FRUITING STRESS INDUCES SHUCK DECLINE AND PREMATURE GERMINATION IN PECAN

The influence of fruiting stress on shuck decline, nut quality, and pr emature germination was evaluated on trees of pecan [Carya illinoensis (Wangenh,) C. Koch], Fruit at the liquid endosperm stage were removed from trees with a mechanical shaker to reduce crop load by 0%, 25%, 4 1%, 56%, or 77%. Shuck decline and premature germination decreased and kernel quality increased with a reduction in crop load, An excessive fruit load or fruit stress elevated the incidence of shuck decline, pr eviously referred to as shuck disease, tulip disease, shuck die-back, or late season shuck disorder; decreased kernel development; and incre ased premature germination, Shucks were dissected from fruit ranging f rom healthy to those with premature shuck opening and examined by scan ning electron, transmission electron, and light microscopy, Fungal gro wth was detectable, but only after tissue degeneration had occurred. T hus, results indicate the onset of shuck decline is caused by stress a ssociated with an excessive crop load and not a pathological disorder. Fungal growth is a secondary, not a primary, factor in deterioration of shucks with decline.