Screening Criteria and Selection Environment for Tolerance to Elevated Plant Density in Maize (Zea mays L.) Inbreds and Hybrids

Indirect selection would be effective if heritability of the secondary trait is greater than that of the primary trait and genetic correlation between them is strong. The objectives of this investigation were to identify secondary trait(s) for selection of high maize grain yield under high plant density (HPD) and to identify whether the best selection environment is the optimum or stressed one. Diallel crosses among diverse inbreds in tolerance to HPD were evaluated in the field in two seasons under two contrasting environments; low density (LD); 47,600 plants/ha and high density (HD); 95,200 plants/ha, using RCBD with three replications. Strong favorable and significant genetic correlations were detected between grain yield/plant (GYPP) or HPD tolerance and each of yield components and days to anthesis (DTA), anthesis silking interval (ASI), plant height (PH), ear height (EH), barren stalks (BS) and leaf angle (LANG) for hybrids. The traits DTA, PH, EH, BS, LANG, ears/plant (EPP), rows/ear (RPE), 100- kernel weight (100 KW), kernels/row (KPR), kernels/plant (KPP), under both LD and HD environments had much higher narrow sense heritability (h2n) than GYPP (> 3 fold). Thus, these traits could be considered secondary traits to HPD tolerance. Selection for high KPP was more efficient in improving grain yield than selection for yield itself with a relative efficiency (RE) of 238.1 and 203.7% under LD and HD, respectively. It can be concluded that choosing the optimum selection environment to achieve maximum gain is affected by the genotype and the trait of interest. With respect of GYPP of hybrids, the direct selection is the best. The optimum selection environment is the target environment, while for inbreds; the indirect selection is the best. The optimum selection environment for high yield under HD is the optimum environment (LD).