Gibberellin Content of Apple Fruit as Affected by Genetical and Environmental Factors

Gibberellin content of fruitlets of different varieties and of different 'Golden Delicious' clones was investigated for two subsequent years in fruit samples collected weekly on the same trees starting when the fruit was 15 mm diameter (two weeks after petal fall), until July, when the fruit reached 50 mm diameter. The analysis of GA3, GA4 and GA7 content of fruitlets, performed by HPLC, showed that the pattern of GA 4 and GA7 variation in that period was different in different clones and varieties, but was substantially identical in the two years, thus highlighting significant differences between cultivars but also confirming the correlation among relative content of GA4 and GA 7 and russeting appearance. The differences observed in GAs level in different years are probably due to different climatic conditions as it was observed in apple fruitlets of the same cultivars grown in different countries. Correlation was found between cultivar sensitivity to russet and fruit shape. Relations between GAs content and early growth rate of fruitlet, fruit lengthening and russeting are discussed.