Exploiting Genetic Variation for Heat Stress Tolerance in Tomato
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Tomato production is vulnerable to extreme heat during the spring-summer cropping season, exacerbated by a lack of superior genetic materials that can perform well in such environments. The selection of resilient varieties through an improved understanding of morpho-physio-biochemical traits is imperative to sustain tomato production under high-temperature conditions. Thus, this study was conducted to determine heat-tolerant tomato varieties through an improved understanding of their physio-biochemical basis of heat-tolerance. The first study was conducted in three stages to select heat-tolerant varieties under persistent heat-stress conditions in controlled and open-field conditions. In the first stage, varieties were screened based on yield responses. Then, eighteen varieties were chosen and exposed to control (green-house: 26/20 ) and constant heat-stress (growth-chamber: 34/24 ) conditions. The last stage was executed in an open field with twenty-four varieties selected from the first two experiments. Plant morphology and physio-biochemistry were assessed under different environments. From this study, we concluded that heat-tolerant genotypes selected through chlorophyll fluorescence measurements and heat injury index rank in controlled heat-stress conditions exhibited heat-tolerance in open-field conditions as well. Electrolyte leakage and heat injury index distinguished the varieties best in open-field conditions as the plants with low electrolyte leakage and heat injury index had higher marketable yield. Heat Master, New Girl, HM-1823, Rally, Valley Girl, Celebrity, and Tribeca were selected as high heat-tolerant varieties. In the second study, selected ten tomato varieties were exposed to three temperature conditions (26/18 as control, 38/28 for seven days as heat-stress, and 40 for 7 hours as heat-shock), and plant physio-biochemical traits were assessed. Electrolyte leakage, malondialdehyde content, and heat injury index most efficiently discriminated the varieties under both heat-stress and heat-shock conditions. Heat Master under heat-shock and Celebrity, Heat Master, Valley Girl, New Girl, and Picus under heat-stress conditions were identified as the most heat-tolerant varieties. Celebrity, Heat Master, Valley Girl, and New Girl were established as heat-tolerant under all environments in the study. Adopting these promising varieties could potentially enhance tomato production in the areas prone to extreme temperatures during the cropping period.
