A partir de meados da década de 80, com a expansão da cultura do milho para além das épocas tradicionais de cultivo, quer pela prática da safrinha ou por plantios irrigados, vem ocorrendo um aumento na incidência de doenças a secundária. Dentro deste contexto, o enfezamento vermelho do milho, relatado no país primeiramente em 1970, vem ocorrendo de forma freqüente, apresentando altos índices de ocorrência, muitas vezes com comprometimento total da produção. As plantas infectadas apresentam uma sintomatologia complexa facilmente confundida com viroses. O sintoma mais característico é o avermelhamento foliar. Além do avermelhamento as plantas apresentam redução na altura, perfilhamento basal e axilar, espigas extranumerárias e colmos afinados. Essa doença é causada por um procarioto não cultivável em meio de cultura, habitante exclusivo do floema, denominado fitoplasma, veiculado de forma persistente e propagativa pela cigarrinha Dalbulus maidis. Devido às características do patógeno, a única forma de controle promissora é a utilização de variedades tolerantes/resistentes. Para eficiência na obtenção destas variedades é necessário um diagnóstico correto e conhecimento sobre a variabilidade metodologia mais eficiente tanto para diagnose correta como para investigar essa variabilidade tem sido o PCR. O PCR, utilizando oligonucleotídeos baseados no gene 16SrDNA seguido da análise de RFLP, proporciona uma identificação mente a classificação de fitoplasmas é fundamentada no perfil molecular obtido por análise de RFLP de fragmentos do gene 16SrDNA amplificados. Com base nestas considerações, o trabalho teve como objetivo caracterizar molecularmente isolados do fitoplasma associado ao enfezamento vermelho do milho, coletados em quatro regiões produtoras de milho do estado de São Paulo. A sintomatologia para cada amostra de milho foi anotada. Foram usados dois pares de oligonucleotídeos universais para fitoplasmas em duplo PCR, um par de oligonucleotídeo especificamente desenvolvido para detecção do fitoplasma do enfezamento vermelho do milho, além de oligonucleotídeos para detecção de fitoplasmas pertencentes a grupos específicos. Após amplificação e eletroforese, 29 isolados foram selecionados para a identificação através de RFLP. Fragmentos de DNA foram submetidos à digestão com diferentes enzimas de restrição com o objetivo de identificar/classificar o fitoplasma. Os padrões de bandas obtidos após a eletroforese em gel de poliacrilamida foram comparados com os padrões atuais para classificação dos fitoplasmas. Todos os isolados analisados apresentaram idênticos padrões de bandas, para cada enzima de restrição, considerada individualmente. Não houve diferenciação de acordo com a região geográfica de coleta ou de acordo com intensidade de sintomas apresentados. Todos os isolados foram identificados como pertencentes ao grupo I e subgrupo B da classificação molecular atualmente adotada para estes microorganismos. / Since the middle 80s, an increase in year round cropping of maize resulted in a spread of secondary diseases in the crop’s major production areas. In this context, maize busy stunt, firstly appointed in Brazil in 1970, is occurring more frequently, often with total damage of production. Infected plants show a complex symptomatology, easily confounded with virus-caused diseases. The most characteristic symptom is leaf reddening. Besides the reddening diseased plants show stunting, often developing tillering. This disease is caused by a phytoplasma, a wall- less prokaryote, uncultivable, phloem inhabitant. This pathogen is transmitted by the leafhopper Dalbulus maidis, a in persistent and propagative manner. Due to the pathogen’s characteristics, the best control measure is the use of tolerant/resistant plants. For efficiency in breeding, accurate procedures of detection and an investigation of the pathogen’s genetic variability are necessary. The more accurate manner is using PCR. PCR, using 16SrDNA based primers pairs and followed by RFLP analysis, offers a safe identification of the pathogen. Today the phytoplasma classification is based in molecular patterns obtained by RFLP analysis of amplified 16SrDNA gene fragments. This work’s objective was the molecular characterization of maize bushy stunt phytoplasma strains collected in four corn production areas in São Paulo state, Brazil. The simptomatology to every maize sample was saved. Two primer pairs in nested PCR and a specific primer pair developed to MBS detection were used, besides group specific phytoplasma primers pairs. After amplification and electrophoresis, 29 samples were selected. These selected samples were digested with different restriction enzymes to identify/classify the phytoplasma. The fragment’s sizes obtained by electrophoresis through 4,5% polyacrilamide gel were compared with the reference’s classification patterns. All analyzed samples showed identical fragment-size patterns, for each restriction enzyme considered individually. There was no difference between these samples according to geographic collect region or according to symptoms. All strains were identified as belonging to group I and subgroup B of molecular classification.

