Abstract:

Nowadays the most common methods for evaluating heterosis population and its genetic pattern in maize are based on analyses of parentage, SCA and molecular markers, but each method has its limitation. In the present study, a mixed linear (AD) model and the Minimum Norm Quadratic Unbiased Estimation (MINQUE) (1) method were introduced to estimate the variance components of yield and the values of F1 heterosis, using 2 tropical and 7 temperate maize (Zea mays L.) populations. The 9 populations were crossed by Griffing Ⅳ design, and 36 combinations were made. All hybrids were planted by random block with 4 replications in Anyang of Henan Province and Shiyan of Hubei Province in 2002 and 2003, respectively. The number of rows per ear (RPE), number of kernels per row (KPR), hundred-kernel weight (HKW) and plot-kernel weight (PKW) were measured with 24 plants in the middle of each plot. A parameter for genetic differences measurement between parent populations, i.e. ω/(2μ) = heterosis over mid-parent value—heterosis over better-parent value, was introduced. The analysis of AD model showed that additive (VA) and dominative (VD) effects of yield and its components as well as their interactions with environment (VAE and VDE) reached highly significant level (P<0.01) (Table 2). For PKW, the ratios of variance components to total variances were sequenced as dominance > dominance ´ environment > additive ´ environment > additive, while the ratios of additive effect to total variances were ranked as RPE > KPR > HKW > PKW (Table 2). The estimation of genetic differences (GD) among the 9 populations was ranged from 0.02% to 21.61% (Table 4), and there was no linear relationship between the GD and heterosis. Three crosses, 3´6 (BSSS C9´Stay Green C4), 2´3 (BS16´BSSS C9) and 1´3 (Suwan1´ BSSS C9), with parents of medium GD in this study showed strong heterosis and great potential in maize breeding in temperate zones. This study provided valuable information for developing new heterosis pattern between tropical and temperate maize germplasm.

Key words: Maize (Zea mays L.), Mixed linear (AD) model, Heterosis over mid-parent value, Heterosis over better-parent value, Genetic differences between parents