O oídio do pimentão e pimenteiras, causado pelo fungo Leveillula taurica, tem sido considerado atualmente a doença mais séria do cultivo protegido, causando perdas de até 75%. O uso de fungicidas é ineficaz sendo a melhor maneira de controle através da resistência genética. As fontes de resistência ao oídio encontradas em Capsicum annuum L., não tem sido satisfatórias por apresentarem resistência parcial e as melhores fontes ocorrem nas espécies C. baccatum e C. chinense. Existem poucos estudos sobre a herança da resistência nessas espécies. O objetivo deste trabalho foi de triar os acessos da coleção de Capsicum da ESALQ/USP, identificando possíveis fontes de resistência nas espécies C. annuum, C. baccatum e C. chinense e obter informações sobre a herança da reação de pimentão e pimentas ao oídio. Para isso 156 acessos de Capsicum foram triados e posteriormente cruzamentos entre progenitores resistentes versus suscetíveis e resistentes versus resistentes foram obtidos. As gerações F2 e alguns retrocruzamentos foram obtidos. As avaliações das reações ao oídio foram feitas na fase de frutificação, através de uma escala de notas de acordo com a severidade da doença de 1 (resistente) a 5 (altamente suscetível). Foram estimados: o número de locos segregantes, os coeficientes de herdabilidade, os progressos esperados na seleção e o tipo de ação gênica envolvida. Foram avaliadas também as reações dos híbridos entre progenitores resistentes. Dentre os materiais triados em C. annuum apenas 5% foram considerados resistentes, em C. baccatum 84% e em C. chinense 85%. A herança da resistência aooídio em Capsicum mostrou ser poligênica. As herdabilidades e ganhos de seleção estimados foram altos, indicando boas perspectivas de progresso seletivo. Os progenitores resistentes em Capsicum annuum possuem diferentes mecanismos genéticos e expressões de resistência. Enquanto em C. baccatum e C. chinense os mecanismos de resistência mostraram ser os mesmos, havendo alelismo entre as fontes. A fonte de resistência do pimentão HV-12 foi a melhor para o uso no melhoramento. / Powdery mildew caused by the fungus Leveillula taurica, is considered the most serious greenhouse sweet pepper disease, causing losses up to 75%. Its control by fungicide is ineffective, and the best way to control would be by genetic resistance. Powdery mildew resistance sources identified in Capsicum annuum L. have been unsatisfactory because they have partial resistance. The best resistant sources seem to be found in the species C. baccatum and C. chinense. However, the resistance inheritance has not been studied in these hot pepper species, except for C. annuum, with few published pappers. The present study aimed to screen the Capsicum ESALQ/USP collection accesses, to identify potential resistance sources in C. annuum, C. baccatum and C. chinense and elucidate the reaction inheritance to powdery mildew in sweet pepper and hot pepper. A total 156 Capsicum access were tested. Crosses among resistant and susceptible progenitors and among resistant ones were carried out. F2 and backcrosses generations were obtained. Reactions evaluations to powdery mildew were carried out during the fruit production using rating system based on score disease severity using scale varying from 1 (resistant) to 5 (highly susceptible). Estimation of segregating loci number, heritability and expected selection gains was made, to investigate the gene action and to evaluate the reaction to powdery mildew from resistant versus resistant single hybrids. Only 5% of the C. annuum accesses evaluated were considered to be resistant, in contrast with 84% and 85% obtained for C. baccatum and C. chinense, respectively. Resistance inheritance to powdery mildew in Capsicum spp. was found to be polygenic. In view of the high heritability and selection gains estimates, good selection progresses are expected. The genetic systems controlling resistance in the Capsicum annuum progenitors have different genetic mechanisms and expressions of resistance, while in C. baccatum and C. chinense showed to be the same in each ones with allelism between the sources. The sweet pepper HV-12 was the best source to use in breeding.

