Identification and validation of rice blast resistance genes in Indian rice germplasm

Blast disease caused by Magnaporthe oryzae is a major constraint in rice production. Identification of new donors for blast resistance is a pre-requisite for effective utilization of diverse germplasm for marker assisted incorporation of blast resistance into improved varieties. Therefore, in the present study, a set of 100 diverse rice germplasm accessions were evaluated for 11 blast resistance genes namely Pik^m, Pik, Pik^h, Pi1, Pi5, Pi54, Pib, Piz5, Piz, Pi9 and Pish, both at genotypic and phenotypic level. Genotyping with gene based/gene linked markers could identify six genotypes from the germplasm possessing as many as six resistance specific alleles. A total of 34 and 67 germplasm lines were found to possess resistance alleles for two genes, Pik^m and Pik, respectively. Phenotypic validation using artificial inoculation in the germplasm was carried out with 4 diverse isolates under controlled conditions. The congruence between marker genotype and disease phenotype on a set of monogenic lines for blast resistance in the LTH background was used to compute Disease Resistance Index (DRI) in the germplasm. Cumulative DRI for each genotype was computed over all the marker loci. The genotypes Heibao, Kalinga-I, Vijetha, Anjali, Bhaubhog, Sada Kaijam, Kala Jeera had high cumulative resistance score. Allelic Cumulative Disease Resistance Index (ACDRI), a measure for comparing the effectiveness of markers was calculated and markers linked to Pik^m, Pik, Piz5, Pi1 were found to possess higher accuracy and better correlation with expected patterns of resistance under artificial inoculation. Based on disease resistance index, 25 germplasm accessions were found carrying blast resistance specific alleles at different loci and were fully validated for disease phenotype, which are valuable in breeding for resistance, allele mining and functional genomics studies.