Evaluation of major Japanese rice cultivars for resistance to bacterial grain rot caused by Burkholderia glumae and identification of standard cultivars for resistance.

Bacterial grain rot (BGR), caused by the bacterial pathogen Burkholderia glumae, is one of the most destructive rice (Oryza sativa) diseases in Japan; however, there are no BGR-resistant cultivars for use in Japan. We previously developed a cut-panicle inoculation method to assess the levels of BGR resistance in the World Rice Collection (WRC). Here, we evaluated major Japanese cultivars for BGR resistance and found that none showed "strong" or "medium to strong" resistance; most were categorized as "medium to weak". On the basis of the screening results, standard cultivars for BGR resistance were selected according to resistance level and relative maturity. Our results indicate that it is necessary to introduce quantitative trait loci (QTLs) from indica or tropical japonica resistant cultivars into Japanese temperate japonica to develop BGR-resistant cultivars for Japan. We previously developed a near-isogenic line (RBG2-NIL) by introducing the genomic region containing RBG2 from 'Kele' (indica) into 'Hitomebore'. In this experiment, we confirmed the resistance level of RBG2-NIL. The resistance score of RBG2-NIL was "medium to strong", indicating its effectiveness against BGR.