O meloeiro (Cucumis melo L.) é uma frutífera largamente cultivada no Brasil, principalmente no nordeste brasileiro, onde vem alcançando grande importância econômica, visto que grande parte da produção é voltada para a exportação. Plantas da família do meloeiro, como pepino e abóbora, são afetadas pelo oídio (Podosphaera xanthii) que causa uma das doenças foliares mais destrutivas destas espécies. Este fungo apresenta diversas raças fisiológicas e a correta identificação destas é de elevada importância para o manejo da doença, pois o melhoramento de meloeiro com o emprego de genes de resistência é o método mais eficiente para o seu controle. A identificação destas raças por meio da prática tradicional de inoculações em uma série diferenciadora de variedades de meloeiro é um método laborioso e passível de erros. Devido a isso, uma alternativa seria o uso de métodos moleculares para determinar a identidade da raça de forma rápida e econômica. O presente trabalho objetivou verificar a variabilidade de isolados de P. xanthii através da técnica de AFLP e de seqüenciamento da região ITS 5.8S do rDNA. A partir de AFLP obteve-se um dendrograma no qual não houve separação de raças, origem geográfica e nem hospedeiro. Com esta técnica verificou-se alta variabilidade entre isolados, com similaridade genética máxima de 69% e similaridade mínima de 23%. Ao contrário, os mesmos isolados apresentaram seqüências idênticas através do seqüenciamento da região ITS 5.8S do rDNA. As duas técnicas são distintas e o AFLP proporciona a obtenção de maior quantidade de fragmentos e com isso mais chances de polimorfismos. O AFLP indica que os isolados testados têm composição genética heterogênea embora isto não tenha sido evidenciado com o seqüenciamento da região ITS. / Melon (Cucumis melo L.) is a largely cultivated fruit in Brazil, especially in the northeastern region where it is achieving great economic importance since a great part of its production is destined to exportation. Plants of the melon crop family, such as cucumbers and pumpkins, are affected by powdery mildew (Podosphaera xanthii) that causes one of the most destructive foliar diseases of this species. This fungus presents various physiological races and their correct identification is of great importance to determine the control of the disease since breeding with the use of resistant genes is the most effective method for its control. Identification of these races by traditional practice of inoculation in a differential series of melon varieties is a laborious method and misleading. Due to this, an alternative would be the use of molecular methods to quickly and economically determine the race identity. The present research has the objective of verifying the variability of isolated P. xanthii through the AFLP technique and sequencing of the rDNA\'s ITS 5.8S region. From the AFLP a dendrogram was obtained where there was no separation of race, geographic region or host. With this technique, a high variability among isolated samples was verified, with 69% maximum genetic similarity and 23% minimum similarity. On the other hand, the same isolated samples presented identical sequence through the sequencing of the rDNA\'s ITS 5.8S region. The two techniques are distinct and the AFLP helps get highest amount of fragments and with this more incidence of polymorphisms. AFLP indicates that the tested isolated samples have an heterogeneous genetic composition although this was not evidenced with the sequencing of the ITS region.

O oídio do pimentão e pimenteiras, causado pelo fungo Leveillula taurica, tem sido considerado atualmente a doença mais séria do cultivo protegido, causando perdas de até 75%. O uso de fungicidas é ineficaz sendo a melhor maneira de controle através da resistência genética. As fontes de resistência ao oídio encontradas em Capsicum annuum L., não tem sido satisfatórias por apresentarem resistência parcial e as melhores fontes ocorrem nas espécies C. baccatum e C. chinense. Existem poucos estudos sobre a herança da resistência nessas espécies. O objetivo deste trabalho foi de triar os acessos da coleção de Capsicum da ESALQ/USP, identificando possíveis fontes de resistência nas espécies C. annuum, C. baccatum e C. chinense e obter informações sobre a herança da reação de pimentão e pimentas ao oídio. Para isso 156 acessos de Capsicum foram triados e posteriormente cruzamentos entre progenitores resistentes versus suscetíveis e resistentes versus resistentes foram obtidos. As gerações F2 e alguns retrocruzamentos foram obtidos. As avaliações das reações ao oídio foram feitas na fase de frutificação, através de uma escala de notas de acordo com a severidade da doença de 1 (resistente) a 5 (altamente suscetível). Foram estimados: o número de locos segregantes, os coeficientes de herdabilidade, os progressos esperados na seleção e o tipo de ação gênica envolvida. Foram avaliadas também as reações dos híbridos entre progenitores resistentes. Dentre