Influence of putrescine on fruit set of apple (cv. Ruby Spur).

Putrescine was sprayed on "Ruby spur/MM 106" apple trees, at different times of application in order to increase fruit set. The putrescine concentration of 10-3M applied at 20-30% open flowers or of 10-2M at full bloom induced the best fruit set. Also the fruit growth was generally increased by putrescine treatment. As far as the uptake study is concerned the amount of polyamines (putrescine, spermidine, spermine) found in samples of flowers and leaves sprayed in open field with 10-3M solution of each polyamine reached a maximum value within 1 hour after treatment.