Combining Ability:

The results appeared that there are highly significant differences in F₁ hybrids for all measured traits. Comparisons of general combining ability (GCA) versus specific combining ability (SCA) indicated that GCA was greater in magnitudes than SCA for all traits studied except number of spikelets per spike. The estimates of GCA and SCA were positive and highly significant for all traits with the exception of spike length even though there are insignfiicant differences in SCA for this trait. It can be concluded from the results obtained in this study that the differences among the hybrids are due to general as well as specific combining ability for all traits except spike length which showed that a large portion of the total genetic variability was a result of GCA. The results obtained for days to heading and plant height are in agreement with that obtained by KRONSTAD and FOOTE (1964), GYAWALI et al. (1968), SOOMRO and AKSEL (1976), and EL-HADDAD and ALI (1979). However, BROWN et al. (1966), and WIDNER & LEBSOCK (1973) found only highly significant general combining ability for plant height. The results concerned with spike length agreed with that obtained by JOHNSON et al. (1966). While, JAIN & SINGH (1976) and EL-HADDAD & ALI (1979) found that both general and specific combining ability estimates were highly significant in the effect on this trait. Regarding to number of spikelets per spike WALTON (1971) and JAIN & SINGH (1976) reached to the same results, contradicted the findings of HASSANIEN et al. (1974). However, KRONSTAD & FOOTE (1964) and EL-HADDAD & ALI (1979) obtained highly significant differences in only GCA. Table 2.

Gene Action:

Variances of general (sigma_G²) and specific (sigma_S²) combining ability and gene action estimation measured in terms of additive (sigma_A²) and dominance (sigma_D²) genetic variance are presented in Table 3 and Table 4.

The results obtained in this study indicated that the variance of general combining ability (sigma_G²), i.e. additive gene action (sigma_A²) estimates were only significant for spike length and spike density. Whereas, significant specific combining ability components (sigma_S²), i.e. nonadditive genetic variance, have been reported for all traits, in comparing the relative magnitudes of general (sigma_G²) versus specific (sigam_S²) combining ability genetic variance components for all traits except spike length had higher (sigma_G²) than (sigma_S²). These results suggest that a large part of the total genetic variability associated with days to heading, plant height and number of spikelets per spike was a result of nonadditive gene action. However, additive as well as dominance genetic variance are responsible for the inheritance of spike length and spike density.

The results of days to heading since only significant dominance genetic variance are in agreement with that reported by JOHNSON et al. (1966), contradicted that findings obtained by BHATT (1972) and ALI & EL-HADDAD (1978). However, AMAYA et al. (1972) found that early genotypes may be attainable only with a system that can exploit both additive and nonadditive genetic effects. AMAYA et al. (1972) came up to similar conclusion regarding plant height, while ABO EL-ENEIN & GOMMA (1977) found only highly significant additive gene action. The results of spike length are in agreement with that obtained by ALI & EL-HADDAD (1978). Similar findings have been reported in number of spikelets per spike by HASSANIEN et al. (1974), while ALI & EL-HADDAD (1978) found that this trait had higher and highly significant additive gene action in relation to nonadditive types.

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