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  • Author or Editor: Harry Swartz x
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Raspberry cultivars and hybrids were screened for reaction to Verticillium alboatrum Reinke and Berth to determine the mode of inheritance of resistance and to assist in the development of resistant germplasm. Greenhouse-grown seedlings of an incomplete partial diallel of two black, purple, and red raspberry Rubus subgenus Idaeobatus progeny were root-dipped in a mycelial slurry and stem-inoculated with a conidial suspension of V. albo-atrum. Fourteen weeks after the initial inoculation, disease symptoms were observed in the seedlings. Disease symptom severity and percentage of black raspberry parentage in the seedlings were correlated (P ≤ 0.01; r 2 = 0.90). A similar significant (P ≤ 0.05; r 2 = 0.66) linear trend was found with fungus reisolation percentages, although isolation of the fungus from symptomless plants indicates Verticillium tolerance among genotypes in Idaeobatus. These trends, coupled with large significant general combining ability (P ≤ 0.01), suggest primarily additive inheritance of resistance. However, considering noninoculated control scores, the possibility of escapes, and skewing of populations, one may hypothesize a gene-gene model for symptom expression, with partial dominance of resistance alleles.

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Shoot proliferation of Acer ginnala Maxim. (Amur maple) from nodal-segments was obtained on Murashige and Skoog salts and vitamins supplemented with 25 nM thidiazuron and 3% sucrose. Higher concentrations of cytokinin resulted in callus formation at the base of explants. Explant orientation had a significant effect on shoot elongation. Explant elongation and proliferation were correlated. Plants inverted in the medium elongated and proliferated readily. Branching was obtained primarily from axillary buds several nodes basal to the apex. Gelling agent type did not affect proliferation. Vitrification was significantly affected by type of gelling agent, gelling agent concentration and thidiazuron concentration. In vitro shoots rooted readily even in medium containing adenine. Greater than 95% of the in vitro plants established in the greenhouse.

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An efficient protocol for plantlet regeneration using petioles and internodes of two blackberry cultivars has been developed for use in genetic transformation. Maximum shoot regeneration was induced on MS medium supplemented with 5 μM Thidiazuron (TDZ) and 0.5 μM IBA. Preconditioning the source shoots on 0.5 μM TDZ containing MS medium did increase the number of regenerated shoots/explant, but did not affect the regeneration percentage. The antibiotic, kanamycin, significantly reduced the growth and regeneration of explants at 10 mg/L or higher. In contrast, cefatoxime at 100-500 mg/L increased explant growth and percentage regeneration.

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Several authors report the synthesis of periclinal chimeras generated from graft unions of Solanaceous plants grown in the greenhouse. As this technique requires shoot organogenesis, in vitro conditions are necessary to adapt this technique to woody species. We now report several in vitro techniques necessary to mimic the in vivo graft chimera process. These include rootstock/scion preparation, micrografting and shoot organogenesis from graft unions. Zeatin and auxins have been helpful in preparing graftable material and for increasing the percentage successful grafts. A shorter exposure to organogenic medium containing thidiazuron resulted in greater percentage shoot regeneration from graft unions. Thorny/thornless Rubus and 'Liberty'/'Golden Delicious' or 'Gala' Malus (color) markers are being used to determine the percentage of these regenerants which are chimeral.

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In previous abstracts (HortScience 23:707;24:121), ABA when added throughout the in vitro production cycle, reversed the tissue culture-induced rejuvenation of the day neutral strawberry `Fern'. Compared to benzyl adenine (BA) proliferated plants, ABA treated tissue culture-produced plants flowered earlier and had more adult leaf patterns. In the present study, we analysed endogenous ABA concentrations in the apices and unexpanded leaves of BA treated tissue culture-propagated plants, selved seedlings and propagated adult runner tip plants at 3, 7 and 15 weeks ex vitro, after germination or after runner tip propagation. Using pentadeuterated standards and single ion monitoring, ABA concentrations in tissue culture produced and juvenile seedling plants were significantly lower than adult plants at 3 and 7 weeks. By 7 weeks, only the adult plants were flowering. At 15 weeks, no differences in ABA concentration were significant and all three types flowered.

