University, 2010. / ENGLISH ABSTRACT: Late blight caused by Phytophthora infestans on potato and tomato causes major economic losses worldwide. Until the 1980s, P. infestans populations outside its centre of origin (either central Mexico or the Andean region) only consisted of one mating type (A1), which prevented the pathogen from reproducing sexually. Pathogen populations outside the centre of origin most likely only consisted of a few genotypes prior to the 1980’s. Pan globally, these genotypes probably first consisted of genotype/s that had mitochondrial DNA (mtDNA) haplotype Ia, which was subsequently replaced by a mtDNA haplotype Ib genotype known as the US-1 lineage. This relative simple population structure of the pathogen changed almost worldwide in the late 1970s and early 1980s, when a second set of migrations took place from the centre of origin. These populations contained both A1 and A2 mating type isolates that consisted of several different genotypes, which were more virulent than the pre-1970s genotypes and resulted in the displacement of these genotypes almost worldwide. Some of the new genotypes were also resistant to metalaxyl, the fungicide that was most effective in controlling late blight. In Sub-Saharan Africa (SSA), the characteristics of P. infestans populations are not well documented in most countries except South Africa, Kenya and Uganda. Previous studies in SSA showed that populations were dominated by the US-1 lineage and its variants. The exceptions were reports of the presence of a few mtDNA haplotype Ia isolates in Rwanda and Ethiopia. The current study aimed to determine the population structure of P. infestans in eight selected SSA countries (Burundi, Kenya, Rwanda, Tanzania, Uganda, Malawi, Mozambique and South Africa), mainly on potato and on a limited scale on tomato and petunia, using ‘old’ markers (mating type determination, glucose-6-phosphate isomerase [Gpi] genotyping, mtDNA haplotyping, DNA fingerprinting with probe RG-57 and metalaxyl sensitivity). Populations were further also genotyped using seven recently published Simple Sequence Repeats (SSRs) markers. This information would help to define the population structure of P. infestans in SSA for the first time on a regional basis, and will also determine whether new migrations have taken place since the last characterization studies took place in 2001. A survey in the eight SSA countries yielded a total of 281 P. infestans isolates, mainly obtained from potato fields (Tanzania, Kenya, Uganda, Rwanda, Burundi, Malawi and South Africa), but also from tomato (Malawi, Mozambique and South Africa) and Petunia ´ hybrida (South Africa) that were characterized. Characterization of subsets of the isolates with the ‘old’ markers (176 isolates for mating type, 281 isolates for mtDNA, 70 isolates for [Gpi] and 49 isolates with restriction fragment length polymorphism analysis with probe RG-57), showed that most of the isolates belonged to the US-1 genotype or its variants (US-1.10 and US-1.11). The exception were isolates that belonged to genotype KE-1 (A1 mating type, mtDNA haplotype Ia, Gpi 90/100 and unique RG-57 genotype) that was identified in two fields in Kenya. Genotype KE-1, based on the ‘old’ marker data, is related to genotypes (RW-1 and RW-2) previously identified in Rwanda, and several Ecuadorean and European genotypes. Metalaxyl sensitivity testing of 64 isolates showed that metalaxyl resistant potato isolates were present in all the countries except Malawi, whereas all the tomato isolates were sensitive. Genotyping of 176 isolates with seven recently published simple sequence repeat (SSR) markers revealed a high number (79) of multi-locus genotypes (MLGs) in SSA. However, when locus D13, which was difficult to score, was excluded only 35 MLGs were identified. When locus