Infectious fungal diseases pose a substantial threat to susceptible plant species, causing host declines, limiting host populations’ community role, and threatening the sustainability of natural ecosystems. Evaluating disease severity and progression is essential for understanding the impacts of these diseases, and this information could provide insights into developing future interventions. On Roan Mountain, Tennessee, native monocot Veratrum viride (Röhl.), was recently discovered to be infected with a fungal pathogen, Pseudocercosporella sublineolata (Thüm. U. Braun.), a Veratrum-specific leaf spot disease. To understand the prevalence and impacts of this disease, a demographic and disease severity study was performed. We hypothesized that P. sublineolata infection was associated with the decline of leaves and the premature seasonal senescence of V. viride plants, and that the increase in the number of leaf spots over the growing season was associated with the decline in plant health. To test these hypotheses, twenty plants from two different populations on Roan Mountain were systematically selected and tagged for a total of forty plants. From June through September 2021, demographic characteristics (plant height, number of leaves, and whether the plant flowered), and disease data (plant health, number of leaf spots, diameter of spots, and whether spots harbored P. sublineolata spores) were recorded over seven visits. To diagnose the disease, leaf spot samples were collected, slides were prepared and examined for spores at 100/200X magnification. We confirmed the diagnosis of P. sublineolata infection based on the conidia’s shape, size, and number of cells. The relationship between P. sublineolata and plant senescence was strengthened because the samples had abundant conidia that were present as pure isolates rather than a mixture of other potential microbial pathogens. All plants in the study declined progressively throughout the growing season, and they senesced earlier than expected, i.e., before the first frost. This early season decline likely limits reserves stored in the overwintering bulb and inhibits seed maturation, thereby posing a threat to the viability of these V. viride populations on Roan Mountain.

Spring dead spot (Ophiosphaerella spp.) (SDS) of bermudagrass (Cynodon dactylon (L.) Pers. x transvaalensis Burtt Davy) is one of the most challenging diseases in the United States transition zone. Six projects were conducted from 2019 to 2022 to better understand the environmental, edaphic, and spatial distribution of SDS epidemics and to examine management strategies for SDS with chemical and cultural practices. A survey of 51 locations provided support of the geographic distribution of Ophiosphaerella species across the Mid-Atlantic United States. Ophiosphaerella herpotricha and O. korrae were isolated from the Mid-Atlantic region, yet O. narmari was not. Cultivars in which parent material originated from the midwestern United States had predominantly O. herpotricha and cultivars in which the parent material originated from the southeastern United States had predominantly O. korrae. In vitro and in situ fungicide efficacy screenings were conducted for O. herpotricha and O. korrae. Additionally, field studies were conducted to optimize fungicide applications and bermudagrass recovery from SDS. Results highlighted that, generally, O. korrae was less sensitive to fungicides than O. herpotricha; the fungicides isofetamid, mefentrifluconazole, penthiopyrad, and pydiflumetofen were generally the most efficacious against SDS; the different fungicide application methods deployed produced mixed results in their effect on fungicide efficacy against SDS with increased efficacy of tebuconazole against SDS with soil surfactant applications and post-application irrigation in certain scenarios; the optimal timing for fungicide applications for SDS was from 13-18°C with tebuconazole and 13-21°C with isofetamid; and nitrogen applications without cultivation practices in the late spring/early summer optimized bermudagrass recovery from SDS. Lastly, a geospatial survey study was conducted to determine the environmental and edaphic factors that influence SDS epidemics. Results were variable with numerous environmental and edaphic factors influencing SDS depending on the year and location; however, soil pH, soil potassium content, and thatch depth were among the most consistent and influential factors on SDS epidemics. Ultimately, these data improve our recommended strategies for successful SDS management. / Doctor of Philosophy / Spring dead spot is a damaging turfgrass disease that causes aesthetically displeasing symptoms and potential safety and playability concerns for pedestrians and athletes traversing turfgrass surfaces. This disease is caused by three fungal species, and the distribution of these species in the Mid-Atlantic US and the management of spring dead spot epidemics are not well understood. Studies were conducted from 2019 to 2022 to determine the geographic distribution of the species that cause spring dead spot in the Mid-Atlantic, best management strategies for spring dead spot with chemical and cultural practices, and factors in the environment and soil that influence spring dead spot epidemics. Results from the geographic distribution study showed that two of the three fungal species that cause spring dead spot were found in the Mid-Atlantic US, which has major implications on management strategies for the disease. The results from the studies focusing on best management strategies for spring dead spot with chemical and cultural practices highlight that the two fungal species found in the Mid-Atlantic US responded differently to fungicides, few fungicides suppressed the disease to an acceptable level, fungicide application methods provided variable suppression of the disease, optimal timing for fungicide applications was in the fall months when soil temperatures were between 13°C and 18°C, and nitrogen fertilization without cultivation optimized bermudagrass recovery from spring dead spot symptoms. Lastly, the study examining the environmental and soil factors that influence spring dead spot epidemics showed that many factors in the soil and environment influenced spring dead spot epidemics with soil pH, soil potassium content, and thatch depth among the most prevalent. These studies provide turfgrass managers and researchers a better understanding of spring dead spot and allow for more informed management decisions for prevention of and recovery from the disease.

