`McIntosh' apple fruit thinning by benzyladenine in relation to seed number and endogenous cytokinin levels in fruit and leaves

The relationship of 6-benzylaminopurine (BA)-induced fruitlet abscission to seed number and endogenous cytokinin levels in the fruit and leaves was examined in `McIntosh' apples (Malus domestica Borkh.). BA applied at the 10 mm stage of fruit development effectively thinned apple fruit and increased fruit size. The seed number of abscising fruit increased as BA concentrations increased. In persisting fruit, BA reduced the number of normal seeds, increased the number of aborted seeds, but had no in ̄uence on the number of total seeds. The total number of seeds was signi®cantly higher in persisting fruit than in abscising fruit. BA increased zeatin riboside levels in the fruit 2 days after application, but it had no effects on zeatin levels in the fruit. The levels of zeatin and zeatin ribosides in the leaves were not affected by BA application. # 2000 Elsevier Science B.V. All rights reserved.