D13 was excluded from analyses of molecular variance (AMOVA), (i) there was no significant genetic differentiation between populations from central-east Africa (Burundi, Kenya, Rwanda, Tanzania and Uganda), south-east Africa (Malawi and Mozambique) and South Africa, (ii) the KE-1 population was genetically differentiated (Fst = 0.33; P = 0.001) from the US-1 and US-1.10 populations and (iii) genetic differentiation between populations from potato and tomato was low (Fst = 0.07; P = 0.004). The study has expanded the worldwide genotypic database of P. infestans for SSA. Previously, no populations were characterized from Burundi, Malawi and Mozambique. The characterization work showed that migrations seem unlikely to have taken place in SSA, or if these did occur, it was on a very limited scale. The more severe epidemics in some SSA countries could be due to the presence of metalaxyl resistance. Furthermore, the occurrence of mutations or mitotic recombination might have resulted in more aggressive and/or better adapted genotypes, for example the US-1.10 lineage that was only detected in the Western Cape Province of South Africa. The significance of the discovery of the KE-1 genotype in Kenya needs further investigation since it might (i) be an asexual descendent of genotypes (RW-1 and RW-2) that were previously reported in Rwanda in the 1980s, (ii) previously have gone undetected due to the small surveys that were conducted in SSA, (iii) be a new migrant from countries other than SSA or (iv) have been introduced in the very first introductions into Kenya prior to the 1970s. The SSR results from the survey will allow comparison of the SSA late blight populations with other populations worldwide through the EucaBlight database in future studies. / AFRIKAANSE OPSOMMING: Laatroes, veroorsaak deur Phytophthora infestans op aartappel en tamatie, veroorsaak groot ekonomiese verliese wêreldwyd. Phytophthora infestans populasies buite hul kern van oorsprong (óf sentraal Meksiko óf die Andes area), het tot die 1980’s slegs uit een paringstipe (A1) bestaan, wat verhoed het dat die patogeen geslagtelik vermeerder. Patogeenpopulasies buite die kern van oorsprong, het heel moontlik vóór die 1980’s slegs uit ‘n paar genotipes bestaan. Wêreldwyd, het hierdie genotipes moontlik aanvanklik uit genotipe(s) bestaan wat mitokondriale DNS (mtDNS) haplotipe Ia bevat het, wat later met ‘n mtDNS haplotipe Ib genotipe, bekend as die US-1 genotipe, vervang is. Hierdie relatiewe eenvoudige populasiestruktuur van die patogeen, het omtrent wêreldwyd in die láát 1970’s en vroeë 1980’s verander, toe ‘n tweede stel migrasies vanaf die patogeen se kern van oorsprong plaasgevind het. Hierdie populasies het beide A1 en A2 paringstipe isolate ingesluit, wat uit verskeie verskillende genotipes bestaan het, wat meer virulent as die vóór-1970’s genotipes was, en wat die verskuiwing van hierdie genotipes omtrent wêrelwyd tot gevolg gehad het. Sommige van die nuwe genotipes was ook weerstandbiedend teen metalaksiel, die fungisied wat mees effektief in die beheer van laatroes was. Die kenmerke van P. infestans populasies is nie goed in die meeste lande in Sub- Sahara Afrika (SSA) gedokumenteer nie, behalwe vir Suid-Afrika, Kenia en Uganda. Vorige studies in SSA het aangedui dat populasies deur die US-1 genotipe en sy variante gedomineer word. Die uitsonderings was aantekeninge oor die teenwoordigheid van ‘n paar mtDNS haplotipe Ia isolate in Rwanda en Etiopië. Die huidige studie was daarop gemik om die populasiestruktuur van P. infestans in agt geselekteerde SSA lande (Burundi, Kenia, Rwanda, Tanzanië, Uganda, Malawi, Mosambiek en Suid-Afrika), hoofsaaklik op aartappel en op ‘n beperkte skaal op tamatie en petunia, vas te stel, deur die gebruik van ‘ou’ merkers (paringstipe-bepaling, glukose-6-fosfaat isomerase [Gpi] genotipering, mtDNS haplotipering, DNS fingerafdrukke met RG-57 en metalaksielsensitiwiteit). Die genotipe van populasies is verder ook bepaal deur gebruik te maak van sewe onlangs-gepubliseerde “Simple Sequence Repeats (SSRs)” merkers. Hierdie inligting sal help om die populasiestruktuur van P. infestans in SSA vir die eerste keer op ‘n streeksbasis vas te stel, en sal ook bepaal of nuwe migrasies sedert die laaste karakteriseringstudies wat in 2001 uitgevoer is, plaasgevind het. ‘n Opname in die agt SSA lande, het ‘n totaal van 281 P. infestans isolate opgelewer, hoofsaaklik vanaf aartappellande (Tanzanië, Kenia, Uganda, Rwanda, Burundi, Malawi en Suid-Afrika), maar ook vanaf tamatie (Malawi, Mosambiek en Suid- Afrika) en Petunia ´ hybrida (Suid-Afrika) wat gekarakteriseer is. Karakterisering van geselekteerde isolate met die ‘ou’ merkers (176 isolate vir paringstipe, 281 isolate vir mtDNS, 70 isolate vir Gpi en 49 isolate met restriksiefragment-lengte-polimorfismeanalise met RG-57), het aangetoon dat die meeste van die isolate aan die US-1 genotipe of sy variante (US-1.10 en US-1.11) behoort het. Die uitsondering was isolate wat tot die genotipe KE-1 behoort het (A1 paringstipe, mtDNS haplotipe Ia, Gpi 90/100 en unieke RG-57 genotipe) wat in twee velde in Kenia geïdentifiseer is. Genotipe KE-1, gebaseer op die ‘ou’ merkerdata, is aan genotipes (RW-1 en RW-2) verwant, wat voorheen in Rwanda, en verskeie Ekwadoreaanse en Europese lande geïdentifiseer is. Metalaksielsensitiwiteitstoetsing van 64 isolate het aangetoon dat metalaksiel-weerstandbiedende aartappel-isolate in al die lande teenwoordig was, behalwe vir Malawi, terwyl al die tamatie-isolate sensitief was. Genotipering van 176 isolate met sewe onlangs gepubliseerde “Simple Sequence Repeat” (SSR) merkers, het ‘n hoë aantal (79) multilokus genotipes (MLGs) in SSA aangedui. Met die uitsluiting van lokus D13, wat moeilik was om te evalueer, is slegs 35 MLGs egter geïdentifiseer. Met die uitsluiting van lokus D13 uit die analise van molekulêre variansie (AMOVA), was (i) daar geen betekenisvolle genetiese differensiasie tussen populasies van sentraal-oos Afrika (Burundi, Kenia, Rwanda, Tanzanië en Uganda), suid-oos Afrika (Malawi en Mosambiek) en Suid-Afrika nie, (ii) die KE-1 populasie geneties (Fst = 0.33; P = 0.001) van die US-1 en US-1.10 populasies gedifferensieerd en (iii) genetiese differensiasie tussen populasies vanaf aartappel en tamatie laag (Fst = 0.07; P = 0.004). Die studie het die wêreldwye genotipe-databasis van P. infestans vir SSA uitgebrei. Voorheen is geen populasies vanuit Burundi, Malawi en Mosambiek gekarakteriseer nie. Die karakteriseringswerk het aangetoon dat die waarskynlikheid klein is dat migrasies in SSA plaasgevind het, of indien dit wel plaasgevind het, dit op ‘n baie beperkte skaal plaasgevind. Die meer ernstige epidemies in sommige SSA lande kan die gevolg wees van die teenwoordigheid van metalaksiel-weerstand. Die voorkoms van mutasies of mitotiese rekombinasie kon verder meer aggressiewe en/of beter aangepaste genotipes tot gevolg gehad het, byvoorbeeld die US-1.10 genotipe wat slegs in die Westelike Kaapprovinsie van Suid-Afrika waargeneem is. Die betekenis van die ontdekking van die KE-1 genotipe in Kenia benodig verdere ondersoek aangesien dit (i) ‘n ongeslagtelike afstammeling van genotipes (RW-1 en RW-2) mag wees wat voorheen in die 1980’s in Rwanda aangeteken is, (ii) voorheen nie waargeneem is nie weens die klein opnames wat in SSA uitgevoer is, (iii) ‘n nuwe genotipe van lande buite die SSA kan wees of (iv) ingebring is tydens die heel eerste inkoms in Kenia vóór die 1970’s. Die SSR resultate van die opname sal vergelykings tussen die SSA laatroespopulasies en ander populasies wêreldwyd toelaat, deur gebruik te maak van die EucaBlight databasis in toekomstige studies.