A alface é a principal hortaliça folhosa do Brasil. A podridão negra das raízes causada pelo fungo Thielaviopsis basicola vem limitando o cultivo da alface americana ´Lucy Brown`. Os objetivos desta pesquisa foram: determinar a reação das cultivares comerciais de alface à T. basicola; elucidar a herança da resistência de alface ao patógeno e selecionar alface americana resistente ao patógeno a partir de variantes da ‘Lucy Brown`. Inocularam-se 37 cultivares de alface usando o isolado patogênico L1 de T. basicola, na fase juvenil. Para todos os ensaios a avaliação foi feita na fase juvenil através de uma escala de notas de acordo com a severidade da doença de 1 (ausência de sintomas) a 5 (mais de 90% das raízes severamente afetadas). A seleção de progênies resistentes ao patógeno foi feita a partir de variantes da ´Lucy Brown` pelo método genealógico usando um critério qualitativo para uniformidade, qualidade da cabeça e adaptação para o cultivo nas condições de verão. As cultivares do tipo crespa e batávia foram resistentes ao patógeno. As do tipo lisa e americana apresentaram variação inter-varietal quanto à reação a T. basicola. A herança da reação de alface a T. basicola foi devido a um gene dominante, designado de Tb. As progênies elites S4 derivadas da alface ´Lucy Brown` foram resistentes ao patógeno, uniformes e estáveis para o mérito hortícola no cultivo de verão. / Lettuce is the major leafy crop in Brazil. Lettuce black root rot (LBRR) caused by Thielaviopsis basicola is one the most limiting disease for the crisphead lettuce cv. Lucy Brown. Research focuses were: cultivars reaction to the pathogen; resistance inheritance elucidation and selections of LBRR resistant variants from cv. Lucy Brown. About 37 cultivars were screened using L1 pathogenic strain of T. basicola at juvenile stage. The reaction reading was made for all trials at juvenile stage using a severity disease scale from 1 (absence of symptoms) to 5 (with more than 90% of root rots). Selection of LBRR variants derived from Lucy Brown was made by pedigree selection and using selective criteria of line uniformity, heading qualities and adaptation for summer season slotting planting. Leaf lettuce Grand Rapids and Batavia types were resistant. There was inter-varietal occurrence of crisphead and butterhead resistance and other susceptible to LBRR. The inheritance to LBRR resistance in lettuce was due to a dominant gene designated as Tb. Elite LBRR resistant S4 lines derived from the crisphead cv. Lucy Brown were identified by their uniformity and stability for summer crop adaptation.

A alface é a principal hortaliça folhosa do Brasil. A podridão negra das raízes causada pelo fungo Thielaviopsis basicola vem limitando o cultivo da alface americana ´Lucy Brown`. Os objetivos desta pesquisa foram: determinar a reação das cultivares comerciais de alface à T. basicola; elucidar a herança da resistência de alface ao patógeno e selecionar alface americana resistente ao patógeno a partir de variantes da ‘Lucy Brown`. Inocularam-se 37 cultivares de alface usando o isolado patogênico L1 de T. basicola, na fase juvenil. Para todos os ensaios a avaliação foi feita na fase juvenil através de uma escala de notas de acordo com a severidade da doença de 1 (ausência de sintomas) a 5 (mais de 90% das raízes severamente afetadas). A seleção de progênies resistentes ao patógeno foi feita a partir de variantes da ´Lucy Brown` pelo método genealógico usando um critério qualitativo para uniformidade, qualidade da cabeça e adaptação para o cultivo nas condições de verão. As cultivares do tipo crespa e batávia foram resistentes ao patógeno. As do tipo lisa e americana apresentaram variação inter-varietal quanto à reação a T. basicola. A herança da reação de alface a T. basicola foi devido a um gene dominante, designado de Tb. As progênies elites S4 derivadas da alface ´Lucy Brown` foram resistentes ao patógeno, uniformes e estáveis para o mérito hortícola no cultivo de verão. / Lettuce is the major leafy crop in Brazil. Lettuce black root rot (LBRR) caused by Thielaviopsis basicola is one the most limiting disease for the crisphead lettuce cv. Lucy Brown. Research focuses were: cultivars reaction to the pathogen; resistance inheritance elucidation and selections of LBRR resistant variants from cv. Lucy Brown. About 37 cultivars were screened using L1 pathogenic strain of T. basicola at juvenile stage. The reaction reading was made for all trials at juvenile stage using a severity disease scale from 1 (absence of symptoms) to 5 (with more than 90% of root rots). Selection of LBRR variants derived from Lucy Brown was made by pedigree selection and using selective criteria of line uniformity, heading qualities and adaptation for summer season slotting planting. Leaf lettuce Grand Rapids and Batavia types were resistant. There was inter-varietal occurrence of crisphead and butterhead resistance and other susceptible to LBRR. The inheritance to LBRR resistance in lettuce was due to a dominant gene designated as Tb. Elite LBRR resistant S4 lines derived from the crisphead cv. Lucy Brown were identified by their uniformity and stability for summer crop adaptation.

