Fluctuation in genetic effects with introduced early- or late-heading-date gene alleles in near-isogenic lines with different genetic backgrounds in rice

Near-isogenic lines (NILs) with introduced external gene alleles are good breeding materials for developing novel rice cultivars with a high agronomic performance. We developed NILs by introducing the Ghd7, Hd1, and Hd16 gene alleles showing an early or late heading date in the genetic backgrounds of three rice cultivars, “Shinko 538”, “Fusaotome”, and “Chiba 28”. The NILs were developed within 5 years by using continuous backcrossing and whole genome DNA marker-assisted selections with each backcrossed generation. The NILs with an introduced early-heading-date allele of the Ghd7 gene had a heading date 9 to 13 days earlier, in comparison with their recurrent cultivar, “Shinko 538”. The NILs with an early-heading-date allele of the Hd16 gene had a heading date from about 1 day earlier to about 8 days later. In the genetic backgrounds of “Fusaotome” and “Chiba 28”, NILs with the late-heading-date alleles of the Hd1, Hd16, and Hd1 + Hd16 genes had heading dates which were about 13 days, 3 days, and 28 days later, respectively, than their recurrent cultivars. The agronomic traits were nearly the same between recurrent cultivars and the NILs with the late-heading-date alleles of the Hd1 gene in the genetic backgrounds of “Fusaotome” and “Chiba 28”. By comparing the evaluation scores in previously developed NILs, the Ghd7, Hd17, and Hd18 gene alleles stably improved the heading date and other agronomic traits, while the Hd1 and Hd16 gene alleles showed variations depending on the recurrent parents and growth environment. For the efficient development of novel climate-resilient rice cultivars derived from NILs, it is necessary to elucidate in detail the genetic interactions between each introduced gene allele and its genetic background.