Breeding of a promising isogenic line of rice (Oryza sativa L.) variety ‘Koshihikari’ with low cadmium and brown spot (Bipolaris oryzae) resistance

The OsNRAMP5-deficient rice (Oryza sativa L.) mutant (osnramp5-2), with a low grain cadmium (Cd) content, was registered as ‘Koshihikari Kan No. 1’ in Japan. Its agronomic traits are almost identical to those of ‘Koshihikari’ except for its low Cd content and its susceptibility to brown spot (BS) caused by Bipolaris oryzae. To restore BS resistance, we introduced the BS resistance quantitative trait locus (QTL) bsr1 into it. The resulting isogenic line (IL) had higher resistance to BS than Koshihikari Kan No. 1 while retaining low grain Cd, with no significant difference from Koshihikari in grain yield or quality. This IL, which we named ‘Kanto IL 31’, can be used for breeding varieties with low Cd content and BS resistance.