Secondary Traits for Maize (Zea mays L.) Tolerance to Drought Combined with Reduced N Fertilization Rate

The secondary trait for a given abiotic stress tolerance, should be of strong correlation (r) with grain yield, high heritability (h2b) and high genetic advance (GA) under stressed conditions. The main objective of the present investigation was to identify secondary trait(s) for drought and/or low-N tolerance in maize genotypes. A two-year experiment was conducted, using a split-split-plot design. Main plots were allotted to two irrigation regimes, i.e. well watering (WW) and water stress at flowering (WS), sub-plots to three N fertilizer rates, i.e. low (LN), medium (MN) and high (HN) and sub-sub-plots to nineteen maize genotypes. Analysis of variance of randomized complete blocks design (RCBD) was also performed under each of the six environments (WW-HM, WW-MN, WW-LN, WS-HN, WS-MN and WS-LN). Tolerance to drought and/or low-N was strongly correlated with grain yield/plant (GYPP) under stressed environments. GYPP had high (h2b) and (GA); thus it is considered the best indicator of drought, low N or both stresses tolerance. The best secondary traits are high 100-kernel weight (100-KW), ears/plant (EPP), kernels/row (KPR), and short anthesis-silking interval (ASI) for low-N tolerance, high EPP, 100-KW, plant height (PH) and short ASI for drought tolerance, high 100-KW, EPP, KPR, PH and short ASI, for tolerance to drought combined with low N, and high 100-KW, rows/ear (RPE) and KPR under optimum conditions (WW-HN), since they show high (r), high (h2b) and high (GA) estimates under the respective environments. Under low-N and/or drought, future research should focus on the incorporation of secondary traits such as EPP, KPR, 100-KW, PH, ASI in the selection programs along with the grain yield trait.