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James K. Mitchell, W. Keith Patterson, and Robert H. Ford

European Vitis vinifera L. (four cultivars); interspecific hybrid (seven cultivars); and American V. aestivalis Michx. (one cultivar), V. labrusca L. (three cultivars), and V. rotundifolia Michx. (two cultivars) grapevines were tested for susceptibility to septoria leaf spot disease. V. rotundifolia cultivars Cowart and Fry exhibited hypersensitive-type resistance. All other American, European, and hybrid cultivars tested were susceptible with varying levels of disease severity. Cultivars with little (e.g., interspecific hybrid) or no (e.g., European) V. labrusca L. heritage were more susceptible to septoria leaf spot than American V. labrusca cultivars.

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M.M. Hossain, H. Inden, and T. Asahira

Pollen morphology was examined in amphidiploid and amphidaploid interspecific hybrids between Brassica oleracea L. and B. campestris L. Pollen of the amphidiploid interspecific hybrids between B. oleracea var. capitata and B. campestris var. pekinensis, and between B. campestris var. chinensis and B. oleracea var. capitata, were significantly longer and wider than those of their diploid parents, presumably due to the phenotypic expression of the hybrid genomes and ploidy effects. The exine ridges and pores of the amphidiploids were well-developed and significantly larger than those of their diploid parents, but they were poorly developed in the amphihaploids.

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Kelly M. Anon and Richard Craig

Interspecific hybrids of Exacum species (Gentianaceae) endemic to Sri Lanka possess excellent qualities for domestication as a new floriculture crop. The exact mode of floral induction and development responses are unknown, impeding the introduction of this potential crop. The interspecific hybrids evaluated are the result of controlled cross pollinations of E. macranthum. Arn. ex Griseb., E. trinervium (L.) Druce ssp. trinervium, and E. trinervium ssp. ritigalensis. (Willis) Cramer. The hybrids exhibit great genetic variability for horticultural traits. In addition, two growth and flowering patterns exist within the Penn State germplasm. Continuous-flowering genotypes flower throughout the year but more profusely and rapidly under late spring and summer conditions. In contrast, periodic-flowering genotypes exhibit two distinct seasonal habits. Under winter conditions, these accessions have a rosetted habit, much secondary branching, and few or no flowers. In summer conditions, they break their apical dominance, bolt, and produce flowers. As members of the Gentianaceae, Exacum hybrids produce an elegant blue flower with a striking yellow eye and bottle-shaped anthers. We evaluated the growth and flowering responses of Exacum interspecific hybrid accessions to photoperiod and irradiance. Accessions were evaluated under greenhouse conditions for floral production, rate of floral development, and growth characteristics. For the 20 accessions evaluated, supplemental irradiance under winter conditions resulted in greater floral production and much greater shoot and root mass accumulation. Little height and branching response occurred with supplemental irradiance. Of the 15 accessions evaluated under four photoperiod regimes, flowering and growth responses to photoperiod occurred under summer conditions but not in winter. An interaction among season, accession, and photoperiod revealed the complexity of Exacum germplasm and environmental responses.

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Glare J. Coyne and Shawn A. Mehlenbacher

Eastern filbert blight (EFB) (Anisogramma anomala) is a serious disease of the European hazelnut (Coryls avellana). A single dominant gene for immunity to EFB from C. avellana `Gasaway' is being combined with good nut and kernel traits using a modified backcross approach. Additional sources of resistance would be highly desirable. Clones and seedlings of six other species (C. columa, C. comuta, C. heterophylla, C. sieboldiana, C. amencana, and C. jaquemontii] and a few interspecific hybrid selections were screened in the greenhouse to identify new sources of resistance. C. jacquemontii seedlings and C. columa clones were highly susceptible. C. comuta, C. hetemphylla, and C. sieboldiana clones were resistant, as were 86% of the C. americana seedlings tested. Five C. americana × C. avellana hybrids from New York were resistant under field conditions. One of four C. comuta × C. avellana and two of three C. hetemphylla × C. avellana hybrids were resistant.

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L.J. Grauke and Richard D. O'Barr

`Oconee' pecan [Carya illinoinensis (Wangenh.) K. Koch] scions were grafted on seedling rootstock from nine open-pollinated seedstocks. Rootstock included three seedstocks each of pecan, water hickory [C. aquatica (F. Michx.) Nutt.], and their interspecific hybrid, Carya × lecontei (Little). Pecan seedlings had the largest basal diameters and water hickory seedlings the smallest. Seedlings of `Elliott' and `Curtis' seedstocks were larger than seedlings from `Moore' seedstock. Pecan and C. × lecontei seedlings were grafted more successfully than water hickory. Graft success varied among seedstocks of pecan and C. × lecontei Foliage color of seedlings, possibly indicative of iron nutritional status, was influenced by species; pecan seedling leaves were darker green than those of water hickory seedlings, but similar to C. × lecontei leaves. `Oconee' scion leaves were darker green on pecan rootstock than when grafted on C. × lecontei rootstock.

