Breeding for high-density planting and yield stability of newly developed maize hybrids across arid agro-environments

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ABSTRACT High planting density is a key strategy for increasing maize (Zea mays L.) productivity. Therefore, this study evaluated 17 newly developed yellow maize single-cross hybrids under three planting densities (59 524, 71 429, and 89 286 plants ha⁻¹). The hybrids were evaluated at two contrasting locations in Sakha in the Nile Delta and Sids in Middle Egypt. Earliness, vegetative traits, ear morphology, and grain yield were recorded at both locations. Combined ANOVA revealed highly significant effects (p < 0.01) of location, planting density, hybrids, and all interactions for most traits. This indicates strong environmental sensitivity and wide genetic variability. Increasing planting density enhanced grain yield by approximately 12.15% at Sakha (from 9.71 to 10.89 t ha⁻¹) and 15.97% at Sids (from 8.39 to 9.73 t ha⁻¹). Otherwise, increasing planting density reduced ear leaf area (5.87% at Sakha and 11.15% at Sids), number of rows per ear (3.91% at Sakha and 6.83% at Sids), and number of kernels per row (7.34% at Sakha and 10.01% at Sids), while grain yield increased at both locations. This confirms that higher number of plants per unit area compensated for the per plant reduction in ear traits. The assessed maize hybrids exhibited highly significant genetic variation for earliness, vegetative growth, and yield-related traits. The hybrids, Hib-6, Hib-11, Hib-7, Hib-16, and Hib-17 produced yields up to 13.6 t ha⁻¹ and maintained stable performance across environments. Hib-6 exhibited the highest mean productivity (12.66 t ha⁻¹ at Sakha and 10.46 t ha⁻¹ at Sids) and the highest stress tolerance index (1.75 and 1.18, respectively), indicating strong adaptation to high-density stress. Multivariate analyses, including cluster analysis, heatmap classification, AMMI, GGE biplot, and tolerance indices, effectively summarized the complex data structure. These analyses distinguished broadly adapted, high-performing hybrids from poorly adapted hybrids. The obtained results demonstrated that breeding for yield potential and tolerance to high planting density is feasible and provides a set of promising hybrids.

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