Marker-assisted screening of Oryza rufipogon accessions for sheath blight tolerance

Abstract

Potential resistant source against sheath blight of rice, caused by the fungus Rhizoctonia solani Kuhn, need to be identified from the wild rice species since no resistant source is reported till now from the cultivated rice germplasm. Eighteen Oryza rufipogon accessions along with tolerant check CR 1014 and susceptible check Swarna were phenotyped for sheath blight tolerance for three consecutive seasons. The accessions were also genotyped using 21 biotic stress responsive cgSSR markers which target the sequence variations in genes which are non-specifically expressed under various biotic stress situations in rice. Two wild rice accessions (AC100444 and AC 100015) were found to be moderately resistant to sheath blight. The cgSSR markers were amplified in both the species indicating their cross transferability across species. Though gene sequence based, the markers were highly polymorphic with the PIC value ranging from 0 to 0.85 with an average value of 0.55. The UPGMA clustering based on 106 marker alleles of 21 cgSSR loci grouped the twenty genotypes into three sub-groups. The first sub- group consisted mainly of tolerant accessions; the second sub- group had predominantly susceptible ones and geographically distinct accessions formed a third subgroup irrespective of their sheath blight phenotype. The two wild rice accessions which are found to be moderately resistant to sheath blight and the completely cross transferable and highly polymorphic cgSSR markers reported in the study can be utilized in future biotic stress breeding programmes.