Nabis kinbergii is a native polyphagous predator in Australia. It has been found in all states and territories of Australia. N. kinbergii has been regarded as an efficient predator of many insect pests in lucerne, cotton and particularly brassica crops. The circadian rhythms, the effects of different prey on development and reproduction, and prey preferences of N. kinbergii have not been studied in South Australia. These are the subjects of this thesis. N. kinbergii is more active at night than in the day. They seemed to be still more frequently at dawn and more active at dusk under natural environmental conditions. Yet, their behaviour was possibly different when they were held in a controlled environment with artificial light. Under both natural and artificial lighting conditions, they would spend more time moving on plants at night. They spent less time moving than other activities. Furthermore, they were more active during the second day of the observations, probably because of the hunger. A mixed diet including Plutella xylostella, Myzus persicae and Brevicoryne brassicae brought the most significant positive influences to the development, survival and longevity of N. kinbergii. It had a shorter preoviposition period and greater egg production when fed on P. xylostella than when fed on M. persicae. Among the three prey, B. brassica was the poorest food because the survival rate between egg hatch and adult eclosion was only 7.5 %, compared to 85 %, 92.5 % and 97.5 % when N. kinbergii fed on M. persicae, P. xylostella and a mixed diet, respectively. Evidence of prey preference was exhibited by N. kinbergii. B. brassica seemed to be the least preferred food. N. kinbergii possibly attacked less mobile prey and delayed eating prey with poor nutrition or that were toxic. In wind tunnel experiments, N. kinbergii may have been attracted by plant volatiles rather than prey odour. These findings may help to refine the timing of experiments and improve the understanding of the role of this predator in integrated pest management. / Thesis (M.Sc.) -- University of Adelaide, School of Agriculture, Food and Wine, 2008

The soil-borne fungi Rhizoctonia solani Kuhn and Sclerotinia sclerotiorum De Bary are ubiquitous plant pathogens with a wide host range. They are among the most widespread and destructive diseases of many crops, including sunflowers. Although in many cases, the use of chemicals appears to be the most economical and efficient means of controlling plant pathogens, their environmental concerns and the development of tolerance in pathogen populations have led to drastic reduction in their usage and increased the need to find alternative means of disease control. The potential benefits of applying Trichoderma harzianum Rifai and silicon (Si) nutrition to plants have been extensively reviewed. In this study, the ability of T. harzianum (Eco-T®), soluble silicon, and their combination was evaluated on sunflower (Helianthus annuus L.), for their potential to suppress pathogenic strains of R. solani and S. sclerotiorum. The ability of this crop to take up and accumulate Si in different plant parts was also investigated. In vitro assessment of fungal responses to Si in PDA showed that both R. solani and S. sclerotiorum were inhibited in the presence of Si. More inhibition was observed as the Si concentration increased with a relative increase in pH. Maximum growth inhibition was observed at 3000 mg ;-1 – 6000 mg ;-1 of PDA. No difference in inhibition between the two pathogens was observed, thus confirming the fungitoxic/suppressive ability of high Si concentrations to fungal growth. In addition, in vivo trials showed that the Si concentration of 200 mg ;-1 applied weekly significantly increased the dry weight of plants inoculated with R. solani and S. sclerotiorum and was therefore considered the optimum concentration. Assessments on in vitro antifungal activities of Eco-T® on R. solani and S. sclerotiorum, showed that Eco-T® significantly inhibited mycelial growth, in both dual culture methods and volatile and non-volatile compounds produced by Eco-T®. In addition, the combination of Eco-T® and Si was most effective in suppressing damping-off and increasing plant dry weight of sunflower seedlings in the greenhouse. The combination of Si and Eco-T® significantly increased percentage germination, number of leaves and head dry weight of the sunflower cultivars tested. Silicon alone increased growth but was unable to control R. solani and S. sclerotiorum effectively. Rhizotron studies showed that S. sclerotiorum infected the host through the roots and the stem, whereas R. solani only infected the host through the roots. A study on Si uptake and distribution showed that sunflower accumulates Si in various plant tissues. Analysis of plant tissues revealed that more Si was accumulated in leaves > stems > roots, with the Si levels in leaves being significantly higher than in stems and roots. In conclusion, Si alone could be used to increase growth but was unable to control R. solani and S. sclerotiorum. However, Si together with Eco-T® provides an environmentally friendly alternative for the control of R. solani and S. sclerotiorum, and enhanced plant growth and yield. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2009.

