Heat Treatment in Two Tomato Cultivars: A Study of the Effect on Physiological and Growth Recovery

Abstract

High temperature (HT) significantly affects crop physiological traits and reduces productivity in plants. To increase yields as well as survival of crops under HT, developing heat-tolerant plants is one of the main targets in crop breeding programs. The present study attempted to investigate the linkage of the heat tolerance between the seedling and reproductive growth stages of tomato cultivars ’Dafnis‘ and ’Minichal.’ This research was undertaken to evaluate heat tolerance under two experimental designs such as screening at seedling stage and screening from reproductive traits in greenhouses. Survival rate and physiological responses in seedlings of tomatoes with 4-5 true leaves were estimated under HT (40 °C, RH 70%, day/night, respectively) and under two control and HT greenhouse conditions (day time 28 °C and 40 °C, respectively). Heat stress significantly affected physiological–chemical (photosynthesis, electrolyte conductivity, proline) and vegetative parameters (plant height, shoot fresh weight, root fresh weight) in all tomato seedlings. The findings revealed that regardless of tomato cultivars the photosynthesis, chlorophyll, total proline and electrical conductivity parameters were varied in seedlings during the heat stress period. The heat tolerance rate of tomatoes in the seedling stage might not always be associated with reproductive parameters. HT reduced fruit parameters such as fruit weight (31.9%), fruit length (14.1%), fruit diameter (19.1%), and fruit hardness (9.1%) compared to NT under HT in heat-susceptible tomato cultivar ‘Dafnis’, while in heat-tolerant cultivar ‘Minichal’ fruit length (7.1%) and fruit diameter (12.1%) was decreased by the effects of HT, but on the contrary fruit weight (3.6%) and fruit hardness (8.3%) were increased. In conclusion, screening and selection for tomatoes should be evaluated at the vegetative and reproductive stages with consideration of reproductive parameters.

Heat-tolerant Hot Pepper Exhibits Constant Photosynthesis Via Increased 4 Transpiration Rate, High Proline Content and Fast Recovery in Heat Stress 5 Condition

“…S1), as was observed in hot pepper 9,11 and tomato 17,22 . The higher chlorophyll content in heat-tolerant cultivar gives better photosynthetic stability than heat-susceptible cultivars 16,17,22 .…”

“…Chlorophyll content in leaves decreased as HT days increased, and the decrease was faster in a heat-susceptible cultivar than a tolerant cultivar (Supplementary Fig. S1), as was observed in hot pepper 9,11 and tomato 17,22 . The higher chlorophyll content in heat-tolerant cultivar gives better photosynthetic stability than heat-susceptible cultivars 16,17,22 .…”

“…Also, a heat-tolerant cultivar had greener leaves than a heat-susceptible cultivar (see Supplementary Fig. S3) and this may contribute to better and stable photosynthesis 17 . The stay-green trait is also an important agronomical characteristic that contributes to higher yield under heat stress in tomato 23 .…”

“…In response to environmental stresses, plants accumulate osmoprotectants including proline 17,25 and they are generally found in large amounts under any stress conditions 15,19,23 . Our results are in line with previous studies.…”

“…Heat tolerance is a developmentally regulated, stage-specific phenomenon and its mechanism in hot pepper is still unknown. Heat tolerance at one developmental stage can be related 16 or not to tolerance at the other developmental stages 17 . Therefore, breeding programs should focus on determining developmental stages susceptible to heat stress -to develop hot pepper cultivars with heat tolerance.…”