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James R. Ault

Shoot proliferation cultures were established in vitro using flower-stem explants from two different interspecific hybrid plants of Liatris. Explants taken on two dates from field-grown plants were successfully established and axillary shoot growth promoted on a medium consisting of Murashige and Skoog basal salts and vitamins with 30 g·L-1 sucrose, 1.0 μm BA, and 7.0 g·L-1 agar, with a medium pH = 5.7. Initial explant contamination rates were significantly higher among explants collected later in the growing season. Addition of BA (1.0, 2.0, 4.0, 8.0, or 16.0 μm) improved shoot formation compared to the control for both plants. Proliferation rates differed between the dates of establishment, the plants, and the BA treatments. Shoots rooted readily in medium without PGRs or with 1.0, 2.0, 4.0, or 8.0 μm K-IBA. Overall rooting was 88%. About 90% of the plants rooted in the presence of 1.0 μm K-IBA were successfully established in the greenhouse. Chemical names used: 6-benzyl adenine (BA); potassium salt of indole-3-butyric acid (K-IBA).

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Timothy M. Spann, Jeffrey G. Williamson, and Rebecca L. Darnell

Experiments were conducted with `Misty' southern highbush blueberry (Vaccinium corymbosum L. interspecific hybrid) to test the effects of high temperature on flower bud initiation and carbohydrate accumulation and partitioning. Plants were grown under inductive short days (SDs = 8 hour photoperiod) or noninductive SDs with night interrupt (SD-NI = 8 hour photoperiod + 1 hour night interrupt), at either 21 or 28 °C for either 4 or 8 weeks. Flower bud initiation occurred only in the inductive SD treatments and was significantly reduced at 28 °C compared with 21 °C. The number of flower buds initiated was not significantly different between 4- and 8-week durations within the inductive SD, 21 °C treatment. However, floral differentiation appeared to be incomplete in the 4-week duration buds and bloom was delayed and reduced. Although plant carbohydrate status was not associated with differences in flower bud initiation between SD and SD-NI treatments, within SD plants, decreased flower bud initiation at high temperature was correlated with decreased whole-plant carbohydrate concentration. These data indicate that flower bud initiation in southern highbush blueberry is a SD/long night phytochrome-mediated response, and plant carbohydrate status plays little, if any, role in regulating initiation under these experimental conditions.

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T.J. Montagno, S.Z. Berry, and P.S. Jourdan

L. hirsutum has been previously reported as recalcitrant to culture and plant regeneration. We have modified tomato protoplasm culture protocols and obtained high frequencies of plant regeneration from leaf protoplasts of L. hirsutum PI 126445, LA 94, and LA 1393, as well as from 8 interspecific hybrids of PI 126445 (male parent) with L. esculentum `Floradade', `Marglobe', `Tropic', `OH7870', `OH7983', `OH832', `OH8243', and `OH8245'. Protoplasts were isolated from 3-week old low light pretreated seedlings and cultured in modified LCM containing 1 mg/L NAA 0.5 m /L BA, and 0.5 mg/L 2,4-D. Cultures were kept in the dark at 30 C, diluted every 3 days with LCM containing only 0.75 mg/L BA and gradually moved to the light. After 2-3 weeks, colonies of 1-2 mm were transferred to solid MS medium containing 0.5 mg/L BA and 0.05 mg/L NAA. Calli containing dark green bud primordia were then placed on MS with 2% sucrose and 2 mg/L zeatin riboside for shoot production.

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Fei-Yun Zhuang, Jin-Feng Chen, Jack E. Staub, and Chun-Tao Qian

The current Cucumis taxonomic classification places C. hystrix Chakr. in subgen. Cucumis based on its morphological similarities to cucumber (C. sativus L., 2n = 14). However, the chromosome number of C. hystrix was identified as 2n = 24, the same number as in subgen. Melo. Cucumis hystrix is therefore considered the first wild Cucumis species of Asiatic origin possessing 12 basic chromosomes. Thus, any research regarding its biosystematics would challenge the basic chromosome number and geographic location theories that govern the current taxonomic system. The production of the amphidiploid species (Cucumis ×hytivus Chen and Kirkbride, 2n = 38) obtained from the cross between C. hystrix and C. sativus and subsequent chromosome doubling would provide an effective means of investigating the relationship between Cucumis species with two different basic chromosome numbers. Thus, RAPD markers were used to study the taxonomic placement of C. hystrix and its interspecific hybrid with cucumber. Of the 220 arbitrary primers screened, 31 were used for analysis where 402 (96.3%) fragments were polymorphic among the germplasm examined. A UPGMA-based cluster analysis partitioned 31 accessions into two main groups [C. sativus (CS) and C. melo (CM)]. Under the similarity coefficient threshold of 0.23, these two groups can be further divided into five clusters with C. hystrix, C. ×hytivus, and C. sativus as separate clusters in the CS group. A modified taxonomic system is proposed based on these results and findings of a previous chloroplast DNA analysis with the genus Cucumis containing subgen. Cucumis with three species and subgen. Melo with six series.

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James K. Mitchell, Robert H. Ford, and W. Keith Patterson

European Vitis vinifera L. (four cultivars); interspecific hybrid (seven cultivars); and American V. aestivalis Michx. (one cultivar), V. labrusca L. (three cultivars), and V. rotundifolia Michx. (two cultivars) grapevines were tested for susceptibility to Septoria leaf spot disease. V. rotundifolia cultivars Cowart and Fry exhibited hypersensitive-type resistance. All other American, European, and hybrid cultivars tested were susceptible with varying levels of disease severity. Cultivars with little (e.g. interspecific hybrid) or no (e.g. European) V. labrusca L. heritage were more susceptible to Septoria leaf spot than American V. labrusca cultivars.