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- Author or Editor: T. E. Thompson x
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 final 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 final 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 final nut quality.
Abstract
Seedling juvenility is one of the main impediments to progress in fruit and nut tree breeding (2, 5). Juvenility prevents young trees from producing flowers and thus lengthens the generation time. Seedling pecan trees [Carya illinoensis (Wangenh.) C. Koch] normally produce nuts for the first time at 7-10 years of age. This severe problem in the pecan breeding program has been reduced to some extent by budding juvenile seedlings onto large cut-back trees and growing them rapidly for 4 to 5 years (4). With this system, the minimum generation time is about 6 years (presuming that the clones flower at the 4th leaf). Since this technique shows that pecan juvenility can be altered by the environment in which the bud grows, methods to shorten the generation time even more were initiated at Brownwood in 1979. My objective is not that proposed by another (8, 9)—that is, to shorten the juvenile period. Rather, it is to induce flowering on plants obviously in the juvenile phase.
Abstract
‘Pawnee’ pecan [Carya illinoensis (Wang.) K. Koch] is a precocious and prolific producer of high quality nuts. It was released by the USDA 2 Nov. 1984. Early maturity, large size, and high kernel percentage make the nuts of this cultivar uniquely suited for the early Thanksgiving and Christmas holiday market. Earlier nut maturity also makes ‘Pawnee’ a potential cultivar for the northern pecan production area where there are few protandrous cultivars from which a grower can choose.
Precocity of pecan [Carya illinoinensis (Wangenh.) C. Koch] seedlings (year of first fruit production) was studied in relation to original seed measurements (nut weight, buoyancy, volume, and density) and in relation to growth index (GI) measurements of seedling trees for 4 years. A total of 2,071 pecan seedlings, representing nine controlled-cross families, were studied. Original seed measurements were not related to precocity of resultant seedling trees; but seed weight, buoyancy, and volume were significantly correlated with seedling growth rates. Nut density was negatively related to growth of seedlings. These relationships show the importance of original seed measurements and seed parentage in determining seedling growth, and have direct relevance in pecan nursery operations to increase general rootstock seedling vigor. Seedling growth rate was significantly correlated to precocity levels, with measurements taken in the later years of the study showing the highest correlations with precocity. This strong growth-precocity relationship may have negative genetic implications since a common breeding objective is to produce more precocious cultivars that maintain smaller tree size in mature orchards.
Heritability estimates for pecan [Carya illinoinensis (Wangenh.) K. Koch] nut weight, nut buoyancy, nut volume, nut density, kernel weight, and percentage kernel were determined from 8748 nut samples representing 152 families collected during 25 years in the U.S. Dept. of Agriculture (USDA) pecan breeding program at Brownwood, Texas. Measurements were corrected for year-to-year environmental variability using least-squares constants of individual year effects. Adjusted values were then regressed on midparent means. Generally, heritability (h2) estimates were low to moderate: nut weight 0.35, nut buoyancy 0.18, nut volume 0.35, nut density 0.03, kernel weight 0.38, and percentage kernel 0.32. The low values are probably due to the extreme alternate bearing tendency of this species, since crop load affects pecan nut characteristics so directly. Phenotypic correlations among these traits showed that larger or heavier nuts had significantly higher kernel weight, buoyancy, and percentage kernel. Nut density increased with higher nut and kernel weight, but decreased with nut volume.
The U.S. Dept. of Agriculture, Agricultural Research Service conducts the largest 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 correlated 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.
The Munsell system of color notation was used to study differences in kernel color arising between four pecan cultivars (`Cheyenne', `Choctaw', `Western', and `Wichita') grown at four locations (Tulare, Calif., and Brownwood, Crystal City and El Paso, Texas) during two seasons (1987 and 1988) and were stored under different temperatures (ambient and frozen). The hue, value, and chroma of pecan kernels varied significantly in the 2 years of the test. Kernels collected in 1987 were more yellow and lighter and had greater color saturation than kernels collected in 1988. Cultivars differed in hue, value, and chroma at the initial color determination. `Cheyenne' kernels were the most yellow (hue of 18.8) and were the lightest (value of 6.4) of any cultivars tested. `Wichita' kernels were more intensely colored (chroma of 4.7) than `Cheyenne' or `Choctaw' kernels. Kernels from pecan trees in El Paso were more yellow than those from other locations and were lighter than kernels from either Brownwood or Tulare, Calif. Kernels evaluated after being frozen 6 or 12 months could be distinguished from fresh kernels on the basis of hue. Frozen samples were more red than fresh kernels. Kernels frozen 12 months were less intensely colored than fresh kernels or those frozen only 6 months. There was a significant linear relationship between time in the freezer and each color attribute. Hue and chroma were negatively correlated with storage time, while value was positively correlated.
Abstract
Eighteen interspecific hybrids from eight different Cuphea species have been confirmed morphologically and cytologically. Seven hybrids from reciprocal crosses of various accessions of the herbaceous annual C. procumbens (N = 9) and the semiwoody perennial C. llavea (N = 9) exhibited a relatively high degree of fertility. Some hybrids have horticultural potential and are currently undergoing evaluation as new pot or bedding plants. Other hybrids that are sterile due to meiotic irregularities are: C. procumbens (N = 9) × C. crassiflora (N = 12); C. procumbens (N = 9) × C. leptopoda (N = 10); C. procumbens (N = 9) × C. leptopoda (N = 8); C. procumbens (N = 9) × C. lanceolata (N = 6); C. lanceolata (N = 6) × C. llavea (N = 9); C. lanceolata (N = 6) × C. lophostoma (N = 8); C. leptopoda (N = 10) × C. laminuligera (N = 10); C. procumbens (N = 9) × C. caesariata (N = 18); and C. lanceolata (N = 6) × C. caesariata (N = 18). C. leptopoda × C. laminuligera is of considerable interest, because it is the first successful interspecific hybrid between species in different fatty acid groups. A relatively fertile amphidiploid of C. leptopoda × C. laminuligera was induced by colchicine. Seed has been produced by self-pollination of the amphidiploid and attempts are being made to backcross the hybrid to the original parents.