Studies on fruit ripening on the vine and after harvest in kiwifruit

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Effects of ethephon application on the fruit ripening of 'Hayward' kiwifruit (Actinidia deliciosa) on the vine were investigated.When 200 ppm ethephon (dissolved with 50% ethanol) was applied at approximately 1-week interval prior to commercial harvest, the 4- and 3-week treatments made the fruits edible. On the other hand, 50% ethanol application was ineffective on fruit ripening. When ethephon was applied at various concentrations 3 weeks before commercial harvest, the 50 and 100 ppm treatments were ineffective on fruit ripening, whereas the 500 ppm treatment hastened fruit ripening more than 200 ppm treatment.In the next year, when fruits were treated with 200 ppm ethephon, they did not ripen as they did in the previous year. We attribute the difference to the lower air temperature and shorter duration of sunshine during this year experiments. From above results, we postulated that the air temperature and duration of solar radiation after ethephon application strongly affect the kiwifruit ripening on the vine.So effects of higher concentration of ethephon on the fruit ripening on the vine were investigated in detail. When 500 ppm of ethephon was applied about 3 weeks before commercial harvest, the fruit became edible about 2 weeks after treatment. But the fruits started to drop strongly about 2 weeks after treatment. And these effects of the treatment did not varied with the year. 500 ppm treatment effectively induced ethylene synthesis by fruits, but it seems that fruit ripening on the vine by the ethephon application is mainly promoted by ethylene produced from ethephon, because fruits immediately started to ripe after treatment.On the other hand, when 500 ppm ethephon was applied with 100 ppm GA_3, the fruit became edible and fruit drop was strongly prevented. It seems that effects of this application method are more stable and effective on the fruit ripening on the vine.