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Timothy F. Wenslaff and Paul M. Lyrene

Two diploid yellowleaf Vaccinium elliottii Chapmn. clones were pollinated with pollen from the tetraploid southern highbush cultivar `Misty' (largely V. corymbosum L). These interspecific crosses, which normally yield few hybrids because of a triploid block, were made with and without the use of V. elliottii mentor pollen mixed with V. corymbosum pollen. Mentoring had no effect on the number of hybrids produced when V. elliottii `Silverhill' was the seed parent, but when V. elliottii `Oleno' was the seed parent, no hybrids were produced unless mentor pollen was utilized. The difference was postulated to be a greater ability to produce one-seeded berries in `Silverhill' than in `Oleno'.

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Muhammet Tonguç and Phillip D. Griffiths

Black rot, caused by Xanthomonas campestris pv. campestris (Pam.) Dawson (Xcc), is a major bacterial disease of Brassica oleracea L. vegetables. In this study the related species Brassica carinata Braun (ethiopian mustard), which can be used to generate interspecific crosses with B. oleracea was evaluated for resistance to Xcc. Fifty-four accessions and susceptible control plants were wound inoculated with four isolates of Xcc race 4 at the juvenile stage. Of the 54 accessions tested, A 19182 and A 19183 exhibited no symptoms when inoculated with Xcc for all plants tested, and the accessions including PI 199947, PI 199949 and PI 194256 segregated for resistance to Xcc.

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J.D. Norton, G.E. Boyhan, and B.R. Abrahams

Forty eight cultivars and seedlings of plum involving the species Prunus americana, P. auqustifolia, P. cerasifiera, P. munsoniana, P. salicina, P. simoni, and P. triflora were evaluated for the presence of xylem limiting bacteria (Xyllela fastidiosa) and tree longevity. Plum leaf scald (PLS) ratings, based on the percent of scalded leaves in the tree were correlated with the concentrations of bacteria in the twigs and leaf petioles. Observations of symptoms of PLS and monitoring of progeny from interspecific crosses, cultivars, and seedlings indicate that resistance to the PLS organism is present in the Auburn material and heritable. Uniform infection of seedlings was made by double budding of one year whips with buds from infected trees. Resistance to PLS has been incorporated into horticultural types and seedlings are currently being evaluated for possible release for commercial and home use.

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H. Huang, F. Dane, J.D. Norton, D.B. Weaver, and F.V. Hebard

Linkage relationships among eight isozyme genes (Acp-3, Est-1, Est-5, Prx-1, Prx-2, Prx-3, Me, and Adh) and two morphological markers (Inh and Twh) were investigated in one F2 and two BC1 families of interspecific crosses between the American chestnut (Castanea dentata Borkh.) and the Chinese chestnut (C. mollissima Blume). Inh was consistently linked with Prx-1 and Est-5 in all families. In addition, four other gene pairs, Acp-3Inh, Acp-3Prx-1, Me–Inh, and Twh–Inh, were linked in one of the three families investigated. The two isozyme genes and two morphological marker genes were tentatively integrated into one linkage group with the gene order TwhInhPrx-1Est-5.

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Hongwen Huang, Fenny Dane, Zhongzen Wang, Zhengwan Jiang, Rehuang Huang, and Shengmei Wang

Isozyme inheritance and variation in Actinidia was investigated using 23 enzyme systems. Ten isozyme loci from six enzyme systems, Acp-2, Est, Prx-1, Prx-2, Prx-4, Prx-5, Pgi-2, Pgm-2, and Tpi, were found to be inherited as single Mendelian genes in families of two interspecific crosses. Disomic inheritance detected at ten loci in progenies of a cross between the hexaploid A. deliciosa × diploid A. chinensis, provided convincing evidence that A. deliciosa is an allohexaploid. Allelic segregation for tetrasomic inheritance at ten isozyme loci was demonstrated in the progenies of a cross between the tetraploid A. chinesis × diploid A. eriantha, a result suggesting the autotetraploid origin of the tetraploid A. chinensis which apparently originated from its diploid ancestor A. chinensis. A high level of isozyme variation and heterozygosity were observed in the 22 cultivars and 56 plants of 28 Actinidia taxa. Allozyme phenotype can be used effectively for cultivar identification.