<p dir="ltr">Efficient management of plant diseases and their spread within fields requires a system capable of early and accurate disease identification and its severity estimation. Many plant diseases have distinct visual symptoms, which can be used to correctly identify, classify, and manage them. Recent technological advancements have led to increased adoption of deep neural networks (DNN) for developing deep learning (DL)-based computer vision systems. An accurate disease identification and severity estimation system using a DL-based computer vision framework is critical for efficiently managing corn diseases under field conditions and further restricting the spread of disease. Image processing and machine learning methods for disease identification and classification have been employed in the last two decades using high-cost sensors that need frequent calibration. Researchers have used low-cost red, green, and blue (RGB) sensors to mostly identify single diseases affecting crops, whereas, in real-world applications, a single leaf can be affected by multiple diseases. This research identifies gaps in knowledge of DL applications to field crops by reviewing 70 research articles published between 1983 and 2022. It creates a much-needed disease database for corn grown under field conditions by adding custom-acquired image data to other publicly available image repositories. The image data was used to train and evaluate the performance of commonly used DL-based image classification models for differentiating single diseases on individual corn leaves under field conditions. However, many disease lesions of different shapes and sizes can simultaneously develop on infected leaves. The performance of DL-based image classification and object detection models was evaluated to accurately identify multiple simultaneous diseases with varying symptoms. Disease identification under field conditions is necessary to implement an effective disease management system. However, recent work has demonstrated poor generalization accuracies of DL models trained on lab-acquired imagery for identifying diseases in the field. Therefore, after achieving promising results for disease identification, DL generalization performance was assessed and improved using different dataset combinations with varying backgrounds. A novel neural network architecture using a hierarchical structure was also proposed, which resulted in improved generalization performance. Additionally, disease severity must be estimated to implement an effective management response. DL models were evaluated to estimate the severity of multiple corn diseases under field conditions using aerial and ground-based platforms to identify specific lesions from above and below the canopy. A progressive web application was designed to empower end users with disease recognition capabilities. Overall, this research reports findings of the performance of deep learning image processing, object detection, and segmentation models for identifying single/multiple diseases on field corn and the development of tools that can potentially be a component of production-ready disease diagnosis systems for implementing effective management practices.</p>

Thesis (MScAgric)--University of Stellenbosch, 2002. / ENGLISH ABSTRACT: Botrytis bunch rot of grape is caused by Botrytis cinerea Pers. :Fr. Conidia of the pathogen, which is dispersed by wind, water droplets and by insects, can penetrate the intact grape berry cuticle, but disease expression occurs only under predisposing conditions. Since relatively high infection rates often occur in vineyards, predisposing factors must play a fundamental role in primary infection and subsequent disease occurrence. Insects can play a very important role in this regard by depositing inocula at wound sites during feeding and by providing fresh wounds during their oviposition and feeding activities. The aim of this study was (i) to determine the potential of the Mediterranean fruit fly to transfer B. cinerea and other bunch and fruit rot fungi in natura, (ii) to investigate the transport, deposition and subsequent disease expression on grape berries in vitro, and (iii) to investigate fruit fly activities and the nature of deposited conidia and mycelia of B. cinerea by aid of digital photography and epifluorescence microscopy, respectively. Two Sensus fruit fly traps containing the para-pheromone, Capilure, were installed in orchards and five neighboring vineyards on four farms in the Stellenbosch region. Ceratitis fruit flies were collected weekly, identified and counted to determine the fluctuations in fruit fly population. Following field collection, the fruit flies were plated on Kerssies' B. cinerea selective medium and the number of flies yielding the pathogen was recorded. Two fruit fly species, C. capitata and C. rosa, were captured during the study period. Ceratitis rosa numbers comprised only 1% of the total number of fruit flies captured. Ceratitis capitata numbers, and the percentage B. cinerea contaminated flies generally increased after harvest in the different orchards and vineyards. Following harvest, the percentage flies yielding B. cinerea was higher in vineyards compared to orchards. Furthermore, in each vineyard an increase in percentage B. cinerea contaminated fruit flies was preceded by a corresponding increase in its neighboring orchard. The levels of both Penicillium and Alternaria contaminated fruit flies stayed