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- Author or Editor: Tommy Thompson x
Abstract
Fresh and dry weights of fruit (nut and shuck) samples of 39 clones of pecan [Carya illinoensis (Wang) K. Koch] were determined weekly from July 23 until harvest. One early maturing clone had accumulated 24% of its final fruit dry weight by July 23, when the average for all clones was 11%. Total fruit dry matter decreased during October for some late-maturing clones. These decreases, which were the most obvious in ‘Mahan’ and its progeny clones, were not as common in early maturing clones.
Variability in soluble solids concentration (SSC, °Brix) in liquid endosperm (LE) among individual pecan [Carya illinoinensis (Wangenh.) K. Koch] fruits and among fruits from different trees and cultivars using a sugar refractometer was determined at College Station, Texas, in 1997. Repeatability of readings from LE from the same fruit was excellent. Fruits from the same tree did not vary for SSC, but significant differences among clones were common. Soluble solids concentration appears to decrease as the fruit matures. The SSC values for two full-sib clones (one susceptible to water split and one resistant to water split) were similar. This information discounts the possibility that high osmotic water potential gradients alone induce the water split phenomenon. A wide range of SSC percents was recorded. A low of 0.5% was recorded for LE from a `Houma' fruit, while 6.1% was recorded for LE from a fruit from a drought-stressed `Burkett' tree.
Putative resistance to the yellow aphid complex (Monellia caryella (Fitch) and Monelliopsis pecanis Bissell) in the `Pawnee' pecan [Carya illinoinensis (Wangenh.) K. Koch] cultivar was first noted in greenhouse tests by rating cultivars for relative amounts of honeydew on adaxial leaf surfaces. This resistance was confirmed in two field tests monitored from mid-June to mid-Oct. `Pawnee' supported significantly lower aphid populations during every rating period when relatively large numbers of these insects were present. `Navaho' also showed resistance, with `Desirable' having intermediate resistance and `Stuart' being very susceptible. Insect populations were also monitored on the four quadrants of each tree, with this quadrant effect being significant in only one test. This test had the highest populations on the West and lowest populations on the East.
Thirty-six cultivars and 948 seedlings from 15 controlled crosses in the U.S. Dept. of Agriculture-Agricultural Research Service pecan [Carya illinoinensis (Wangenh.) K. Koch] breeding program at Brownwood, Texas, were rated for susceptibility to nut scab [Cladosporium caryigenum (Ell. et Lang.) Gottwald] to determine heritability of this trait. Differences between parents and progenies, and within progenies, were highly significant. Within most families, a complete range of resistance reactions were evident, from fully susceptible to fully resistant. Heritability of resistance was determined by regressing individual progeny values on female, male, and midparent values, with the midparent heritability estimate being the highest (0.54). This moderate level of additive gene action and the identification of superior parents in this study will contribute to the efficiency of breeding resistant cultivars.
Thirteen cultivars of pecan [Carya illinoinensis (Wangenh.) K. Koch] were monitored for bud break, pollen shed and stigma receptivity for 4 years at LSU Pecan Station, Robson, LA. Cultivars were generally consistent in displaying clear patterns of protogyny or protandry, although patterns were uncertain for some cultivars in some years. Mean dates of cultivar phenology varied significantly by year. Years with warm winter and spring temperatures had earlier seasons of growth and flowering than years with cooler temperatures. The duration of pollen shed and stigma receptivity varied between years. Protogynous cultivars, as a group, had greater bloom overlap than protandrous cultivars, although overlap varied between years for both dichogamy classes. The sequence of cultivar flowering relative to other cultivars varied between years, resulting in variable amounts of bloom overlap between cultivars in different years.
Putative resistance to the blackmargined aphid (Monellia caryella Fitch) in `Pawnee' pecan [Carya illinoinensis (Wangenh.) K. Koch] was first noted in greenhouse tests by rating cultivars for relative amounts of honeydew on adaxial leaf surfaces. This resistance was confirmed in two field tests monitored from mid-June to mid-October. `Pawnee' supported significantly lower aphid populations during every rating period when relatively large numbers of these insects were present. `Navaho' also showed resistance, with `Desirable' having intermediate resistance and `Stuart' being very susceptible. Insect populations were also monitored on the four quadrants of each tree, with quadrant effect being significant in only one test. This test had the highest populations on the western quadrant and lowest populations on the eastern quadrant. In determining individual clone resistance, it is recommended that the general orchard aphid infestation level be determined so that only two or three well-timed clonal ratings are needed. We also recommend that all sides of the tree be monitored.