Thesis (Ph. D.)--Oregon State University, 2007. / Printout. Includes bibliographical references. Also available on the World Wide Web.

Podosphaera aphanis which causes powdery mildew of strawberry is of economic importance in strawberry production in United Kingdom as it affects yield and fruit quality. Silicon has been shown to reduce the severity of a number of plant diseases. In strawberry, the mechanism of suppression against powdery mildew remains uncertain. Therefore, it has been suggested that supplying silicon would help strawberry plants to absorb silicon and improve resistance against the pathogen. The silicon based wetter Omex SW7 was used and three different concentrations of silicon wetter were applied on the leaves of the strawberry plants (foliar application). Each treatment was applied at three different timings. Enhanced level of silicon was quantified by the Autoclave Induced Digestion (AID) method. Whilst the main study has used the variety Elsanta, other varieties have also been used. It was observed that the weekly application (total 5 sprays) of 3 different concentrations of Omex SW7 on leaves showed significantly (P<0.05) higher silicon concentrations compared to application 3 times in weeks 1, 3 and 5 or twice in weeks 1 and 5. Microscopic observations showed that weekly application of standard, high and very high concentrations of Omex SW7 significantly (P<0.05) increased the number and length of leaf hairs on both the upper and lower surfaces of strawberry leaves. The different varieties of strawberry used showed morphological changes in the leaves with regard to the density and length of leaf hairs. Untreated leaves from Rhapsody had no hairs on the upper leaf surface, but a low density of hairs was observed after treatment with the high concentration of Omex SW7. In this study, Omex SW7, a silicon based wetter was applied to the roots of strawberry plants (root application) and silicon accumulation and physical changes in leaves were assessed. Strawberry variety Elsanta was used in this experiment. Results revealed that weekly application (total 5 applications) of 2 different concentrations (standard and high) of Omex SW7 to roots showed significantly (P<0.05) higher silicon concentrations compared to application 3 times in weeks 1, 3 and 5 or twice in weeks 1 and 5. It was found that the weekly application of two different concentrations of Omex SW7 showed significantly higher (P<0.05) leaf hair numbers and significantly (P<0.05) longer leaf hair length on both the upper and lower surfaces of leaves compared to application 3 times in weeks 1, 3 and 5 or twice in weeks 1 and 5. The effect of foliar application of silicon and potassium carbonate to limit P. aphanis infection was examined in a field trial under polythene tunnel at Wisbech. Treatments were arranged in a randomised block design of 3 replicates. There were a total of 18 plots. There were six treatments and all treatments were applied to the strawberry variety Sonata. Results revealed that application of silicon based wetter Omex SW7 onto the leaf surface does result in accumulation of silicon in the leaves. The application of Omex SW7 has stimulated an increase in the number and length of leaf hairs in strawberry plants. Results showed that germinating ascospores and colonies were present in all plots before the trial was sprayed. Treatments with standard and high Omex SW7 significantly (P<0.05) reduced the number of germinating ascospores and colonies in this trial. However, Potassium carbonate alone gave some reduction in the number of colonies and germinating ascospores. Moreover, potassium carbonate mixed with silicon based wetter Omex SW7 significantly (P<0.05) reduced the number of germinating ascospores and colonies.

An important disease of Vitis vinifera production in Oregon and all other commercial growing regions is powdery mildew of grape, caused by the obligate fungal pathogen Uncinula necator (Schwein.) Burril. Grape production can be characterized as a long-term investment in the establishment and maintenance of the vineyard. Establishment times have been reduced with the use of plastic vine shelters, but powdery mildew disease pressure within vine shelters had been an unaddressed issue. Control of the pathogen requires frequent spray applications and costly cultural management of the grape canopy. Industry interest in forecasting programs have shown promise in regulating spray applications to times when they are most effective, or needed. The timing of when to begin spray programs is believed to be a point of weakness in the forecasting programs currently available for grape powdery mildew. The influence of vine shelter use on the development of powdery mildew was investigated in the field during the 1998 and 1999 growing season. Industry standard installations of various brands of vine shelters were tested against modified installations for both incidence and severity of Uncinula necator infection. The industry standard installation of 76 cm high tubes hilled with 8 cm of soil at the bottom to prevent airflow, were effective in reducing the incidence of powdery mildew in both field seasons. Disease reduction was associated with prolonged temperatures above 36��C and the exclusion of infective spores by the artificial barrier created by the vine shelters. The effectiveness of three forecasting programs for predicting the initial spray application was investigated for three seasons. Actual disease onset dates were determined by using trap leaves or plants. The forecasting programs consistently predicted initial spray dates between 31 and 44 days prior to the detection of powdery mildew with the trapping system. Modifications to the existing forecasting programs were attempted to adjust the forecasting programs to more closely predict the actual detected disease onset dates. The UC-Davis program performed the best over the three years of the study, but improvements will be necessary for an adequate forecasting program in the region. Flag shoots were reported for the first time in Oregon. / Graduation date: 2000