26

Epidemiology and management of Fusarium circinatum in the Western Cape Province of South Africa

Van Wyk, Schalk Jacobus Petrus 03 1900 (has links)
Thesis (MScAgric )--Stellenbosch University, 2011. / ENGLISH ABSTRACT: Pine pitch canker, caused by Fusarium circinatum, is a major constraint to the production of high quality timber in the Western Cape Province of South Africa. Under nursery conditions the pathogen causes a serious root and collar rot disease, and in plantations it causes stem cankers and branch die-back. In this thesis, sources of inoculum within a forestry nursery were investigated and novel approaches developed to eradicate the pathogen. Plant material was evaluated for plantation establishment in the Western Cape Province, and epidemiological studies conducted to better understand the infection, disease development, spore release and dissemination of F. circinatum in pine plantations. Fusarium circinatum was first reported in a forestry nursery in the Mpumalanga Province of South Africa in 1990, and now causes significant economic losses to most forestry nurseries in the country. The irrigation system, planting tray inserts, seeds and air at Karatara nursery were screened as potential sources of F. circinatum. Both the irrigation water and planting tray inserts were found to serve as sources of inoculum. An oxidation reduction potential (ORP)-based system, using hydrogen peroxide, was tested to sanitize irrigation water and planting tray inserts. An ORP level of 400 mV for 6 hours was effective in killing F. circinatum spores in irrigation water without being phytotoxic to pine seedlings. An ORP value of >500 mV cleaned planting tray inserts of all inoculum. Pinus radiata is the principal pine species grown in the Western Cape Province, but this species is also highly susceptible to F. circinatum. There are numerous different varieties or families of P. radiata available that can be planted, and it is known that tolerance levels between these varieties and families vary. Pinus radiata families, as well as other Pinus spp. that could potentially be planted in the Western Cape Province in future, were evaluated for tolerance to the pitch canker fungus. The P. radiata families were moderately to highly susceptible to F. circinatum. Pinus taeda was the Pinus spp. most tolerant, while P. elliottii also had good tolerance to the pathogen. None of the P. radiata families screened showed tolerance comparable to that of either P. elliottii or P. taeda. Pine pitch canker was first reported from the Tokai plantation in the Western Cape Province in 2005. In order to develop a disease management strategy for the disease in pine plantations, we investigated the effect of pruning wounds as potential entry sites for the pathogen, and how fast the disease spread under South African climatic conditions. The amount and time of sporulation was also investigated. Pitch canker increased slowly over a 3-year period, and pruning wounds appeared not to serve as primary entry points for F. circinatum. Spore quantification over a 12-month period using quantitative real-time PCR showed that inoculum was produced throughout the year, but that significantly more spores were released during the cold, rainy winter months. The role of insects in pathogen transmission and spread should be investigated in the Tokai plantation. / AFRIKAANSE OPSOMMING: Fusarium circinatum veroorsaak “pine pitch canker”. Hierdie siekte is een van die grootste beperkinge op die Suid Afrikaanse bosbou industrie. In kwekerye veroorsaak die patogeen wortelvrot en wortelkraagvrot. In plantasies veroorsaak F. circinatum kankers op die hoofstam van dennebome en die terugsterwing van sytakke. In hierdie tesis was bronne van inokulum in ‘n bosbou kwekery ondersoek. Nuwe tegnieke was gebruik om die bronne uit te wis. Plantmateriaal wat in die Wes-Kaap geplant kan word, was geëvalueer vir toleransie teen F. circinatum. Epidemiologiesie studies was uitgevoer om die infeksieproses, siekte-ontwikkeling, spoorvrystelling, en verspreiding van F. circinatum binne denneplantasies beter te verstaan. Die eerste verslag van F. circinatum in ‘n bosboukwekery was in 1990 in die Mpumalanga Provinsie. Verliese word tans veroorsaak deur die patogeen in die meeste bosbou kwekerye in Suid Afrika. Die besproeiingstelsel, planthouers en saad was getoets as potensiële bronne van inokulum. Daar was gevind dat beide die besproeiingstelsel en die planthouers dien as bronne van F. circinatum inokulum. ‘n Oksidasie reduksie potensiaal (ORP)-gebaseerde sisteem waar waterstofperoksied gebruik was, was getoets of dit die besproeingwater en planthouers kan ontsmet. ‘n ORP-vlak van 400 mV vir ‘n blootstellingstydperk van 6 ure is effektief om al die F. circinatum spore dood te maak, sonder dat dit fitotoksies is teenoor die dennesaailinge. ‘n ORP-vlak van >500 mV het die F. circinatum in die planthouers uitgewis. Pinus radiata is die belangrikste dennespesie wat geplant word in die Wes-Kaap Provinsie, maar hierdie spesie is hoogs vatbaar vir F. circinatum. Verskillende variteite van P. radiata met verskillende tolleransie vlakke bestaan. Pinus radiata families en ander spesies wat in die toekoms potensieel geplant kan word in die Wes-Kaap was geevalueer vir toleransie teen F. circinatum. Die P. radiata families was matig to hoogs vatbaar vir F. circinatum. Pinus taeda het die hoogste toleransie vlak gehad en P. elliottii was matig tolererant. Nie een van die P. radiata families wat getoets was het toleransie vlakke gehad wat vergelykbaar was met die toleransie vlakke van P. taeda of P. elliottii nie. In 2005 was F. circinatum vir die eerste keer geraporteer in die Tokai plantasie op volwasse dennebome in die Wes-Kaap Provinsie. Die rol van snoeiwonde in die infeksieproses van F. circinatum was bestudeer asook hoe vinning die siekte ontwikkel en versprei. Die hoeveelheid en tyd van sporulasie was ook bestudeer. “Pitch canker” het stadig toegeneem oor die 3-jaar moniteringsperiode en dit blyk asof snoeiwonde nie die primêre ingangspunt vir die patogeen is nie. Kwantifisering van die sporulasie van F. circinatum deur middel van qPCR het aangedui dat spore reg deur die jaar geproduseer word. Meer spore word geproduseer in die koue nat wintersmaande. Die rol van insekte in die infeksieproses en verspreiding van F. circinatum in die Tokai plantasie moet ondersoek word.
