Erez, A., Institute of Horticulture, Volcani Center, Bet-Dagan, 50250, Israel
Yablowitz, Z., Institute of Horticulture, Volcani Center, Bet-Dagan, 50250, Israel
Korcinski, R., Institute of Horticulture, Volcani Center, Bet-Dagan, 50250, Israel
Zilberstaine, M., Ext. Service, Ministry of Agriculture, Hadera, Israel

A major problem in greenhouse growing of stone fruit species is the excessive vegetative development. The concomitant development of vegetative and floral buds has significance with regards to the potential set and persistence of the floral organ. Vegetative buds need normally more heat units to break than floral buds and they respond differently to higher temperatures. With peach and nectarine, vegetative and floral buds are located on the same node and in a normal arrangement of a central vegetative bud and two lateral floral buds. Competition among the vegetative and floral sinks for root supplies: water, nutrients and hormones and for carbohydrates may affect flower and fruitlet drop depending on the developmental ratio of the two types of sink. Under natural cool climate flowers always develop quicker than vegetative buds so that when a vigorous vegetative development starts, a setting fruit is already developing. Under warm conditions, and especially under greenhouse conditions, leafing may advance to the extent that flowering will occur concomitantly with vigorous vegetative growth. This situation often leads to poor retention of flowers and fruitlets and may cause also a drop of even large developing fruits. By preventing exposure to extreme high temperatures an advantage to the reproductive sink is maintained leading to prevention of drop of flowers and fruits. Use of chemicals to break dormancy may also affect the relative level of development of the vegetative and reproductive organs leading accordingly to specific effects on persistence of the reproductive organ.