Secondary Traits and Selection Environment of Plant Density Tolerance in Maize Inbreds and Testcrosses

Secondary traits in maize are used in screening programs for selecting tolerant genotypes to a specific abiotic stress. Indirect selection would be effective if heritability of the secondary trait is greater than that of the primary trait and correlation between them is substantial. The objectives of the present investigation were to identify secondary trait(s) for plant density tolerance (PDT) in maize and to identify the best selection environment for improving traits related to plant density tolerance. Testcrosses were produced between 23 inbreds and 3 testers. Evaluation of 69 testcrosses and 23 inbreds for 30 traits was carried out in 2016 season under 3 plant densities using a split plot design in 3 replications. Under high density (HD), out of 30 traits, favorable and significant correlation coefficients (r) were exhibited between stress tolerance index (STI) and 23 traits of testcrosses (all 7 yield traits, all 9 tassel traits, penetrated light at ear (PL-E), penetrated light at bottom (PL-B), chlorophyll concentration index (CCI), lower stem diameter (SDL), upper stem diameter (SDU), ear leaf area (ELA), and barren stalks (BS). Based on high (r), high heritability and high genetic advance estimates, it is evident that the secondary traits for plant density tolerance in our study were grain yield/plant, grain yield/ha, kernels/plant, kernels/row, rows/ear, ears/plant, SDU, ELA, plant height, tassel dry weight, central spike length, and branch length. The best environment in achieving the highest predicted gain from selection was low density for 8 traits (grain yield/plant, grain yield/ha, 100-kernel weight, kernels/plant, ears/plant, tassel branch number, total spike length and PL-E), medium density for 4 traits (DTS, ear height, SDL and CCI) and HD for the rest of studied traits. These traits could be used by maize breeder as selection criteria for improving PDT.