Mapping of a Major QTL, <i>qHD6-SD</i> Responsible for Days to heading Under Natural Short Day Conditions to Develop Rice Varieties adaptable to Tropical Regions

Breeding Temperate Japonica Rice Varieties Adaptable to Tropical Regions: Progress and Prospects

“…Kim et al [4] reported that the yields of the Korean temperate japonica varieties showing extra-early heading in the tropical region were 0.6 to 1.4 ton/ha, while those in Korea located in the temperate region were 7 to 10 ton/ha. The interplay of flowering factors under different photoperiodic conditions limits the speed of japonica rice's adaptation to the tropics [5], and it was one of the main challenges of temperate japonica rice breeding in the tropics. The transition from the long-day conditions in the temperate areas to the short-day conditions in the tropics appeared to be the cause of stunted growth, weak tillers, small panicles, and premature headings of the temperate japonica rice in the tropics [5].…”

“…The interplay of flowering factors under different photoperiodic conditions limits the speed of japonica rice's adaptation to the tropics [5], and it was one of the main challenges of temperate japonica rice breeding in the tropics. The transition from the long-day conditions in the temperate areas to the short-day conditions in the tropics appeared to be the cause of stunted growth, weak tillers, small panicles, and premature headings of the temperate japonica rice in the tropics [5]. Fortunately, early GUVA scientists found that some japonica rice germplasm sources such as Jinmibyeo showed delayed heading [4] which were deployed in the GUVA breeding program.…”

“…These results indicate that the functional Hd1 alleles of temperate japonica varieties induced extremely early flowering in the tropics and the non-functional Hd1 alleles brought about the adaptation of temperate japonica rice to tropical regions. Bombay et al [5] also suggested that a non-functional Hd1 allele was critical for the tropical adaptation of temperate japonica rice, since it delays the heading date, which is essential for prolonging the vegetative state and achieving optimum biomass, an increased spikelet number, and a high grain-filling capacity.…”