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Development of a model to predict sporulation of Bremia lactucae in lettuceTchervenivanova, Eli January 1995 (has links)
The effect of temperature and duration of leaf wetness (DLW) on sporulation of Bremia lactucae was determined for lettuce cv. Ithaca. A single spore isolate of B. lactucae was produced and was identified using lettuce differential lines each of which had known gene for resistance. Potted lettuce plants were inoculated with the isolate and incubated at 15 C, at 100% relative humidity for 24 h and then at a relative humidity lower than 70%. Seven days later, the plants were submitted to five different temperatures (5, 10, 15, 20 and 25 C) and six durations of leaf wetness (4, 6, 8, 10, 12 and 14 h). The number of spores produced was determined at the end of each wet period. After 4 h of incubation no spores were observed at any of the temperatures. Highest number of spores was found at 10 and 15 C for more than 10 h of DLW. The rate of sporulation rapidly increased between 8 and 10 h for all the temperatures, including 25 C, where the amount of spores produced was very low. The observed number of spores was transformed into proportion of maximum sporulation (PMS) by providing each data by the maximum number of spores observed for each experiment. The Richards model was used to describe sporulation as a function of leaf wetness duration and the rate and maximum value expressed as a function of temperature. This approach resulted in a three-dimensional equation that explained 87% of the variation in the PMS. Spore viability was also estimated for each temperature and DLW. It was zero after 6 h of incubation and reached almost the maximum after 10 h for all the temperatures. The sporulation model was validated under field conditions and it predicted high, medium, low, or no sporulation in 8 out of 11 times.
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The role of birds as predators and potential biocontrol agents of insect pests in corn fields /Tremblay, Annie C. January 1999 (has links)
This project investigated the impact of bird predation on insect pest populations within two cornfields of Southwestern Quebec. Birds were excluded from portions of these fields through the use of bird-proof netting. Rhopalosiphum maidis, Ostrinia nubilalis, Agrotis spp. and Sphenophorus spp. were all found at greater densities in plots where birds were excluded as compared with the non covered plots. Only the adult Diabrotica longicornis population was not reduced by birds. Results significantly suggest that birds can reduce insect pest populations. Bird visits in cornfields with respect to distance from field edge, type of edge habitat and corn phenology were also studied. Red-winged Blackbird, Song and Chipping Sparrows and American Robin were the most frequently observed bird species inside cornfields. Early in the summer, birds tended to stay closer to the field edge, especially when composed of mature coniferous trees. Different bird species visited the cornfields at specific periods during corn development.
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Towards integrated control of cotton pests in Guatemala : an economic analysisPira, Lars Henrik. January 1981 (has links)
No description available.
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The status of the biological control of pineapple mealybugs in HawaiiGonzalez-Hernandez, Hector January 1995 (has links)
Thesis (Ph. D.)--University of Hawaii at Manoa, 1995. / Includes bibliographical references (leaves 120-122). / Also available in microform / xvii, 128 leaves, bound ill. 29 cm
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Agricultural change as an adaptive process : adoption of modern methods and responses to pest outbreaks by rice farmers in Chachoengsao Province, Central ThailandStone, Frederick Doren January 1983 (has links)
Typescript. / Thesis (Ph. D.)--University of Hawaii at Manoa, 1983. / Bibliography: leaves [459]-474. / Microfiche. / xxiv, 474 leaves, bound ill. (some col.), maps 29 cm
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Controlling Soilborne Diseases of Potato and Influencing Soil Microbiology with Brassica Cover CropsLynch, Ryan P. January 2008 (has links) (PDF)
No description available.
