Abstract
Low-temperature germinability is a crucial trait for seedling establishment at low temperatures, which is essential for the direct-sowing culture of rice. We pyramided four quantitative trait loci (QTLs) for germinability at low temperatures in the genetic background of the Japanese cultivar Akitakomachi. In the QTL pyramiding lines, the accumulated QTLs additively increased the low-temperature germination rate, despite the weak effects of the individual QTLs. This can be observed when considering the QTL qLTG3-2, which alone did not increase the germination rate at low temperatures but further enhanced the germination rate when combined with either qLTG3-1 or qLTG11-1. Low-temperature germinability remarkably improved in proportion to the number of accumulated QTLs. Thus, QTL pyramiding was an effective method to enhance this trait. Furthermore, the improved low-temperature germinability in the lines that accumulated the four QTLs also enhanced the seedling establishment compared to Akitakomachi. Seedling establishment at low temperatures is a complex trait that involves continuous growth from seed germination to seedling development. The remarkable improvement in low-temperature germinability is likely to contribute to the improved seedling establishment at low temperatures. However, the four QTL pyramiding line exhibited a reduced brown rice appearance quality. To avoid the introduction of undesirable traits, pyramiding using new QTLs for low-temperature germinability is expected to develop a superior rice variety suitable for direct-sowing cultivation.