GIBBERELLINS AND CONTROL OF FRUIT RETENTION AND SEEDLESSNESS IN VALENCIA ORANGE

Applications of gibberellin A₃ (GA₃) or paclobutrazol (PBZ) to fruitlets indicated that GA level influences fruit retention in Valencia orange. 29% of GA-treated fruits were retained to maturity compared with 2% for untreated controls.
PBZ, which inhibits GA biosynthesis, caused 100% fruit drop within 35 days of application.
Regulation of GA levels may therefore be a means to control alternate bearing.
Nine different GAs have been identified from Valencia tissues using combined gas chromatography-mass spectrometry.
Levels of GA₃ varied between individual fruitlets by over 1000-fold, suggesting that fruit retention may be related to endogenous GA levels.

Uniform trees grown under glass had between 0 and 100% seedless fruit, despite flowering at the same time and the presence of honey bees as pollinators.
Data from two successive seasons showed that different trees were seedless in different seasons.
Seed-produced GAs do not appear to be an important factor in fruit retention.

VI International Symposium on Growth Regulators in Fruit Production

C.G.N. Turnbull

https://doi.org/10.17660/ActaHortic.1989.239.52