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- Author or Editor: Gregory L. Reighard. x
A field planting of 18 selections and 10 named cultivars of pawpaw (Asimina triloba) was established in November 1996 near Clemson, S.C., as part of the Pawpaw Regional Variety Trial coordinated by Kentucky State University. Trees were planted at 2.0 × 5.5 m spacing with drip irrigation and straw mulch in a randomized complete block design consisting of 8 single-tree replications. Data collected through 2005 included tree survival, total tree yield, and yield and average weight of fruit weighing >150 g. Since the start of the trial, 3 selections, 1-7-1, 11-5 and 8-58 have been named and released as `Shenandoah', `Susquehanna' and `Rappahannock', respectively. The highest yielding cultivars were `Shenandoah', `Rappahannock', and `PA-Golden'. The cultivars with the largest percentage of large fruit were `Shenandoah' and `Susquehanna'. `Middletown', `Mitchell', `Rappahannock', `Taytwo', `Wells' and `Wilson' produced the largest percentage of small fruit (<150 g). After 9 years, 66% of the original trees (i.e., scions) were alive. `Rappahannock', `PA-Golden', `Sunflower' and `Wilson' had either one or zero trees die, whereas `Middleton' and `Wells' had only 2 trees alive. Among the selections, 2-54, 9-58, 11-13, 1-68, 3-11, and 8–20 had either 88% or 100% survival. The highest yielding selections were 10-35, 1-7-2, 1-68, and 2-10, and 1-7-2, 2-10, 4-2, and 5-5 produced the highest percent of large fruit. Fruit quality characters such as aroma, flavor, aftertaste and texture were not quantified or evaluated.
Trees of `Redhaven' peach [Prunus persica (L.) Batsch] budded to Lovell, Bailey and Nemaguard rootstocks were grown with either bahiagrass or cultivated row-middles. Terminal shoots and roots were collected on four dates during 1991-92 (Nov. 15, Jan. 16, Feb. 26 and Apr. 1). On the April 1 collection date, trees grown with cultivated row-middles had higher levels of total soluble sugars and total carbohydrates in shoot tissue than trees grown with sod. There were no differences on any of the other dates. Orchard floor management did not affect the levels of Ca, Mg, K, P or Fe in shoots or roots. Trees on Nemaguard rootstock had significantly less starch and total carbohydrates in shoot tissue than those on Lovell on the last two collection dates. Shoot tissue of trees on Nemaguard and Bailey rootstocks had lower levels of K than those on Lovell. Sorbitol and total soluble sugar levels were higher in the root tissue of Lovell than Bailey and Nemaguard. Nemaguard had significantly higher levels of starch in root tissue than Lovell and Bailey. Nemaguard and Bailey had lower levels of Mg in roof tissue than Lovell.
This paper outlines the development of regional-scale peach [Prunus persica (L.) Batsch] phenology models for the southeastern United States. We constructed regression-based models to predict full bloom and first harvest using phenological data for eight peach cultivars grown in Georgia, South Carolina, and Texas and meteorological data from nearby cooperative weather stations. The mean absolute error (MAE, absolute value of predicted date minus observed date) of the all-cultivar full bloom model was 3.48 days. Bloom model errors were roughly 6 to 7 days (or less) 90% of the time, while comparable natural bloom date variability at a single station is about 12 to 13 days. Only two cultivars (`Dixired' and `Elberta') had first harvest models with 90% error thresholds at or less than the natural harvest date variability at a single station (9 to 10 days). Thus, first harvest appears to be less predictable than full bloom, at least in terms of the temperature variables used in this study. The bloom model could serve as a prognostic tool, while the two cultivar harvest models are appropriate only for diagnostic studies, such as evaluating the potential response of a peach cultivar in a new location. The appeal of the models is that they consider numerous cultivars over a wide region and they use readily available meteorological data.
Evergreen genotypes of peach [Prunus persica (L.) Batsch] have been identified in Mexico, where terminal growth on evergreen trees is continuous under favorable environmental conditions. This evergreen trait in peach is controlled by one single gene (evg), and this evergreen condition is homozygous recessive. Four dominant AFLP markers, EAT/MCAC, ETT/MCCA2, EAT/MCTA, and ETT/MACC, were found to be tightly linked to the evg locus at 1 cM, 4.6 cM, 5.8 cM, and 11 cM, respectively. All four markers were sequenced and identified. A peach BAC library was constructed by using the pBeloBAC11 vector for building the physical map for the evg gene. This library represents four times the coverage of the peach genome with the average insert size of 50 to 70 kb. The EAT/MCAC AFLP marker fragment was used for screening the peach BAC library. A single BAC clone, 18F12, was confirmed to contain this fragment. The final BAC contig for this evg gene region and the potential homology between peach and Arabidopsis thaliana will be presented and discussed.
