Useful Heterosis Estimates under Different Nitrogen Fertilizer Levels in Half Diallel Crosses of Wheat

The breeding materials used herein included eight genotypes of wheat i.e., CHAM-6/MayoN's, LAKTA-1, MELLAL-1, NABEK-4, Gemmeiza 7, Gemmeiza 9, Gemmeiza 10 and Sakha 94. These genotypes were crossed in half diallel mating system in 2003/04 season at the experimental farm of Gemmeiza Agriculture Research Station, Egypt. The parental genotypes and their crosses were evaluated in 2004/05 season under three nitrogen fertilizer levels i.e., 25, 50 and 75 kg N/fad. The reduction in yield and its components under the lowest N level relative to the highest one ranged from 16% to 25%, while the present materials were earlier under the lowest N level relative to the highest one by 13.75% and 4.73% for heading and maturity date, respectively. This would revealed the possibility to minimize the losses of yield and maximize the earliness of the present materials by suitable breeding program under the lowest N level which consider as one of the ways to safe the environment from the pollution. The significant mean squares of genotypes, parents and crosses, where its magnitudes were several times larger than their corresponding mean square of error, indicating the successful of the planned crosses due to the presence of sufficient variability. Parents vs crosses mean squares were found to be highly significant for all studied traits at all nitrogen fertilizer levels and their combined data. The interaction of parents vs crosses. N fertilizer levels was found to be significant for most traits, indicating that average heterosis overall crosses changed from environment to another. The range of mid-parental heterosis was -0.58% to -1.84% under 25 kg N/fad., -0.52% to -2.38% under 50 kg N/fad. and 0.00 to -1.15 under 75 kg N/fad. for earliness attributes. For yield, the range of mid- parental heterosis was 2.76% to 27.71% under 25 kg N/fad., 2.25 % to 23.34% under 50 kg N/fad. and 2.34 % to 32.60 % under 75 kg N/fad. However, in most cases the mid-parental heterosis were due to over-dominance as the potence ratios pointed out. On the other hand, the range of better parental heterosis (useful heterosis) was 2.31 to 26.75% under 25 kg N/fad., 2.72 to 22.86% under 50 kg N/fad. and 2.37 to 25.53 % under 75 kg N/fad. This would indicate that comparable useful heterosis was detected under the lowest level of N (25 kg) which considered as a favorable environment which had low level of pollution in comparison with the other N levels. However, it could be concluded also that the cross- combinations; LAKTA-1 x Sakha 94 and METLLAL-1 x Gemmeiza 10 could be used in breeding programs with low level of N fertilization according to their mean performance and the results of heterosis for most studied traits. The estimates of narrow-sense heritability confirmed the above results.