27

Biological control of Phytophthora root rot of citrus seedlings and cuttings.

Abraham, Abraha Okbasillasie. January 2005 (has links)
With an increasing realization that many agrochemicals are hazardous to animals and humans, came the desire to replace these chemical agents with biological approaches that are more friendly to the environment and human health. Microorganisms play an important role in plant disease control, as naturally occurring antagonists. Microorganisms may also have beneficial effects on plant development when applied to plant roots. Research efforts worldwide have recorded successes in biological control and growth stimulation on many crops, particularly when using members of the genera Bacillus and Trichoderma. Their use on citrus rootstock could be advantageous to nurserymen and growers in reducing the incidence of seedling mortality and increasing production. To achieve these objectives, laboratory and tunnel experiments were conducted to develop effective biocontrol agents for citrus seedlings and cuttings. Nineteen 0 ut 0 f 23 Trichoderma isolates tested in vitro against Phytophthora p arasitica sp showed antagonistic activity by hyperparasitism and four out of eight Bacillus isolates resulted in antagonism by forming inhibition zones. The positive in vitro activity of Trichoderma and Bacillus isolates on Phytophthora provided motivation step for further trials in the greenhouse to evaluate their biological control activity on citrus seedlings and cuttings. A greenhouse trial was carried out to evaluate the biological control potential of 23 Trichoderma isolates (drenched at 5 x 105 spores / rnI) and two Bacillus isolates (drenched at 1 X 106 or 1 X 108 colony forming units (CFU) / rnI) to suppress Phytophthora parasitica sp. of rough lemon (Citrus jambhirini Lush.) seedlings. Five isolates ofTrichoderma (AA12, AA5, Trichoderma harzianum (AA16), SY3F and Eco-T~ were highly effective in suppressing Phytophthora root rot, with AA12 providing the best control. The Bacillus isolates also suppressed the pathogen but were not as effective as the Trichoderma isolates. This trial was used to test for growth stimulation activity by some of the biocontrol agents. To verify these results, a further trial was carried out to evaluate growth stimulation capabilities in the absence of any pathogen. Trichoderma Isolates AA13 and AA17 caused no 111 change in seedling growth, while other Trichoderma and Bacillus isolates had an inhibitory effect on the seedling growth. This trial indicated that the biocontrol activity was affected by inoculum densities, and as a result in vitro sporulation capacity was evaluated. TrichodermaIsolate AA16 was the largest spore producer, followed by Eco-T®. Spore production was lowest from Trichoderma isolates AA4 and AA12. Growth stimulation responses of Trichoderma Isolates AA4, AA16, Eco-TID and SYN6 were further studied at four different doses (1 X 103, 1 X 104, 5 X 105 or 1 X 106 spores / ml) on rough lemon and trifoliate orange seedlings. Trifoliate oranges responded positively to 1 X 104 and 5 X 105 spores / ml of Eco-TID, but rough lemon responded negatively to all dosages of the Trichoderma isolates applied. This indicates that the inoculum density responses may be host specific. Higher population density of 1 X 106 spores / ml of all tested Trichoderma isolates had a stunting effect on seedling growth of both species. Based on t he positive results 0 f individual applications of some Trichoderma and Bacillus isolates, of the biological control agents on rough lemon seedlings against Phytophthora parasitica in an earlier greenhouse trial, their combined effect in the control of the pathogen was performed. Before carrying out a greenhouse trial, activities of the isolates to be combined were evaluated in vitro. This trial showed that Trichoderma Isolates AA16 and Eco-T®were compatible. Trichoderma isolates AA16 and Eco-T®were also found to be compatible with Bacillus Isolates B77, B81 and PHP. As a result, further in vivo trials were conducted. The tunnel trials were carried out as two separate experiments: In the first experiment, a combination of two Trichoderma Isolates A A 16 and Eco-T®was conducted assayed at 5 X 105 or 1 X 106 spores / ml, on rough lemon seedling, and cuttings and trifoliate orange and sour orange seedlings. A combination of Trichoderma isolate AA16 and Eco-T®at 5 X 105 spore / ml increased significantly the new flush biomass of rough lemon cuttings compared to AA16 alone, but was not different from Eco-TID alone. The combination of