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The construction of an infectious clone of grapevine virus A (GV A)Du Preez, Jacques 04 1900 (has links)
Thesis (MSc (Genetics))--University of Stellenbosch, 2005. / An infectious clone of a viral RNA genome is one that can be used, either as an in vitro transcript or as
cDNA, to produce an infection in a susceptible plant. Infectious clones serve as a tool to study viral
RNA genomes at a molecular level to gain deeper insight into genome organization, viral gene
function, presence of regulatory sequences and gene expression. In the Western Cape (and elsewhere) a
new crippling grapevine disease, known as Shiraz disease, is emerging of which the aetiology and
pathogenic agents involved are not yet fully understood. Grapevine virus A (GVA), genus Vitivirus,
family Flexiviridae, is thought to be the associated with this disease. The aim of this study was to
construct a full-length infectious cDNA clone of GVA, which will aid in the molecular study of the
viral genome. This clone could ultimately be used to investigate GVA’s involvement in Shiraz disease,
which could lead to the unravelling of the aetiology and control of the disease. A full-length clone of
GVA, named GVA-IC2/T7-2972-3, was constructed in several steps using restriction digestion/ligation
and primer overlap extension PCR. Grapevine virus A cDNA fragments were obtained from GVAinfected
Nicotiana benthamiana and Vitis vinifera plants using three different techniques, of which the
Rapid direct-one-tube RT-PCR was most successful. A 5’ T7 promoter and a 3’ poly-A tail were
incorporated and the full-length clone was cloned into pBluescript II SK (+). Full-length sequencing
of the clone, revealed two significant frameshift mutations. The first mutation was a single base pair
insertion (one G) in a slippery site of 6 G’s at position 1380 – 1385 in open reading frame one (ORF 1)
of the viral genome. This mutation was corrected by PCR-based site-directed mutagenesis, which
resulted in pSK-GVA-mutagen-3 and pSK-GVA-mutagen-4. The second mutation was a single base
pair deletion (one G) at position 6959 in ORF4, which coded for the coat protein (CP). Several
techniques were attempted to correct this mutation, but none were successful. Even though the second
mutation could not be corrected, in vitro transcriptions were performed on three clones followed by
subsequent infections of N. benthamiana plants. The three clones included pSK-GVA-mutagen-3, pSKGVA-
mutagen-4 (both hosting the mutation at position 6959) and GVA-IC2/T7-2972-3 (hosting both
mutations). At 21 days post-inoculation no significant visual symptoms were observed in plants
infected with in vitro RNA or in plants infected with wild type GVA. Rapid direct-one-tube RT-PCR
results revealed the presence of viral RNA in infected leaves and apical leaves of infected plants, and
provided preliminary evidence that the mutated clones were still capable of systemic infection and viral
movement. These results are still inconclusive, and several post-infection studies will have to be
performed to confirm these findings. Koch's postulates will also have to be proved in order to confirm the infectious nature of the clones. The effect of the two mutations in the constructed clones will be
investigated further and post-infection analysis performed to deduce whether the viral progeny are
devoid of the mutations. Three full-length GVA cDNA clones (hosting mutations) seemingly capable
of systemic infection in N. benthamiana plants were constructed in this study and have laid the
foundation for molecular and mutational analysis of the GVA genome. This could lead to the study of
pathogen-host interactions in order to unravel the aetiology of Shiraz disease in the future.
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Leaf blackening and the control thereof in selected Protea species and cultivarsWindell, Nicole Elizabeth 03 1900 (has links)
Thesis (MScAgric)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Leaf blackening, a postharvest disorder which is characterized by a dark brown to black
discoloration, is found in most commercially important Protea cut flower species and cultivars. As
this disorder is known to increase with storage time, it is a major concern to the South African
industry as the use of sea freight is increasingly preferred due to lower transport costs and a more
favourable carbon footprint. The cause of leaf blackening has been strongly linked to a carbohydrate
stress exerted by the large inflorescence, thus requiring the utilization of sugar bound polyphenols in
the foliage, which when removed, can oxidize enzymatically or non-enzymatically.
A study where harvesting was done throughout the season as well as on selected days at
08:00, 12:00, 15:00 and 17:00, concluded that leaf blackening incidences in Protea cv. Sylvia stems
varies significantly throughout the season, between years and even with the harvest time of day.
Leaf blackening incidences increased from October onwards and remained high until February,
before decreasing to acceptably lower levels towards March to May. Carbohydrate- and phenolic
content together with water status of leaves at harvest was not able to accurately predict incidence
of the associated leaf blackening. However, irrespective of the season of harvesting, leaf blackening
was significantly lower when stems were harvested later in the day than compared to stems
harvested in the morning. Low sucrose and high water content at these harvest times was positively
correlated to high incidences of leaf blackening.
In a next study where uptake dynamics of glucose pulsing was investigated, Protea cv. Sylvia
was harvested at different times throughout the day, dehydrated to various levels and pulsed with
an increasing range of glucose concentrations. Pulsing solution uptake per stem was found to be
highly influenced by these factors, as dehydration of stems and a harvest time later during the day
both decreased stem water potential, which then increased pulse-solution uptake within a certain
time period. The daily harvest time influenced transpiration, whilst pulse-solution uptake decreased
with an increase in glucose pulse concentration.
When stems were pulsed pre-storage with an increasing range of glucose concentrations, not
only did pulses of between 4.7 – 13.7% glucose significantly delayed the incidence of leaf blackening,
but it also maintained a positive water balance longer in stems during vase life.
