Effect of different stress treatments on mature green tomatoes (Solanum lycopersicum) to enhance fruit quality

Tomato (Solanum lycopersicum) is a crop of immense economic importance and is grown worldwide. Its fruit is of great nutritional importance as it forms a major part of human diet. Global production of tomato has been estimated at over 153 million metric tonnes in 2009. Consumption of tomato is believed to benefit the heart among other things, as it contains lycopene, one of the most powerful natural antioxidants. The present study was conducted to find the effect of multiple stresses; salt, mannitol, drought and methyl jasmonate on fruit quality of tomato as determined by the evaluation of the content of lycopene, beta-carotene, sucrose and total phenolics. Levels of antioxidants in the tomato after exposure to different stresses during the mature green stage of fruit development were assessed at the Rice Genomics laboratory in the Department of Crop, Soil and Environmental Sciences at the University of Arkansas, USA. Seeds of the tomato cultivar M82 were germinated in the dark for 48 hours. The seedlings were then transplanted into commercial potting soil before being transferred to the greenhouse. The plants were watered every other day until the mature green stage of fruit development (85-90 days post germination). The plants were then divided into five groups and treated with 200mM NaCl, 200 mM mannitol, drought, 100 μM methyl jasmonate and tap water for a period of 72 hours. Afterwards, the stress treatments were removed and fruits allowed to ripen. After ripening the fruits were assayed for lycopene, beta-carotene, phenolics and sucrose content. Tomato plants (S. lycopersicum) subjected to salt stress showed the highest increase in lycopene (2.8x) while for other stresses the increase was by 1.1-1.2x. Beta-carotene content was increased by 2.5-2.7x after salt and drought stress were applied. The highest level of phenolic compounds (2.3x) was observed after treatment with methyl jasmonate. Salt stress increased the sucrose content by 3.2x. Thus the application of stress at the mature green stage of fruit development leads to an increase in bioactive compounds in tomato. This condition has the potential for production of enhanced fruit quality in tomato.Keywords: Tomato (Solanum lycopersicum), stress, antioxidant compounds, lycopene, beta-carotene, sucrose, phenolics