Molecular analysis and phenotypic validation of blast resistance genes Pita and Pita² in landraces of rice (Oryza sativa L.)

Rice (Oryza sativa L.) crop confronts several major and minor diseases of which blast disease caused by Magnaporthe oryzae is a serious constraint causing moderate to huge economic losses world over. Exploitation of genetic resistance in cultivars is a preferred management strategy. Though the number of genes for resistance to blast have been cloned and mapped, however, as because of their variable efficacy and donor traits there remains a scope for discovery of alleles and hence fresh donors among local collections and landraces. Present investigation was undertaken with the objective towards screening of 100 germplasm accessions for Pita-Pita², the two tightly linked dominant genes governing major gene blast resistance. An attempt was made to identify the genotypes carrying individually or in combination the genes Pita and Pita² with the help of molecular markers and differential screening using diagnostic isolates. Based on PCR assay using two gene based markers, 27 accessions were found carrying resistance specific alleles. Differential screening results coupled with marker information helped to classify the genotypes in five categories. Out of the marker positive accessions, 11 were supposed to possess Pita and in 9 other genotypes the presence of Pita and (or) Pita² was validated. Besides this, the validation of markers linked to Pita-Pita² locus was performed across varieties and landraces grown in India to assess their use and relevance in MAS. The identified gene sources may serve as new donors and a subject for further genetic and genomic investigations.