os materiais triados em C. annuum apenas 5% foram considerados resistentes, em C. baccatum 84% e em C. chinense 85%. A herança da resistência aooídio em Capsicum mostrou ser poligênica. As herdabilidades e ganhos de seleção estimados foram altos, indicando boas perspectivas de progresso seletivo. Os progenitores resistentes em Capsicum annuum possuem diferentes mecanismos genéticos e expressões de resistência. Enquanto em C. baccatum e C. chinense os mecanismos de resistência mostraram ser os mesmos, havendo alelismo entre as fontes. A fonte de resistência do pimentão HV-12 foi a melhor para o uso no melhoramento. / Powdery mildew caused by the fungus Leveillula taurica, is considered the most serious greenhouse sweet pepper disease, causing losses up to 75%. Its control by fungicide is ineffective, and the best way to control would be by genetic resistance. Powdery mildew resistance sources identified in Capsicum annuum L. have been unsatisfactory because they have partial resistance. The best resistant sources seem to be found in the species C. baccatum and C. chinense. However, the resistance inheritance has not been studied in these hot pepper species, except for C. annuum, with few published pappers. The present study aimed to screen the Capsicum ESALQ/USP collection accesses, to identify potential resistance sources in C. annuum, C. baccatum and C. chinense and elucidate the reaction inheritance to powdery mildew in sweet pepper and hot pepper. A total 156 Capsicum access were tested. Crosses among resistant and susceptible progenitors and among resistant ones were carried out. F2 and backcrosses generations were obtained. Reactions evaluations to powdery mildew were carried out during the fruit production using rating system based on score disease severity using scale varying from 1 (resistant) to 5 (highly susceptible). Estimation of segregating loci number, heritability and expected selection gains was made, to investigate the gene action and to evaluate the reaction to powdery mildew from resistant versus resistant single hybrids. Only 5% of the C. annuum accesses evaluated were considered to be resistant, in contrast with 84% and 85% obtained for C. baccatum and C. chinense, respectively. Resistance inheritance to powdery mildew in Capsicum spp. was found to be polygenic. In view of the high heritability and selection gains estimates, good selection progresses are expected. The genetic systems controlling resistance in the Capsicum annuum progenitors have different genetic mechanisms and expressions of resistance, while in C. baccatum and C. chinense showed to be the same in each ones with allelism between the sources. The sweet pepper HV-12 was the best source to use in breeding.

La peronospora della vite è causata dall’Oomicete eterotallico Plasmopara viticola ed è ampiamente diffusa in tutte le aree caratterizzate da primavere miti e piovose. Gli organi svernanti di questo patogeno sono le oospore, che rappresentano l’unica fonte di inoculo per le infezioni primarie. Recenti studi molecolari hanno evidenziato l’importanza delle infezioni primarie e suggerito una revisione dell’epidemiologia di P. viticola. Questa tesi è costituita dagli studi epidemiologici realizzati per indagare il processo di maturazione e germinazione delle oospore mirati all’elaborazione di un modello dinamico per la simulazione delle infezioni primarie di P. viticola. Il modello è stato successivamente validato in diverse aree viticole italiane e, inoltre, utilizzato come base per un warning system in tempo reale per la gestione dei trattamenti in vigneto. / The heterothallic Oomycete Plasmopara viticola represents the causal agent of downy mildew of grapevine (Vitis spp.). The unique source of inoculum is represented by the overwintering sexual spores, originated by the fusion between anteridium and oogonium, so called oospores. Despite their critical impact on the epidemiology of this disease, knowledge about oospores presents some inconsistencies that are engaged in the present dissertation. Initially, the effect of water moistening the grape leaf litter holding overwintering P. viticola oospores was investigated. A close relationship was found between vapour pressure deficit (VPD in hPa) and aW (water activity) of the leaf litter, so that when VPD is lower than 2.13 hPa there is sufficient water for oospores to develop. Results showed that moisture of the leaf litter due to the water flow from the atmosphere makes the oospore development possible also during non rainy periods. Then, the effects of environmental conditions on the variability in germination dynamics of Plasmopara viticola oospores were studied over five years. The germination course was determined indirectly as the relative infection incidence (RII) occurring on grape leaf discs kept in contact with oospores sampled from a vineyard between March and July. The time elapsed between the 1st of January and the infection occurrence was expressed as