AA16 and Eco-T® achieved no change of biomass of rough lemon and trifoliate orange seedlings. The combination of AA16 and Eco-TID did not increase the root biomass of sour orange compared to AA16 or Eco-r® alone. The combination of AA16 and Eco-r® at higher doses (1 x 106 spores / ml) showed significantly better suppression of Phytophthora root rot of rough lemon cuttings but did not show disease suppression in all seedling species verities tested. In a second experiment, individual and combined effects of Trichoderma isolates (drenched at 5 X 105 spores / ml) with Bacillus isolate (drenched at 1 X 106 colony forming units (CFU) / ml) for suppression of Phytophthora root rot on rough lemon and trifoliate orange seedlings was performed. The combination of Trichoderma Isolate AA16 and Bacillus Isolate B81 increased root biomass on rough lemon seedlings compared to the combination of Trichoderma AAI6 or Bacillus PHP but was not significantly different to Trichoderma AA16 alone. Bacillus PHP combined with Trichoderma AA16 or singly had no effect on rough lemon seedlings. Combining Trichoderma Eco--r® and with Bacillus B8I or PHP did not increase biomass of rough lemon seedlings compared to Trichoderma Isolate Eco--r® alone. There was no statistically significant differences in the effects of the combinations of the Trichoderma and Bacillus isolates compared to their individual applications on the biomass of trifoliate oranges. This study established the antagonistic potential of several South African isolates of Trichoderma and Bacillus as a viable alternative to agrochemicals for controlling Phytophthora parasitica. The growth stimulation capabilities of Trichoderma isolates in terms of seedling development was also demonstrated. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2005.
28

Development of free-living diazotrophic (FLD) inoculants and their effects on crop growth.

Kifle, Medhin Hadish. January 2008 (has links)
In this study several free-living diazotrophs (FLD) were isolated and screened for their nitrogen fixing ability on a range of crops grown in greenhouse, hydroponics and field trials. Rhizosphere isolates of free-living diazotrophs (FLD) may be effective biofertilizer inoculants, and may improve plant health where crops are grown with little or no fertilizer, as is the case in the Developing World. FLD isolates from rhizospheric soils in KwaZulu-Natal were assessed by growing them on N-free media, which is a key isolation method. They were then evaluated for their nitrogenase activity by quantifying ethylene production from acetylene by gas chromatography (GC). The free living isolates that produced greater quantities of ethylene were detected by an acetylene reduction assay (ARA). These were further assessed for colony formation on N-free media with different carbon sources, and at a range of temperatures (20, 25 and 300C) and pH values (6.0, 7.0 and 8.0). Isolates G3 and L1 were identified using DNA sequencing by Inqaba Biotechnical Industries (Pty) Ltd as Burkholderia ambifaria Coenye et al, and Bacillus cereus Frankland, respectively. These isolates grew significantly better on an ethanol medium, at temperatures of 20, 25 and 300C and pHs of 6.0, 7.0 and 8.0. Isolates B3 (Burkholderia sp.) and D6 (Bacillus cereus Frankland) also grew well on an ethanol medium, but only at 200C and at a pH of 6.0 and 7.0, respectively, while Isolate E9 (Burkholderia cepacia Frankland) grew well on an ethanol medium only at 300C, and pH 6.0 and 7.0. Temperature and pH strongly influence FLD growth on N-free media using different carbon sources. Further trials were conducted to screen the best isolates under greenhouse condition, using both seed treatments and drenching application techniques onto several crops. The drenching application resulted in an increase in the growth and N-total of all the evaluated crops, relative to an unfertilized control. Growth and N-total of maize and sorghum increased with seed treatments, but did not increase the growth of lettuce and zucchini. Drenching of FLD isolates at 106cfu ml-1, applied on weekly basis, resulted in an increase in the growth of lettuce. Increased doses and frequency of application of the FLD bacteria resulted in a decrease in lettuce growth. This led to the conclusion that application of FLD bacteria at high doses and short intervals may create a situation where the applied FLD bacteria and the resident rhizosphere microbes compete for root exudates. High doses at low frequencies and low doses at high frequencies may be more effective on lettuce. Inoculation