Baculoviruses are arthropod-specific DNA viruses that are highly virulent to most lepidopteran insects. Their host specificity and compatibility with IPM programmes has enabled their usage as safe microbial insecticides (biopesticides). Two baculovirus-based biopesticides, Cryptogran and Cryptex, which have been formulated with Cryptophlebia leucotreta granulovirus (CrleGV) have been registered for the control of false codling moth (FCM), Thaumatotibia (=Cryptophlebia) leucotreta (Meyrick) (Lepidoptera: Tortricidae) in South Africa and have been successfully incorporated into IPM programmes. However, several studies have indicated that insects can develop resistance to baculovirus-based biopesticide as was shown with field populations of codling moth (CM), Cydia pomonella (L.), which developed resistance to the biopesticide Cydia pomonella granulovirus (CpGV-M) in Europe. Other studies have shown that, under laboratory conditions, FCM populations differ in their susceptibility to Cryptogran and Cryptex. In order to investigate difference in susceptibility as well as protect against any future resistance by FCM to Cryptogran and Cryptex, a search for novel CrleGV-SA isolates from diseased insects from different geographic regions in South Africa was performed. Six geographic populations (Addo, Citrusdal, Marble Hall, Nelspruit, Baths and Mixed colonies) of FCM were established and maintained in the laboratory. Studies on the comparative biological performance based on pupal mass, female fecundity, egg hatch, pupal survival, adult eclosion and duration of life cycle of the Addo, Citrusdal, Marble Hall, Nelspruit and Mixed colonies revealed a low biological performance for the Citrusdal colony. This was attributed to the fact that FCM populations found in the Citrusdal area are not indigenous and may have been introduced from a very limited gene pool from another region. When insects from five colonies, excluding the Baths colony, were subjected to stress by overcrowding , a latent baculovirus resident in the Addo, Nelspruit, Citrusdal, Marble Hall and Mixed colonies was brought into an overt lethal state. Transmission electron micrographs revealed the presence of GV occlusion bodies (OBs) in diseased insects. DNA profiles obtained by single restriction endonuclease analysis of viral genomic DNA using BamH 1, Sa/1, Xba1 , Pst1, Xh01 , Kpn1, Hindlll and EcoR1 revealed five CrleGV-SA isolates latent within the insect populations. The new isolates were named CrleGV-SA Ado, CrleGV-SA Cit, CrleGV-SA Mbl, CrleGVSA Nels and CrleGV-SA Mix isolates. The novelty of the five CrleGV-SA isolates was confirmed by the presence of unique submolar bands, indicating that each isolate was genetically different. PCR amplification and sequencing of the granulin and egt genes from the five isolates revealed several single nucleotide polymorph isms (SNPs) which, in some cases, resulted in amino acid substitutions. DNA profiles from RFLPs, as well as phylogenetic analysis based on granulin and egt sequencing showed the presence of two CrleGV-SA genome types for the CrleGV-SA isolate. Cryptex and CrleGV-SA Ado, CrleGV-SA Cit, CrleGV-SA Mbl and CrleGV-SA Mix were placed as members of Group one CrleGV-SA, and Cryptogran and CrleGV-SA Nels isolate were placed into Group two CrleGV-SA. In droplet feeding bioassays, the median survival time (STso) for neonate larvae inoculated with Group one and two CrleGV-SA were determined to range from 80 - 88 hours (3.33 - 3.67 days), for all five colonies. LDso values for Group one and two CrleGV-SA against neonates from the Addo, Citrusdal, Marble Hall, Nelspruit and Mixed colonies varied between some populations and ranged from 0.80 - 3.12 OBs per larva, indicating some level of variation in host susceptibility. This is the first study reporting the existence of genetically distinct CrleGV baculovirus isolates infecting FCM in different geographical areas of South Africa. The results of this study have broad-ranging implications for our understanding of baculovirus-host interactions and for the application of baculovirus basedbiopesticides.

