Characterization of maize inbred lines using principal component and cluster analysis for heat tolerance at the seedling stage under in vitro conditions

Heat stress faced by the crop plants at seedling stage hinders its growth and if faced at reproductive stage affects crop production. Globally, maize (Zea mays L.) loses a substantial amount of its production due to very high temperatures at anthesis stage during spring season. So, development of heat tolerant maize cultivars is important for maize breeders. The ability of a plant to tolerate heat stress at seedling and reproductive stage is linked with each other and screening at the seedling stage could accelerate the selection process. In the present study, 50 maize inbred lines were screened for heat tolerance at seedling stage under in vitro conditions. Our results showed that parameters such as root length (RL), shoot length (SL), shoot fresh weight (SFW), shoot dry weight (SDW), root fresh weight (RFW), root dry weight (RDW), leaf area (LA), leaf fresh weight (LFW), leaf dry weight (LDW), relative water content (RWC), membrane stability index (MSI) and total chlorophyll (TCHL) showed a significant decrease under heat stress (p < 0.05). Further, morpho-physiological traits were delineated by principal component analysis (PCA). Hierarchical cluster analysis (HCA) was done with the objective to characterize the maize inbred lines based on their response under heat stress. Among the four column clusters, column cluster I showed highest mean values for maximum traits, i.e., RL (16.45 cm), RFW (0.27 g), SL (28.42 cm), SFW (0.74 g), SDW (63.03 mg), LFW (0.16 g), LDW (20 mg) and RWC (48.63%), suggesting that these traits were superior over other traits and inbred lines falling in this cluster would be selected directly on the basis of these traits. The heat tolerance index (HTI) of all the inbred lines based on individual traits was calculated and inbred lines were ranked accordingly. The top five inbred lines: LM22, CML579, LM13, LM16 and RIL 33 performed best under heat stress as they had high heat tolerance index value. The results obtained by PCA and HCA were in accordance with those obtained on the basis of HTI. Our study identified heat tolerant inbred lines of different heterotic pools which, after field validation, can be used for development of heat tolerant maize hybrids.