Abstract
Drought poses threats to the production of tomato (Lycopersicon esculentum Mill.). Tomato plants need a large amount of water for proper growth, development and productivity. We screened four important tomato varieties for their potential to withstand drought. The variety that resisted the drought most 'SNU' was studied for drought and calcium sulfate (gypsum; hereinafter called CS) induced changes in growth photosynthesis, antioxidant and metabolite levels. Tomato plants were divided into four sets viz. 1. Set 1: Control, Set 2: Drought, 3: Control+Gypsum (2% w/v CS, calcium sulfate), and 4. Drought+CS. Gypsum CS (2% w/w). Thus plants of Set 3 and Set 4 were provided with a supply of additional sulfur and calcium. Plants were grown for 80 days under controlled conditions and estimations were made at 35 and 70 days after treatment (DAT). Drought induced oxidative stress in tomato estimated as thiobarbituric acid reactive substance (TBARS); however, gypsum treated plants suffered lesser damage. Loss to chlorophyll contents was lesser when gypsum was applied. Ascorbate-glutathione antioxidant system was affected by drought but operated finely with gypsum treatment. Drought-exposed plants accumulated higher amount of osmolyte proline in the presence of CS. The ratio of reduced forms of ascorbate and glutathione shifted towards oxidized forms; levels of glutathione increased under gypsum-application both at 35 (flowering stage) and 70 (fruiting stage) DAT. Gypsum treatment elevated the activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), glutathione reductase (GR) and catalase (CAT), glutathione S-transferase (GST) and ATP-Sulfurylase (ATPS). In tomato fruits, contents of beta-carotene, lycopene and ascorbic acid increased under drought, but average fruit weight decreased significantly. To conclude, water stress induced oxidative stress but tomatoes elevated its antioxidant system, sulfur metabolism and osmolyte defense minimize the losses incurred by the drought in a better way when gypsum was applied both at 35 DAT and 70 DAT. This study highlighted the critical importance of calcium and sulfur, applied as gypsum in proper growth and improved defense system of tomato plant besides improving fruit quality. (C) 2020 Friends Science Publishers