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James P. Romer, Jeffery K. Iles, and Cynthia L. Haynes

Crabapples (Malus spp.) are commonly planted ornamental trees in public and private landscapes. Hundreds of selections are available that represent a wide range of growth habits, ornamental traits, and varying degrees of resistance/susceptibility to disease. We distributed 1810 questionnaires in 13 states (Oregon, Washington, Utah, Colorado, Minnesota, Iowa, Missouri, Illinois, Indiana, Michigan, Ohio, New York, and Pennsylvania) to members of either nursery and landscape associations or the Associated Landscape Contractors of America (ACLA, Herndon, Va.) to identify crabapple preferences across a broad geographic region of the United States. We also were interested in learning if regional disease problems were important to green-industry professionals as they decide which crabapples to include in their inventories. Our respondent population numbered 511 (28.2% response rate). A large percentage of respondents (79.4%) said their retail clients focused mostly on fl ower color when choosing crabapples for the home landscape, while commercial clients showed slightly more interest in growth habit (32.5%) than fl ower color (28.7%). `Prairifire' was identified by respondents in all regions, except the west-central (Colorado and Utah), as the crabapple most frequently recommended to clients when tree size is not important. Respondents in the west-central region most often (48.7%) recommend the fruitless selection `Spring Snow'. Respondents in all regions, except the west-central, identified apple scab (Venturia inaequalis) as the most prevalent crabapple disease and named scab-susceptible `Radiant' as the selection most frequently discontinued.

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Iwan F. Labuschagné, J.H. Louw, Karin Schmidt, and Annalene Sadie

Significant response to selection for budbreak number (NB) based on data recorded on 1-year-old shoots of young apple (Malus sylvestris (L.) Mill var. domestica (Borkh.) Mansf.) seedlings (Expt. I) and branches from adult seedling trees (Expt. II) has been demonstrated in clonally propagated seedling trees. Between family variation for NB was low and masked by year × family interaction effects. Realized heritability for NB was estimated as 40% to 60%. Correlated response in uniformity and position of budbreak, and in the number and length of side shoots, was found. Association between the time of budbreak (TB) and NB, according to midparent and cross groupings, and according to the parental means, indicate a positive genetic correlation between these traits. Where data on adult trees were used as a measure of selection response and tested on young clonal trees, significant response and genetic variation was shown, confirming the presence of utilizable genetic variance and that this procedure may be successfully applied as an early screening method for increased budbreak in adult trees. Combined selection utilizing genetic variance between crosses as well as within crosses is proposed as the best procedure to increase the frequency of seedlings with increased budbreak and to improve adaptation to low winter chilling conditions.

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Asadolah Aslani Aslamarz, Kourosh Vahdati, Majid Rahemi, Darab Hassani, and Charles Leslie

cause injury and subsequently economic losses. Available data for the frost tolerance, supercooling, and cold acclimation of walnut cultivars and selections, especially Iranian native selections, are scarce. This study was conducted to screen a range of

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B.S. Wilkins, R.C. Ebel, W.A. Dozier, J. Pitts, D.J. Eakes, D.G. Himelrick, T. Beckman, and A.P. Nyczepir

Twelve peach [Prunus persica (L.) Batsch] seedling rootstocks [Lovell, Nemaguard, Flordaguard, 14DR51, five Guardian™ (BY520-9) selections, and three BY520-8 selections] budded with `Cresthaven' were planted in 1994 and evaluated through 2000 to determine performance under commercial management practices. Mesocriconema xenoplax population densities were above the South Carolina nematicide treatment threshold of 50 nematodes/100 cm3 of soil after 1996. However, symptoms of peach tree short life (PTSL) were not observed. Tree mortality was less than 14% through 1999, with most of the dead trees exhibiting symptoms consistent with Armillaria root rot. About 13% of the surviving trees in 1999 were removed in 2000 due to symptoms of phony peach. There were no differences in tree mortality among rootstocks. Tree growth, photosynthesis, and suckering varied among rootstocks, but leaf conductance, internal CO2, and leaf transpiration did not. Foliar calcium, magnesium, iron, and phosphorus varied among rootstocks, but all were within the range considered sufficient for peach trees. Fruit yield varied among rootstocks, but yield efficiency did not, indicating that higher yield corresponded with larger trees. Bloom date did not vary among rootstocks, but harvest date was advanced as much as 2 days for some rootstocks, compared to Lovell. Fruit weight varied among rootstocks but skin color, flesh firmness, and soluble solids content were similar. All rootstocks performed satisfactorily for commercial peach production.