of Isolate L1 (B. cereus) at 106cfu ml-1 or in combination with Eco-T® (Trichoderma harzianum Rifai), significantly increased growth of lettuce. This result may have been due to nitrogen fixation, or to secretion of growth promoting substances by both the FLD and T. harzianum, and to biocontrol effects of Eco-T®. Application of Isolate L1 (B. cereus) at 106cfu ml-1 with or without Eco-T® was an effective tool for enhancing plant growth and nitrogen fixation. An FLD, Isolate L1 (B. cereus), was applied to lettuce plants together with a complete hydroponics fertilizer at 25% strength (Ocean Agriculture 3:1:3 (38) Complete), with the N level at 25mg l-1. These plants grew significantly better than the control plants grown on 25% of normal NPK fertilization, or with an inoculation of L1 alone. This indicates that it may be possible to integrate FLD applications with the application of low levels of commercial fertilizers, which is what resource poor farmers can afford. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2008.
29

In vitro and in vivo screening of Bacillus spp. for biological control of Rhizoctonia solani.

Kubheka, Bongani Petros. January 2003 (has links)
The increasing concerns about chemical pesticides that are environmentally hazardous and the continuous development of resistance by palhogens to chemical pesticides have led to this study. Many studies have shown that some Gram-negative bacteria, such as Pseudomonas flouresens, control plant diseases and promote plant growth. In this study Gram positive bacteria, Bacillus sp., were chosen because of their ability to produce endospores. Endospores can be used in stable, dry formulations. The advantage of using endospores is their ability to survive harsh conditions such as droughts and high temperatures, which give a long shelf life to the biological control agent. Bacillus isolates were recovered from the rhizosphere of 12 different crops, and were subsequently screened in vitro for their antimicrobial activity. Of 130 isolates, 87 exhibited antimicrobial activity against the test organisms: Rhizoctonia solani, Pythium sp., Phytophthora cinnamoni, Fusarium sp., and single representatives of Gram negative and Gram positive bacteria, namely, Erwinia carotovora and Staphylococcus aureus respectively. The Bacillus isolates B77, B81 and B69 inhibited all the test organisms investigated, which suggests that they produced broad spectrum antimicrobial compounds or more than one antimicrobial compound. Of the isolates that showed antimicrobial activity, 78 of them did not inhibit Trichoderma harzianum K D, which is a registered biological control agent; indicating their potential for combined application. Selected Bacillus isolates were tested for the biological control of R. solani under greenhouse conditions in wheat, cabbage, tomato, maize, and cucumber seedlings. Bacillus isolates were applied as seed treatments, and the inoculated seeds were planted in R. solani infested speedling trays. Shoot dry weight measurement of seedlings indicated that 12 out of 19 Bacillus isolates showed significantly different shoot dry weight in wheat whereas all the isolates tested in tomato and cucumber gave significantly different shoot dry weight. No significantly different shoot dry weight was obtained for maize or cabbage. Seed emergence findings indicated that none of the Bacillus isolates gave significantly different emergence percentage on wheat, cabbage, tomato, and maize but all of them showed significantly different emergence percentage on cucumber. The results indicate that both the pathogen and the biological control agents exhibited varying levels of specificity on each crop tested. The biological control potential of the best Bacillus isolates was tested on bean and maize crops in the field. Green bean and maize seeds were coated with the selected Bacillus isolates and then sown under field conditions. For each isolate, four replicate treatment plots were established, with and without a R. solani inoculum. Percentage emergence, plant survival levels to harvesting and yield of maize cobs and green beans pods were measured. For all parameters measured the positive and negative controls were not significantly different thereby rendering the results for the entire field study inconclusive. However, Bacillus isolates B77, BII, R5 and R7 improved green bean pod yield and Bacillus Isolate B8I increased maize yield, indicating their potentials as plant growth promoting rhizobacteria (PGPR). / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 2003.
