IDENTIFICATION OF A MAJOR QUANTITATIVE TRAIT LOCUS CONFERRING RICE BLAST RESISTANCE USING RECOMBINANT INBRED LINES

Blast disease caused by Pyricularia oryzae is one of the limiting<br />factors for rice production world wide. The use of resistant<br />varieties for managing blast disease is considered as the most<br />eco-friendly approaches. However, their resistances may be<br />broken down within a few years due to the appearance of new<br />virulent blast races in the field. The objective of the present<br />study was to identify the quantitative trait locus (QTL) conferring<br />resistance to blast disease using 126 recombinant inbred<br />(RI) lines originated from a crossing of a durably resistant upland<br />rice genotype (Laka) and a highly susceptible rice accession<br />cultivar (Kencana Bali). The RI population was developed<br />through a single seed descent method from 1997 to 2004.<br />Resistance of the RI lines was evaluated for blast in an endemic<br />area of Sukabumi, West Java, in 2005. Disease intensity of the<br />blast was examined following the standard evaluation system<br />developed by the International Rice Research Institute (IRRI).<br />At the same year the RI lines were analyzed with 134 DNA<br />markers. Results of the study showed that one major QTL was<br />found to be associated with blast resistance, and this QTL was<br />located near RM2136 marker on the long arm of chromosome<br />11. This QTL explained 87% of the phenotypic variation with<br />37% additive effect. The map position of this QTL differed<br />from that of a partial resistant gene, Pi34, identified previously<br />on chromosome 11 in the Japanese durably resistant variety,<br />Chubu 32. The QTL, however, was almost at the same position<br />as that of the multiple allele-resistant gene, Pik. Therefore, an<br />allelic test should be conducted to clarify the allelic relationship<br />between QTL identified in this study and the Pik. The RI lines<br />are the permanent segregating population that could be very<br />useful for analysing phenotypic variations of important agronomic<br />traits possibly owned by the RI lines. The major QTL<br />identified in this study could be used as a genetic resource in<br />improvement of rice varieties for blast resistance in Indonesia