Ten maize (Zea mays) commercial hybrids were screened for checking their comparative response against high temperature / heat stress at Botany Department, Agriculture University, Faisalabad. Germinated maize seedlings / plants were placed in the glass fitted canopies, where canopy temperature was found 7-10°C higher than ambient temperature along with light reflection was enough for optimum photosynthesis. The plants were raised under heat stress environment for 15 days and harvested. Data regarding seedling parameters were recorded and analyzed. The study revealed that SB-11 and 32-F-10 were able to produce longer shoots under heat stress while SB-11 and ND 6339 produced longer root under heat stress. The hybrids like SB-11, Hycorn-984 were able to retain greater shoot and root water contents as evident from their increased fresh weight. The hybrid including Hycorn-984, ND6339 and SB-11 manifested greater shoot dry matter yield, while none of the hybrids displayed greater root dry weight under heat stress than root respective controls. The Hybrid SB-11 incurred a minimal loss of leaf area followed by Hycorn-11 and Hycorn-984 while hybrids ICI-984 and SB-11 were the most affected. These data indicated that like conventional synthetic maize varieties, the hybrids also respond differentially to the prevailing high temperature stress condition. The results also showed that hybrids capable of producing greater root mass were better able to withstand the heat stress than those with a lesser root volume. In the current screening effort, the hybrid SB-11 emerged as heat tolerant while ICI-984 was ranked as heat sensitive hybrid based on the investigated growth parameters.
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