high throughout the investigation period, especially after harvest of the orchard cultivars. Low incidence of Aspergillus, Mucor and Rhizopus spp. were recorded on C. capitata. These findings suggest that the Mediterranean fruit fly may play an important role in the dispersal of inocula of fungi associated with postharvest decay from early-maturing stone fruit orchards to mid- and late-maturing wine grape vineyards, and in disease induction under conditions unfavourable for natural infection. Three experiments were conducted to determine the potential of fruit flies in provoking B. cinerea decay. In the first experiment, transport of conidia and disease expression were investigated on rachis segments bearing unwounded berries only. In the second experiment, the effect of wounding on disease expression was investigated. In the third experiment, the effect of inoculum type (mycelia and conidia) on transportation and disease expression was investigated on rachis segments bearing unwounded berries, and on segments with wounded berries. The table grape cultivar, Dauphine, and the wine grape cultivar, Shiraz, were used at véraison, two weeks before harvest and harvest, and the transport studies were conducted in ethanol-disinfected perspex cages. Disease expression was studied in dry (~56% RH), ethanol-disinfected perspex chambers incubated at 22°C. The isolations from berries revealed that the flies deposited, without preference, high amounts of B. cinerea at various positions on the grape berry's surface. The freezing studies showed that the deposited conidia germinated and penetrated the berry skin at various positions. However, B. cinerea developed more often at the pedicel end than on the cheek or style end, which indicated a peculiar interaction between B. cinerea, the fruit fly and host tissue at this part of the berry. This phenomenon was substantiated by the finding that B. cinerea also developed more often at the pedicel end of berries that were not frozen. Further evidence for this interaction was found on intact berries exposed to flies that carried mycelia after feeding on berries without sporulating colonies of the pathogen, but showing symptoms of slippery skin. Significantly more decay developed on wounded berries compared to the unwounded berries and more so at the wound site. In addition, female fruit flies were responsible for significantly more decay development than male fruit flies. The study thus proved that the Mediterranean fruit fly can promote B. cinerea disease development under conditions unfavorable to natural infection. The activities of the Mediterranean fruit fly, Ceratitis capitata, on grape berries were monitored by aid of digital photography. In addition, the deposition of conidia and mycelia of Botrytis cinerea at three sites (pedicel end, cheek and style end) on the grape berry, germination of the fungal structures after dry (±56% RH) and moist (±93% RH) incubation and wounds inflicted during ovipositioning were examined with an epifluorescence microscope. The observations revealed that the fruit fly's activities were generally restricted to the grape berry. They visited the grape berry cheek more often, but visitations to the pedicel end of berries increased substantially from véraison to harvest, indicating the possibility of nutrient leakages at this site. Microscopy revealed that the flies deposited conidia singular, in feeding packages and in faecal excrements on the berry surface. The conidia in feeding packages were ensheathed by salivical fluids and occurred in clusters of 10 to 50 conidia. An average of 60% of the conidia in feeding packages germinated under dry conditions (±56% RH). Conidia that passed through the intestinal tract of the fruit fly and that were deposited in faecal excrements were deformed and low in viability. These conidia did not occur in cluster format, but were proportionally spread with the faeces on the surface of the grape berry. Conidia that were deposited singular and in faecal excrements did not germinate unless incubated under moist conditions (± 93% RH). Wounds inflicted by female fruit flies during ovipositioning were most frequently observed on the cheek. This predisposition to B. cinerea infection of grape berries by the activities of fruit flies, suggested an important role for the flies in the initiation of Botrytis bunch rot epidemics in vineyards. / AFRIKAANSE OPSOMMING: DIE ROL VAN DIE MEDITERREENSE VRUGTEVLIEG, CERATITIS CAPITATA, IN BOTRYTIS CINEREA TROSVERROTTING VAN DRUIWE Botrytis-trosverrotting van druiwe word deur Botrytis cinerea Pers. :Fr. veroorsaak. Konidia van die patogeen wat deur wind, waterdruppels en insekte versprei word, kan die intakte druiweskil binnedring, maar siekte-uitdrukking vind slegs onder spesiale omstandighede plaas. Aangesien relatief hoë infeksie vlakke algemeen in wingerde voorkom, moet predisponerende faktore 'n fundamentele rol in die primêre infeksie, en die daaruit voortspruitende siektetoestand speel. Insekte kan 'n baie belangrike bydrae lewer deur inokuia tydens voeding by wonde te deponeer. Nuwe wonde kan ook tydens oviposisionering en voeding ontstaan. Die doel van hierdie studie was om (i) die potensiaal van die Mediterreense vrugtevlieg om B. cinerea en ander tros- en vrugverrottingswamme in natura oor te dra, te bepaal; om (ii) die verspreiding, deponering en daaropvolgende siekteuitdrukking op druiwekorrels in vitro te ondersoek; en om (iii) die aktiwiteite en