Genetic study of the main agronomic characters of five cold tolerance standard varieties of Yunnan rice (Oryza sativa L.) under different ecotones.

Five standard varieties of rice (Oryza sativa L.) with different cold tolerance were crossed in 15 combinations and grown in Sanya, Hainan (Alt. 15 m), Kunming, Yunnan (Alt. 1916 m) and Yiliang, Yunnan (alt. 1532 m), and the main agronomic characters were recorded in their P 1,P 2,F 1,F 2 and F 3. Great differences were observed among various varieties and their cross combinations in the GCA and SCA of their agronomic characters investigated in this study. Plant height, ear length, filled grains per spike and total grains per spike tended to increase with altitude, and seed setting rate showed a reverse trend: it dropped with the increase in altitude. The extent of difference in the SCA of the agronomic characters between different rice cultivating regions and between different generations was shown to be closely associated with the affinity of the parents. It is concluded that in deciding rice breeding targets, the conditions of specific rice-cropping regions should be taken into consideration.