Performance Assessment of F2:3 Testcrosses of Maize (Zea mays L.) for Physiological Traits Vis-a-Vis Grain Yield Under Heat Stress and Drought Conditions

Heat and drought stresses negatively affect maize grain yields. Identification and deployment of high-yielding and stress-tolerant maize hybrids adapted to stress-prone agro-ecologies is important for improving smallholding farmers' food security and livelihoods. The adaptation level among maize genotypes under heat and drought stresses is strongly affected by morphological and physiological aspects. The physiological traits, Normalised Difference Vegetative Index (NDVI), Soil Plant Analysis Development (SPAD) values, and morphological trait, leaf rolling, can be used as important secondary traits for the identification of the stress-tolerant genotypes, in addition to grain yield. In this view, the present study was conducted at the Agricultural Research Station, Bheemarayangudi, and the Main Agricultural Research Station, Raichur, under heat stress (Summer-2020 & 2021) and drought (Rabi-2021-22) conditions. NDVI values ranged from 0.23–0.44 in bi-parental population 1 (BIP1) and 0.25–0.57 in bi-parental population 2 (BIP2) under drought conditions. The range of SPAD values was less under drought conditions, as 9.2–22.3 in BIP1 and 10.6–24.8 in BIP2, compared to heat stress, as it ranged from 12.0–24.7 in BIP1 to 14.1–31.4 in BIP2. It may be due to a decrease in mean chlorophyll content values under drought stress conditions. The entry ZH201138 showed delayed leaf rolling and recorded a lower leaf rolling score of 2, registering a higher grain yield of 1.81 t ha⁻¹ under drought stress condition. SPAD values registered a significant positive correlation with yield under heat stress (r = 0.77 and 0.68) and under drought stress condition (r = 0.49 and 0.83). NDVI showed a significant positive correlation with the grain yield (r = 0.63 and 0.63) under drought stress condition. Leaf rolling was negatively correlated with the grain yield. Therefore, it was concluded that NDVI and SPAD could be used as secondary traits to identify genotypes tolerant to both heat and drought stress, while the entries that showed delayed leaf rolling could be considered tolerant to drought stress.