aard van die gedeponeerde konidia en miselia met behulp van digitale fotografie sowel as epifluoressensiemikroskopie waar te neem. Twee Sensus-vrugtelokvalle met die paraferomoon, Capilure, IS In vrugteboorde en aangrensende wingerde in die Stellenbosch-omgewing aangebring. Ceratitis-vrugtevlieë is weekliks versamel, geïdentifiseer en getel om fluktuasies in die vrugtevliegpopulasie te bepaal. Na die veldversameling is die vrugtevlieë op Kerssies se B. cinerea-selektiewe medium uitgeplaat. Gedurende die studie is twee spesies vrugtevlieë, C. capitata en C. rosa, gevang. Na oesstyd het die aantal Ceratitis-vrugtevlieë en die persentasie vrugtevlieë, besmet met B. cinerea, in die verskillende boorde en wingerde toegeneem. Na oestyd was die persentasie vrugtevlieë wat B. cinerea gedra het, hoër in die wingerde as in die boorde. Elke toename in die persentasie B. cinerea-besmette vrugtevlieë in 'n wingerd is voorafgegaan deur 'n ooreenkomstige toename in die aangrensende vrugteboord. Die aantal vrugtevlieë besmet met Penicillium en Alternaria spp. het tydens die navorsingstydperk deurgaans hoog gebly, veral nadat die vrugteboord-kultivars geoes is. Die voorkoms van Aspergillus-, Mucor- en Rhizopus spp. op Ceratitis-vrugtevlieë was deurgaans laag. Hierdie bevinding wys daarop dat vrugtevlieë 'n belangrike rol speel in die verspreiding van swarninokula, wat met na-oes verrotting geassosieer word, van vroegrypwordende steenvrugteboorde na mid- en laatrypwordende wyndruifwingerde. Drie eksperimente is in vitro onderneem om vrugtevlieë se potensiaal om B. cinereaverrotting te veroorsaak te bepaal. In die eerste eksperiment is ragi met slegs ongewonde korrels gebruik om die oordrag van konidia en siekte-ontwikkeling te ondersoek. In die tweede eksperiment is die effek van verwonding op siekte-ontwikkeling ondersoek. In die derde eksperiment is die effek van inokulumtipe (miselia en konidia) op verspreiding en siekte-ontwikkeling ondersoek deur ragis-segmente met gewonde korrels sowel as ragissegmente met ongeskonde korrels te gebruik. Die tafeldruif-kultivar Dauphine en die wyndruif-kultivar Shiraz, by kleurbreuk, twee weke voor oes en by oestyd, is in die eksperimente gebruik. Die oordragstudies is in etanol-ontsmette perspex-hokke uitgevoer. Siekte-ontwikkeling is bestudeer in droeë (±56% RH), etanol-ontsmette perspex-kamers en geinkubeer by 22°C. By ondersoek is gevind dat vlieë, sonder voorkeur, groot hoeveelhede B. cinerea op verskeie dele op die druiwekorrel-oppervlak deponeer. Bevriesingstudies het aangetoon dat die gedeponeerde konidia op verskeie dele van die korrelontkiem en die skil binnedring. Botrytis cinerea het egter meer dikwels by die korrelsteelkant as by die stempelkant, of op die wang, ontwikkel. Hierdie bevinding het 'n eiesoortige interaksie tussen B. cinerea, die vrugtevlieg en gasheerweefsel by die korrelsteelkant van die korrel aangetoon. Die verskynsel is gestaaf deur die bevinding dat B. cinerea ook meer dikwels by die korrelsteelkant van die korrels wat nie gevries is nie, ontwikkel het. Verdere bewys van hierdie interaksie is gevind by ongeskonde korrels wat aan die vlieë wat miselia gedra het blootgestel is. Die siekte het beduidend meer dikwels op gewonde as ongewonde korrels en verder aansienlik meer dikwels op die wondoppervlakte ontwikkel. Dit was ook duidelik dat vroulike vrugtevlieë baie meer vir verrotting verantwoordelik was as manlike vrugtevlieë. Die studie bewys dus dat Mediterreense vrugtevlieë die ontwikkeling van B. cinerea kan bevorder in omstandighede wat ongunstig is vir natuurlike infeksie. Die aktiwiteite van die Mediterreense vrugtevlieg C. capitata op die druiwekorrels is met behulp van digitale fotografie waargeneem. Verder is die deponering van konidia en miselia van B. cinerea op die verskillende dele (korrelsteelkant, wang en stempelkant) van die korrel, ontkieming van die swamstrukture na droeë (±56% RH) en nat (±93% RH) inkubasie en wonde wat tydens oviposisionering veroorsaak is, met epifluoressensie-mikroskopie ondersoek. Die waarnemings het onthul dat die vrugtevlieg se aktiwiteite gewoonlik tot die druiwekorrel beperk is. Hulle het korrelwange meer dikwels besoek. Besoek aan die korrelsteelkant het aansienlik toegeneem van kleurbreuk tot oestyd, wat op die moontlikheid van voedingstof-lekkasie by die deel aandui. Mikroskoopstudies het aangedui dat vlieë konidia enkel, in voedingspakkies en in fekale uitskeidings op die korreloppervlakte deponeer. Die konidia in die voedingspakkies is deur speekselvloeistof omhul en het in groepe van 10 tot 50 konidia voorgekom. Gemiddeld 60% van die konidia in voedingspakkies het in droeë omstandighede (±56% RH) ontkiem. Konidia wat deur die spysverteringskanaal van die vrugtevlieg gegaan het en in die fekale ekskresie gedeponeer is, was misvorm en het lae lewensvatbaarheid gehad. Laasgenoemde konidia was nie in groepe gedeponeer nie, maar is proporsioneel met die feces op die oppervlak van die druiwekorrel versprei. Konidia wat enkel en in feces gedeponeer is, het nie ontkiem nie, tensy toestande vogtig (±56% RH) was. Wonde wat deur die vroulike vrugtevlieë tydens oviposisionering veroorsaak is, is meer dikwels op die wang van die korrelopgemerk. Hierdie predisposisie van druiwekorrels tot B. cinerea-infeksie, meegebring deur die aktiwiteit van die vrugtevlieg, dui daarop dat die rol wat die vrugtevlieg in die inisiëring van Botrytis trosverrottingepidemies in wingerde speel, van beduidende belang is.

