EFFECT OF METHYL JASMONATE AND SALICYLIC ACID ON CHILLING INJURY OF 'EUREKA' LEMONS

Abstract

South Africa is the second largest exporter of citrus fruit in the world, with long shipping distances demanding high quality, pest- and disease-free fruit. For certain markets fruit are subjected to low temperatures (-0.5°C) for varying periods of time as an obligatory quarantine treatment; however, lemons are sensitive to low temperature exposure and easily develop chilling injury during obligatory quarantine treatments. This has become a major limitation to the expansion of South Africa's lemon industry. In other horticultural crops postharvest treatments with methyl jasmonate (MJ) or salicylic acid (SA) have been successfully used to reduce chilling injury. Therefore, ‘Eureka’ lemons were dipped either in 10 or 50 µM MJ or in 2 or 2.5 mM SA solutions and subsequently stored at -0.5°C for 0, 7, 14, 21, 28, 35, or 42 days, before being transferred to room temperature for 7 days. Fruit weight, total phenolics, carbohydrates and proline concentrations of the rind were determined. Although no visual symptoms of chilling injury were observed, treatment with either 10 µM of MJ or 2 mM of SA significantly (P<0.05) reduced fruit mass loss, increased antioxidant compounds, such as phenolics and carbohydrates as well as symptoms of chilling injury such as high proline concentrations in the rind. These alterations of the chemical composition of the rind may have increased the chilling tolerance of fruit to cold storage. Therefore, postharvest treatments with either 10 µM MJ or 2 mM SA should be further tested as treatments to reduce chilling injury in lemons.