HETEROSIS OF NEW MAIZE HYBRIDS IN YIELD, YIELD COMPONENTS, PHYSIOLOGICAL TRAITS AND SOME GENETIC PARAMETERS UNDER LOW AND HIGH NITROGEN CONDITIONS

M.A. ABDEL-MONEAM¹*, F. IBRAHEEM^2
1Agronomy Department, Faculty of Agriculture, Mansoura University, Mansoura, Egypt.
²Botany Department, Faculty of Science, Mansoura University, Mansoura, Egypt.
* Corresponding Author : maaelmoneam@mans.edu.eg

Received : 13-01-2015     Accepted : 03-03-2015     Published : 10-06-2015
Volume : 6     Issue : 1       Pages : 131 - 141
J Crop Sci 6.1 (2015):131-141

Keywords : Maize, Heterosis, Correlation, Heritability, Expected gain from selection, nitrogen
Academic Editor : I.s. Tokatlidis
Conflict of Interest : None declared
Acknowledgements/Funding : This work was supported by a Mansoura University's award to the authors

Heterosis has been the biggest motivation for improving maize grain yield. Thirteen new maize single cross hybrids were developed via cross combinations between B73 inbred line and some American and Egyptian inbred lines. The field performance of these new hybrids was evaluated along with two commercial varieties (Pioneer SC 3084 and SC 10) under low (30 Kg N/fed=71.4 Kg N/ha) and high (120 Kg N/fed=285.7 kg N /ha) nitrogen (N) fertilization rates to study heterosis over commercial varieties, phenotypic, physiological, and genotypic correlations, as well as heritability and anticipated gain from direct and indirect selection for yield and its related traits under low and high N conditions. The results indicated that mean squares of crosses were highly significant for all studied traits under both low and high N fertilization rates, indicating significant genotypic differences among the studied crosses and suggest that almost all variables exhibited some degree of heterosis. Crosses no. 6 (B73 x CML103) and no. 7 (B73 x Tzi8) were the best crosses and recorded the highest percentages of heterosis over the studied commercial check varieties (Pioneer SC 3084 and SC 10) with significant values in grain yield per plant and most of studied yield components and yield-related physiological traits under both low and high N conditions. Phenotypic and genotypic correlation coefficients were positive and highly significant (strong correlation) between grain yield plant-1 and each of ear diameter and kernel depth under both low and high N conditions. Whereas, such correlation coefficients were positive and significant (moderate correlation) between grain yield plant-1 and each of ears number plant-1, kernels number row-1, ear length, and shelling %, under both low and high N conditions. Interestingly, the phenotypic and genotypic correlation coefficients between grain yield plant-1 and the tested yield-related physiological traits were positive and strongly correlated with N-use efficiency (NUE), crop growth rate (CGR) under both limited and adequate N conditions as well as with relative potential photosynthesis for grain yield (RPPG.Y.) under high N input only. On the other hand, such correlation was positive and moderate with harvest index (HI) under both N rate as well as with RPPG.Y. under N stress. The results suggest that, to increase grain yield plant-1, selection should be carried out for most of the studied yield components especially; ears number plant-1, rows number ear-1, ear diameter, ear length and kernel depth under both low and high N conditions as well as tested yield-related physiological traits such as NUE, CGR, RPPG.Y and HI. The present results also showed that genetic variance (σ2g) of the new maize hybrids were higher than environmental (σ2e) variance in all studied traits at both low and high N conditions. Therefore, broad-sense heritability estimates for all studied traits exhibited high percentages and ranged from 70.2% to 99.9%. The values of expected gains in grain yield from indirect selection for related traits, and their percentages to direct selection were lower at low N than at high N conditions for all studied traits, except for traits of rows number ear-1 and ear diameter. The results also showed that direct selection for grain yield plant-1 was likely to be more efficient than indirect selection for all studied traits. It is concluded that for studied traits, the expected gain from direct selection would improve the trait under consideration in a way better than the indirect selection.