Ethanol or acetaldehyde vapour did not provide a viable alternative for reducing leaf
blackening incidence in Protea cv. Sylvia, although a synergistic effect was found when ethanol
vapour or pulsing was used in combination with glucose. A commercial verification trial disclosed
that Protea magnifica and Protea ‘Pink Ice’ reacted more beneficial to ethanol vapour than was
observed in ‘Sylvia’. This study confirms that carbohydrate availability within the Protea cut stem remains a key
factor in the control of leaf blackening. Factors which assist in maintaining high internal
carbohydrate levels, such as enhanced glucose pulse uptake or effective vase solution utilization will
contribute to providing an optimum control of leaf blackening during vase life following long-term
cold storage. / AFRIKAANSE OPSOMMING: Loofblaarverbruining is ‘n na-oes defek wat gekarakteriseer word deur ‘n donker bruin na
swart verkleuring wat voorkom in meeste kommersieël belangrike Protea snyblom spesies en
kultivars. Hierdie defek is bekend daarvoor dat dit toeneem met stoortyd, dus is dit ‘n groot
kommer vir die Suid-Afrikaanse industrie, met toenemende gebruik van seevrag as vervoer keuse
wat laer vervoer kostes en meer gunstige ‘koolstof voetspoor’ bevoordeel. Die oorsaak van
loofblaarverbruining word sterk gekoppel aan ‘n koolhidraat stres wat uitgeoefen word deur die
groot bloeiwyse op die loofblare, waar suiker-gebonde polifenoliese verbindings ensiematies of nieensiematies
geoksideer word met die verwydering van die suiker verbinding.
'n Studie waar geoes was regdeur die seisoen, sowel as op geselekteerde dae om 08:00, 12:00,
15:00 en 17:00, het bevind dat die voorkoms van loofblaarverbruining in stele van Protea kv. Sylvia
aansienlik geskil regdeur die seisoen, tussen jare en selfs met die oes tyd gedurende die dag. Die
voorkoms van loofblaarverbruining het toegeneem vanaf Oktober en het hoog gebly tot en met
Februarie, voordat dit gedaal het tot aanvaarbare laer vlakke teen Maart, tot en met Mei.
Koolhidraat-en fenoliese inhoud sowel as die water status van die blare by oes was onsuksesvol om
die voorkoms van die gepaardgaande loofblaarverbruining akkuraat te voorspel.
Loofblaarverbruining was egter aansienlik laer as stele geoes later in die dag teenoor stele geoes in
die oggend, ongeag die seisoen van oes. Lae sukrose en 'n hoë water inhoud geassosieer met
hierdie oes-tye was positief gekorreleerd met ‘n hoë voorkoms van loofblaarverbruining.
In 'n volgende studie waar die opname dinamika van glukose pulsing ondersoek was, is Protea
kv. Sylvia stele geoes op verskillende tye dwarsdeur die dag, gedehidreer tot verskillende vlakke en
met 'n toenemende reeks van glukose konsentrasies gepuls. Pulsoplossing opname per steel is sterk
beïnvloed deur hierdie faktore, aangesien dehidrasie van die stele asook stele geoes later gedurende
die dag die afname van steel waterpotensiaal veroorsaak het, terwyl die puls-oplossing opname
versnel het binne ‘n bepaalde tyd. Die tyd van oes beïnvloed ook transpirasie, terwyl vaas oplossing
opname afgeneem met 'n toename in glukose puls konsentrasie.
Wanneer ‘Sylvia’ stele gepuls was voor stoor met 'n reeks van toenemende glukose
konsentrasies, het nie net die puls van tussen 4.7 – 13.7% glukose aansienlik die voorkoms van
loofblaarverbruining vertraag nie, maar dit het ook ‘n positiewe water balans langer in stele
gedurende die vaas lewe behou.
Nie etanol of asetaldehied dampe is bevind as geskikte alternatief vir glukose pulsing om die
voorkoms van loofblaarverbruining in Protea kv. Sylvia te verlaag nie, alhoewel ‘n sinergistiese effek
waargeneem was wanneer etanol in kombinasie met glukose gebruik was. ‘n Kommersieële bevestigingstoetsing het bevind dat Protea magnifica en ‘Pink Ice’ meer voordeel uit ‘n ethanoldamp
behandeling kon trek teenoor ‘Sylvia’.
