Exploring Morpho-Physiological Variation for Heat Stress Tolerance in Tomato.

Area of Science:

• Horticultural Science
• Plant Physiology
• Agronomy

Background:

• Texas tomato production faces significant yield losses due to extreme spring-summer heat.
• A lack of heat-tolerant genetic material hinders the development of resilient tomato varieties.
• Developing tomatoes with stable yields under heat stress is a critical agricultural need.

Purpose of the Study:

• To identify heat-tolerant tomato varieties suitable for warm environments and stable yields under heat stress.
• To evaluate the effectiveness of various physiological and morphological traits for screening heat tolerance.
• To validate heat tolerance identified in controlled conditions within open-field environments.

Main Methods:

• Screened 43 tomato varieties for yield in natural conditions, selecting 18 for further study.
• Exposed selected varieties to controlled greenhouse (26/20 °C) and growth-chamber (34/24 °C) heat-stress conditions.
• Assessed physiological traits including chlorophyll fluorescence, SPAD, electrolyte leakage, and heat injury index (HII) in controlled and open-field trials.

Main Results:

• Heat-tolerant genotypes identified using chlorophyll fluorescence and HII in controlled settings demonstrated similar tolerance in open fields.
• Electrolyte leakage and HII were key indicators of heat tolerance in open-field environments, correlating with higher total yields.
• 'Heat Master,' 'New Girl,' 'HM-1823,' 'Rally,' 'Valley Girl,' 'Celebrity,' and 'Tribeca' were identified as superior heat-tolerant varieties.

Conclusions:

• Chlorophyll fluorescence and HII are reliable indicators for selecting heat-tolerant tomato genotypes under controlled heat stress.
• Low electrolyte leakage and HII are strongly associated with high yield stability in heat-stressed open-field tomato cultivation.
• The identified heat-tolerant varieties and screening traits offer valuable resources for breeding programs aimed at improving tomato resilience to heat waves.