Pecan Nut and Kernel Traits Are Related to Shelling Efficiency

Additional index words. Carya illinoinensis, breeding, genetics, nut quality Abstract. The U.S. Dept. of Agriculture, Agricultural Research Service conducts the larg- est and oldest pecan (Carya illinoinensis (Wangenh.) K. Koch) breeding program in the world. This program evaluates thousands of nut and kernel samples each year using a standard nut and kernel evaluation system developed and refined for more than 70 years. This report relates the effectiveness of these evaluations to commercial shelling efficiency by direct comparison of these data to commercially shelled samples from the same clone performance test. Visual ratings of shelled kernel samples (1-5, with 1 = best) were cor- related with time required to hand clean kernel samples (r = 0.55). As percent kernel increased, visual ratings of shelled kernels improved (decreased) (r = -0.73). More intact halves were recovered from shelled samples with the best (lowest) visual ratings (r = -0.67). Conversely, fewer pieces of any size were present in samples with the best visual ratings. Visual ratings improved as nut density decreased (r = 0.33). Samples with the lightest kernel color also had the best visual ratings (r = 0.38). These data show that the standard U.S. Dept. of Agriculture pecan nut and kernel evaluation system needs to be refined by modifying selection pressure placed on various standard evaluation traits. A century ago, almost all pecans were col- lected from natural stands (native trees). The nuts were small and had thick shells that were hard to remove. The portion of the U.S. crop that is collected from native trees has steadily decreased due to habitat annihilation and poor economic returns. Breeding efforts to improve pecan nut quality have been successful (Grauke and Thompson, 1996). The U.S. Dept. of Agriculture, Agricultural Research Service pecan breeding program is headquartered at College Station, and Brown- wood, Texas. This program, which began in s 1932, has released 24 cultivars in cooperation with various state agricultural experiment sta- tions ( Thompson and Grauke, 1991; Thompson and Young, 1985). Controlled crosses are made between selected parents, trees are evaluated under field conditions, and the best clones are selected for further testing in the National Pecan Advanced Clone Testing System (NPACTS). In NPACTS orchards, clones are vegetatively propagated and their performance is compared to standard commercial cultivars. Tests are con- ducted in several major pecan production areas to determine specific environmental suitability of new cultivars. The average time from cross- ing to cultivar release is 27.25 years (shortest time 13 years; longest time 60 years). Con- sidering the year to make the controlled cross, the 10-year cycle for evaluation in the Basic Breeding Program (BBP), and the 9- to15-year evaluation period in NPACTS, a development time of 20 years is required. Since about 90% of pecans are shelled before retail sale, and all are eventually shelled, ease of shelling and yield of large kernel halves or pieces is of major economic importance. Yet little is known about the effects of basic nut and kernel traits in determining ease of machine shelling. In this breeding program, ease of shelling and removal of packing mate- rial from the dorsal grooves, ventral grooves, and other kernel surfaces are major continuous selection criteria. In the NPACTS program, basic nut evalu- ation is routine, but the relationship of these measurements to actual commercial shelling efficiency has been inadequate. Therefore, the objective of this study was to compare data collected in the laboratory with results obtained from commercial shelling operations.