Effect of nitrogen regimes on combining ability variation in oil and protein contents in cottonseed (Gossypium hirsutum L.)

Eight parental cultivars and 56 hybrids of cotton (Gossypium hirsutum) were grown in normal and nitrogen-deficient conditions in the field to investigate the effect of nitrogen regime on the oil and protein contents and their combining ability. The mean oil and protein contents of the parental cultivars greatly varied with the nitrogen regime, which indicated their nitrogen sensitivity The genetic variability of oil and protein contents was low in the same nitrogen regime, but was high in the comparison between the normal and nitrogen-deficient conditions. The nitrogen regime affected not only the oil and protein contents and ranking of parental cultivars, but also the combining ability. A normal nitrogen level was found to be more useful for selecting the additive type of gene action in breeding of cotton.