Elevated Plant Density Effects on Performance and Genetic Parameters Controlling Maize (Zea mays L.) Agronomic Traits

Studying mode of gene action for maize traits under high plant density is a prerequisite for conducting an appropriate breeding program for developing high density tolerant varieties. The objective of this study was to assess maize diallel crosses for mean performance, combining ability and genetic parameters controlling studied traits under elevated plant densities. Experiments were carried out in 2013 and 2014 seasons, using a split-plot design with 3 replicates; main plots were assigned to plant densities, i.e. low- (LD), medium- (MD) and high- (HD) density (20,000, 30,000 and 40,000 plants/fed) (fed=feddan=4200 m2), respectively and sub-plots to 17 genotypes (15 crosses and two checks). Combined analysis across seasons indicated that elevating plant density from 20,000 to 40,000 plants/fed caused a significant decrease in grain yield/plant (GYPP) by 40.18%, leaf angle (LANG) by 25.51% and all yield components, but caused a significant increase in grain yield/fed (GYPF) by 30.0%, plant height (11.34%), ear height (19.41%), days to anthesis (4.35%) and days to silking (3.79%). Significant increase in GYPF due to elevating density to 40,000 plants/fed varied among crosses from 12.22 to 51.90%. The best general combiners for GYPP and GYPF were IL92 and IL172 under MD, IL92 for GYPP and IL24 and CML104 for GYPF under HD. Both additive (δ2A) and dominance (δ2D) variances played important role in controlling the inheritance of most studied traits under all environments. The δ2A component was higher than δ2D for most studied traits under all plant densities. Estimates of broad- and narrow-sense heritability and genetic advance from selection were the highest in magnitude under high density for 5 traits (barren stalks, ear height, leaf angle, kernels/row and GYPF), under medium density for 3 traits (GYPP, 100-kernel weight and number of kernels/plant and under low density for 6 traits (days to anthesis, days to silking, anthesis-silking interval, plant height, ears/plant and rows/ear).