For a successful and economical integrated control program aimed at a particular disease, pertinent information, regarding the environmental conditions prevailing in the growing area, the crop itself and the pathogen, must be available. Recently, the control of powdery mildew disease on cashew has moved from the use of non-systemic fungicides with a wide range of action, to highly specific systemic ones. Such a shift requires a more effective integrated control system, whereby tolerant varieties in combination with fungicide unaffected biocontrol agents are timely used to ensure disease control and reduce the hazards associated with excessive fungicide applications. The purpose of this study was to understand the relationship between the disease epidemic and some climatic factors over time. Appropriate periods for management interventions were determined. The cellular host reaction to infection by Oidium anacardii Noack was studied with a view to rapidly identify disease tolerant host types. Potential antagonists were isolated, screened and compared with commercial biocontrol products using in vivo techniques and chemical control programs were finally evaluated. Electron microscopy elucidated that the powdery mildew tolerant cashew variety (H1) had a relatively higher consistency of cytoplasmic aggregates upon infection by O. anacardii when compared to the susceptible clone. Based on conidia and conidiophore morphology, conidial germination and conidiogenesis processes observed indicated that O. anacardii belongs to the subgenus Pseudoidium (Y.S. Paul&J.N. Kapoor) comb.Et. Stat. Nov. (Holomorph Erysiphe Sect. Erysiphe U. Braun). There was no direct relationship between the progress of the cashew powdery mildew epidemic and temperature, relative humidity or dew point over time. However, the epidemic did not start until conditions of average temperatures under the tree canopy were below 30°C, relative humidity was 80% and dew point was above 15. In vivo screening of 72 isolates, amongst them bacteria and fungi, from cashew leaves and florets showed that none were effective against O. anacardii, the causal agent of cashew powdery mildew. However, commercial antagonists, Candida saitoana, Bacillus subtilis and B. licheniformis, significantly reduced the growth and branching of primary hyphae. One antagonist, B. licheniformis, was as effective as the commercial fungicide triadimenol 25% EC (Bayfidan). Chemical fungicides were found to be effective against powdery mildew; however, the currently prevailing economic environment in Mozambique was found inappropriate for the use of expensive organic fungicides. Additional gain from the use of fungicides was found to be solely qualitative and thus did not represent a fair investment return ratio in terms of cashew nut prices and production costs. The use of integrated cashew management was finally recommended. Further studies should focus on development of integrated and cost effective disease management strategies. / Dissertation (MSc(Plant Pathology))--University of Pretoria, 2003. / Microbiology and Plant Pathology / unrestricted

FundaÃÃo Cearense de Apoio ao Desenvolvimento Cientifico e TecnolÃgico / O cajueiro tem uma grande importÃncia sÃcio-econÃmica e cultural para a regiÃo Nordeste, por gerar emprego para os agricultores, sendo por muitas vezes a sua Ãnica fonte de renda. Assim, as pesquisas com esta fruteira tÃm aumentado bastante nos Ãltimos anos, visando primariamente, reduzir os danos fitossanitÃrios e elevar a produtividade. As doenÃas, como nas demais espÃcies cultivadas, causam significativos danos. Dentre as doenÃas do cajueiro, a resinose e a podridÃo preta das hastes, ambas causadas pelo fungo Lasiodiplodia theobromae, se destacando entre as principais doenÃas em algumas regiÃes do semi-Ãrido nordestino. PorÃm, ainda hà poucos estudos sobre a biologia, morfologia, caracterizaÃÃo genÃtica desse patÃgeno, fato que dificulta o seu manejo. Este estudo objetivou caracterizar a diversidade genÃtica e patogÃnica de uma populaÃÃo com 22 isolados de L. theobromae associada ao cajueiro, utilizando marcadores microssatÃlites e inoculaÃÃes em plantas de cajueiro. Para a caracterizaÃÃo molecular, extraiu-se o DNA de cada isolado a partir do micÃlio do fungo crescido em meio lÃquido. Cada amostra foi submetida à reaÃÃo de polimerase em cadeia (PCR) com 15 pares de iniciadores desenvolvidos para flanquear regiÃes especificas contendo sequÃncias simples repetidas (microssatÃlites) dessa espÃcie. Os produtos amplificados foram observados em gel de eletroforese corados com brometo de etÃdio, e os dados tabulados em planilha binÃria e analisados pelo mÃtodo de agrupamento nÃo balanceado baseado na mÃdia aritmÃtica (UPGMA), utilizando o programa MVSP. As similaridades genÃticas foram estimadas pelo coeficiente de Nei e Li. Os resultados indicaram uma grande variabilidade genÃtica da populaÃÃo avaliada, representada por diversos grupos de similaridade variando de 22,2% a 100%. TrÃs destes isolados apresentaram entre si, 100% de similaridade genÃtica com os marcadores testados. No entanto, eram morfologicamente diferentes e um deles era procedente de localidade diferente que os demais. Os dados mostraram que a similaridade genÃtica por si sà nÃo deve ser aplicado como Ãnico fator de diversidade entre isolados. Para se testar a patogenicidade, os isolados foram inoculados em mudas de cajueiro, analisando-se o tamanho da lesÃo e a taxa de crescimento do fungo. Os resultados mostraram nÃo haver diferenÃas estatÃsticas entre os isolados, fato que demonstra que, independente do local de origem, todos os isolados mostraram-se patogÃnicos, e a sua taxa de crescimento decresce, isto Ã, a planta deve produzir algum tipo de defesa contra o patÃgeno, o que dificulta a sua infecÃÃo. / The cashew has a major socio-economic and cultural development for the Northeast region, by generating employment for farmers and is frequently their only source of income. Thus, research on this fruit has increased greatly in recent years, aimed primarily to reduce damage and increase plant productivity. Diseases, as in other crops, cause significant damage. Among cashew diseases, gummosis and black stem rot, both caused by the fungus Lasiodiplodia theobromae, stand out among the major diseases in some regions of the semi-arid. However, there are few studies on the biology, morphology, genetic characterization of this pathogen, a fact that burden their management. This study aimed to characterize the genetic and pathogenic diversity of a population of 22 isolates of L. theobromae associated with cashew, using microsatellite markers and inoculations in cashew plants. For molecular characterization, DNA was extracted from mycelium of each isolated of the fungus grown in liquid medium. Each DNA sample was subjected to a polymerase chain reaction (PCR) with 15 pairs of primers designed to flank specific regions containing simple repeated sequences (microsatellites) in this species. The amplified products were observed in gel electrophoresis stained with ethidium bromide, and the data recorded on a binary and analyzed by grouping unbalanced based on arithmetic mean (UPGMA) using the program MVSP. Genetic similarities were estimated by the coefficient of Nei and Li The results indicated a large genetic variability of the population, represented by different groups of similarity ranging from 22.2% to 100%. Three of these isolates showed 100% genetic similarity with the markers tested. However, they were morphologically differences and one of them was originated from different location than the others. The data showed that the genetic similarity alone should not be applied as the only factor of diversity among isolates. To test the pathogenicity, each isolate was inoculated on cashew seedlings. Lesion development size and recovery of the fungus were recorded. The results showed no statistical differences between the isolates, which demonstrates that, regardless of place of origin, all isolates were pathogenic, and its growth rate decreases, i. e, the plant must produce some form of defense against pathogen, which hinders their infection.