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W.R. Okie and A.P. Nyczepir

Roots of dormant peach trees can grow when soil temperatures are >7 °C, which commonly occurs in the southeastern U.S. during the winter. In our tests, root growth on 1-year-old nursery trees was minimal at 7 °C, and increased with temperature up to at least 16 °C, but rootstocks varied greatly in their regeneration at a given temperature. Trees on seedling rootstocks of `Guardian™', `Halford' and `Lovell' regenerated roots more slowly than those on `Nemaguard' at soil temperatures >7 °C. The regeneration rates mirrored the relative susceptibility of these rootstocks to peach tree short life syndrome in the southeastern U.S., which is associated with parasitism by ring nematode.

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W.R. Okie and D.J. Werner

Spring frosts often kill all or a portion of the flowers on peach [Prunus persica (L.) Batsch] trees in the southeastern United States. Increased flower bud density increases the likelihood of sufficient flowers surviving to produce a crop. The effect of environment on flower bud density (buds/node) was studied using two locations over 3 years. Bud density of 25 peach and nectarine varieties grown in completely randomized designs was measured in Georgia and North Carolina. Genotypic variability was greater than location or year effects. Varieties selected for high bud density at one location can be expected to have high densities at other locations with similar chilling.

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W.R. Okie, W.R. Joyner, and T.G. Beckman

Large field plantings are often difficult to label and to plant randomly. A DOS computer program was developed in SAS and BASIC to randomize lists of experimental factors and print sorted paper labels to apply to trees or plants. Tagged trees can be resorted readily by block or row to speed planting. The computer lists are useful for plot verification and subsequent data collection, especially if data are collected and inputted directly to a computer. Copies of the programs are available from W.R. Joyner if a formatted diskette and self-addressed mailer are supplied.

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Desmond R. Layne*, W.R. “Dick” Okie, and Eric J. Hitzler

The evaluation of peach and nectarine cultivars and advanced selections for suitability of production in the southeastern U.S. has been conducted at Clemson Univ. since 2000. Currently, there are 240+ cultivars and advanced selections being tested at the university's Musser Fruit Farm in Seneca, S.C. The harvest season begins in early May and ends in the middle of September. Additionally, two on-farm grower trials were planted in the primary peach growing regions of the Piedmont (Cowpens, S.C.) and the Ridge (Monetta, S.C.). At the grower locations, advanced selections are compared with industry standard cultivars. Evaluation data collected includes bloom and ripe date, fruit set, shape, color, size, firmness, taste and disease susceptibility. Digital photos are taken to scale at commercial maturity. Evaluation information, photos, plus chill hours, variety descriptions and other valuable information are on the website. In 2004, substantial improvements were made to the site utilizing a database, search and compare tools. The website has been well received by the southeastern commercial peach growers and is utilized to assist them in cultivar selection and to learn more about peach culture in general.

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D. Michael Glenn, R. Scorza, and W.R. Okie

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.

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W.R. Okie, T. G. Beckman, and A.P. Nyczepir

Lovell rootstock is recommended for Peach Tree Short Life (PTSL) sites in the Southeast because it outlives Nemaguard. No genetic studies of PTSL tolerance have been done. Clonally replicated peach seedlings [Prunus persica (L.) Batsch] of Lovell, Nemaguard and four F1 selections of Lovell × Nemared were tested for field survival in a high density planting on a PTSL site. Rootstock families (12 seedlings × 8 ramets each) differed in growth, survival and longevity. Genetic variation was comparable to environmental variation for most families. Based on seedling within rootstock family, estimated broad-sense heritabilities for survival and longevity were high. The use of clonally replicated seedlings allowed the selection of apparently superior individuals from both Lovell and the other more short-lived rootstock families in a single screening after 6 years. Survival of Lovell at that time was 50% compared to 16-29% for other families. Across all families, all 8 ramets were dead for 21 seedlings, whereas all 8 were alive for only 3 seedlings.

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W.R. Okie, J.A. Robertson, and F.I. Meredith