Call number: LD2668 .T4 1957 R68 / Master of Science

O brócolis (Brassica oleraceae var. italica) é uma das hortaliças mais importantes do país, cujo volume de comercialização na CEAGESP é de aproximadamente 13 mil toneladas por ano. Recentemente, uma nova doença tem causado perdas relevantes para as culturas instaladas na maior região produtora do Estado de São Paulo. Os sintomas característicos da doença são expressos pelo enfezamento da planta e necrose dos vasos de floema. Devido ao fato destes sintomas indicarem a presença de fitoplasmas nas culturas de repolho e couve-flor, localizadas na mesma região geográfica onde foi observada esta nova doença, levantou-se a suspeita de que estes mesmos agentes patogênicos pudessem estar associados com as plantas doentes de brócolis. Assim, o DNA total de plantas de brócolis sintomáticas foi analisado por PCR com primers específicos para a região 16S rDNA de fitoplasmas. Os resultados revelaram que estes patógenos estavam associados com as plantas doentes. Através das técnicas de RFLP do sequenciamento de nucleotídeos desta mesma região genômica, os fitoplasmas foram identificados como pertencentes aos grupos 16SrI, 16SrIII e 16SrXIII. Através de análise de RFLP, fitoplasmas também foram identificados em diversas espécies de plantas daninhas e em cigarrinhas da família Cicadellidae coletadas em áreas adjacentes a campos de produção de brócolis. Fitoplasmas do grupo 16SrIII foram identificados em plantas daninhas das espécies Agetarum conyzoides (mentrasto), Crotalaria lanceolata (crotalária), Lepidium virginicum (mentruz), Nicandra physalodes (juá-de-capote), Paulicourea marcgravii (erva-de-rato), Ricinus communis (mamona), Sida rhombifolia (guanxuma), Sonchus oleraceae (serralha amarela), Bidens pilosa (picão preto), Erigeron bonariensis (buva), Emilia sonchifolia (falsa serralha), Leonorus sibiricus (rubim), enquanto que fitoplasmas do grupo 16SrVII foram encontrados as últimas quatro espécies citadas. Com relação aos insetos, fitoplasmas foram detectados em indivíduos das subfamílias Deltocephalinae, Agalliinae e Typhlocybinae. Dentro da subfamília Deltocephalinae, a cigarrinha Balclutha hebe portava fitoplasma do grupo 16SrI, enquanto que cigarrinhas das espécies Atanus nitidus, Planicephalus flavicosta e Schapytopius fuliginosus abrigavam fitoplasmas do grupo 16SrIII. Nos tecidos de duas cigarrinhas da subfamília Agalliinae e uma da Typhlocybinae, as quais não foram identificadas quanto a espécie, foram encontrados fitoplasmas do grupo 16SrIII. As análises epidemiológicas revelaram um padrão espacial agregado de plantas doentes e a ocorrência de um maior progresso da doença nos bordos dos campos de cultivo de brócolis, que estão localizados nas proximidades de áreas com a presença de plantas daninhas. / Broccoli (Brassica oleraceae var. italica) is one of the most important vegetables in Brazil, whose trading volume in CEAGESP is approximately 13 000 tons per year. Recently, a new disease has caused significant losses in this crop cultivated in the largest producing region of the São Paulo State. The characteristic symptoms of the disease are expressed by plant stunting and necrosis of phloem vessels. Because these symptoms indicate the presence of phytoplasmas in cabbage and cauliflower crops, grown in the same geographical region, it was suspected that the same pathogens could be associated with the affected broccoli plants. Therefore, the total DNA from symptomatic plants of broccoli was analyzed by PCR with specific primers for the 16S rDNA of phytoplasmas. Through the techniques of RFLP and nucleotide sequencing of the same genomic region, the phytoplasmas were identified as belonging to the groups 16SrI, 16SrIII and 16SrXIII. Through RFLP analysis, phytoplasmas were also identified in several species of weeds and leafhoppers in the family Cicadellidae collected in adjacent areas of broccoli fields. Phytoplasmas belonging of the 16SrIII group were identified in the weeds belonging to the species Agetarum conyzoides, Crotalaria lanceolata, Lepidium virginicum, Nicandra physalodes, Paulicourea marcgravii, Ricinus communis, Sida rhombifolia, Sonchus oleraceae, Bidens pilosa, Erigeron bonariensis, Emilia sonchifolia, Leonorus sibiricus, while phytoplasmas of the 16SrVII group were found in the last four mentioned species. In respect to insects, phytoplasmas were detected in individuals from subfamilies Deltocephalinae, Agalliinae and Typhlocybinae. Within the subfamily Deltocephalinae, the leafhopper Balclutha hebe carried phytoplasmas of the 16SrI group, while that of the species Atanus nitidus, Planicephalus flavicosta e Schapytopius fuliginosus harbored phytoplasmas of the 16SrIII group. In the tissues of two leafhoppers of the subfamily Agalliinae and one of the Typhlocybinae, which were not identified as specie, were found phytoplasmas of the 16SrIII group. The epidemiological analysis revelead an aggregated pattern of the diseased plants and a higher progress of the diseased in the border of the broccoli fields, whitch were located nearby areas where the presence of weeds was abundant.