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T.J.K. Radovich*, R.C. Pratt, L.A. Duncan, N. Welty, and M.D. Kleinhenz

Cucurbita maxima and C. pepo are difficult to hybridize, and it was our objective to generate F1 hybrids between ornamental cultivars of the two species. C. maxima `Lakota' and C. pepo `Jack O'Lantern'; and `OZ'; were selected as parents. `Lakota' (L) is an heirloom, hubbard-type cultivar producing pear-shaped, red-orange fruit with dark green mottling, `Jack O'Lantern'; (J) is an open-pollinated Halloween-type pumpkin cultivar and `OZ' is a Halloween-type hybrid. Sixteen plants of each cultivar were greenhouse-grown in a CRB design during the period July-Sept. 2003. Interspecific crosses were made in both directions, with intraspecific crosses (J × O) and selfs (L) serving as controls. Fruits were harvested about 20 d after pollination. Embryos were excised under aseptic conditions and grown on either full strength Murashige and Skoog (MS) media with 6% sucrose (S6), full strength MS media with 6% maltose (M6), or half strength MS media with 3% sucrose (S3). Fruit set was generally greater in the intraspecific crosses (33%) and selfs (67%) than in the interspecific crosses (15 %), with the notable exception of the interspecific combination L × J (85% fruit set). Embryos of interspecific and control crosses were about 1.5mm and >1cm long, respectively. Hypocotyl and root growth 10 d after plating was better on S3 (3.2 and 1.7 cm) than on S6 (1.6 and 0.25 cm) or M6 (0.35 and 0 cm), and a greater number of functional hybrids were obtained from embryos grown on S3 (6 plants) than on S6 (2 plants) or M6 (2 plants). The interspecific plants were backcrossed to one of the parents and novel combinations of shape, color and variegation in hybrid fruit were observed.

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Margaret R. Pooler, Ruth L. Dix, and Joan Feely

The issue of invasive plants has become a concern to a variety of groups, including environmentalists, policymakers, and nurserymen. Although many surveys of invasive plants have been made, little research on the biology of hybridization has been conducted. Bittersweet (Celastrus) species serve as a good model system to test the effects of interspecific hybridizations since native and introduced species are found in the U.S. The American bittersweet (Celastrus scandens L.) is a deciduous climbing or twining shrub native to eastern and central North America. Although the bark has been used for medicinal purposes, the plant is cultivated as a nursery crop primarily for its bright red berries. In its natural habitat, native bittersweet is also an important source of food and cover for wildlife. Over the past several decades, populations of native bittersweet have declined to such low levels that some states are considering listing it as a threatened species. One reason for the rarity of American bittersweet in the wild is thought to be competition and possibly hybridization with an aggressive introduced species, oriental bittersweet (Celastrus orbiculatus Thunb.), which was introduced from Asia into the U.S. in 1860 as an ornamental. This plant can form dense, tangled, impenetrable thickets or climb small trees to girdle and smother them. It has been seen in at least 21 states since it was first recorded as an escape plant in 1912. Our objective was to determine whether oriental bittersweet can hybridize with native bittersweet, thus contributing to the loss of native populations in the United States. We performed controlled pollinations using C. scandens as the female parent and C. scandens or C. orbiculatus as the male parent. Although the intraspecific pollinations resulted in significantly more germinating seedlings than the interspecific crosses, the seedlings from the interspecific crosses had less seed dormancy and were more vigorous and more quick to vine than the intraspecific seedlings. These results indicate that the decline of the American bittersweet may be due to interspecific hybridizations with the invasive introduced species.