The interaction between farmers, agricultural scientists and extension workers is sometimes overlooked in agricultural entomology. In an attempt to respond to this reality this study examines some foundation of this interaction in relation to the pest management practices of subsistence and small-scale farmers and also highlights the problems that might arise in the implementation of IPM. Problems involving pests occurrence; language barriers; beliefs, knowledge and perception about insects, and visual literacy are examined. The thesis has a two-fold focus, firstly the study of pests on cabbages of subsistence farmers in Grahamstown and secondly a broader focus on other aspects such as cultural entomology, perception of insects and visual literacy specifically in relation to Xhosa speaking people in the Eastern Cape. The most important crop for emergent farmers in the Eastern Cape are cabbages, which have a variety of pests of which diamondback moths and are the most important. Traditional pest management practices tend to influence the development of IPM programmes adopted by these farmers. Eastern Cape farmers apply periodic cropping systems, which had an effect on the population densities of diamondback moth (DBM), other lepidopteran pests and their parasitoids. Considering the maximum population densities of DBM, which were 0.2 - 2.9 larvae/plant, there were no major pest problems. The availability of parasitoids, even in highly disturbed and patchy environments, showed good potential for biological control. Since some extension officers cannot speak the local farmers’ language, a dictionary of insect names was formulated in their language (isiXhosa) to assist communication. Response-frequency distribution analysis showed that the dictionary is essentially complete. The literal translations of some names show that isiXhosa speakers often relate insects to people, or to their habitat or classify them according to their behaviour. Farmers from eight sites in the Eastern Cape were interviewed regarding their knowledge and perception of insect pests and their control thereof. To some extent, farmers still rely on cultural control and have beliefs about insects that reflected both reality and superstition. There is no difference between the Ciskei and Transkei regions regarding insect-related beliefs. Farmers generally lack an understanding of insect ecology. There is a need for farmers to be taught about insects to assist with the implementation of IPM. Leftover pesticides from commercial farms or detergents are sometimes used to manage the pests. When training illiterate or semi-literate farmers, it is important to understand their media literacy so as to design useful graphic and object training media. Generally farmers showed that they either understand graphic or object media depending on the features of the insects being looked at. These findings are discussed with regard to the potential development of IPM training material for subsistence and small-scale farmers in a community.

Three sampling methods for estimating abundance of alfalfa weevil (AW) larvae (Hypera postica Gyllenhal) were evaluated for both accuracy and precision. Calibration equations were developed to convert intensity estimates of AW larvae among sampling methods. Greenhouse experiments evaluating the interaction of moisture stress and defoliation by AW larvae indicated that yield response of alfalfa to AW feeding is dependent on moisture stress levels. Field studies on the influence of AW feeding on alfalfa confirmed the importance of moisture stress in alfalfa tolerance to weevil feeding. Quadratic regression models are presented to predict yield loss and changes in stem density as a function of weevil intensity. A sequential sampling plan was developed and validated for use in pest management decision making. Validation of the plan indicated an average error rate of 1.8%, with the number of samples needed reduced by 55% in 1980, 53% in 1981, and 28% in 1982. A net benefit analysis the Virginia Alfalfa IPM program indicated that growers participating in the program during 1981-84 realized an estimated average increase in net revenue of $8.80 per hectare from the alfalfa weevil scouting program, and $28.13 per hectare from the potato leafhopper scouting program. / Ph. D. / incomplete_metadata