Made available in DSpace on 2014-06-11T19:26:08Z (GMT). No. of bitstreams: 0 Previous issue date: 2008-07-25Bitstream added on 2014-06-13T20:54:10Z : No. of bitstreams: 1 demore_ps_me_jabo.pdf: 1002271 bytes, checksum: a27ac944079c717a8ba5366fe7e35456 (MD5) / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / O oídio em soja, trata-se de uma doença praticamente presente em todos os paises produtores. Os marcadores moleculares microssatélites ou SSR (Simple Sequence Repeat) têm sido amplamente utilizados no processo de seleção assistida de genótipos de soja. Assim, o objetivo deste estudo foi obter marcadores microssatélites próximos ao gene de resistência ao oídio em soja. O estudo foi realizado em duas populações F2, oriundas de cruzamentos entre parentais contrastantes quanto à resistência ao oídio. Para o estudo, foram selecionados marcadores microssatélites a uma distância de até 42 cM ao redor do gene Rmd (resistência ao oídio). Utilizou-se o método de BSA (Bulked Segregant Analysis) na avaliação dos marcadores, para a comparação com a análise fenotípica das populações. Na análise foram utilizados dez iniciadores SSRs para as duas populações, sendo identificados quatro marcadores polimórficos para o cruzamento 1 (MGBR95-20937 x IAC-Foscarin 31) e três para o cruzamento 2 (MGBR 46/Conquista x EMBRAPA 48). Pela análise de Qui-quadrado da avaliação fenotípica, confirmou-se à segregação esperada (3:1) de um gene dominante condicionando a resistência. Os marcadores polimórficos também segregaram conforme o esperado (1:2:1) já que possuem natureza codominante. Para as populações 1 e 2, os melhores resultados foram obtidos com os marcadores Sat_366 e Sat_393, respectivamente, localizando-se a 9,41 e 12,45 cM de distância do gene, sendo considerados promissores na seleção assistida para resistência ao oidio em soja. / Powdery mildew in soybeans, it is a disease present in virtually all producing countries. The molecular markers microsatellites or SSR (Simple Sequence Repeat) have been widely used in the assisted selection of soybean genotypes. The objective of this study was to obtain microsatellites markers near the gene for resistance to powdery mildew in soybeans. The study was conducted in two populations F2, from crosses between contrasting parents about the resistance to powdery mildew. For the study, were selected microsatellites markers at a distance of 42 cM around the gene Rmd (resistance to powdery mildew). It was used the method of BSA (Bulked Segregant Analysis) in the evaluation of markers, for comparison with the phenotypic analysis of populations. In the analysis were used in ten initiators SSRs for the two populations, and identified four polymorphic markers for the crossing 1 (MGBR95-20937 x-IAC Foscarin 31) and three for the crossing 2 (EMBRAPA MGBR 46/Conquista x 48). For the analysis of chi-square of the phenotypic evaluation, it is confirmed the segregation expected (3:1) of a dominant gene conditioning the resistance. The polymorphic markers also segregation as expected (1:2:1) that have already codominante nature. For the populations 1 and 2, the best results were obtained with the markers Sat_366 and Sat_393, respectively, finding itself to 9.41 and 12.45 cM distance of the gene and are considered promising in assisted selection for resistance to soybean in powdery mildew.

