Cell and Tissue Damage Associated with Pistillate Flower Abscission of Persian Walnut

Abstract

Pistillate flowers from walnut trees having > 80% pistillate flower abscission (PFA) were examined from the time of anthesis until shortly before abscission. In addition to normally developing flowers, two types of abortive flowers were found. One abnormal flower type, seen in only two cases, lacked a developed embryo sac and had cellular degeneration in the nucellus. The second type of damaged flowers, which were more commonly observed, had apparently normal development of the nucelli and embryo sacs, but cell and tissue necrosis became evident beginning at the tip of the stigma, in the integuments, and throughout the placental evaginations. No cell or tissue damage was observed until after ovary growth in these flowers had stopped. We conclude that this second type of damage is associated with PFA.