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Dennis J. Werner

Catalase isozymes were examined in a wide range of peach [Prunus persica (L.) Batsch] cultivars representing historical U.S. cultivars, commercial cultivars from numerous North American breeding programs, and the peach plant introduction (PI) collection. All historical peach cultivars from the United States and those released from commercial breeding programs were fixed for the slow (Cat l-2) allele, with the exception of `Belle of Georgia', `Honeyglo' nectarine, and various cultivars from the Univ. of Florida breeding program, which possessed a fast-migrating (Cat 1-l) allele in homozygous or heterozygous state. Polymorphism was revealed in the 51 peach PI clones examined, with allelic frequencies of 0.69 and 0.31 for the Cat l-2 and Cat l-1 alleles, respectively. Most PIs that originated directly from China were homozygous Cat l-l/Cat l-l, while most PI clones introduced from Europe were homozygous Cat l-2/Cat l-2. Examination of the catalase genotype of cultivars previously proposed as the possible male parent of `Belle of Georgia' (`Champion', `Early Crawford', `Late Crawford', `Oldmixion Free', and `Stump-the-World') revealed that none of these cultivars could have been the male parent of `Belle of Georgia'. Segregation data from various peach crosses was consistent with the hypothesis that catalase polymorphism could be explained by the presence of two alleles at a single locus.

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David J. Roberts and Dennis J. Werner

Cercis is an ancient member of Fabaceae, often cultivated as an ornamental tree, and can be found in numerous regions around the world. Previous studies have reported Cercis canadensis as being diploid with 2n = 2x = 14. However, there have been no further investigations into ploidy and genome size variation among Cercis taxa. A study was conducted to evaluate the relative genome size and ploidy levels of numerous species, cultivars, and botanical varieties of Cercis, representing taxa found in North America, Asia, and the Middle East. In addition, the genome size of Bauhinia forficata, a close relative of Cercis, was also determined. Genome size estimates (2C values) were determined by calculating the mean fluorescence of stained nuclei via flow cytometry. Propidium iodide was used as the staining agent and Glycine max was used as an internal standard for each taxon analyzed. Genome size estimates for all Cercis sampled ranged from 0.70 to 0.81 pg with an average size of 0.75 pg. The genome size of B. forficata was found to be smaller than any other Bauhinia sp. currently on record, with an average size of 0.87 pg. This study confirmed an initial estimation of the genome size of Cercis chinensis and found that floral buds of Cercis proved to be an excellent source of plant tissue for obtaining intact nuclei. All species, botanical varieties, and cultivars of Cercis surveyed for this study had remarkably similar genome sizes despite their wide range of distribution. This information can facilitate a better understanding of phylogenetic relationships within Cercideae and Cercis specifically.

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Michael A. Creller and Dennis J. Werner

Surface morphology of peach [Prunus persica (L.) Batsch] Plant Introduction 133984 (`Marina') differs from standard peach and nectarine clones. Scanning electron microscopic examination of `Marina', a standard peach (`Contender'), and a nectarine (`Sunglo') was conducted. At anthesis, `Marina' ovaries were glabrous, similar to `sunglo' nectarine. Fruit of `Contender' were fully pubescent at anthesis. Examination of `Marina' fruit two weeks after anthesis revealed the presence of both pubescent and glabrous sectors on the fruit surface. At fruit maturity, most of the fruit surface of `Marina' was covered with pubescence, but trichome density was considerably less than `Contender' peach. Trichome morphology of `Marina' differed from that of `Contender'.

