Estimate of combining ability in diallel cross of eight lines (Ricinus communis L.) at two locations

Eight characteristics were evaluated namely yield, yield from primary racemes, yield from lateral racemes, number of seed per plant, 100 seed weight, primary raceme lenght, number of raceme per plant, and height to base of primary raceme. Different response was obserbed in each hybrid when grown at different environments. All of the characters studied were statistically different at Experimental Station of Thai Castor Oil Industries Co.,Ltd. On the other hand, yield from lateral racemes, primary raceme lenght and number of racemes per plant were not statistically different at Experimental Station of Pioneer Overseas Corp. (Thailand) Ltd. All the characters studied were obserbed to be controlled by both additive and dominant gene effects in which the additive gene effect was higher than the dominant gene effect and the level of dominant gene effect was higher under the unfavorable condition. Germplasm from tropical region tended to have the high adaptability and general combining ability under the low level of rainfall condition the germplasm from France. Under the low level of rainfall condition, TCO 2 the germplasm from tropical region, have the highest general combining ability in yield, yield from lateral racemes, number of seed per plant and 100 seed weight. On the other hand TCO 7, the line developed from the France cultivar, have the lowest combining ability in yield, yield from primary racemes, yield from lateral racemes and number of seed per plant. Under the high level of rainfall condition, castor lines developed from germplasm of tropical region, TCO 1, have the highest combining ability in yield, yield from primary receme, number of seed per plant and primary raceme lenght, while castor lines developed from France germplasm, TCO 7, have the highest combining ability in yield from lateral racemes. Heterosis was observed in most of hybrid in yield, yield of primary racemes, yield of lateral racemes and number of seed per plant in bath locations. Under the high rainfall condition, the heterosis in yield from lateral racemes was decreased. Moreover, hybrids from the close parents had lower combining ability than those from the wide parents. Results from the evaluation of correlation coefficient between yield and other characters revealed that yield had the high correlation coefficient with yield from primary racemes, yield from lateral racemes and number of seed per plant. The evaluation of path-coefficient revealed that number of seed per plant had the high direct effect to yield, while yield from lateral racemes had the low direct effect to yield but had relatively high indirect effect through number of seed per plan