30

Biological control and plant growth promotion by selected trichoderma and Bacillus species.

Yobo, Kwasi Sackey. January 2005 (has links)
Various Trichoderma and Bacillus spp. have been documented as being antagonistic to a wide range of soilborne plant pathogens, as well as being plant growth stimulants. Successes in biological control and plant growth promotion research has led to the development of various Trichoderma and Bacillus products, which are available commercially. This study was conducted to evaluate the effect of six Trichoderma spp. and three Bacillus spp. and their respective combinations, for the biological control of Rhizoctonia solani damping-off of cucumber and plant growth promotion of dry bean (Phaseolus vulgaris L.). In vivo biological control and growth promotion studies were carried out under greenhouse and shadehouse conditions with the use of seed treatment as the method of application. In vitro and in vivo screening was undertaken to select the best Trichoderma isolates from 20 Trichoderma isolated from composted soil. For in vitro screening, dual culture bioassays were undertaken and assessed for antagonisms/antibiosis using the Bell test ratings and a proposed Invasive Ability rating based on a scale of 1-4 for possible mycoparasitic/hyperparasitic activity. The isolates were further screened in vivo under greenhouse conditions for antagonistic activity against R. solani damping-off of cucumber (Cucumis sativus L.) cv. Ashley seedlings. The data generated from the in vivo greenhouse screening with cucumber plants were analysed and grouped according to performance of isolates using Ward‟s Cluster Analysis based on a four cluster solution to select the best isolates in vivo. Isolates exhibiting marked mycoparasitism of R. solani (during ultrastructural studies) viz, T. atroviride SY3A and T. harzianum SYN, were found to be the best biological control agents in vivo with 62.50 and 60.06% control of R. solani damping-off of cucumber respectively. The in vitro mode of action of the commercial Trichoderma product, Eco-T®, and Bacillus B69 and B81 suggested the production of antimicrobial substances active against R. solani. In vitro interaction studies on V8 tomato juice medium showed that the Trichoderma and Bacillus isolates did not antagonise each other, indicating the possibility of using the two organisms together for biological control and plant growth promotion studies. Greenhouse studies indicated that combined inoculation of T. atroviride SYN6 and Bacillus B69 gave the greatest plant growth promotion (43.0% over the uninoculated control) of bean seedlings in terms of seedling dry biomass. This was confirmed during in vivo rhizotron studies. However, results obtained from two successive bean yield trials in the greenhouse did not correlate with the seedling trials. Moreover, no increase in protein or fat content of bean seed for selected treatments was observed. In the biological control trials with cucumber seedlings, none of the Trichoderma and Bacillus combinations was better than single inoculations of Eco-T®, T. atroviride SY3A and T. harzianum SYN. Under nutrient limiting conditions, dry bean plants treated with single and dual inoculations of Trichoderma and Bacillus isolates exhibited a greater photosynthetic efficiency that the unfertilized control plants. Bacillus B77, under nutrient limiting conditions, caused 126.0% increase in dry biomass of bean seedlings after a 35-day period. Nitrogen concentrations significantly increased in leaves of plants treated with Trichoderma-Bacillus isolates. However, no significant differences in potassium and calcium concentrations were found. Integrated control (i.e. combining chemical and biological treatments) of R. solani damping-off of cucumber seedlings proved successful. In vitro bioassays with three Rizolex® concentrations, viz., 0.01g.l-1, 0.1g.l-1 and 0.25g.l-1 indicated that the selected Trichoderma isolates were partly sensitive to these concentrations whereas the Bacillus isolates were not at all affected. In a greenhouse trial, up to 86% control was achieved by integrating 0.1g.l-1 Rizolex® with T. harzianum SYN, which was comparable to the full strength Rizolex® (1g.l-1) application. Irrespective of either a single or dual inoculations of Trichoderma and/or Bacillus isolates used, improved percentage seedling survival as achieved with the integrated system, indicating a synergistic effect. The results presented in this thesis further reinforce the concept of biological control by Trichoderma and Bacillus spp. as an alternative disease control strategy. Furthermore, this thesis forms a basis for Trichoderma-Bacillus interaction studies and proposes that the two organisms could be used together to enhance biological control and plant growth promotion. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2005.

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