High temperature induced by climatic fluctuations are an important threat for plant growth, development and quality of agricultural produces. Adaptableness to environmental changes generally derives from a large set of genetic traits affecting physio-morphological, biochemical and agronomic parameters. Therefore, the identification of genotypes with higher yield and good quality parameters at high temperatures is becoming increasingly necessary for future breeding programs. Here, we analyzed the performance of different tomato genotypes grown under elevated temperatures in terms of yield and nutritional quality of the fruit. High temperature stress was induced from flower initiation to maturity stage by keeping the pots in a temperature controlled green house facility for 45 days. The quality and yield parameters were taken at the harvesting stage. Starch and soluble sugar concentration in the leaves of tomato genotypes showed significant reduction in its amount under heat stress. Titrable acidity (TA), total soluble solids (TSS) and ascorbic acid content of tomato fruits were highest under high temperature conditions compared to ambient condition but lycopene content decreased with rise in temperature. The yield attributes viz., number of fruits/plant, fruit set %, average fruit weight (g), yield per plant (g/plant) were significantly lower for Arka Saurabh, Arka Rakshak and Pusa Rohini when compared to other genotypes under study. Molecular characterization of selected 22 tomato genotypes were assessed using 25 simple sequence repeat (SSR) markers. Phylogenetic tree was constructed by the unweighted neighbour-joining method (UPGMA) using NTSYSpc cluster analysis software. The Jaccard's similarity matrix was constructed using the SIMQUAL method using UPGMA algorithm in NTSYSpc. Jaccard's similarity matrix among these tomato genotypes ranged from a minimum of 0.22 to a maximum of 1 with an average genetic similarity of 0.67. Hence this study has importance in identifying genotypes that could maintain good quality and higher yield under high temperature condition.
The impact of heat stress on agriculture is severe and negatively impacts crop productivity. In tropical and subtropical tomato-growing regions around the world, poor fruiting of tomato plants caused by heat stress is a major factor in low output. Exceeding optimum temperatures can shorten plant life and greatly accelerate fruit flowering and maturation. Temperatures above the reference temperature cause irregular flower development, reduced pollen production, pollen viability, fruit drop, ovule abortion, and ultimately reduced yield, generates an excess of reactive oxygen species (ROS), oxidative stress, and metabolic mechanism instability. High temperatures severely affect flower shedding, with tomato plants losing 80% of their flowers and reducing fruit set. For the characteristics pollen viability, photosynthetic rate, membrane stability and fruit number, high values of genotypic coefficient of variability, phenotypic coefficient of variability, heritability, and genetic progress were discovered. All nine separate traits demonstrated additive gene action in trait expression and should be given the utmost weight in phenotypic selection. Eigen value > 1 and cumulative variance of 75.04% were shown for the four main components.
Heat stress affects the source and sink activities, growth and development, economic yield and harvest index of plants negatively. Heat stress has got severe effects on the biochemical reactions of photosynthesis which included irreversible damages of RuBisCO, oxygen evolving complexes, PSII reaction centres and disruptions of chloroplast ultrastructure and thylakoid membrane. Sugars are products of photosynthesis in plants which serve as substrates for energy metabolism and are required for synthesis of cellulose and starch polysaccharides. Glucose, fructose, sucrose, mannose, trehalose, maltose etc. are the sugars present in plants. Abiotic stresses like temperature, drought, flood and salinity causes crucial differences in the carbohydrate metabolism. Sugars acts as primary signaling molecules and regulate signals that control the expression of many genes and enzymes involved in carbohydrate metabolism. Decrease in crop productivity under heat stress is chiefly associated with alterations in carbohydrate accumulation and resulting defects in assimilation partitioning from source to sink. It is essential to understand the responses and acclimatization processes to extreme temperatures in plants, such that the mechanisms underlying can be used for developing heat-tolerant varieties. Sugars such as glucose, sucrose, fructan, raffinose and trehalose not only acts structural component and metabolic resources also regulate genes associated with heat stress tolerance and reduce the chances of crop loss. The external application of compounds like osmoregulators, phytohormones, signaling molecules, etc., have exhibited positive responses in stress tolerance due to its growth promoting and antioxidant activities.
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