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- Author or Editor: R. Scorza x
- Journal of the American Society for Horticultural Science x
The response of young, nonbearing peach [Prunus persica (L.) Batsch] trees to pruning was studied in six distinct growth forms including semidwarf, spur-type, upright, columnar or pillar, weeping, and standard. Two years after field planting, pillar and upright trees were trained to slender spindle. Semidwarf, spur-type, and standard trees were trained to the open or delayed vase form. Weeping trees were pruned in a manner similar to the Lepage hedge for pear. Branch density before pruning was highest in semidwarf, spur-type, and upright trees and lowest in pillar trees. Standard, semidwarf, and spur-type trees reacted similarly to pruning, but semidwarf trees produced as much wood in the following season as had been pruned off, and produced large numbers of fruiting branches. The small size of semidwarf trees suggested their use for medium-density plantings (MDPs). Pillar trees needed only light pruning. No major cuts were necessary and many fruiting branches were produced even on nonpruned trees. The pillar canopy was 60% thinner and required 50% fewer pruning cuts than the standard canopy and may be particularly suited to high-density plantings (HDPs). The upper canopy of weeping trees grew more than most other forms. They were intermediate in branch density and required an intermediate amount of pruning. Most striking was the unique canopy form of weeping trees, which may be used in developing new training systems. The results of this study suggest that new growth forms have the potential to reduce pruning and training requirements for peach, particularly in MDPs and HDPs. This potential suggests further investigation and exploitation of alternate peach tree growth forms.
Four peach [Prunus persica (L.) Batsch] scion cultivars, `Jerseyqueen', `Redskin', `Suncrest', and `Sunhigh', that were propagated by tissue culture techniques and by bud-grafting onto `Lovell' seedlings, were compared at Kearneysville, W.Va., and at Beltsville, Md. At Kearneysville, total fruit production was higher for tissue-cultured (TC) trees when compared with budded trees in the first 3 years of fruiting, whereas trunk diameter increases were generally larger for budded trees. In the following year, fruit production was similar for both TC and budded trees, although trunk diameter increases continued to be larger for budded trees. At Beltsville, fruit production was significantly higher for TC trees in 1987, the first fruiting season, but the same for both in the second season. Trunk diameter increases were larger for budded trees both years. Differences in tree growth and productivity in the early years of orchard establishment appeared to be related to the size of plants that were planted. Budded trees, which were smaller than TC trees at planting, increased in size faster than TC trees but were less productive. Crop efficiency was cultivar-specific, but differences among cultivars was less if trees were TC propagated. These results suggested that based on yield and growth, own-rooted TC trees should be an acceptable tree type for commercial orchards.
Two unpruned narrow-leaf and two unpruned standard-leaf peach [Prunus persica (L.) Batsch.] selections were evaluated for physiological components related to water use efficiency {WUE [carbon assimilation (A) per unit of transpiration (T)]}. The purpose of the study was to assess the value of narrow-leaf phenotypes to improve WUE in peach and separate the environmental component of canopy geometry from the genetic components. The narrow-leaf characteristic itself did not confer improved WUE. The interception of light was a key determinant of WUE in these genotypes. Internal shading of the tree by excessive leaf area reduced daily WUE measured in gas exchange studies. Canopies that intercepted more than 75% of the photosynthetically active radiation (PAR) had reduced daily WUE. Dormant season pruning of the four genotypes lowered isotopic carbon discrimination and therefore increased seasonal WUE compared to unpruned trees. None of the genotypes had a significant correlation of seasonal WUE with leaf and fruit weight. Analysis of covariance indicated that `Bounty' and both narrow-leaf genotypes had greater leaf and fruit weight than `Redhaven' for a given level of PAR interception. `Bounty' had the least internal canopy shading of the four genotypes. Genetic differences in peach growth types can be selected for factors increasing WUE as well as increased productivity. Future work in peach breeding to improve WUE and productivity must take into consideration light interception, productivity, and WUE in an integrated manner to make real progress in the efficient use of water and light in the orchard environment.
Damage by lesser Peachtree borer (LPB) (Synanthedon pictipes Grote & Robinson) and Leucostoma canker that had accumulated during 6 (Orchard A) and 8 (Orchard B) years were compared in peach (Prunus persica L.) and peach-almond [P. amygdalus (Mill.) D. A. Webb] hybrids. Afterward, the main trunk and scaffold limbs of the trees received 10 wounds 26 mm in diameter and a subset of these trees in Orchard A had wounds inoculated with Leucostoma persoonii Hohn. Before wounding, Leucostoma canker infection and LPB infestations that had accumulated for 6 to 8 years on peach-almond hybrids was ≈60% and 98% less than on peach in Orchard A and B, respectively. One month after wounding the trees, no significant differences in Leucostoma canker infection and LPB infestations were found among the peach-almond hybrids, treated or not treated with L. persoonii, or untreated peach. Yet, Leucostoma- treated and untreated peach-almond hybrids had 33% and 25% less Leucostoma canker and LPB, respectively, when compared with Leucostoma- treated peach. Ten months after wounding, peach-almond hybrids treated with L. persoonii still had significantly less Leucostoma canker (60%) and LPB (25%) when compared with Leucostoma- treated peach. Wound gumming and wound closure rates seemed to influence the degree of LPB infestation and Leucostoma canker. Based on these data, peach-almond hybrids could be valuable sources of resistance to LPB and Leucostoma canker.