Hierdie studie het bevestig die belangrikheid van koolhidraat beskikbaarheid in die Protea
snyblom, vir beheer van loofblaarverbruining. Faktore wat die handhawing van hoë interne
koolhidrate vlakke, soos bevorderde glukose puls opname of effektiewe vaas oplossing benutting sal
bydra tot ‘n optimal beheer van loofblaarverbruining tydens vaas lewe na langtermyn koueopberging. / National Research Fund (NRF) for their financial support in 2009; Protea
Producers of South Africa (PPSA) and Productschap Tuinbouw (PT) as well as the Frank
Batchelor Will Trust Grant for the financial support.
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Ecologia da paisagem e controle de pragas agrícolas /Garcia, Adriano Gomes. January 2014 (has links)
Orientador: Paulo Fernando de Arruda Manera / Banca: Wesley Augusto Conde Godoy / Banca: Carlos Roberto Padovani / Resumo: / Abstract: / Mestre
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Metodologias de aplicação de sulfonamida heterocíclica no controle de Meloidogyne javanica e Pratylenchus brachyurus em soja /Oriani, Eduardo Elias. January 2015 (has links)
Orientador: Pedro Luiz Martins Soares / Banca: Rita de Cássia Panizzi / Banca: Sílvia Renata Siciliano Wilcken / Resumo: Os problemas com nematoides aumentaram significativamente nas áreas de cultivo de soja e práticas de redução populacional são fundamentais para minimizar as perdas na produtividade. Três metodologias de aplicação, utilizando a nova sulfonamida nematicida, para controle do M. javanica e P. brachyurus em soja foram avaliadas: 1) aplicação no sulco de plantio sobre as sementes, 2) aplicação em área total 5 dias antes do plantio, 3) aplicação no sulco de plantio sobre as sementes, e mais uma aplicação complementar 20 dias após a emergência (DAE) em área total. Foram avaliados: i) número de plantas por metro linear (14 DAE); ii) altura das plantas e massa fresca da parte aérea (45 e 90 DAE); iii) população de diferentes estádios de desenvolvimento de nematoide (ovos, juvenis e adultos) nas raízes (45 e 90 DAE); iv) índice de galhas (45 e 90 DAE); v) produtividade. Dentre as metodologias testadas, a aplicação da sulfonamida nematicida aplicada no sulco de plantio sobre as sementes apresentou redução populacional de M. javanica aos 45 DAE na dose de 1.500 g i.a/ha e na dose de 2.000 g i.a/ha foi detectada redução populacional aos 90 DAE. Essa metodologia não mostrou efeito sobre P. brachyurus nas doses testadas. A segunda metodologia, com aplicação da sulfonamida, em área total 5 dias antes do plantio, reduziu a população de M. javanica aos 90 DAE nas doses de 500 e 1.500 g i.a/ha. Essa metodologia também reduziu a população de P. brachyurus aos 45 DAE na dose de 1.500 g i.a/ha. A terceira metodologia, com aplicação da sulfonamida nematicida no sulco de plantio (150 g i.a /ha) e mais uma aplicação complementar em área total 20 DAE (750 g i.a /ha) reduziu significativamente a população de M. javanica até 45 DAE e reduziu as galhas até 90 DAE. Essa metodologia não... / Abstract: Problems with nematodes have been increasing on soybeans fields. Programs for nematode population reduction are essential to reduce yield losses. Three application methodologies, using the novel sulfonamide nematicide, were tested to control M. javanica e P. brachyurus in soybean: 1) furrow application at sowing planting 2) broadcast application in the total area 5 days before planting, 3) furrow application at sowing and an additional total area application 20 days after emergence (DAE). Evaluations consisted in: i) number of plants per linear meter (14 DAE); ii) plants height and fresh weight of shoots (45 and 90 DAE); iii) nematode population of different developmental stages (eggs, juveniles and adults) in the roots (45 and 90 DAE); iv) gall index (45 and 90 DAE); v) yield. Among tested methodologies, sulfonamide nematicide furrow application at sowing presented M. javanica population reduction 45 DAE with 1.500 g a.i/ha and with 2.000 g a.i/ha was detected population reduction 90 DAE. This methodology did not reduce P. brachyurus population in any of the doses tested. The second methodology, with application in the total area 5 days before planting, reduced M. javanica population with 500 and 1.500 g a.i/ha 90 DAE. This methodology also reduced P. brachyurus with 1.500 g a.i/ha 45 DAE. The third methodology, sulfonamide nematicide furrow application at sowing (150 g a.i/ha) and an additional total area application 20 DAE (750 g a.i/ha) significantly reduced M. javanica population until 45 DAE and showed gall index reduction until 90 DAE. This methodology also did not have any effect on P. brachyurus population in any of the doses tested. In all methodologies tested the sulfonamide did not show negative crop response, did not increase the plant height, fresh weight and yield / Mestre
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