The role of free polyamines in the alternate-bearing of pistachio (Pistacia vera cv. Pontikis)

The present study was conducted in order to examine the physiological role of free polyamines in flower bud abscission. For this reason five 15-year old pistachio trees cv. "Pontikis" were selected and half of the main branches were manually defruited in early May. Polyamines were analyzed in three different organs (shoots, leaves and flower buds) from both fruiting and non-fruiting branches, during the period of kernel growing. Five samplings took place and the polyamines putrescine, spermidine and spermine were assayed. The flower bud abscission percentage was recorded every 5–10 days during kernel formation. Polyamine concentration declined during the period that coincides with that of kernel development, in both fruiting and non-fruiting branches, while significant bud abscission occurred from mid-July till late September in fruiting branches. Polyamine concentration in organs from fruiting branches was in most cases lower than that of non-fruiting ones. Most of the individual polyamines exhibited a high and significant negative correlation with bud abscission. By measuring the spermidine content of leaves and the spermine content of buds, it was possible to estimate the forthcoming bud abscission with significant accuracy (approximately 93%). On the other hand, the total polyamine content of the buds exhibited a significant strong negative relationship with bud abscission. Consequently, polyamines could have an important physiological function in the development of flower bud abscission of pistachio.