The first serious outbreak of brown rust of sugarcane caused by Puccinia melanocephala Syd. & P. Syd. was reported in India in 1907. It was first reported in South Africa (SA) in 1941 on the variety Co301 and is now present in almost all the sugarcane growing areas of the world. In SA, it is now described as an important disease of sugarcane, causing yield losses of up to 26% in susceptible varieties. Within the SA sugar industry, rust is controlled through the use of resistant varieties as it is the most economical method of control. However, most of the newer varieties that are being released have an intermediate resistance rating for rust. An integrated management approach for the control of rust is therefore being investigated. Aspects investigated in this study included environmental conditions required for development of the disease i.e. epidemiology, the use of silicon (Si) as a cultural control method against brown rust and identification of gene sequences expressed in response to brown rust infection. For the epidemiology study, inoculated plants were incubated in a dew chamber at different temperatures and leaf wetness periods. The choice of leaf wetness duration and temperature was based on urediniospore germination studies. The optimum temperature for urediniospore germination and disease development at > 98% relative humidity was found to be between 20 and 25°C with nine hours of leaf wetness. Silicon has been shown to reduce the incidence of diseases and pests in a number of crops. The ability of sugarcane to accumulate Si and the location of Si deposition was established using two uptake and deposition trials. Different concentrations of Si were applied to the plant and accumulation in the roots, stalks, old leaves and young leaves was determined using inductively coupled plasma optical emission spectrometry, with accumulation found to be roots > old leaves > stalks > young leaves. Silicon deposition in the leaves was determined using energy dispersive X-ray mapping on freeze dried specimens and significant differences were found between the upper epidermis, lower epidermis and mesophyll with the most Si being deposited in the lower epidermis. For disease severity, plants were naturally infected with rust and rated weekly. A significant decrease in disease severity and area under disease progress curve was noted when the Si concentration increased, indicating that Si has potential in reducing rust incidence. Currently, the most reliable and economical method of managing brown rust is with the use of resistant varieties. Identification of resistance within breeding lines is therefore important. For this part of the study, suppression subtractive hybridization was used as a tool to identify differentially expressed genes between a susceptible and resistant variety and a susceptible and intermediate variety, in response to brown rust infection. Two efficient subtracted cDNA libraries were generated and differentially expressed sequences were identified within each library. The results of this study show potential for the development of molecular markers which could be used for the early identification of brown rust resistance during the breeding process. This study forms a firm basis on which an integrated management strategy, for the management of brown rust in the SA sugar industry, could be designed. The cDNA sequences identified could be further investigated and used to develop molecular markers to select for rust resistant varieties, the epidemiology results together with further field data could be used to develop a disease prediction model and Si has potential in the field to reduce brown rust severity. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2009.

Submitted by Milena Rubi (milenarubi@ufscar.br) on 2017-08-08T17:44:33Z No. of bitstreams: 1 GHIOTTO_Thais_2016.pdf: 18907197 bytes, checksum: 0779f8ac869df152bdd7747df97a15e5 (MD5) / Approved for entry into archive by Milena Rubi (milenarubi@ufscar.br) on 2017-08-08T17:44:43Z (GMT) No. of bitstreams: 1 GHIOTTO_Thais_2016.pdf: 18907197 bytes, checksum: 0779f8ac869df152bdd7747df97a15e5 (MD5) / Approved for entry into archive by Milena Rubi (milenarubi@ufscar.br) on 2017-08-08T17:44:49Z (GMT) No. of bitstreams: 1 GHIOTTO_Thais_2016.pdf: 18907197 bytes, checksum: 0779f8ac869df152bdd7747df97a15e5 (MD5) / Made available in DSpace on 2017-08-08T17:44:55Z (GMT). No. of bitstreams: 1 GHIOTTO_Thais_2016.pdf: 18907197 bytes, checksum: 0779f8ac869df152bdd7747df97a15e5 (MD5) Previous issue date: 2016-05-09 / Não recebi financiamento / Megastigmus transvaalensis is an exotic wasp that attacks Brazilian pepper tree drupes Schinus terebinthifolius in native forests and areas of restoration and ecological restoration in Brazil. The parasitism begins with the oviposition M. transvaalensis in drupes S. terebinthifolius where the larvae hatch and remain internally feeding of nutrients and tissue, affecting germination. The aim of this work was to study the effect of temperature, rainfall and humidity in the population dynamics of M. transvaalensis and determine the parasitism rate and sex ratio of this wasp in drupes S. terebinthifolius. The study was performed with yellow sticky traps and collection of S. terebinthifolius drupes in seasonal semideciduous forest during August 2014 to September 2015, in the region of Sorocaba, São Paulo, Brazil. The capture of insects through the sticky traps proved satisfactory, and thus can be applied to the monitoring of small Hymenopteros. Populations of M. transvaalensis were negatively correlated with the maximum temperature and population peak in the fall of 2015, meaning that when the maximum temperature has