Effect of shuttle breeding with rapid generation advancement on heading traits of Japanese wheat

In order to develop an efficient method of shuttle breeding with rapid generation advancement applicable to the breeding programme of early maturity wheat in the central to southwestern regions of Japan, the possibility of eliminating late heading plants was investigated by combining fall-sown cultivation on Ishigaki Island (24°N), Okinawa, with spring-sown cultivation at Memuro (42°N), Hokkaido. The analysis of heading traits using wheat cultivars and F₂ populations indicated that the earliness of heading in Okinawa and Hokkaido was closely related to both Ppd and Vrn genotypes and the Vrn genotype, respectively. The two hybrid populations segregating for the Ppd or Vrn genes were subjected to rapid generation advancement (F₂: Okinawa, F₃: Hokkaido). The analysis of their photoperiod and vernalization responses showed that the plants with photoperiod sensitivity and winter growth habit were eliminated in Okinawa and those with winter growth habit in Hokkaido. The elimination of photoperiod-sensitive plants significantly decreased the proportion of late heading plants in the F₄ population cultivated in the southwestern region of Japan, whereas it was not influenced by the elimination of the winter type plants. It was confirmed that the earliness of heading in the southwestern region of Japan was closely related to the Ppd genotype and was independent of the Vrn genotype, and also indicated that this system of rapid generation advancement was effective in eliminating the late heading plants with photoperiod sensitivity.