physiological time, using sums of hourly rates from a temperature-dependent function only in hours when VPD was not a limiting factor (hydro-thermal time, HT). The Gompertz equation calculated over hydro-thermal time produced a consistent modelling of the general relationships between the germination dynamics of a population of P. viticola oospores and weather conditions. It represents the relative density of the seasonal oospores that should have produced sporangia when they have experienced favourable conditions for germination. Finally, a dynamic model for Plasmopara viticola primary infections on grapevine was elaborated according to a mechanistic approach. Development of the sexual stage of the pathogen was split into different state variables, in which changes from one state to another were regulated by rates depending on environmental conditions. The conceptual model was based on the definition of a primary inoculum season, a seasonal oospore (inoculum) dose, and its division into many coeval cohorts. Each cohort progresses along the primary infection cycle (production and survival of sporangia, release, survival and dispersal of zoospores, infection, appearance of disease symptoms) simultaneously, with a time step of one hour. The model was evaluated by comparing model predictions with disease onset in: i) 100 vineyards of Northern, Southern and Insular Italy (1995 to 2007); ii) 42 groups of potted grapevine plants exposed to inoculum (2006 to 2008). Most of the wrong positive predictions occurred in early season, when the host was in the earlier growth stages, or when the oospore germination was triggered by isolated weak rain events. Considering that neither calibration nor empirical adjustment of model parameters were necessary to obtain accurate simulation, it was concluded that this model produces a reasonable approximation of the primary infection processes underlying oospore development. A warning system based on such a model and on short-term weather forecasts was developed and its use was evaluated in experimental vineyards over a 3-year period in North Italy. An unsprayed control was compared with a “warning” treatment (fungicides were applied when the warning system predicted an infection), a “threshold” treatment (fungicides were applied as in the warning treatment, but only for the oospore cohorts higher than a fixed threshold), and the grower’s schedule. Average efficacy in decreasing disease incidence on leaves compared to the unsprayed control was > 90% for all treatments. On the average, 6.8 sprays were applied following the grower’s schedule; use of the warning system reduced applications by about one half (warning treatment) or two third (threshold treatment). The grower’s schedule was the most expensive control strategy, with average of 337 €/ha; the average saving was 174 and 224 €/ha for the warning and the threshold treatments, respectively. The value of this dissertation consists in two relevant and connected aspects. From one side the studies performed on the oospore maturation and germination allowed to better understand and clarify a key point of the downy mildew epidemics still wrapped by a lack of information. From the other side the model elaborated during this thesis represents a practical and efficient tool that leads to the reduction both of growers’ costs and chemical input in the environment.

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.

Bibliography: leaves 173-200 / iv, 200 leaves, 7 leaves of plates : ill. (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, 1986

Knowledge of disease epidemiology and the impact of plant nutrient status on development of disease is fundamental in establishing effective management strategies for crop pathogens such as Podosphaera aphanis Br. (Braun et al., 2002), the causal agent of powdery mildew on strawberries. The following study investigated the conditions conducive for powdery mildew in strawberry crops in South Australia, the effect of foliar concentration of potassium and calcium on yield and pathogen development on the strawberry cultivars Aromas (resistant to powdery mildew) and Selva (susceptible), the potential for use of foliar-applied potassium silicate to control disease and identification of genes differentially expressed during disease. Meteorological conditions associated with establishment of powdery mildew were observed over three consecutive seasons in commercial strawberry crops grown in Woodside, South Australia. Conducive conditions appear to be >28 oC, <55 % relative humidity (RH) with no rain during the day (for conidiation), followed by a night with >10 oC, >90 % RH and no rain (for germination). Colony development was then promoted by days of >15 oC and <70 % RH, with nights of >8 oC, >80 % RH and less than 2 mm rain in every 24 hour period. These are consistent with epidemiological studies of this pathogen (Peries, 1962a; Jhooty and McKeen, 1964; Mukerji, 1968; Perera and Wheeler, 