Strawberry powdery mildew, caused by Podosphaera aphanis, has the potential to cause over 20% yield loss, particularly where strawberries are grown under cover. A holistic approach to the control of strawberry powdery mildew (P. aphanis) is important, since the disease is never absent from the crop. The new disease assessment key was developed to assess strawberry powdery mildew (the old one is for assessing red blotches on leaves, See appendix 8). The results (Chapter 3) showed that the disease is present in the crop when new plants are bought in from a propagator, with 14% of strawberry crowns were infected by P. aphanis in July 2013 and 4% of the strawberry plants had symptoms of powdery mildew in pre-assessment of plants for the 2013 Si nutrient fertigation field experiment. Control measures used in one growing season reduced the disease carry-over, thus reducing the initial inoculum in the following season. The use of a late autumn fungicide spray and a fungicide spray before the plants were covered by fleece in spring reduced the number and maturity of overwintering chasmothecia, thus contributing to a reduction in initial inoculum. The use of silicon (Si) nutrient (foliar spray and root treatment) also suppressed strawberry powdery mildew development (Chapter 4). The results of Area Under Disease Progress Curve (AUDPC) and the rate of epidemic growth curve (r) in 2012 indicated that the high concentration of Si nutrient foliar spray inhibited (r = 0.002, AUDPC = 44) the epidemic build-up of P. aphanis better than the low concentration of Si nutrient (r = 0.012, AUDPC = 51) and untreated (r = 0.018, AUDPC = 70). The Si nutrient root treatment (AUDPC = 12.8) was better in inhibiting strawberry powdery mildew development than the Si nutrient foliar spray treatment. Moreover, the high concentration of Si nutrient foliar spray resulted in fewer chasmothecia compared to the untreated. Si nutrient foliar spray and root treatments increased the concentration of Si in the plants and produced physiological changes in the plants, including wax formation on the adaxial leaf surface, greater leaf thickness and cuticle layer and increased Brix0 value in plants, which all were associated with reduced disease incidence. The integrated use of all these control strategies suppresses disease development so that control is achieved with less use of conventional fungicides.

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

No description available.

Strawberry powdery mildew, caused by Podosphaera aphanis, affects leaves, fruit, and runners of strawberry plants. Infected leaves have reduced photosynthetic capability and infected fruit become unmarketable. Both of these factors translate to economic loss for the grower and therefore merit taking measures to control the disease. One objective of this study was to evaluate the resistance developed in populations of strawberry powdery mildew to chemical control measures. A fungicide assay was developed to evaluate the efficacy of six treatments (penthiopyrad, quinoxyfen, myclobutanil, trifloxystrobin, cyflufenamid, fluopyram + trifloxystrobin) for control of the disease. Nineteen isolates of strawberry powdery mildew were collected from Balico, Salinas, Watsonville, San Luis Obispo, Santa Maria, Ventura, and Oxnard CA and tested through the assay. The number of isolates resistant to each treatment was: penthiopyrad (7), quinoxyfen (6), myclobutanil (7), trifloxystrobin (2), cyflufenamid (1), fluopyram + trifloxystrobin (0). This documents resistance in P. aphanis to multiple chemicals used for its control. Documentation of any resistance is novel in California and novel worldwide with resistance to Fungicide Resistance Action Committee (FRAC) codes 7 and 13. Another objective of this study was to evaluate host plant resistance to strawberry powdery mildew. Twelve cultivars were evaluated in a winter greenhouse trial, sixteen cultivars in a summer greenhouse trial, and the ten cultivars shared in both trials were also evaluated in two fields. The cultivars found to be most susceptible to mildew infection were BG 3.324 and Royal Royce. The cultivars found to be the least susceptible to mildew infection were Fronteras, San Andreas, and Sweet Ann. The cultivars evaluated represent more than 55% of the state’s acreage and the host plant resistance information will be a valuable tool to growers looking to culturally control powdery mildew.

The effectiveness of the biocontrol product Actinovate® at enhancing tomato plant growth and yield, and reducing the presence of fungal pathogens was studied in greenhouse and field conditions. In the greenhouse, no differences were found among seed germination or plant survival rates, seedling heights, dry root weights, and dry shoot weights of tomato seedlings grown from seeds drenched with Actinovate® or Rootshield®. The effects of one initial Actinovate® seed drench at sowing, repeated applications through the drip irrigation throughout the season, or repeated applications through the drip irrigation plus foliar applications throughout the season at reducing plant infection by fungal plant pathogens, and increasing yield and quality for tomato plants (Solanum lycopersicum) were investigated in Los Alamos, CA, on a sandy loam soil. No significant differences in plant height were found among the four treatments. Marketable fruit weight was greater in the drip plus foliar treatment than in the Actinovate® seed drench treatment. The foliar plus drip treatment resulted in the greatest amount of powdery mildew present, although the disease pressure was low. No significant differences were found among the four treatments in the presence of Verticillium wilt or Sclerotinia.

No description available.