ScienceAsia 32 (2006): 133-142 QTL Mapping for Leaf and Neck Blast Resistance

ABSTRACT: Blast disease caused by a fungus called Pyricularia grisea Sacc. (perfect stage = Magnaporthe grisea Sacc.) is one of the most devastating rice diseases in the world. To date, the genetic relationship of leaf and neck blast is not well understood. Some rice cultivars known to carry leaf blast resistance genes are susceptible to neck blast. Five hundred eighty-seven recombinant inbred lines (RILs) derived from a cross between Khao Dawk Mali 105 (susceptible) and Jao Hom Nin (resistant) cultivars were developed by single seed descent and used as rice materials to identify quantitative trait loci (QTL) associated with leaf and neck blast resistance. Rice materials were assayed for both leaf and neck blast resistance using three selected blast isolates, designated THL191, THL318 and THL899. Correlation coefficients between leaf and neck blast resistance were low (0.28-0.56), suggesting the presence of two different pathosystems. A chi-square (X2) test fitted a ratio of approximately 3:1, reflecting the presence of at least 2 resistance QTL functioning against leaf and neck blast. Fourteen QTL were identified and mapped on three chromosomes: 1, 11 and 12. The QTL for resistance against leaf and neck blast on chromosome 1 were coincidentally mapped to the RM5-RM10