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Shiow Y. Wang, Gene J. Galletta, and John L. Maas

Fruit quality of 24 selected strawberry cultivars and selections were evaluated. There were great variations in the contents of soluble solids, titratable acidity, carbohydrates, organic acids, and ascorbic acid among different cultivars, reflecting primary genetic differences. Fructose, glucose, and sucrose were found to be the three major sugars, comprising >65% of the total soluble solids in strawberry. Fruit contained lower sucrose compared to fructose and glucose, whereas leaves contained comparable amounts of fructose, glucose, and sucrose. Citric acid was the major organic acid in strawberries. Strawberries were also rich in ascorbic acid. Leaves were much higher in ascorbic acid than fruit. There appeared to be no correlation between fruit and leaves on carbohydrate, organic acid, and ascorbic acid contents.

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Peng Shi

Seedling selections in pomegranates began in 1986. `Giant Green Sweet' (GGS) was used as the female parent. GGS was characterized by fruit size from 340 to 500 g, a green color with slight blush, thin fruit coat, hexalobate calyx, and semi-open ovary with 8 to 12 loculi. The seeds are red, abundant, juicy, and sweet. The seeds contain 15% to 16% soluble solids. The male, pollinating cultivars in the same garden were `Giant Red Sweet', `Giant Horse Teeth', `White Sweet', `Red Sour', `Bing Tang Zi', and `Qing Gang Liu'. Seeds were harvested from fruit that were open-pollinated and weighed 500 g. Seeds were germinated and planted at the end of March. One-year-old seedlings grew to 30 to 50 cm. Two-year-old seedlings grew to 1 to 1.5 m tall with many branches. Seedlings passed the juvenile period after 3 years of growth. Some seedlings blossomed, and a few blossoms developed into fruit. Seedlings were adult by the fourth year, and all of them blossomed and developed fruit. This is a shorter interval to maturation than the parent cultivars. Fruits were located from the lower middle of the tree crown to the top. Adult seedlings produced fruit of ≈400 g with a few seedlings producing fruits of 500 to 600 g. There were 400 to 500 seeds per fruit averaging 40 g per 100 seeds. Seeds from the offspring were bright red and larger than those of the female parent. Fruit flavor was similar to the female parent. Offspring were more cold hardy than the parent cultivars. There were no signs of cold injury in hybrid seedlings to –19°C. This study indicates that seedling selection in pomegranates has a high potential to create higher yield and quality pomegranates. Continuing experiments will reselect the best offspring to develop higher quality cultivars.

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R. Neal Peterson

The pawpaw (Asimina triloba) is a new crop in the early stages of domestication. Recently commercialization has become feasible with the availability of high quality varieties. The history of pawpaw varieties is divided into three periods: 1900-50, 1950-85, and 1985 to the present. The history before 1985 was concerned primarily with the discovery of superior selections from the wild but experienced a serious break in continuity around 1950. The third period has been characterized by greater developmental activity. Larger breeding programs have been pursued, regional variety trials initiated, a germplasm repository established, and a formal research program at Kentucky State University (KSU) instituted. Future breeding will likely rely on dedicated amateurs with the education and means to conduct a 20-year project involving the evaluation of hundreds of trees. For the foreseeable future, governments and universities will not engage in long-term pawpaw breeding.

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Vidyasagar R. Sathuvalli, Shawn A. Mehlenbacher, and David C. Smith

’, conferred by a dominant allele at a single locus ( Mehlenbacher et al., 1991 ), has been extensively used in the hazelnut breeding program at Oregon State University (OSU). Most resistant selections from the breeding program carry ‘Gasaway’ resistance. In

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Iwan F. Labuschagné, J.H. Louw, Karin Schmidt, and Annalene Sadie

Genetic variation in chilling requirement was investigated over three growth periods using clonal progenies of six apple [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] families derived from crosses of high and low chill requiring cultivars. Two quantitative measurements related to chilling requirement, viz., the time of initial budbreak (vegetative and reproductive) and the number of breaking buds over a specified time interval, were used as evaluation criteria. Genetic and environmental variances of the traits are presented as intra-class correlation coefficients for clones within and between families. For budbreak time, reproductive and vegetative, broad-sense heritability averaged around 75% and 69% respectively, indicating a high degree of genetic determination in this material. For budbreak number, moderate to low genetic determination was found with broad-sense heritabilities around 30%. Estimates of genetic components of variance between families were generally very low in comparison to the variance within families and predict potentially favorable responses to truncation selection on the traits within these progeny groups. Analysis of the data showed that distribution of budbreak time is typical of quantitative traits with means distributed closely around midparent values. Skewed distributions towards low budbreak number were obtained in varying degrees in all families.

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Ricardo Goenaga, Heber Irizarry, and Brian Irish

obtained from a few unique segregating ‘F 1 ’ trees. Additionally, the yield data needed from long-term experiments to validate this assumption are not available. Lockwood et al. (2007) observed that the optimal strategy for clone selection is by family