Coffee crop is of major importance to Brazil, being cultivated on more than 2 million hectares. It is a strategic commodity for the country, which is the main world producer. Several factors influence the yields, mainly a disease known as coffee leaf rust (CLR), caused by the fungus Hemileia vastatarix. This disease can reduce yield up to 35% and the most common strategy for CLR controlling is by spraying fungicides, with interval based on the residual period and according to regional CLR intensity. This traditional way does not consider the climate influence on disease development. With the aim of developing a forecast system (FS) for CLR management, employing weather data from CLR field assessments since 1998, several steps were performed: a) CLR epidemiology analysis; b) correlation between disease progress rates and weather variables; c) development of a forecast system, in order to rationalize chemical control; d) assessment of the FS performance on field trials; e) generation of an agro-climatic index for CLR risk assessment in Brazilian coffee areas; and f) evaluation of possible El Niño Southern Oscillation (ENSO) influence on CLR epidemics. Analising 88 siteseason CLR epidemics, from Varginha, Boa Esperança and Carmo de Minas, MG, the best fit was obtained by Gompertz model. Using stepwise method, CLR infection rates were estimated with multiple linear regressions, using minimum temperature and relative humidity as inputs. The model performed well, presenting less than 9.5% of false negatives in the months assessed. To evaluate CLR forecast system, two field trials were performed during 2015-16 season (Varginha and Boa Esperança), and five during 2016-17 season (Varginha, Boa Esperança, Uberlândia, Buritizal, and Campinas). The FS treatments performed better than the calendar spray system in six trials, with the exception for Campinas. The poor FS performance in Campinas evidenced the necessity of FS threshold calibration at sites different from the region where the FS was developed, once it is empirical. In order to assess the risk, the estimated CLR infection rate was evaluated for 46 different sites in Brazilian coffee producing region. Historical weather data since 1961 to 2015 for each site was used to estimate daily values of cumulative infection rate (CIR). Each site and season were classified into five CIR scores from Very Low (score 0) to Very High (score 4). The risk was spatialized using multiple linear regression based on geographical coordinates and altitude. The Brazilian coffee region was classified into four risk classes, being most of them between Medium to High risks in the area currently cultivated with coffee. For the same historical serie, CIR was estimated for 45 locations and then classified by ENSO phases: El Niño (EN); Neutral (NT); and La Niña (LN). A predominant absence of ENSO effect on CLR in Brazil was observed. Only in Paraná and São Paulo states there was ENSO effect, with higher CIR during EN seasons. / O cultivo do cafeeiro é de grande importância para o Brasil, sendo cultivado em mais de 2 milhões de hectares. Diversas doenças influenciam a produtividade, sendo a ferrugem do cafeeiro (CLR), a principal. Ocasionada pelo fungo Hemileia vastatrix, a CLR é capaz de reduzir a produtividade em até 35%. A estratégia mais comum de controle dessa doença é a aplicação de fungicidas foliares, baseado no período residual e de acordo com a intensidade da doença na região. Este método tradicional não considera a influência do clima no desenvolvimento da doença. Com o objetivo de desenvolver um sistema de previsão (FS) para o manejo da CLR utilizando dados de experimentos de campo obtidos desde 1998, diversas etapas foram realizadas: a) análise epidemiológica; b) relação da taxa de progresso da doença com variáveis ambientais; c) desenvolvimento do FS, visando racionalizar o controle químico; d) avaliação do desempenho do FS, em experimentos de campo; e) geração de índices agroclimáticos de favorabilidade para a ocorrência da CLR nas áreas produtoras de café do Brasil; e f) avaliar efeitos do fenômeno El Niño Oscilação Sul (ENOS) nas epidemias de CLR. Foram analisadas 88 epidemias de CLR, em Varginha, Boa Esperança e Carmo de Minas, MG, sendo o modelo de Gompertz o que resultou em melhor ajuste à curva de progresso da doença. Usando metodologia stepwise, as taxas de progresso mensais da doença foram estimadas com regressões lineares múltiplas, baseada em dados de temperatura mínima e umidade relativa do ar. O melhor modelo de estimativa resultou em menos de 9.5% de ocorrências de falso negativos, durante os meses avaliados. Para avaliar o desempenho do FS, dois experimentos foram realizados na safra 2015-16 (Varginha e Boa Esperança, MG) e cinco na safra 2016-17 (Varginha, Boa Esperança, Uberlândia, Buritizal e Campinas). Os tratamentos baseados no FS resultaram em melhor desempenho que o sistema tradicional em seis experimentos, à exceção de Campinas. Este desempenho inferior evidenciou a necessidade de calibração de limiares em diferentes locais, diferentes da região onde o FS foi desenvolvido, devido a sua base empírica. Para avaliar o risco da doença, a taxa de progresso diária foi estimada em 46 locais da região produtora de café, durante as estações de cultivo disponíveis, em uma base de dados históricos de 1961 a 2015, gerando as taxas de progresso acumuladas (CIR). Para cada local e estação, cinco classes com pontuação de Muito Baixo (0) a Muito Alto (4) foram atribuídas, gerando valores de risco. Utilizando regressão linear múltipla, o risco para a CLR foi espacializado em função dos valores de coordenadas geográficas e altitude. Os riscos Médio e Alto foram os mais comuns onde atualmente se cultiva café. No mesmo período de dados meteorológicos, a CIR de 45 locais foi estimada, sendo as estações classificadas em função das possíveis fases de ENOS: El Niño (EN), Neutro (NT) e La Niña (LN). Houve predominio da ausência de efeito do ENOS na CLR no Brasil. Apenas nos estados do PR e SP o EN induziu a uma maior CIR.