Evaluation of a M-202 × Oryza nivara advanced backcross mapping population for seedling vigor, yield components and quality

Oryza nivara, the ancestral species of cultivated rice (O. sativa), has been the source of novel alleles for resistance to biotic and abiotic stress lost during domestication. Interspecific advanced backcross (ABC) populations permit the introgression of desirable alleles from the wild species into O. sativa and allow traits to be mapped to chromosomal regions by QTL mapping. An ABC population was developed by crossing M-202, a California medium grain, temperate japonica cultivar with O. nivara (IRGC100195). The population has 177 BC₂F_2:5 progeny lines and was evaluated for 17 traits including seedling vigor under cool temperature (mesocotyl, coleoptile, shoot and root lengths), agronomic (days to heading, plant height, culm angle, panicle type), yield components (panicles per plant, panicle length, florets and seeds per panicle, 100-seed weight) and quality [kernel length and width, apparent amylose content (AAC), alkali spreading value (ASV)]. Most exciting was that the O. nivara parent improved seedling vigor by increasing both the coleoptile and shoot lengths. Wild donor alleles increased the panicles per plant and seed weight, but M-202 alleles improved fertility. For one locus, the O. nivara alleles accounted for increased kernel length even though this parent had smaller seeds than M-202. The AAC mapped to the WAXY locus and ASV to the ALK locus, with most progeny being similar to M-202 for these quality traits. Select progeny lines could be useful for improving seedling vigor. This interspecific population is the first in the background of a U.S. temperate japonica rice cultivar.