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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.
A chimeric, willow-leaf mutation of a standard peach [Prunus persica (L.) Batsch.] phenotype was evaluated for its water use efficiency (WUE). The willow-leaf phenotype had greater WUE than its standard-leaf parent under both nonstressed and well-watered conditions, and this was supported by isotopic carbon discrimination. Under water-stress conditions, willow-leaf trees developed less water potential gradient from the roots to the leaves. The mechanisms associated with increased WUE by the willow-leaf phenotype include a reduced water potential gradient within the plant and uncoupling of the leaf from the aerial environment. Willow-leaf peach trees in seedling populations, descended from a different willow-leaf parent, also had reduced carbon isotopic discrimination than did sibling standard-leaf seedlings.
The objective was to study selected physiological characteristics of the canopy and examine changes in dry matter partitioning between the root and shoot in two genetically reduced size growth types (dwarf and pillar) relative to the standard growth type. The dwarf phenotype had reduced leaf/root ratio, less allocation of dry matter to woody tissue and more to leaf tissue, high net photosynthesis, and lower leaf respiration compared to the standard and pillar phenotypes. The dwarf and pillar types had greater resistance to water flow than the standard type. Genetic changes in growth habit significantly alter many physiological parameters of peach tree growth and structure.
Abstract
Stone fruit breeding programs by the USDA have been a major source of improved peach and nectarine cultivars. A nearly complete turnover has occurred in locations, personnel, and cultivars in the 23 years since Havis reviewed these programs (15). It is appropriate to review the changes and note the progress that has been made in the last 2 decades.
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.
Flow cytometric analysis, of leaf nuclei from three cultivars, was used to estimate the DNA content of peach (∼0.61 pg or ∼0.59 × 109 bp/diploid nucleus; 2x=16), and ndicated that the peach genome is only slightly larger than that of Arabidopsis. This value was indirectly confirmed by measurements of nuclei from haploid, triploid and “tetraploid” (cytochimera) peach accessions. cDNA and genomic clones have been used to determine the level of polymorphism among various peach cultivars and related species. Overall, ∼33% of the clones detected polymorphic loci. As expected, the highest level of polymorphism was found in interspecific hybrids (∼50%); whereas in intraspecific populations, only 1 in 5 genomic clones, and 1 in 3 cDNA clones were able to detect polymorphisms (RFLPs). These clones, as well as RAPD primers, are being used to construct a genetic linkage map by analyzing their segregation in 3 intraspecific peach populations (an Fl from France and two F2s from the U.S.). Taken together, these populations are segregating for 12 Mendelian traits and a number of quantitative traits. Our results have enabled us to identify a number of linkage groups, some composed of both molecular and phenotypic markers. The current structure of the peach map is reported.
The lack of dwarfing rootstocks for peach has led to cultural and genetic approaches that reduce tree size and vegetative growth to establish high-density plantings. The objectives of the study were to evaluate the interactions of pruning strategies, groundcover management, tree densities, and peach (Prunus persica) architecture combined in eight peach production systems on components of yield and economic value. The use of sod management reduced pruning time and costs, but the reduction of crop load reduced net return. High-density plantings in large vegetation-free areas (VFAs) had greater economic return than low-density plantings.
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.
Two unpruned willow leaf and two unpruned standard leaf peach [Prunuspersica(L.) Batsch.] selections were evaluated for physiological components related to water use efficiency (WUE). The purpose of the study was to assess the value of willow leaf phenotypes to improve water use efficiency in peach and separate the environmental from the genetic components. The willow leaf characteristic itself did not confer improved water use efficiency. Light interception was a key determinant of WUE in these genotypes and the relationship of WUE with intercepted photosynthetically active radiation (PAR) by the entire canopy indicated a significant negative correlation. Internal shading of the tree by excessive leaf area reduced WUE and canopies that intercept more than 60% of the PAR have reduced WUE. While WUE is improved by reducing the amount of PAR interception of the canopy, productivity is reduced. Neither of the willow leaf genotypes had a significant correlation of WUE with yield (leaf and fruit weight); however, the standard leaf type cultivars, `Bounty' and `Redhaven', had significantly different regressions that indicate greater productivity in `Bounty' for a given level of WUE. `Redhaven' was the least productive cultivar; `Bounty' was the most productive, and the two willow leaf genotypes were intermediate in the relationship of intercepted PAR with yield. Therefore, genetic differences in peach growth types can be selected for both increased 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 progress in the efficient use of water and light.