reduced, there is a higher incidence of insect field. The parasitism rate of S. terebinthifolius drupes ranged from zero to 36.34% during this period, making this value an aggravating factor for the emergence of new individuals, since this phytophagous wasp has the potential to be spread throughout Brazil and It poses a threat to the natural regeneration of S. terebinthifolius. The sex ratio of M. transvaalensis was 0.42 and 0.08 in the laboratory field. The bio-ecology and the damage caused by M. transvaalensis in drupes S. terebinthifolius warrant further studies to integrated management / Megastigmus transvaalensis é uma vespa exótica que ataca drupas de aroeira-pimenteira Schinus terebinthifolius em florestas nativas e em áreas de recomposição e restauração ecológica no Brasil. O parasitismo inicia com a oviposição de M. transvaalensis nas drupas de S. terebinthifolius, onde as larvas internamente eclodem e permanecem alimentando-se dos nutrientes e tecidos, prejudicando a germinação. O objetivo desse trabalho foi estudar o efeito da temperatura, precipitação e umidade na flutuação populacional de M. transvaalensis e determinar o índice de parasitismo e razão sexual dessa vespa nas drupas de S. terebinthifolius. O estudo foi realizado com armadilhas adesivas amarelas e coleta de drupas de S. terebinthifolius em fragmento de floresta estacional semidecidual, durante agosto de 2014 a setembro de 2015, na região de Sorocaba, São Paulo, Brasil. A captura dos insetos através das armadilhas adesivas se mostrou satisfatória, podendo assim ser aplicada para o monitoramento de pequenos Hymenopteros. As populações de M. transvaalensis apresentaram correlação negativa com a temperatura máxima e pico populacional no outono de 2015, significando que, quando a temperatura máxima apresenta redução, há maior incidência do inseto em campo. O índice de parasitismo das drupas de S. terebinthifolius variou de zero a 36,34% no período avaliado, tornando este valor um agravante para o surgimento de novos indivíduos, uma vez que, essa vespa fitófaga tem potencial de ser disseminado por todo Brasil e representa ameaça para a regeneração natural de S. terebinthifolius. A razão sexual de M. transvaalensis foi de 0,42 no laboratório e 0,08 em campo. A bioecologia e os danos causados por M. transvaalensis em drupas de S. terebinthifolius justificam mais estudos visando o manejo integrado dessa vespa fitófaga.

Plant health system is an important element for the control and management of plant pests to ensure food production and security as well as safe trade. The objectives of this study were to: identify the existing knowledge gaps on current plant health system at the national and provincial level, identify critical areas to be addressed in the current plant health institutional framework and identify the existing limitations and risks on current legislation. A semi-structured questionnaire was used to collect the data. The data was analysed statistically using the one-way frequency and Spearman’s Rank correlation coefficients.The study found that the Provincial Departments of Agriculture (PDAs) (below 50%) lack knowledge of plant health system as compared to the national authorities: DAFF and DEA (above 70%). The study also found that there were no formal linkages between the national and provincial authorities. The study further revealed that there is a need for harmonisation of relevant legislation. It can be concluded that there are knowledge gaps on plant health matters between the national authority and the provincial level and that there are no formal linkages within the spheres of government on plant health matters. / Agriculture, Animal Health and Human Ecology / M. Sc. (Agriculture)

Thesis (MScConsEcol (Conservation Ecology and Entomology))--University of Stellenbosch, 2009. / ENGLISH ABSTRACT: Pseudococcus viburni (Signoret) (Hemiptera: Pseudococcidae) (obscure mealybug), is a common and serious pest of apples and pears in South Africa. Consumer and regulatory pressure to produce commodities under sustainable and ecologically compatible conditions has rendered chemical control options increasingly limited. Information on the seasonal occurrence of pests is but one of the vital components of an effective and sustainable integrated pest management system needed for planning the initiation of monitoring and determining when damage can be expected. It is also important to identify which orchards are at risk of developing mealybug infestations while development of effective and early monitoring tools for mealybug populations will help growers in making decisions with regards to pest management and crop suitability for various markets. It is also essential to determine the presence and efficacy of naturally occurring biological control agents in orchards so as to ascertain the potential of biological control as a viable alternative in orchards. However, under the current integrated pest management protocol, it has been difficult to determine this, due