Reconsideration of the Cause of Inflorescence Bud Abscission in Pistachio

Data collected 2 consecutive years revealed that 30% to 38% of the inflorescence buds of ‘Kerman’ pistachio (Pistacia vera L.) abscised mainly during an initial 5- to 6-week period from trees devoid of fruit. Bearing trees, by contrast, progressively dropped 99% of their buds during a 10- to 12-week period. Abscission during the initial 5- to 6-week period in bearing and nonbearing trees is apparently the result of a stimulus originating in the roots. Continued abscission during the subsequent 5- to 6- week period coincided with the initiation and growth and development of the kernel. It appears, therefore, that a stimulus originating in the fruit (kernel) is responsible for the second phase of a two-phased abscission process.