Effects of Polyamines on Fruit-set of Apple1

Aliphatic polyamines (spennine, spermidine, and putrescine) were sprayed 9 days after full bloom on open- and self-pollinated flowers of a spur-type apple ( Malus domestica Borkh. cv. Ruby Spur). Concentrations of 10 -6 and 10 -5 M substantially increased fruit-set and yield per tree. Polyamines generally increased fruit growth rate during stage 1 (cell division), but not thereafter (cell enlargement). Flower bud formation was also increased by higher concentration of polyamines.