to the sporadic and relatively low incidence of mealybug infestations in some orchards, or by simply relying on naturally occurring field populations of biocontrol agents. Knowledge of the environmental conditions under which P. viburni population levels may become destructive is also essential for timing the release of insectary reared natural enemies as well as understanding the population ecology of this pest and its natural enemies. Information was gathered regarding the seasonal phenology of P. viburni and its natural enemies in pome fruit orchards in the Western Cape Province during the 2007/08 and 2008/09 growing seasons. Seasonal population studies showed that P. viburni has multiple overlapping generations with all life stages present throughout the year. The highest orchard infestations occurred during the summer period until early winter (January to early June). This was followed by a decrease in population from late June to November, before another increase in December. Presence-absence sampling of mealybugs on the host plant revealed that woody parts of the tree, such as the trunk and old stems were the most preferred sites for mealybug habitation, due to the availability of protected refuge sites. Migration of mealybug populations to newer growth and the upper sections of the tree crown, such as the new stems, leaves and eventually the fruit, was observed from December throughout the summer period until the early winter in June. Fruit colonization in both apples and pears commenced in January, when the fruit had developed a size sufficient for P. viburni to penetrate and occupy spaces such as the fruit core, calyx and stem end. There was no evidence of P. viburni occurring beneath the soil surface or on the roots of host trees. Two natural enemies of mealybugs, namely Pseudaphycus maculipennis (Mercet) and Coccidoxenoides perminutus (Girault), were found to be active in apple and pear orchards in the Western Cape. However, the status of C. perminutus as a parasite of P. viburni still needs to be verified despite evidence of emergence from P. viburni mummies, which was not sufficient enough to suggest that it is a useful biological control agent. Seasonal abundance trends of the two natural enemies revealed that their lifecycle is synchronized with that of the host. However, there was no evidence of P. maculipennis activity in Ceres. No predators were found during the course of this study. The rate of P. viburni parasitism at harvest was 46.52%, with P. maculipennis and C. perminutus constituting 98.966% and 1.034% of the parasitoids recovered from mealybug mummies, respectively. Studies on the use of pheromone traps as early monitoring tools for P. viburni showed that there was a positive and significant relationship between the fruit infestation and number of P. viburni adult males caught in pheromone-baited traps (r2 = 0.454). The action threshold level was estimated to be 2.5 male P. viburni caught per trap per fortnight at an economic threshold of 2% fruit infestation. / AFRIKAANSE OPSOMMING: Pseudococcus viburni (Signoret) (Hemiptera: Pseudococcidae) (ligrooswitluis), is ‘n algemene en ernstige plaag van appels en pere in Suid-Afrika. Druk deur verbruikers en regulasies om kommoditeite onder volhoubare en ekologies verenigbare toestande te produseer het chemiese beheeropsies toenemend beperk. Inligting oor die seisoenale voorkoms van plae is een van die essensiële komponente van ‘n effektiewe en volhoubare geïntegreerde plaagbestuurprogram. Dit is in die aanvanklike beplanning van monitering en om te bepaal wanneer skade verwag kan word. Dit is ook belangrik om boorde vroegtydig te identifiseer wat die risiko het om witluisbesmettings te ontwikkel. Die ontwikkeling van effektiewe en vroeë moniteringstegnieke vir witluisbevolkings sal produsente help met besluitneming rakende plaagbestuur en die geskiktheid van gewasse vir verskeie markte. Dit is ook noodsaaklik om die teenwoordigheid en effektiwiteit van biologiese beheer agente wat natuurlik in boorde voorkom te bepaal ten einde die potensiaal van biologiese beheer as ‘n lewensvatbare alternatief vas te stel. Onder die huidige geïntegreerde plaagbestuurprotokol was dit egter moeilik om laasgenoemde te bepaal weens die sporadiese en relatiewe lae voorkoms van witluisbesmettings in sommige boorde of deur bloot staat te maak op die veldpopulasies van biologiese beheer agente wat natuurlik voorkom. Kennis van die omgewingstoestande waaronder P. viburni bevolkingsvlakke skadelik raak is ook noodsaaklik vir die beplanning van vrylating van biologiese beheer agente, asook om die bevolkingsekologie van hierdie plaag en sy natuurlike vyande te verstaan. Inligting oor die seisoenale fenologie van P. viburni en sy natuurlike vyande in sagtevrugte boorde in die Westelike Kaapprovinsie is gedurende die 2007/08 en 2008/09 groeiseisoene versamel. Seisoenale bevolkingstudies het getoon dat P. viburni verskeie oorvleuelende generasies het met alle stadia teenwoordig regdeur die jaar.

