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An experiment entitled “Effect of high temperature on physiological, biochemical and yield parameters in tomato (Solanum lycopersicum L.)” was conducted in the Department of Plant Physiology, College of Agriculture, Vellayani during Rabi 2019-2020 with the objective to study the effect of high temperature on physiological, biochemical, yield and quality parameters in tomato. Twenty two different tomato varieties were used for the study. The experiment was laid out in completely randomized design with two treatment levels i.e. control and high temperature stress (36+/-2oC) with three replications each. The high temperature stress was induced from flower initiation to maturity stage by keeping the pots in a temperature controlled green house facility for 45 days. Phenological, physiological, biochemical parameters were taken at flowering stage. Also quality parameters and yield parameters were taken at harvesting stage.
All the tomato genotypes under heat stress showed delayed flowering and fruiting. Delay in flowering was found to vary between the varieties. Kashi Vishesh showed minimum delay in first flowering (10-12 days) than that of control whereas, Pusa Rohini showed maximum delay in flowering (25-30 days) than that of the control plants. Kashi Vishesh showed less delay in first fruiting (8-12 days) than that of control whereas, genotypes like Arka Rakshak, PKM-1, Pusa Rohini showed maximum delay (30-35 days) in fruiting under stress conditions. Under high temperature condition, Arka Sourabh
showed the highest exerted stigma length and there is significant variation for flower burning and flower drop.
A decrease in Membrane Stability Index (MSI) was observed for varieties on 15th day after stress induction and further reduction for 25th day after stress induction when compared to control plants. Under heat stress conditions, Nandi (51.8%) and Arka Rakshak (25.13%) showed maximum and minimum MSI respectively. The percentage reduction in MSI was highest in Pusa Ruby (52%) and lowest in IIHR-2200 (11%). Under high temperature conditions pollen viability reduced significantly for all varieties with maximum viability for Nandi (87.38%) and minimum for Arka Vikas (36.31%). Similar results were obtained for physiological parameters like total chlorophyll content (mg g-1 fresh weight), photosynthetic rate (A) μ CO2 moles m-2 s-1), transpiration rate (E) (mmol H2O m-2 sec-1), stomatal conductance (Gs) (mmol H2O m-2 sec-1) and chlorophyll fluorescence (CF-Fv / Fm). The percentage reduction in photosynthetic rate under high temperature condition was highest in Palam Pride (30%) and minimum for Manulakshmi (9%). The percent reduction in transpiration rate was maximum for Arka Sourabh (67%) and minimum for Kashi Vishesh (12%).
Significant genotypic differences for starch content and soluble sugar content were observed in tomato plants under high temperature. Among the genotypes, Vaibhav (312.97 mg g-1 fresh weight) recorded the maximum starch accumulation while the minimum starch content was recorded in Arka Vikas (209.70 mg g-1 fresh weight) under control conditions. Under heat stress condition, the highest starch content was observed in Anagha (235.67 mg g-1 fresh weight), while the lowest was observed in Arka Sourabh (84.37 mg g-1 fresh weight). The percent decrease in soluble sugar content was more in Arka Rakshak (31.2%) and less in IIHR-2200 (3%) under high temperature condition.
Titrable acidity (TA) and total soluble solids (TSS) of tomato fruits were highest in concentration under high temperature conditions compared to low temperature regimes. The percent increase in titrable acidity under heat stress was highest for Arka Alok (27%) and minimum for Pusa Rohini (2%). Highest TSS was recorded for Arka
Samrat (5.72%) and lowest for IC-45 (2.32%) under control ambient condition. But under high temperature conditions highest TSS was recorded for Kashi Vishesh (6.23%) and lowest for IC-45 (2.57%). The lycopene content decreased with rise in temperature and the ambient condition recorded the highest lycopene content in fruits. The percent reduction in lycopene content under heat stress conditions was maximum for IIHR-2200 (52%) and minimum for Kashi Vishesh (3%).
The yield attributes viz., number of fruits/plant, fruit set %, average fruit weight (g), yield per plant (g /plant) were significantly lower for varieties like Arka Saurabh, Arka Rakshak and Pusa Rohini. Under heat stress conditions only those genotypes that are tolerant as well as moderately tolerant, namely Nandi, Anagha, Akshaya, IIHR-2200, Vellayani Vijay, Kashi Vishesh, Arka Abha, Arka Alok, Vaibhav, Manuprabha, Manulakshmi, IC-45 and IIHR-26372 produced higher fruit yield per plant. But the varieties like Arka Saurabh, Arka Rakshak, PKM-1, Sakthi, Palam Pride, Arka Samrat recorded the maximum percent reduction in yield per plant (99%) and the minimum was recorded in Kashi Vishesh (69%). In polyhouse conditions, all the genotypes showed an increment in the plant height and total dry weight because of the shaded environment, high temperature and enhanced CO2 (570 ppm) conditions inside.
With respect to yield and physiological data the varieties sharing similar characteristics can be classified under three categories viz, tolerant varieties, moderately tolerant and susceptible varieties. Tolerant genotypes (Nandi, Kashi Vishesh, Vellayani Vijay) exhibited similar characteristics like yield (10-30 g-1 plant), MSI (60-70 %), PV (50-70%), starch content (190-200 mg g-1 fresh weight), A (17-22 μmol CO2 m-2 sec-1), Gs (47-68 mmol H2O m-2sec-1), CF (Fv / Fm) (0.6-0.7). Moderately tolerant varieties (Akshaya, Manuprabha, IIHR-2200, Vaibhav) showed similar characteristics like yield (5-15 g-1 plant), MSI (40-50 %), PV (45-50 %), starch content (200 mg g-1 fresh weight), A (17-19 μmol CO2 m-2 sec-1), Gs (55-65 mmol H2O m-2sec-1), CF(Fv / Fm) (0.6-0.7) and susceptible varieties (Arka Vikas, Pusa Rohini, Arka Sourabh, Arka Rakshak) showed similar features like yield (0.5-5 g-1 plant), MSI (25-40 %), PV (44-45 %), starch content (90-110 mg g-1 fresh weight), A (13-16 μmol CO2 m-2 sec-1), Gs (30-37 mmol H2O m-
2sec-1) and CF (0.4-0.5). The correlation analysis revealed that under heat stress conditions yield showed positive and significant correlation with MSI, photosynthetic rate, stomatal conductance, starch content, soluble sugar content, CF(Fv / Fm), pollen viability, total chlorophyll content, number of fruits per plant, fruit set %, average fruit weight and negatively correlated with intensity of flower drop. Hence this study has importance in identifying genotypes that possesses important physiological traits to increase the thermo-tolerance, so that they could give moderately higher yield even under high temperature.