Utilization of Aromatic Rice in Improving Grain Quality of Hybrid Rice

To improve grain quality of the high-yielding hybrid rice in China, we introduced the aromatic rice MR365, an improved Indian cultivar with aroma and other desirable grain quality characters such as long grain and low chalkiness, from IRRI in 1984 and began to transfer its aroma and good quality characters into the existing maintainer lines with good combining ability but poor grain quality. In the meantime, we also conducted the research on the inheritance of aroma for increasing the breeding efficiency. Through years of research and breeding practices, two cytoplasmic male sterile （CMS） lines Xiangxiang 2 A and Xinxiang A and a series of quasi-aromatic hybrids mated from these aromatic CMS lines have been developed and released for commercial production in China. It was found that the inheritance of aroma in MR 365 and its derivatives including Xiangxiang 2 A, Xinxiang A and Xiang 2B S was controlled by one pair of recessive major genes based on the identification of aroma by the KOH-soaking method. We also found that there existed disparity in aroma degree among different grains of F2 generation, and different aromatic CMS lines derived from the same aromatic donor such as Xiangxiang 2 A and Xinxiang A had also a little difference in the degree of aroma, which implies that, besides the major genes, aroma may also be affected by the genetic backgrounds or minor genes. Xiangxiang 2 A, developed from the cross of V20A∥V20B/MR365, is the first aromatic CMS line bred in China. It is not only aromatic but has good grain quality and combining ability. Using it as female parent, Xiangyou 63 （Xiangxiang 2A/Minghui 63）, the first quasi-aromatic hybrid rice combination in China, was developed and approved to release to farmers in 1995. Xiangyou 63 is characteristic of quasi-aromatic or partially aromatic （because only a portion of or NOT ALL grains are aromatic）, good grain quality, high-yielding ability, good blast resistance and wide adaptability. However, Xiangxiang 2 A has an evident drawback, i.e., instablility in male sterility under higher temperature conditions resulting from the existence of restoring minor genes in it, which greatly hampered the extension of its elite hybrid Xiangyou 63 with both high yield and fine quality in commercial production.To improve Xiangxiang 2 A, we made hybridization of Xiangxiang 2 B with V20 B again in 1990. A new aromatic CMS line Xinxiang A was successfully developed in 1994. It not only retains the favorable characteristics of Xiangxiang 2 A in grain quality and combining ability, but also expresses complete and stable male sterility and high seed production yield potential. Up to now, by using it as female parent, a series of quasi-aromatic hybrids have been developed. Some of them such as Xinxiangyou 63 （Xinxiang A/Minghui 63）, Xinxiangyou 77 （Xinxiang A/Minghui 77）, Xinxiangyou 80 （Xinxiang A/R80）, Xinxiangyou 207 （Xinxiang A/R207） and Xinxiangyou 96 （Xinxiang A/R96） have been released to farmers. Such hybrids have been preferred and well welcome by the farmers in China, because they can not only yield higher or as high as but also possess a better grain quality than the current common high-yielding hybrid rice varieties, especially, they are naturally-mixed aromatic rice so that it can be consumed daily just like non-aromatic common rice. The planting area under these hybrids is increasing rapidly in China. It is expected that the quasi-aromatic hybrid rice will have a good prospect in the coming years.