Influence of prolonged high temperature stress on physio-biochemical traits of tomato at late fruit maturing stage

Tomato ( Solanum lycopersicum L.) plants can survive a range of temperatures; however, the tissues are damaged below 10°C and above 38°C. High temperature stress severely affects not only physiological parameters leading to lower yield, but also the fruit quality of tomato cultivars. In this study, the influence of prolonged high temperature stress on twelve tomato genotypes were evaluated for physiological as well as fruit quality traits at late fruit maturing stage at Indian Institute of Vegetable Research, Varanasi during summer season of 2012. Responses under stress, were investigated between ten better performing tomato genotypes and two highly sensitive tomato genotypes subjected to day/night temperature range of 23.3/6.1 o C to 44/30.4 o C and maximum/minimum relative humidity between 94/36% to 59/23% in field condition. Variation in photosynthetic rate (Pn) was observed to be maximum in VRT101A (21.01 µmolm −2 s −1 ), which was 11-fold higher than the most sensitive genotypes (EC625659, 1.79 µmolm −2 s −1 ). Similarly, for the chlorophyll fluorescence, highest reduction with 55.42% was found in EC-625659 as compared to EC-620431 (20.48%). The effect of heat stress was prominent on the chlorophyll and carotenoids contents. Higher chlorophyll ‘a’ content (µg mL -1 ) was observed in EC-620438 (7.6), EC-620431(7.4), VRT-101 A (7.3) and VRT-102 (6.8). Increase in Chlorophyll a/b ratio was observed in VRT-102 (2.64). An increase in the chlorophyll a/b ratio, resulting from faster degradation of Chl b indicated a preferential decrease in light-harvesting chlorophyll a/b-binding proteins (LHC) associated with PSII (LHCII) to transfer excitation energy to the PSII core complex which could reduce the risk of photo oxidative damage due to a relative decrease in the absorption section of photosystems. Better carotenoids content was recorded for VRT 101-A and IVRT-102 with 1.68 and 1.50µgmL -1 , respectively. It is well documented that carotenoids, which has higher value in the best performing genotypes not only play a role as accessory light-harvesting pigments but they also protect photosynthetic systems against reactive oxygen species. Though proline content showed non-significant variation, genotype EC-620421 and VRT-102 retained higher concentration (1.31 and 1.18 µg FW -1 ) among the 12 genotypes under high temperature stress. EC-538380 with least percent electrolyte leakage (76.59%) showed the highest membrane stability among the genotypes. Fruit quality traits such as pH, and titrable acidity ranged between 4.5 (EC-620568) to 6.1 (EC-620421) and 0.022 (VRT-102) to 0.056 (EC-620419), respectively. Total soluble solid (TSS) ranged between 1.55% (EC-620421) to 5.6% (EC-620568), lycopene, b-carotene, chlorophyll a and b and ascorbic acid contents were also studied among better performing genotypes and variations were observed. In response to stress, VRT 101A, was found better for physiological traits whereas VRT-102 retained better fruit quality traits than rest of the genotypes.