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Carol D. Robacker and Sloane M. Scheiber

Abelia ×grandiflora is a hardy shrub in the landscape, surviving heat and drought with few pest problems. However, improved cultivars with better form, the ability to retain foliage during drought, and unique flowering and foliage characteristics are in demand. `Plum Surprise' is a new cultivar of Abelia that was developed at the University of Georgia in response to these needs. `Plum Surprise' is a seedling selection from the cross `Edward Goucher' × `Francis Mason'. It forms an unusual weeping, spreading mound with fine-textured foliage. In March and April, foliage is yellow-green with scattered red/purple leaves. In late spring, the foliage becomes emerald green, changing to a lighter green throughout the summer. New stem growth is red. The most striking features of `Plum Surprise' are the fall and winter foliage color and the evergreen habit of the cultivar. As autumn progresses, the outer shoots and leaves transform to red/purple or crimson, while the inner foliage is bright emerald green. Foliage is glossy in the winter, and a deep purple or burgundy color. `Plum Surprise' is a relatively light bloomer, with flowers scattered individually or in pairs. The flowers appear white, but on close examination have a purple blush with a pale yellow throat. `Plum Surprise' is noteworthy for its heat and drought tolerance. In both the summers of 2002 and 2005, when check cultivars had lost 50% to 80% of their foliage, `Plum Surprise' exhibited little leaf drop. `Plum Surprise' performs well in a pot under nursery conditions. The foliage cascades down over the pot, making an attractive appearance in both form and color.

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G. Tehrani and W. Lay

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David W. Ramming and Owen Tanner

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Ralph Scorza and Harold W. Fogle

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Richard H. Uva, Thomas H. Whitlow, and William F. Clark

Beach plum is a shrub native to Atlantic coastal sand dunes from Maine to Maryland, where it is subject to drought and low nutrient and water holding soil. Since colonial times beach plum fruit has been collected from the wild for the production of preserves, an activity that endures today as a cultural tradition and cottage industry. Currently, the supply of fruit from wild stands does not meet the market's demand; hence, beach plum could be a new crop for many growers in the Northeastern U.S. For the past 4 years, a partnership of growers, Univ. of Massachusetts Extension, and Cornell Univ. has experimented with standard orchard cultural methods for beach plum production in coastal Massachusetts. During Aug. 1999, we harvested the first crop from our experimental orchard. The factorial experiment evaluates the effects of irrigation, mulch, and fertilizer on growth and yield of beach plum. Basal and axial growth were strongly correlated and were greater in fertilized than unfertilized treatments. Within fertilizer regime irrigation and mulch had less effect on growth than fertilizer. Fruit yield (dry weight and fresh weight) was greater in fertilized plots. Irrigation had no positive influence on yield. Average fruit diameter and °Brix were greater in the fertilized and unirrigated treatments.

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C.H. Crisosto, W.A. Retzlaff, L.E. William, T.M. DeJong, and J.P. Zoffoli

We investigated the effects of three seasonal atmospheric ozone (0,) concentrations on fruit quality, internal breakdown, weight loss, cuticle structure, and ripening characteristics of plum fruit from 3-year-old `Casselman' trees in the 1991 season. Trees were exposed to 12-hour daily mean O3 concentrations of 0.034 [charcoal-filtered air (CFA)], 0.050 [ambient air (AA)], or 0.094 [ambient plus O3 (AA+O)] μl·liter-1 from bloom to leaf-fall (1 Apr. to31 Oct. 1991). Fruit quality and internal breakdown incidence measured at harvest and after 2, 4, and 6 weeks of storage at 0C were not affected by any of the O3 treatments. Following an ethylene (C2H4) preconditioning treatment, the rate of fruit softening, C2H4 production, and CO, evolution was higher for plums harvested from the AA + O than from those grown in CFA. Weight loss of fruit from the AA + O exceeded that of fruit from CFA and AA. Anatomical studies of mature plums indicated differences in wax deposition and cuticle thickness between fruit grown in AA + O, AA, and CFA. Differences in gas permeability, therefore, may explain the difference in the ripening pattern of `Casselman' plum fruit grown in high atmospheric O3 partial pressures.

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Agustín Rumayor-Rodríguez

The annual yield variation in a Japanese plum (Prunus salicina Lindl.) germplasm collection [with 32 cultivars (cv)] was used to generate regression models to describe fruit yields in terms of climate. A Geographic Information System (GIS) combined with generated regression models was used for a regional analysis of potential areas for growing plums in Zacatecas, Mexico. Three distinct cv groups were obtained by principal component analysis and were included in the study: a) `Frontier'–`Santa Rosa', b) `Ozark Premier'–`Burbank', and c) `Shiro'. The amount of winter chilling and temperatures during bloom time were the climatic conditions most related to yield. `Frontier'–'Santa Rosa' had relatively low chilling requirements (700 chill units) compared to `Ozark Premier'–`Burbank', which required the most chilling (900 chill units). `Shiro' yields were more consistent than those of the other two groups, suggesting that it has less strict requirements and received sufficient chilling every year. High temperatures at bloom reduced fruit yield in all cultivars; however, the dependence of yield on temperatures during bloom in `Shiro' was modified by summer temperatures the previous year, suggesting that temperatures at the floral induction and formation stages affect flower primordia development. Using GIS, three potential areas for growing plums in the region were defined on maps, and the differences in potential yield between the cultivar groups were determined. `Frontier'–`Santa Rosa' may be good choices as plum cultivars for the region because they were the cultivars with the highest potential yield in the largest area; however, the flexibility of the method used allows the user to get a regional gradient of the expected yields with several plum cultivars. Using experimental information and a GIS can extend the applicability of germplasm collection data to regional planning in the establishment of orchards and new fruit industries.

