Carbohydrate content of inflorescent buds of defruited and fruiting pistachio (Pistacia vera L) branches in relation to biennial bearing

Changes in carbohydrate content of inflorescent buds of fruiting and defrui ted branches of the same tree were measured in 1994 and 1995 in the period before and during bud abscission in pistachio (Pistacia vera L. cv. Aegenes ) to investigate its relationship to inflorescent bud abscission. HPLC was used for soluble sugar analysis, while starch was hydrolyzed to glucose enz ymatically and the amount of glucose was then determined using the glucose oxidase-peroxidase method. The effect of fruit on leaf net photosynthesis ( Pn), chlorophyll a and b (Chl (a+b)) in leaves and specific leaf weight (SL W) was also investigated in 1995. Starch concentration was initially simila r in buds of fruiting and defruited branches but became greater in buds of defruited branches from early June 1994 (57 d after full bloom (AFB)) and 2 0 June 1995 (61 dAFB), resulting in higher starch contents. Glucose and fru ctose concentrations were similar in flower buds throughout the whole perio d of measurement; inositol and sucrose (the most abundant sugar in flower b uds) both became much lower in fruiting branches from early July 1994 (83 d AFB) and mid July 1995 (88 dAFB). The rapid decrease in sucrose concentrati on coincided with rapid seed growth and the greatest period of bud abscissi on in fruiting branches. During the same period, total sugar and total carb ohydrate concentrations and contents were greater in buds of defruited bran ches. The presence of fruit increased Chi (a+b) content in leaves while dec reasing SLW between 43 and 61 dAFB. During this same period, leaf Pn rates were greater in fruiting shoots than in defruited ones.