Radius of gyration (size), intrinsic viscosity, molecular weight, percentage of galacturonate, and percentage of neutral sugars were measured for chelate-soluble (CSP) and alkaline-soluble (ASP) pectins extracted from the cell walls of melting flesh (MF) and nonmelting flesh (NMF) peach [Prunus persica (L.) Batsch]. Weight percentage of cell walls, pectin content, and firmness were measured also. Peaches were extracted at 20, 21, and 22 weeks after flowering (WAF) and after various lengths of shelf storage at 25 ± 2C for the peaches picked at 21 WAF. Weight percentage of cell walls and firmness decreased markedly between the 21st and 22nd WAF; and between the 3rd and 6th day of storage for MF peaches as compared to NMF peaches. During these same periods, there were marked drops in the pectin content and the uronide content for MF as compared to NMF peaches. Size and intrinsic viscosity dropped markedly for CSP of MF peaches in comparison with NMF peaches during these same periods, whereas the molecular weight of CSP and ASP increased in MF peaches over that measured for NMF peaches. These results suggested that α -D-galacturonase (E.C. 3.2.1.15) was involved in softening only in the latter stages of ripening MF peaches. Further, cell wall polymers containing long thin pectin aggregates were destroyed, whereas cell wall polymers containing short thick pectin aggregates remained.
The evergreen (EVG) peach, first described in Mexico, was used as a parent with deciduous (DE) peaches to develop F1 and F2 hybrid populations in Mexico, Florida, Georgia, and West Virginia. F1 trees were DE and F2 plants segregated 3 DE: 1 EVG. In West Virginia, the most temperate location, the heterozygous class could be distinguished in the first few years of growth by late leaf abscission in the fall. Segregation ratios suggest that the EVG trait is controlled by a single gene, evg, the EVG state being homozygous recessive. Evergreen trees were characterized by insensitivity of shoot tips to daylength and failure of terminal growth to cease growth until killed by low temperature. Lateral buds of EVG trees went dormant in the fall. Deep supercooling occurred in both EVG and DE trees, but it appeared later in EVG trees, was of shorter duration, and occurred to a lesser extent. Evergreen germplasm may be useful in developing peach cultivars for frost-free subtropic and tropical areas. It also presents a useful system for studying dormancy and cold hardiness.
Abstract
Sample sizes for detection of differences of flower bud survival in peach and nectarine [Prunus persica (L.) Batsch] were chosen on the basis of theoretical confidence intervals (Cl) and least detectable differences (LDD) for the binomial distribution. Theoretical Cl and LDD for 1000-bud samples were comparable to Cl and Duncan's multiple range test separation computed from an analysis of variance for 1000 buds, based upon 10 replicates of 100 buds. Variability in survival was a function of eultivar, height of bud in canopy, and bud type. Variability may be minimized by sampling a given bud type (single, double, distal) at >1.5 m above ground level.
`Wisconsin 38' tobacco (Nicotiana tabacum L.) leaf discs were transformed with the disarmed Agrobacterium tumefaciens strain EHA101 carrying the rolC gene from A. rhizogenes (Oono et al., 1987) and NPT II and GUS genes. Shoots that regenerated on kanamycin-containing medium were confirmed as transgenic through GUS assays, polymerase chain reaction (PCR), Southern blot analyses, and transmission of the foreign genes through the sexual cycle. Transgenic plants were as short as half the height of control plants; were earlier flowering by up to 35 days; and had smaller leaves, shorter internodes, smaller seed capsules, fewer seeds, smaller flowers, and reduced pollen viability. The number of seed capsules, leaf number, and specific root length were similar between transgenic and control plants. Transgenic clones varied in the expression of the rolC-induced growth alterations as did the first generation of seedlings from these clones. Such differences suggested the potential for selecting for different levels of expression. Transformation with the rolC gene presents a potentially useful method of genetically modifying horticultural crops, particularly for flowering date, height, and leaf and flower size. Chemical names used: neomycin phosphotransferase (NPTII), β-glucuronidase (GUS).
Transgenic grape plants were regenerated from somatic embryos derived from leaves of in vitro-grown plants of `Thompson Seedless' grape (Vitis vinifera L.) plants. Somatic embryos were either exposed directly to engineered Agrobacterium tumefaciens or they were bombarded twice with 1-μm gold particles and then exposed to A. tumefaciens. Somatic embryos were transformed with either the lytic peptide Shiva-1 gene or the tomato ringspot virus (TomRSV) coat protein (CP) gene. After cocultivation, secondary embryos proliferated on Emershad/Ramming proliferation (ERP) medium for 6 weeks before selection on ERP medium containing 40 μg·mL-1 kanamycin (kan). Transgenic embryos were identified after 3 to 5 months under selection and allowed to germinate and develop into rooted plants on woody plant medium containing 1 μm 6-benzylaminopurine, 1.5% sucrose, 0.3% activated charcoal, and 0.75% agar. Integration of the foreign genes into these grapevines was verified by growth in the presence of kanamycin (kan), positive β-glucuronidase (GUS) and polymerase chain-reaction (PCR) assays, and Southern analysis.