Graft-transmissible agents found in `Ta Tao 5' peach have been associated with phenological changes, including delay in bloom, reduced shoot vigor, and early autumn defoliation. Peach Latent Mosaic Viroid (PLMVd) is present as a graft-transmissible agent in `Ta Tao 5'. In order to further characterize the changes occurring in trees exposed to PLMVd from `Ta Tao 5' grafts, total fatty acid content was measured for peach buds during chilling accumulation and release from dormancy in `Coronet' peach trees and `Coronet' trees treated with `Ta Tao 5' bud grafts. Palmitic (16:0), stearic (18:0), oleic (18:1), linoleic (18:2), and linolenic (18:3) acids were the major fatty acids in dormant and releasing peach buds of both the controls and treated trees. The degree of unsaturation increased immediately following completion of chilling requirement in both the untreated controls and in the treated trees. However, the desaturation of linoleic acid to linolenic acid was significantly inhibited in the trees treated with `Ta Tao 5' bud grafts, which was accompanied by a concomitant delay in the resumption of growth. The disparity between the control and treated trees in the trend toward increased fatty acid unsaturation continued through the resumption of growth. The changes in degree of fatty acid saturation correlated with a response to forcing conditions and the release from dormancy. The presence of PLMVd in `Coronet' peach trees affects membrane fatty acid saturation during chilling accumulation and dormancy release. These findings suggest that metabolic pathways involving fatty acid desaturation are linked to the phenotypic variation in trees exposed to PLMVd.
Peach [Prunus persica (L.) Batsch (Peach Group)] trees infected with peach latent mosaic viroid (PLMVd) have been associated with phenological changes including delay in bloom, reduced shoot vigor, and early autumn defoliation. In order to further characterize the changes occurring in trees inoculated with PLMVd, total fatty acid content was measured for floral buds during release from dormancy in `Coronet' peach trees. Palmitic (16:0), stearic (18:0), oleic (18:1), linoleic (18:2), and linolenic (18:3) acids were the major fatty acids in dormant and releasing peach buds of both control and PLMVd-inoculated (VI) trees. The degree of unsaturation increased immediately following release from dormancy in both the control and VI trees. However, desaturation of linoleic acid to linolenic acid was significantly inhibited in VI trees, which was accompanied by a concomitant delay in the resumption of growth. The disparity between the control and VI trees in the progression of increased fatty acid unsaturation continued through petal fall. The presence of PLMVd in `Coronet' peach trees slowed membrane fatty acid desaturation during release from dormancy and suggested that metabolic pathways involving fatty acid desaturation were linked to the delayed phenology of the VI trees.
Two F1 hybrid Prunus rootstocks, K62-68 and P101-41, developed from a cross of `Lovell' [susceptible to both Meloidogyne incognita (Kofoid and White) Chitwood and M. javanica (Treub) Chitwood] and `Nemared' (resistant to both root-knot nematode species), were selfed to produce two F2 seedling populations. Vegetative propagation by herbaceous stem cuttings was used to produce four or eight self-rooted plants of each F2 seedling for treatment replications. Eggs of M. incognita and M. javanica were inoculated into the potted media where plants were transplanted, and plants were harvested and roots examined for signs and symptoms associated with root-knot nematode infection ≈120 days later. Segregation ratios in both F2 families suggested that resistance to M. incognita in `Nemared' is controlled by two dominant genes (Mi and Mij) and that to M. javanica by a single dominant gene (Mij). Thus, Mij conveys resistance to both M. incognita and M. javanica.
Delaying bloom to reduce spring frost risk and reducing labor costs by increasing orchard efficiency are important goals of peach producers. At the Musser Fruit Research Center near Clemson, S.C., `Coronet' peach trees were inoculated with Peach Latent Mosaic Viroid (PLMVd) to induce bloom delay and reduce shoot vigor. Trees were grown in a high-density, Y-trained orchard system to determine the potential benefit of reduced shoot vigor on labor efficiency in summer pruning operations. In Aug. 1997, `Ta Tao 5' buds were grafted onto the scaffolds of 2-year-old `Coronet' peach trees to transmit PLMVd. Transmission was confirmed by dot-blot on N+ nylon membranes using cRNA probes. Bloom was not delayed in the following year, Spring 1998, but bloom was delayed 7 days in Spring 1999. Yields were unaffected in 1998, but the total fruit weight produced on PLMVd-treated trees was significantly less in the 1999 harvest. Individual fruit weight, firmness, and color were improved on the treated trees. Shoot vigor was reduced on the PLMVd treated trees in the summers of 1998 and 1999, resulting in a significant reduction in pruning time and pruning weights. Light penetration was significantly increased in the treated trees when compared to the untreated controls in the summers of 1998 and 1999. Fruiting shoot length and the number of fruit per shoot was unaffected by the PLMVd presence. The trunk cross-sectional area was significantly less on the treated trees when compared to the untreated controls after each year of growth. Autumn defoliation occurred earlier on the treated trees in Fall 1998 and Fall 1999. The manipulation of peach tree growth and development was accomplished using graft transmissible agents as PLMVd induced several beneficial growth and developmental modifications in established peach trees.
`Evergrowing' (evg) peach is a naturally occurring mutant unable to enter winter dormancy in response to dormancy inducing conditions. The evg mutant is one of only two described mutants affecting winter dormancy in woody perennial trees. The evg mutation segregates as a single recessive gene and previous work by our group has fine mapped the trait between flanking markers separated by 3.3 centiMorgans. This region was physically mapped using a bacterial artificial chromosome (BAC) library from and a contig of overlapping genomic fragments identified. We have utilized several approaches to complete the sequencing of a 132 kilobase region of the peach genome derived from three overlapping BACs that encompass the complete EVG gene containing region. We present here our analysis and annotation of the genomic region, including putative and experimentally verified gene coding sequences. A primary feature of the region is a large tandem duplication of a region containing a MADS-box type DNA binding transcription factor resulting in six similar copies of the gene, all of which appear to be expressed at the mRNA level in wild-type germplasm. Hybridization analysis revealed the presence of a large deletion in the mutant genome. Five of the identified genes fall within the evg mutation and represent new candidates for the control of entrance into winter dormancy.