Differential responses to short-term salinity stress of heat-tolerant cherry tomato cultivars grown at high temperatures

Although many new tomato cultivars with various degrees of heat-tolerance have been released, year-round tomato production in subtropical lowlands is still challenged by summer heat and an increasing risk from salinity stress. Little information about the simultaneous effects of heat and salinity on growth and fruiting in tomatoes is available. It was hypothesized that cultivars which perform better in high temperatures are also more tolerant to salinity stress. Two highly heat-tolerant cultivars, ‘Tainan ASVEG No. 19’ (TA19) and ‘Taiwan Seed ASVEG No. 22’ (TSA22), and one moderately heat-tolerant cultivar, ‘Hualien ASVEG No. 21’ (HA21), were grown under high temperature conditions and were irrigated with a 0, 50, 150, or 200 mM NaCl solution for 20 days. Vegetative growth, fruiting behavior, and fruit quality were monitored. Number of leaves, leaf area, shoot fresh and dry weights, and root fresh weight were generally decreased with increasing level of salinity stress, but root dry weight was not affected, resulting in an increase in root to shoot ratio in all three cultivars. Yield was also decreased by salinity treatments in all three cultivars due to reduced number of flowers, fruit set, and fruit size. The highly heat-tolerant ‘TA19’ had the lowest vegetative growth and the highest yield under the high temperature condition, but the yield was strongly suppressed by the short-term mild salinity treatment. On the other hand, vegetative growth was little affected and the degree of yield reduction was less intense with the short-term mild salinity treatment in the moderately heat-tolerant ‘HA21’. The result indicated that effects of heat stress and salinity stress are not additive and differential responses to salinity under high temperatures exist among cultivars with various degrees of heat-tolerance.