1975; Byrne et al, 2000; Miller et al, 2003; Blanco et al, 2004; Davik and Honne, 2005; Amsalem et al, 2006). This knowledge may facilitate prediction of times considered high risk for establishment of powdery mildew in strawberry crops. Subsequently, this may allow optimisation of fungicide application and improved management of this disease and reduced yield loss and management expenses. P. aphanis developed at an increased rate on leaves of Selva with low calcium content compared with development on normally fertilised leaves. Increased numbers of conidia germinated successfully on leaves of Aromas with low calcium content compared with development on normally fertilised Aromas leaves, however, the germinated conidia still failed to develop into sporulating colonies. Potassium nutrition had no obvious effect on P. aphanis development. Foliar concentration found to be adequate for growth of cultivars, Selva and Aromas were 6.0 mg/g and 4.5 mg/g Calcium, dry weight and 11.0 mg/g and 12.5 mg/g potassium, dry weight (respectively). Potassium silicate, buffered to pH 7.0 and applied as a foliar fertiliser, reduced the severity of powdery mildew below the economic threshold, though not below the disease severity on plants treated with the fungicide, Systhane® (Bayer CropScience). As potassium silicate can be produced organically this compound may provide a useful management tool for both organic and conventional strawberry growers. Although the cultivar Aromas was not immune to disease under conducive conditions and high inoculum load in the field, inoculation of healthy Aromas plants with P. aphanis in the laboratory failed to produce disease. Conidia were seldom found attached to the leaf surface of healthy Aromas leaves. Germination and subsequent colony development were also not observed in inoculated samples. This suggests there is some mechanism of Aromas that inhibits development of this fungus. Preliminary investigation of differential expression in Aromas inoculated with P. aphanis, identified sequences with homology to a putative antimicrobial protein and photosynthesis-related genes. The results of these studies should enable growers to increase both crop yields and control of powdery mildew, one of the major economic diseases in South Australia. The epidemiological knowledge attained will be valuable, and may provide the basis for future forecast modelling for P. aphanis in strawberry crops in South Australia. Recommendations for calcium and potassium leaf content will allow growers to monitor their fertiliser regime for increased yield of these cultivars. Aromas was identified as a powdery mildew resistant cultivar potentially suitable for production in South Australia, and the genes associated with this resistance response may be used in studies of Fragaria species and breeding for powdery mildew resistant cultivars. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1297684 / Thesis (Ph.D.) -- University of Adelaide, School of Agriculture, Food and Wine, 2007

Knowledge of disease epidemiology and the impact of plant nutrient status on development of disease is fundamental in establishing effective management strategies for crop pathogens such as Podosphaera aphanis Br. (Braun et al., 2002), the causal agent of powdery mildew on strawberries. The following study investigated the conditions conducive for powdery mildew in strawberry crops in South Australia, the effect of foliar concentration of potassium and calcium on yield and pathogen development on the strawberry cultivars Aromas (resistant to powdery mildew) and Selva (susceptible), the potential for use of foliar-applied potassium silicate to control disease and identification of genes differentially expressed during disease. Meteorological conditions associated with establishment of powdery mildew were observed over three consecutive seasons in commercial strawberry crops grown in Woodside, South Australia. Conducive conditions appear to be >28 oC, <55 % relative humidity (RH) with no rain during the day (for conidiation), followed by a night with >10 oC, >90 % RH and no rain (for germination). Colony development was then promoted by days of >15 oC and <70 % RH, with nights of >8 oC, >80 % RH and less than 2 mm rain in every 24 hour period. These are consistent with epidemiological studies of this pathogen (Peries, 1962a; Jhooty and McKeen, 1964; Mukerji, 1968; Perera and Wheeler, 1975; Byrne et al, 2000; Miller et al, 2003; Blanco et al, 2004; Davik and Honne, 2005; Amsalem et al, 2006). This knowledge may facilitate prediction of times considered high risk for establishment of powdery mildew in strawberry crops. Subsequently, this may allow optimisation of fungicide application and improved management of this disease and reduced yield loss and management expenses. P. aphanis developed at an increased rate on leaves of Selva with low calcium content compared with development on normally fertilised leaves. Increased numbers of