Abstract
The identification of heat tolerance traits that express across environments is key to the successful development of high temperature tolerant tomatoes. A replicated experiment of 145 tomato genotypes was established at two temperature regimes in two planting seasons using hydroponics in a poly greenhouse to assess high temperature tolerance. Electrolyte leakage, number of inflorescences, number of flowers and fruits, fresh fruit weight and fresh and dry plant weight were measured and genotype and temperature treatment differences were observed for all traits. Planting season impacted all traits except electrolyte leakage and number of flowers. High temperature reduced number of fruits by 88.8%, flower fruit set ratio by 77.2% and fresh fruit weight by 79.3%. In contrast, traits little impacted by temperature included number of flowers per inflorescence (1.3%) and plant dry weight (11.1%). The correlation between plant dry weight under both high and optimal temperature was significant (R2 = 0.82). To assess the effectiveness of plant dry weight and flower-fruit set ratio for selection under heat stress two subsets of genotypes (A and B) comprising ten and six genotypes respectively, were subsequently selected on the basis of their dry weight loss and flower-fruit set ratio under high temperature. Organic metabolite analyses of set A and B respectively, showed a significant change (%) in citric acid (77.4 and 15.4), L-proline (117.8 and 40.2), aminobutyric acid (68.6 and 11.8), fructose (24.9 and 21.3), malic acid (50.3 and 42.7), myo-inositol (55.1 and 6.1), pentaerythitol (54.1 and 39.0) and sucrose (34.7 and 25.8). The change (%) in all metabolites was greater in heat tolerant genotypes with the exception of fructose and sucrose where sensitive genotypes produced a higher variation. The change in sucrose in tolerant genotypes was variable in subset A and more uniform in subset B. Flower-fruit set ratio was found as a reliable trait for discriminating between heat tolerant and sensitive genotypes and the sucrose levels in plant tissues provided confirmation of the heat stress response.
Highlights
Tomato (S. lycopersicum) belongs to the family solanaceae and was domesticated in the Andean region of South America and Mexico [1]
This study evaluated the impact of heat stress on the vegetative and reproductive development of diverse tomato genotypes with the aim of identifying traits of high heritability that could be used to improve the high temperature tolerance of tomato
Genotype and heat treatment effects were significant for electrolyte leakage, numbers of inflorescences, numbers of flowers, number of fruit, fruit set, fresh fruit weight, fresh plant weight and dry plant weight (Table 1)
Summary
Tomato (S. lycopersicum) belongs to the family solanaceae and was domesticated in the Andean region of South America and Mexico [1]. Tomato was introduced to Europe in the 16th century and later spread throughout the Mediterranean region [2] [3] [4]. Thousands of tomato cultivars have subsequently been developed through breeding and selection [5]. Several traits have been implicated in heat stress tolerance in tomato including membrane thermo stability (MTS), floral characteristics, cone splitting, pollen viability, fruit set and fruit yield [8]-[13]. High temperature at the reproductive stage of development causes significant flower drop [14] resulting in decreased fruit set and yield [15]. Heat shock at extremely high temperature (≥45 ̊C) can lead to programmed cell death (PCD), release of cytochrome c and activation of caspase-like enzymes [17]. Plant reproductive organs are clearly more sensitive to heat stress than vegetative parts [18] [19]
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