Studies On Cold Tolerance Of Dongsiang Wild Rice And Its Utilization In Rice Breeding

It is the world wide problem that the low temperature damage (abbr. LTD) in rice, especially in Japan, South Korea, the USA, and China where there are yearly losses of 3~5 billion kg of rice grain caused by the LTD. The LTD is not only an obstruct to the rice yield in the north paddy section of China but influencing badly the seedlings of early season Indica rice and the flowering & milking of later season Indica rice in the south rice section. Thus, Scientists are now accelerating the development and utilization of the germplasm source of cold tolerance (abbr. CT) in rice. This paper reported that the' strong CT of Dongxiang Wild Rice (abbr. DxWR) was transferred into some modern cultivated rice to enhance their CT at seedling and heading stages as well as their high and stabilizing yield.Materials including Indica and Japonica cultivars with different degree of CT, DxWR with strong CT and Indica cultivars without CT were used to study the degree of CT and its genetic law in DxWR by intercrossing and backcrossing. After hybridization the CT of DxWR was transferred into some cultivars, and from the segregated crossing progenies the cultivar "Dongye No.l" (line 4913-1) was bred. Experiments were also conducted to identify the CT of this new cultivar and evaluate its traits of yield, quality, resistance and adaptability for its further demonstration and commercial release.The results showed that the CT of DxWR was one degree higher than that of Japonica rice when at seedling stage, and at heading and flowering stages DxWR showed stronger CT for its seed setting period was about 6d longer than that of Indica or Japonica cultivars with similar CT while they had the same period of normal seed set (70% and above). DxWR is one of the perennial common wild rice, its dormant buds can overwinter and will develop into seedlings within the last lOd of February, its initial heading is observed at the beginning of September and the last date of normal seed set is October 31.It is worthwhile to pay attention, when conducting rice breeding of cold'tolerance, that DxWR performed "double strong tolerances" to cold and freeze. The overwinter dormant buds have strong tolerance to freeze for even under -5D they would not be damaged. The seedlings, developed from dormant buds or seeds, would not die under OH for 2d even they had already been affected by LTD.On inheritance of the CT of DxWR, it was found that the characteristic of CT was complete dominant to that of no CT and dominated by two pairs of repeated genes, and the cytoplast of DxWR would further influence the CT of the cross progenies.The CT of DxWR could be transferred into cultivated rice by general crossbreeding. When selecting the single plant with strong CT among the cross progenies the "double low temperature" pressing method, which was simple and convenient to operate, was conducted to improve the selective efficiency.Using DxWR as the donor of CT to conduct transfer breeding it was more difficult to develop a Indica variety or cultivar line with strong CT, for while a Japonica cultivar was chosen as pollen parent and after once backcross or repeated cross it was little easier to select a single plant or a line with CT among the cross progenies, and once a Indica cultivar was chosen as pollen donor it was difficult to repeat the same selection effect.The methods of CT identification are worthwhile to develop. At present, the degree of CT of a rice variety is identified only according to the results obtained from once treatment of low temperature on this variety. According to this experiment, the combining treatment of low temperature, i.e. treated continually from low temperature to the lower, would be more accurate to identify the characteristic.