conidia germinated successfully on leaves of Aromas with low calcium content compared with development on normally fertilised Aromas leaves, however, the germinated conidia still failed to develop into sporulating colonies. Potassium nutrition had no obvious effect on P. aphanis development. Foliar concentration found to be adequate for growth of cultivars, Selva and Aromas were 6.0 mg/g and 4.5 mg/g Calcium, dry weight and 11.0 mg/g and 12.5 mg/g potassium, dry weight (respectively). Potassium silicate, buffered to pH 7.0 and applied as a foliar fertiliser, reduced the severity of powdery mildew below the economic threshold, though not below the disease severity on plants treated with the fungicide, Systhane® (Bayer CropScience). As potassium silicate can be produced organically this compound may provide a useful management tool for both organic and conventional strawberry growers. Although the cultivar Aromas was not immune to disease under conducive conditions and high inoculum load in the field, inoculation of healthy Aromas plants with P. aphanis in the laboratory failed to produce disease. Conidia were seldom found attached to the leaf surface of healthy Aromas leaves. Germination and subsequent colony development were also not observed in inoculated samples. This suggests there is some mechanism of Aromas that inhibits development of this fungus. Preliminary investigation of differential expression in Aromas inoculated with P. aphanis, identified sequences with homology to a putative antimicrobial protein and photosynthesis-related genes. The results of these studies should enable growers to increase both crop yields and control of powdery mildew, one of the major economic diseases in South Australia. The epidemiological knowledge attained will be valuable, and may provide the basis for future forecast modelling for P. aphanis in strawberry crops in South Australia. Recommendations for calcium and potassium leaf content will allow growers to monitor their fertiliser regime for increased yield of these cultivars. Aromas was identified as a powdery mildew resistant cultivar potentially suitable for production in South Australia, and the genes associated with this resistance response may be used in studies of Fragaria species and breeding for powdery mildew resistant cultivars. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1297684 / Thesis (Ph.D.) -- University of Adelaide, School of Agriculture, Food and Wine, 2007

Knowledge of disease epidemiology and the impact of plant nutrient status on development of disease is fundamental in establishing effective management strategies for crop pathogens such as Podosphaera aphanis Br. (Braun et al., 2002), the causal agent of powdery mildew on strawberries. The following study investigated the conditions conducive for powdery mildew in strawberry crops in South Australia, the effect of foliar concentration of potassium and calcium on yield and pathogen development on the strawberry cultivars Aromas (resistant to powdery mildew) and Selva (susceptible), the potential for use of foliar-applied potassium silicate to control disease and identification of genes differentially expressed during disease. Meteorological conditions associated with establishment of powdery mildew were observed over three consecutive seasons in commercial strawberry crops grown in Woodside, South Australia. Conducive conditions appear to be >28 oC, <55 % relative humidity (RH) with no rain during the day (for conidiation), followed by a night with >10 oC, >90 % RH and no rain (for germination). Colony development was then promoted by days of >15 oC and <70 % RH, with nights of >8 oC, >80 % RH and less than 2 mm rain in every 24 hour period. These are consistent with epidemiological studies of this pathogen (Peries, 1962a; Jhooty and McKeen, 1964; Mukerji, 1968; Perera and Wheeler, 1975; Byrne et al, 2000; Miller et al, 2003; Blanco et al, 2004; Davik and Honne, 2005; Amsalem et al, 2006). This knowledge may facilitate prediction of times considered high risk for establishment of powdery mildew in strawberry crops. Subsequently, this may allow optimisation of fungicide application and improved management of this disease and reduced yield loss and management expenses. P. aphanis developed at an increased rate on leaves of Selva with low calcium content compared with development on normally fertilised leaves. Increased numbers of conidia germinated successfully on leaves of Aromas with low calcium content compared with development on normally fertilised Aromas leaves, however, the germinated conidia still failed to develop into sporulating colonies. Potassium nutrition had no obvious effect on P. aphanis development. Foliar concentration found to be adequate for growth of cultivars, Selva and Aromas were 6.0 mg/g and 4.5 mg/g Calcium, dry weight and 11.0 mg/g and 12.5 mg/g potassium, dry weight (respectively). Potassium silicate, buffered to pH 7.0 and applied as a foliar