Effect of foliar application of methyl jasmonate in cold tolerance improvement of greenhouse-grown cucumber cv.  Negin seedlings

Cold stress is one of the limiting factors in production of greenhouse vegetables. Chemicals offer useful approach to reduce low temperature-induced damages. This study was conducted to evaluate the effect of foliar application of methyl jasmonate (MeJA) at concentrations of 0 (control)، 50، 100، 200 µM) on electrolyte leakage (EL)، relative water content (RWC)، soluble carbohydrates، proline، chlorophyll content and chilling index of greenhouse- grown cucumber (Cucumis sativus L. cv ‘Negin’) in 4-6 leaf stage. MeJA was sprayed two times/day on cucumber seedling in a greenhouse of Bu-Ali Sina University، as a factorial based on completely randomized design with five replications per treatment، inlate- summer of 2013. Two days after spraying، seedlings were transferred from 25ºC to cold chamber and were subjected to chilling treatments of 15، 10 and 5 ºC for 4 hours. The EL of all plants increased with reducing the temperature. However، in MeJA-treated plants، especially in application of 200 µM، a lower leaf EL was observed. A clear increase in soluble carbohydrates and proline concentration was observed with decreasing temperature from 15 to 5ºC in all plants while in MeJA -treated seedlings، especially in application of 200 and 100µM، a greater amount of these osmolytes were observed in compared to control. Moreover، exogenous application of MeJA reduced RWC and visual damage of cold-stressed seedlings but increased chlorophyll content in compared to control plants. These changes correlated with the increment of cold tolerance in the cucumber plants. The results indicated that MeJA application especially at 200 µM، has the capacity to improve chilling tolerance of seedlings and can be used as a prophylactic tool to protect against chilling injury of cucumber cultivars in greenhouses