Pecan Fruit Shuck Thickness is Related to Nut Quality

Pecan (Carya illinoinensis (Wangenh.) K. Koch) fruit presents a considerable weight for the tree to support during the growing season. A major part of this weight is due to the pecan shuck that surrounds the developing nut and kernel. Pecan clones vary considerably for the amount of shuck per nut, and little is known as to the value of this weight in determining fi nal nut quality. Six cultivars differing in basic nut shapes and sizes were studied and found to vary greatly for shuck thickness, and weight of shuck per unit fi nal nut weight and volume. Shuck thickness was shown to be a favorable genetic characteristic since fruit with thicker shucks had slightly greater nut fresh and dry weight, nut volume, nut density, kernel weight and content, and shuck weight per nut volume. 'Sioux' had the thickest shucks (4.70 mm), while 'Pawnee' had the thinnest shucks (3.72 mm). Fresh weight per fruit varied from 21.25 g for 'Podsednik' to 10.18 g for Osage. Weight of fruit per tree was extrapolated using average shuck and nut weights, and it was determined that the fruit on each tree would weigh about 104 kg. This is a considerable weight, and adds substantially to limb breakage. However, thicker shucks contribute to fi nal nut quality. The fruit of pecan (Carya illinoinensis (Wangenh.) K. Koch) can be divided into three parts: shuck (involucre), shell, and kernel (Thor and Smith, 1935, 1939; Woodroof, 1927). The various functions of the shuck in relation to nut development and fi nal nut quality have been of interest to pecan scientists for years. Shucks constitute a major source of fruit weight that contributes to limb breakage during wind storms. Conversely, we know that all nutrition to the developing kernel is routed through the vascular system of the shuck (Calcote et al., 1984). Shuck thickness in relation to insect