fertiliser, reduced the severity of powdery mildew below the economic threshold, though not below the disease severity on plants treated with the fungicide, Systhane® (Bayer CropScience). As potassium silicate can be produced organically this compound may provide a useful management tool for both organic and conventional strawberry growers. Although the cultivar Aromas was not immune to disease under conducive conditions and high inoculum load in the field, inoculation of healthy Aromas plants with P. aphanis in the laboratory failed to produce disease. Conidia were seldom found attached to the leaf surface of healthy Aromas leaves. Germination and subsequent colony development were also not observed in inoculated samples. This suggests there is some mechanism of Aromas that inhibits development of this fungus. Preliminary investigation of differential expression in Aromas inoculated with P. aphanis, identified sequences with homology to a putative antimicrobial protein and photosynthesis-related genes. The results of these studies should enable growers to increase both crop yields and control of powdery mildew, one of the major economic diseases in South Australia. The epidemiological knowledge attained will be valuable, and may provide the basis for future forecast modelling for P. aphanis in strawberry crops in South Australia. Recommendations for calcium and potassium leaf content will allow growers to monitor their fertiliser regime for increased yield of these cultivars. Aromas was identified as a powdery mildew resistant cultivar potentially suitable for production in South Australia, and the genes associated with this resistance response may be used in studies of Fragaria species and breeding for powdery mildew resistant cultivars. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1297684 / Thesis (Ph.D.) -- University of Adelaide, School of Agriculture, Food and Wine, 2007

Resumo: Avaliaram-se 54 germoplasmas de quiabeiro (Abelmoschus esculentus (L.) Moench) quanto à resistência ao fungo Erysiphe cichoracearum, em cultivo de outono-inverno, no Vale do Ribeira-SP. Dois experimentos foram instalados no município de Pariquera-Açú, em solo orgânico-álico, utilizando-se 10 plantas por introdução, em linhas contínuas com 1,0 x 0,5 m de espaçamento e 3 repetições. No experimento 1 foram utilizadas 31 introduções e no experimento 2, 23 introduções. As avaliações constaram de medidas de número de folhas caídas e presentes na planta, produção, número de ramos laterais e incidência de oídio na folha. A colheita dos frutos foi realizada três vezes por semana, sendo estes colhidos a partir de um comprimento mínimo de 7 cm. A análise dos dados permitiu concluir que houve variação das cultivares quanto a vários fatores estudados: não foi possível encontrar introduções totalmente resistentes; ao oídio, as introduções que mostraram melhores condições de serem aproveitadas em programas de melhoramento, foram N45 (Exp.1) e N25 (Exp.2) quanto à produção, N20 e N50 (Exp1) e N9, N358 (Exp.2) quanto à resistência a oídio, N20, N50 (Exp.1) e N9, N49, N62, N63, N101, N339, N358, N4374, CBVE, CBVC e Sta. Cruz, quanto ao número de folhas caídas... / Abstract: In the present work, 54 okra (Abelmoschus esculentus (L. ) Moench) germoplasms ware evaluated related to the resistance against Erysiphe cichoracearum, in autumn-winter cultivation in the Vale do Ribeira-SP, Brazil. The appraised material consisted of 03 commercial cultivars, 43 introduction from germoplasm bank of the National Center of Vegetables Researches (CNPH), 13 from the Federal University of Viçosa and 02 from V. O. P. R. D. C. (Japan Min. Agric.). The experiment was installed at Pariquera-Açú, in organic-alic soil; it consisted of 10 plants/introduction, in line with 1,0 x 0,5 m of spacing with 03 repetitions. The evaluations consisted of measures of height of the plants, number of fallen leaves, according to the powdery mildew incidence in the leaf, and yield. Thirty one introductions were evaluated in the experiment 1 and 23 introductions in experiment 2. Fruits harvest was done in a frequency of three times a week. Fruits were picked with a minimum length of 7 cm. Analysis of data allowed the following conclusions: a) there was variation among cultivars with relationship to several studied characteristics; b) it was not possible to find a cultivar completely resistant to powdery mildew, appearing presence of polygenic resistance; c) cultivars that showed able conditions to be used at breeding programs were N45 (Exp.1) and N25 (Exp.2), high powdery mildew resistance: N20, N50 (Exp.1), N9,N358 (Exp.2), CBVE and N29; e) fallen leaves N20, N50 (Exp.1) and N45, N49, N62, N63. N101, N339, N358, N4374, CBVE, CBVC and Sta. Cruz. (Exp.2)... / Orientador: Francisco Luiz Araújo Câmara / Coorientador: Edson Luiz Furtado / Banca: Nilton Luiz de Souza / Banca: Antonio Ismael Inácio Cardoso / Banca: Stela Maria Carvalho Vilhena / Banca: Atila Francisco Mogor / Doutor