There is a growing recognition globally that many agrochemicals are hazardous to humans, animals and the environment. Therefore, there is a need to substitute these chemical products with biological and physical treatments, and to change agronomic practices in order to control pests and diseases in agriculture. The primary objective of this thesis was to develop and test in laboratory, field and commercial packhouses trials as alternative control measures against green mould of citrus (caused by Penicillium digitatum Pers: Fr. Sacc) and Penicillium molds of litchi (caused by several Penicillium). A South African isolate of P. digitatum, isolated from an infected orange fruit, was found to be resistant to imazalil (the standard postharvest fungicide used in South Africa). Sixty yeast and 92 Bacillus strains were screened for their antagonistic activity against this isolate of P. digitatum. None of the yeasts or Bacillus isolates produced a curative action against P. digitatum on oranges. However, yeast Isolate B13 provided excellent preventative control of P. digitatum, superior to all the Bacillus isolates, when it was applied to citrus fruit prior to artificial inoculation with P. digitatum. Electron microscopy showed that yeast Isolate B13 inhibited conidial germination of P. digitatum. For the control of P. digitatum pre-harvest, trees were sprayed with a yeast, Isolate B13, a few months or a few days before harvest. However, this treatment alone proved to be ineffective in providing preventative control of green mould on Valencia oranges. For the control of P. digitatum preharvest, trees were treated with potassium silicate for a full season. Regular potassium silicate treatments resulted in a significant preventative control of P. digitatum infection on both navel and Valencia oranges. Treatment of Eureka lemons with potassium silicate as a postharvest treatment for the control of P. digitatum resulted in reduced disease lesion diameters when applied preventatively or curatively. Electron microscopy showed that potassium silicate inhibited germination of P. digitatum conidia and growth of its mycelium. Hot-water dip treatment at 50-58°C for 60-180 seconds (in increments of 15 seconds), significantly reduced infection development in inoculated wounds of Valencia oranges compared with control fruit treated with tap water, without causing any rind damage. The integration of the yeast, a hot water dip and potassium silicate pre-and postharvest applications provided control of P. digitatum control in multiple packhouse trials. The control achieved by the yeast Isolate B13 or hot-water, and potassium silicate in the packhouse alone was superior or equivalent to that provided by imazalil. A similar study was also carried out to determine possible control measures for Penicillium sp. on litchis. In this study, a total of 23 yeast and 13 Bacillus isolates were obtained from litchi fruit surfaces. Ten yeast and 10 Bacillus isolates that had shown good efficacy against P. digitatum of citrus were added to these for screening against Penicillium sp. of litchis. None of the yeasts or Bacillus isolates produced a curative action against Penicillium sp. infection on litchis. However, several yeast isolates (YL4, YL10, YLH and B13) resulted in reduced severity of the pathogen, when applied preventatively, compared with an untreated control. The yeast isolates were superior to all the Bacillus isolates, when applied to litchis prior to artificial inoculation by Penicillium infection on litchis. Potassium silicate as a postharvest treatment for the control of the pathogen caused reduced lesion diameters when applied preventatively or curatively to naturally infected litchis. The results presented in this thesis highlight the use of biological, physical and agronomic practices singly or in combination as an alternative control strategy against citrus postharvest green mould. This thesis also provides an insight into expanding these strategies, partly or fully, for the control of other postharvest Penicillium infections using litchi as an example. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2010.