Genetics of resistance to powdery mildew (Microsphaera diffusa) in Brazilian soybean populations

Crosses between resistant and susceptible soybean cultivars were performed and the F2 populations were obtained to study the inheritance of soybean resistance to powdery mildew and to estimate the number and action of genes related to resistance. The reaction to powdery mildew was studied in a greenhouse and pots carrying plants with symptoms were distributed among the pots carrying the genotypes to be tested as a source of inoculum. Individual plants were scored according to the method of Yorinori (1997), with modifications, and classified as resistant or susceptible. The results showed that adult soybeans plants can present resistance to powdery mildew, which is controlled by one major gene with a dominant effect.

Inheritance of resistance to powdery mildew in pea and pathogenesis-related aspects

A herança da resistência ao oídio na cultivar de ervilha MK-10 e alguns aspectos histológicos da infecção foram estudados. Para o estudo da herança, as gerações F1, F2, retrocuzamentos e geração F3 de MK-10 com duas populações suscetíveis foram avaliadas. Nas avaliações histológicas observou-se a porcentagem de conídios germinados, porcentagem de conídios que formaram apressório, porcentagem de conídios que estabeleceram colônia e número de haustórios por colônia. Para comparar as razões de segregação obtidas no estudo da herança da resistência, adotou-se o teste do Qui-quadrado (X²) e para os dados das análises histológicas, utilizou-se o teste Tukey a 5% de probabilidade. Concluiu-se que a resistência de MK-10 ao oídio é devida a um par de alelos recessivos e que a resistência é expressa na fase de pré-penetração, completada por uma morte celular localizada pós-penetração, característica da presença do par de alelos recessivos er1er1.

Validation of microsatellite markers for assisted selection of soybean genotypes resistant to powdery mildew

Powdery mildew is one of the most serious diseases of soybean and is found in all producing countries. The purpose of this study was to validate microsatellite markers previously identified as associated with resistance to powdery mildew in soybean. The study was conducted in two F, parent populations with contrasting resistance to powdery mildew, In the analysis 10 SSR primers were used for the populations. and tour polymorphic markers were identified for cross I (MGBR95-20937 x IAC-Foscarin 31) and three for cross 2 (MGBR-46 x Empresa Brasileira de Pesquisa Agropecuária (EMBRAPA) 48). The Chi-square analysis of the phenotypic evaluation confirmed the expected segregation (3: 1) of a dominant gene related to resistance. The polymorphic markers also segregated as expected (1:2:1). The markers Sat 366 and Sat 393 in the crosses 1 and 2. respectively, located at 9.41 and 12.45 cM from the gene. were considered promising for marker-assisted selection for resistance to powdery mildew in soybean. at a selection efficiency of 92.7% and 60.3% respectively.