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Dennis J. Werner and Dana F. Moxley

The relationship between malate dehydrogenase (MDH) genotype and plant vigor in peach [Prunus persica (L.) Batsch] was examined in two F2 populations (selfed `Belle of Georgia' and `Cresthaven') segregating at the Mdhl locus. Total numbers of progeny examined were 1610 and 998 in the `Belle of Georgia' and `Cresthaven' populations, respectively. In both populations, plant vigor (as defined by total height and trunk caliper after 1 year of growth) was significantly less in homozygous F/F (Mdh1-1/Mdh1-1) individuals. Homozygous S/S (Mdh1-2/Mdh1-2) individuals showed the greatest vigor, and were significantly different in vigor from homozygous F/F (Mdh1-1/Mdh1-1) individuals in both populations and from heterozygous F/S (Mdh1-1/Mdh1-2) individuals in the `Belle of Georgia' population. A significant deviation from the expected 1 F/F:2 F/S:1 S/S ratio was observed in the `Belle of Georgia' population, suggesting moderate lethality of homozygous F/F genotypes.

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Lyn A. Gettys and Dennis J. Werner

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Bruce D. Mowrey and Dennis J. Werner

To determine the earliest developmental stage at which isozyme screening could be accomplished, 10 isozyme systems were examined in peach [Prunus persica (L.) Batsch] for differential expression during development. Differences in isozyme expression based on stage of development were detected in nine systems. The earliest stage for complete screening of most isozymes examined is in l-month-old seedlings. The significance of these results relative to genetic mapping is discussed.

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Dennis J. Werner and Jose X. Chaparro

Genetic interaction of the pillar (PI) and weeping (WE) growth habit genotypes was investigated in peach [Prunus persica (L.) Batsch]. Data from F2, BC1P1, and BC1P2 families showed that PI (brbr) was epistatic to the expression of WE (plpl). A unique growth habit not previously described in peach, and referred to as arching (AR), was recovered in the F2 family. Arching trees showed an upright phenotype similar to Brbr heterozygotes, but had a distinct curvature in the developing shoots. Progeny testing of AR trees revealed their genotype is Brbrplpl.

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Lyn A. Gettys and Dennis J. Werner

Stokes aster is a herbaceous perennial native to the southeastern United States. Stokesia is a monotypic genus belonging to the tribe Vernonieae Cass. (family Asteraceae Dumont). The level of genetic diversity within the genus is unknown. The goal of this study was to determine the level of genetic diversity and relatedness among cultivars of stokes aster. The genetic relatedness among 10 cultivars of stokes aster, one accession of Vernonia crinita Raf. (syn. V. arkansana DC.), and one accession of Rudbeckia fulgida Ait. var. sullivantii (Beadle et Boynton) Cronq. `Goldsturm' was estimated using 74 randomly amplified polymorphic DNA (RAPD) primers. Similarity indices suggest that cultivars of stokes aster are very closely related, with values for all pairwise comparisons of cultivars of stokes aster ranging from 0.92 to 0.68. One cultivar, `Omega Skyrocket', had markedly lower similarity indices from the other cultivars, ranging from 0.72 to 0.68. Similarity indices between stokes aster and Vernonia and between stokes aster and Rudbeckia were 0.44 and 0.50, respectively.

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Dennis J. Werner and Dana F. Moxley

The relationship between malate dehydrogenase (MDH) isozyme genotype and plant vigor in peach [Prunus persica (L.) Batsch] was examined in two F2 populations (selfed `Belle of Georgia' and `Cresthaven') segregating at the Mdh1 locus. Total progeny examined were 1610 and 998 in the `Belle of Georgia' and `Cresthaven' populations, respectively. In both populations, plant vigor (as defined by total height and trunk caliper after 1 year of growth) was significantly less in Mdh1-1/Mdh1-1 homozygotes. Homozygous Mdh1-2/Mdh1-2 individuals showed the greatest vigor, and were significantly different in vigor from Mdh1-1/Mdh1-1 homozygotes in both populations and from Mdh1-1/Mdh1-2 heterozygotes in the `Belle of Georgia' population. A significant deviation from the expected 1 Mdh1-1/Mdh1-1: 2 Mdh1-1/Mdh1-1: 1 Mdh1-2/Mdh1-2 ratio was observed in the `Belle of Georgia' population, suggesting moderate lethality of homozygous Mdh1-1/Mdh1-1 genotypes.