Confirming and Identifying New Loci for Rice Blast Disease Resistance usingMagnaporthe oryzaeField Isolates in the US

Quantitative trait loci (QTL) play important roles in controlling rice blast disease. In the present study, 10 field isolates of the races IA1, IB1, IB17, and IC1 of US rice blast fungus Magnaporthe oryzae collected in 1996 and 2009 were used to identify blast resistance QTL with a recombinant inbred line (RIL) population consisting of 227 F₇ individuals derived from the cross of rice (Oryza sativa L.) cultivars Lemont and Jasmine 85. Jasmine 85 is an indica cultivar that is moderately resistant, and Lemont is a tropical japonica cultivar susceptible to rice blast in greenhouse inoculation. Disease reactions of the parents and RILs were evaluated under greenhouse conditions. A total of six resistance QTL, qBLR8, qBLR10-1, qBLR10-2, qBLR10-3, qBLR12-1, and qBLR12-2, were identified on chromosomes 8, 10, and 12, respectively. Phenotypic variation, conditioned by these six resistance QTL, ranged from 5.37 to 39.18%. Among them, qBLR12-1 and qBLR12-2 provided the strongest resistance to the newest isolates of the most virulent race IA1 of M. oryzae. Three of these resistance QTL have been identified using different blast isolates in a previous study. qBLR10-1, qBLR10-2, and qBLR10-3 have not been previously found in this cross. These confirmed and new resistance QTL will be useful for the development of rice cultivars with improved effective resistance to rice blast via a marker-assisted selection (MAS) approach.