Different response of apple and peach fruits to 1-MCP: a case of different sensitivity to ethylene?

1-methylcyclopropene (1-MCP) is known as an antagonist of ethylene action. A number of different trials demonstrated that not all climacteric fruits respond in a similar way to 1-MCP treatment: two examples are represented by apple and peach fruits. When applied on apples, 1-MCP is particularly effective in delaying ripening, while in peaches the rate of softening is slowed down only during the incubation period and a quick recovery of ripening parameters occurs in the post-treatment phase. In order to elucidate this different behavior, specific trials on peaches and apples have been performed. As expected, apple (cv. ‘Golden Delicious’ and ‘Royal Gala’) fruits responded to 1-MCP (0.625 ppm for 24h) maintaining firmness and producing little ethylene for the considered period (24 days) at 20°C, whereas in peaches (cv. ‘Summer Rich’), 1-MCP (1ppm for 24 or 72h) was effective in reducing ethylene evolution and slowing down the softening process only during the incubation time and a short period thereafter. The quick recoveries of ethylene biosynthesis and the softening process observed in peaches during the post-treatment phase are associated with increases of PpACO1 and polygalacturonase (PG) gene expression. A molecular approach was used to investigate the sensitivity of both apples and peaches to ethylene. ETR1 (a member of the ethylene receptor family) gene expression was monitored via RT-PCR and a different behavior between apples and peaches has been observed: in fact, following 1-MCP treatment, MdETR1 transcript accumulation showed a decreasing trend, whereas the amount of PpETR1 mRNA did not significantly change throughout the considered periods.