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Phillip Griffiths*

Cucumber mosaic virus (CMV) is an aphid-transmitted virus that infects snap bean growing regions in New York State and Wisconsin. The core collection of common bean accessions (Phaseolus vulgaris), the complete collection of scarlet runner bean accessions (Phaseolus coccineus) and snap/dry bean cultivars were screened for resistance to CMV. Although variation in foliar symptom expression was observed, no resistance was observed in 93 snap bean and16 dry bean cultivars tested, and only one of the 406 accessions from the core collection (PI 309881) was symptomless. PI 309881 did not have common bean characteristics, and was later identified as a tepary bean (Phaseolus acutifolius) accession based on morphology and PCR-RFLP of chloroplast DNA. Screening of 260 P. coccineus accessions was inaccurate when a visual rating of foliar symptoms was used. It was necessary to determine infection using ELISA and test plant screening with grey zuccini. Using this approach it was determined that 80 P. coccineus accessions were susceptible to CMV; however, the remaining accessions provided possible sources for transfer of CMV resistance to snap bean. Crosses of P. coccineus accessions were made to breeding line 5-593 and backcrossed to 5-593 and snap bean cultivar `Hystyle'. PI 309881 was crossed with ICA Pijao in order to develop interspecific hybrids. Populations were developed from the interspecific crosses/backcrosses and evaluated for CMV resistance using ELISA and visual ratings of foliar symptoms.

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Geunhwa Jung, Paul Skroch, James Nienhuis, and Dermot Coyne

One of the highest levels of common bacterial blight (CBB) resistance identified in Phaseolus vulgaris is found in XAN-159, which was developed for leaf resistance to CBB through six generations of pedigree selection of progenies derived from the interspecific cross [(`Pinto UI 114' × PI 319441) × P. acutifolius PI 319443] × `Masterpiece'. A RAPD genetic linkage map was previously constructed in a recombinant inbred population derived from the common bean cross PC-50 × XAN-159 for identification of genomic regions associated with bacterial disease resistance in XAN-159. To confirm that chromosomal regions associated with CBB resistance in XAN-159 were introgressed from tepary bean, we investigated the parentage of each genomic interval in XAN-159 by studying the genomic constitutions of the four different parents involved in the pedigree. The results indicate that all genomic regions associated with CBB resistance contain intervals derived exclusively from tepary bean. The uniqueness of marker polymorphisms associated with resistance to CBB in XAN-159 will allow the application of marker assisted selection for these resistance genes in most populations of common bean.

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Cindy L. Flinn and Edward N. Ashworth

Thermal analysis of Forsythia × intermedia `Spectabilis' flower buds had previously detected the occurrence of low temperature exotherms (LTE) during freezing. The LTE apparently resulted from the freezing of supercooled water and corresponded to the death of the florets. The genus Forsythia encompasses a wide array of species and interspecific crosses ranging in flower bud hardiness and floret size. The ability of buds to supercool, the relationship between the LTE and flower bud hardiness, and the extent to which floret size affects both were studied in flower buds of the following Forsythia species: F. × intermedia `Spectabilis', F. × intermedia `Lynwood', F. `Meadowlark', F. suspensa var. fortunei, F. `Arnold Dwarf, F. europaea, F. giraldiana, F. × intermedia `Arnold Giant', F. japonica var. saxatilis, F. mandshurica, F. ovata, and F. viridissima. Flower buds used for thermal analysis were also used in subsequent size determinations. Hardiness evaluations were conducted using controlled freezing tests, and the sampling interval defined using the temperature range of the LTEs. Initial evaluation indicated a high degree of correlation (α>.50) between mean LTEs and mean killing temperatures. The Forsythia genus, with its broad range of bud hardiness and size provides an excellent system in which to study the mechanisms of supercooling. Thermal analysis of cultivars which exhibit LTEs can accurately assess bud hardiness with minimal plant material.