Effect of Cold Stress on Thermal Time Requirements in Maize Inbred Lines (Zea mays L.)

Abstract

Growing degree days are a key metric for characterizing phenological traits across growth and developmental stages of a plant. Therefore, this research was conducted to determine the maximum thermal accumulation of phenological traits during the developmental phase of maize. The study was conducted at the Maize Sorghum and Millet (MSM) Program, Crop Sciences Institute (CSI), National Agricultural Research Centre (NARC), Islamabad, during the autumn growing seasons of 2024 and 2025, with normal and late sowing dates. The analysis of variance revealed that all traits differed significantly across years (P≤0.001) for normal, except days to maturity, while majority of traits were non-significant for cold, except days to germination, days to tasseling, and days to germination growing degree days; maize inbred lines were significant only for grain yield (P≤0.001); however, the genotype × year interaction was non-significant for all traits. In contrast, under cold conditions, the genotype × year interaction differed significantly for all traits (P≤0.05), indicating the greatest variation among genotypes under cold conditions. The mean performance showed that, under cold conditions, genotypes accumulated the most thermal units and delayed phenological development. This suggests that cold conditions affected tasseling and silking days more than maturity days. Hence, selection under cold conditions for cold-tolerant and early-maturing inbred lines could be more effective than under normal conditions.