| Results and Discussion Heterosis. - Two of the 6 F1 hybrids had significantly higher grain protein percentage than the better parent in the cross for 1% (Bezostaja 1 x Kavkaz) and 10% (Sava x Bezostaja-1) in 1973, and only one for 3% (Sava x Kavkaz), in 1975, showing positive heterosis. However, the rest of F1 hybrids showed no heterosis for grain protein percentage. This suggests that the considerable amount of heterosis for grain protein percentage may be encountered only in certain F1 hybrids, and that this depends strongly on the environmental conditions. GRIFFING and ZSIROS (1971) reported that plant density and environmental conditions has an effect on the amount of heterosis in wheat, which agrees with the results obtained in this study regarding the grain protein content. From the stand point of the practical hybrid wheat growing and development of a breeding programme it is neccessary for F1 hybrids to express heterosis under local environmental conditions. Because of this the obtained results approved the need that the breeders should evaluate the F1 hybrids and parents under local environmental conditions. Combining ability. - The analysis of variance for combining ability for grain protein percentage showed that both, general (GCA) and specific (SCA) combining ability variances were highly significant in 1973 as well as in 1975. In 1975 the GCA variances were larger than the SCA variances with the ratio of GCA/SCA being 4,71, while in 1973 the SCA variances were larger than the GCA variances, with the ratio of GCA/SCA being 0,047. The relatively higher magnitude of the GCA variance than that of the SCA variance indicates the predominance of additive (fixable) gene effects in the genetic control of the grain protein percentage among parents used in the diallel cross. On the other hand, the significant SCA variance suggests considerable amount of non-additive (dominance and overdominance) variance among the parents used for the diallel crossings. CHAPMAN and MCNEAL (1970) ; RAM and SRIVASTAVA (1975), and KETATA et al., (1976) ; BHULLAR et al., (1978), also reported that additive gene effects in grain protein content were significant in all crosses and consistently greater than dominance effects, while Brown et al., (1966) found the predominance of non-additive gene effects to be significant. Of particular importance to the wheat breeder seeking improvement of grain protein content is the predominance of additive gene action for this attribute, because it suggests that the improvement of this character can be achieved through the standard breeding procedure, from which may result superior pure-line varieties. The occurence of a rather pronounced non-additive gene action, as was found in this study, could also be of practical value to the wheat breeder. If this is a general phenomenon, it may be possible to obtain higher protein content by hybrid wheat breeding through appropriate choice of crossing parents for producing the F1 hybrid seeds. The comparison of GCA performances of individual varieties (Tab. 1) shows that Cajeme-71 and Sava had positive GCA effects in 1973 and Kavkaz and Cajeme-71 in 1975. It should be pointed out that expression of GCA effects of parents used in this study depended on the year in which the hybrids were tested. In both years Bezostaia-1 had negative GCA effects and Cajeme-71 positive GCA effects, while Sava and Kavkaz had in one year positive and in one year negative GCA effects. The variety Cajeme-71 proved to be the best general combiner and Bezostaja-1 very poor general combiner for the grain protein content. The other tested varieties were an average in this respect. |
| <-- Back | | | --> Next |