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Regeneration of adventitious shoots from in vitro-derived leaves of several Rubus genotypes was tested with various concentrations of cytokinins and auxins, different basal media, duration of dark incubation periods, temperatures and photosynthetic photon fluxes (PPF). Thidiazuron (TDZ) was significantly more effective than benzyladenine (BA), and indolebutyric acid (IBA) more effective than naphthaleneacetic acid (NAA). Leaves of `Summit' and `Sentry' raspberries and MD-ETCE-1 blackberry were most responsive (percentage of leaves responding, number of shoots formed) to 1 μM or 10 μM TDZ plus 0.5 μM or 1 μM IBA; MD-ETCE-1 leaves did not respond to BA or TDZ with either 2.7 or 5.4 μM NAA. More organogenesis occurred on MS than on half-strength MS, Anderson modified, WPM or N6 media. For the five cultivars tested (`Autumn Bliss', `Canby', `Sentry', `Summit', MD-ETCE-1), the most shoots formed when leaves were incubated at 20°C (vs. 25°C) for 1 week in the dark before they were exposed for 16 h per day to a PPF of 40 μmol·m-2·s-1. Significant differences in regeneration frequency were observed among four cultivars with the highest 71% for `Autumn Bliss' and the lowest 29% for `Summit'.

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Abstract

Ethylene evolution in excised apple (Malus domestica Borkh.) spurs was measured following the application of thinning treatments. Within 1 day (20 hours) of application, ethylene evolution by spurs of ‘Golden Delicious’ trees treated with 15 ppm napthaleneacetic acid (NAA) and 100 ppm (2-chloroethyl)phosphonic acid (ethephon) was 5 times greater than in control spurs, and those treated with 200 ppm ethephon evolved seven times more. Less fruit thinning occurred in response to the application of 100 ppm ethephon than 15 ppm NAA. Increased ethylene evolution was also detected in attached ‘Spatbluhender’ fruitlets 8 hours after NAA treatment.

Open Access

Abstract

‘Allstar’ is a vigorous and productive Junebearing strawberry (Fragaria × ananassa Duch.) that produces very large, firm fruit of good quality in late midseason. It is the most recent introduction in a series of red stele root rot-resistant cultivars developed in the cooperative strawberry improvement program of the U.S. Department of Agriculture and the University of Maryland. ‘Allstar’ combines multiple-race resistance to red stele incited by Phytopthora fragariae Hickman with resistance to other root and leaf diseases, has unusually broad adaptation within the eastern United States, and performs well under a number of cultural regimes. Its name implies superior performance under diverse soil, climatic and cultural conditions.

Open Access

Abstract

‘Tribute’ and ‘Tristar’ are everbearing strawberry cultivars (Fragaria × ananassa Duch.) that fruit in spring, summer, and fall (as indicated by the prefix “Tri-”). They are the first everbearing strawberries bred for culture in the eastern United States which combine resistance to red stele root rot, incited by Phytophthora fragariae Hickman, with a high degree of tolerance to verticillium wilt, incited by Verticillium albo-atrum Reincke & Berth. Their generally consistent good health, productivity, and fruit quality under a number of cultural systems suggest that these cultivars will offer new opportunities to the strawberry home gardener and commercial grower alike.

Open Access

Abstract

Tissue culture-propagated (TC) strawberry plants (Fragaria × ananassa Duch.) had a cultivar-dependent shift in susceptibility to Phytophthora fragariae Hickman and Verticillium albo-atrum Reinke and Berthold root-rotting fungi. TC-propagated ‘Tribute’, a resistant cultivar, had a disease reaction similar to that of runner-propagated ‘Tribute’ plants. TC-propagated and juvenile selfed seedlings of ‘Raritan’, a susceptible cultivar, were more susceptible to these diseases than ‘Raritan’ runner plants. The TC plant disease reaction shifted toward the runner plant (or usual clonal) reaction with increasing time out of in vitro culture.

Open Access