Quantitative Trait Loci Associated with Leaf and Neck Blast Resistance in Recombinant Inbred Line Population of Rice (Oryza Sativa

Blast is an economically important disease of rice. To map genes controlling blast resistance, re-combinant inbred lines (RIL) were developed from Khao Dawk Mali 105, an aromatic, blast-susceptible cultivar and the blast resistance donor, CT 9993-5-10-M (CT). A linkage map encompassing 2112 cM was constructed from 141 RILs using 90 restriction fragment length polymorphisms (RFLPs) and 31 simple sequence repeats (SSR). Virulent isolates of blast fungus were identified by screening differential host sets against 87 single-spore isolates collected from the north and northeast of Thailand. Fifteen virulent blast isolates were selected for leaf blast screening. Neck blast was evaluated both under natural conditions and controlled inoculations. Quantitative trait loci (QTLs) for broad resistance spectrum (BRS) to leaf blast were located on chromosomes 7 and 9. In particular, the QTLch9 was mapped near the Pi5(t) locus. The QTLch7 was located close to a previously mapped partial resistance QTL. Both loci showed significant allelic interaction. Genotypes having CT alleles at both QTLch7 and QTLch9 were the most resistant. Two neck-blast QTLs were mapped on chromosomes 5 and 6. The inconsistent map locations between the leaf and neck blast QTLs indicate the complexity of fixing both leaf and neck blast resistance. Th