Association between molecular markers and blast resistance in an advanced backcross population of rice.

An advanced backcross population consisting of 80 BC(3)F(3) lines derived from rice vars. Vandana/ Moroberekan was analysed for blast resistance and genotyped with 50 candidate genes and 23 simple sequence repeat (SSR) markers. Six candidate defence response genes [thaumatin, three nucleotide-binding site-leucine-rich repeat sequences from maize and two resistance gene analogue (RGA) markers] and one SSR marker (RM21) were significantly associated with partial blast resistance in rice ( P=0.01). These markers accounted for phenotypic variation ranging from 9.6% to 29.4% and contributed to 76% of the total variation of percentage diseased leaf area (DLA) observed under natural infection. Four candidate genes (oxalate oxidase, 14-3-3 protein and two RGA markers) and four SSR markers (RM21, RM168, RM215 and RM250) were significantly associated with resistance to a single pathogen isolate, PO6-6. Among these, two markers were for DLA, five for lesion number and one for lesion size. These markers accounted for 9.1-28.7% of the phenotypic variation. A moderate correlation ( r=0.48, P<0.01) was found between the level of partial resistance measured in the greenhouse and that measured under natural conditions. Analysis of BC(3)F(4) progeny using genotypes of BC(3)F(3) confirmed the phenotypic contribution of these markers. Cluster analysis of DNA profiles showed that the BC(3) population was genetically similar (>85%) to the recurrent parent Vandana. Although no obvious relationship between DNA profiles and resistant phenotypes was observed, three lines (VM19, VM46 and VM76) in a cluster with high similarity to Vandana (89-96%) expressed a high level of partial blast resistance in the field. Analysis of disease progress in the field confirmed the performance of selected lines based on greenhouse and nursery analyses. The advanced backcross progeny with resistance phenotypes tagged by markers will be useful for accumulating blast resistance in upland rice.