Investigation of pectolytic and PR genes expression, quality and phytochemical contents in organic and non-organic table grapes at harvest and during storage.

The demand for organic table grapes is increasing worldwide. However, comprehensive information of quality parameters and phytochemical compounds in organically grown fruit remain unclear. Furthermore, table grapes are perishable and postharvest quality retention and waste prevention is very important. In this study we have compared the differences between organic and non-organic table grapes in terms of phytochemical compounds and quality parameters as well as the changes in the expression levels of pathogen related and lytic genes during storage. Organic fruit showed higher levels of phenolics, flavonoids, caffeic acid, hydrogen peroxide, protein content, antioxidant and anti-stress enzymes and total antioxidant activities at harvest and during storage. Although, the expression levels of polygalactronases, pectin methyl esterase, chitinase and glucanase genes was lower in organically grown table grapes at harvest, but the expression of all these genes was significantly increased during cold storage. After 60 days of cold storage the expression levels of pectin methyl esterase, chitinase and glucanase genes was significantly higher than the conventionally grown grape berries in organic ones. The highest expression of polygalacturonase was recorded in organic samples after 30 days of storage. There was no significant difference between the two types of table grapes for decay extension and tissue deterioration rate. The results of this study indicate that due to higher levels of phytochemicals and antioxidant compounds the organic table grapes have a higher nutritional quality. Furthermore, the increase in PR and pectolytic genes expression levels is enough for decreasing the fruit susceptibility to decay pathogens and enhancing the postharvest life of organic grapes.