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W.T. Liu, C.L. Chu, and T. Zhou

Fumigation with 1 mg·L-1 of thymol vapor retarded mycelial growth of Monilinia fructicola (G. Wint.) Honey. Mean colony diameter was reduced from 49 mm in the control to 13 mm when the conidia were cultured on potato dextrose agar. Fumigation of apricots (Prunus armeniaca L.) with 2 mg·L-1 of thymol vapor reduced the germination of M. fructicola conidia to 2% compared with 98% on untreated fruit. Microscopic observations showed that the spores fumigated with thymol were shrunken and had collapsed protoplasts. In in vivo experiments, surface-sterilized apricots and plums (Prunus salicina L.) were inoculated with conidia of M. fructicola by applying 20 μL of a spore suspension to wounds on the fruit, and then were fumigated with thymol or acetic acid. The incidence of brown rot was reduced to 3% and 32% when `Manch' apricots were fumigated with thymol or acetic acid at 5 mg·L-1, respectively, compared with 64% incidence in untreated fruit. Fumigation of `Violette' plums with thymol or acetic acid at 8 mg·L-1 reduced brown rot from 88% in the control to 24% and 25%, respectively. Fumigation of `Veeblue' plums with thymol at 4 mg·L-1 reduced brown rot from 56% in the control to 14%. Fumigation of apricots with thymol resulted in firmer fruit and higher surface browning, but total soluble solids and titratable acidity were not affected. Fumigation of plum with thymol resulted in higher total soluble solids, but firmness and titratable acidity were not affected. Thymol fumigation caused phytotoxicity on apricots but not on plums.

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W.A. Retzlaff, L.E. Williams, and T.M. DeJong

Nursery stock of plum (Prunus salicina Lindel., `Casselman') was planted 1 Apr. 1988 in an experimental orchard at the Kearney Agricultural Center, Univ. of California, near Fresno. The trees were enclosed in open-top fumigation chambers on 1 May 1989 and exposed to three atmospheric ozone partial pressures (charcoal-filtered air, ambient air, and ambient air + ozone) from 8 May to 15 Nov. 1989 and from 9 Apr. to 9 Nov. 1990. Trees grown outside of chambers were used to assess chamber effects on tree performance. The mean 12-hour (0800-2000 hr Pacific Daylight Time) ozone partial pressures during the 2-year experimental period in the charcoal-filtered, ambient, ambient + ozone, and nonchamber treatments were 0.044, 0.059, 0.111, and 0.064 μPa·Pa-1 in 1989 and 0.038, 0.050, 0.090, and 0.050 pPa·Pa-1 in 1990, respectively. Leaf net CO2 assimilation rate of `Casselman' plum decreased with increasing atmospheric ozone partial pressure from the charcoal-filtered to ambient + ozone treatment. There was no difference in plum leaf net CO2 assimilation rate between the ambient chamber and nonchamber plots. Trees in the ambient + ozone treatment had greater leaf fall earlier in the growing season than those of the other treatments. Cross-sectional area growth of the trunk decreased with increasing atmospheric ozone partial pressures from the charcoal-filtered to ambient + ozone treatment. Yield of plum trees in 1990 was 8.8, 6.3, 5.5, and 5.5 kg/tree in the charcoal-filtered, ambient, ambient + ozone, and nonchamber treatments, respectively. Average fruit weight (grams/fruit) was not affected by atmospheric ozone partial pressure. Fruit count per tree decreased as atmospheric ozone partial pressure increased from the charcoal-filtered to ambient + ozone treatment. Decreases in leaf gas exchange and loss of leaf surface area were probable contributors to decreases in trunk cross-sectional area growth and yield of young `Casselman' plum trees during orchard establishment.

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Unaroj Boonprakob and David H. Byrne

Six controlled crosses of cultivated and advanced selection Japanese-type plums adapted to southeast and southwest regions of the United States were made in 1990 and 1991. Over 800 seedlings from these crosses along with open pollinated seedlings of the parents were established in Suiting nurseries. The long range objective of this study is to determine linkage relationships between RAPD markers and commercially important traits (soluble solid, resistance to bacterial leaf spot, chilling requirement, fruit development period). The first step in the projects to characterize RAPD genotypes in the progenies. Eighty oligodecamers have been screened and 57 yielded successful reactions with an average of two to three bands per primer. The variability and inheritance of the RAPD markers in these plum populations will be described.