Secondary Traits and Selection Environment for Drought Tolerance at Flowering in Maize (Zea mays L.) Inbreds and Their F1 Diallel Crosses

The objectives of this investigation were to identify secondary trait(s) for selection of high maize grain yield under drought stress conditions and to identify whether the best selection environment is the optimum or stressed one. Diallel crosses among diverse inbreds in tolerance to drought were evaluated in the field in two seasons under two contrasting environments; well watered (WW) and water stressed (WS) at flowering using RCBD in 3 replications. Results across seasons revealed significant differences among inbreds and among hybrids for most studied characters. Strong favorable and significant genetic correlations (> 0.91) were detected between grain yield/plant (GYPP) or drought tolerance index and each of yield components for inbreds and hybrids and days to anthesis (DTA), plant height (PH), ear height (EH), barren stalks (BS) and leaf angle (LANG) for hybrids. The traits DTA, LANG, kernels/row (KPR), kernels/plant (KPP), 100- kernel weight (100 KW) under both WW and WS environments and anthesis silking interval (ASI) under WS had high narrow sense heritability (h2n). Thus, low DTA and LANG and high rows/ear (RPE), 100KW, KPR and KPP could be considered secondary traits to drought tolerance. Selection for low PH and high KPP was more efficient in improving grain yield than selection for yield itself with a relative efficiency (RE) of -160.6 and 240.1%, respectively. Results 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, i.e. the optimum selection environment is the target environment, while for inbreds, the indirect selection is the best, i.e. the optimum selection environment for high yield under WS is the optimum environment (WW).