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  • Author or Editor: H. Mathews x
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Zygotic embryo explants of grape cultivar AXR#1 were isolated from maw-e seeds and cultured on medium supplemented with naphthoxy acetic acid beta-(NOA) and benzylaminopurine (BA). Embryo explants dedifferentiated to form embryogenic callus. Globular stage embryos were visible in 9-10 months. On transfer 10 a growth regulator free medium supplemented with charcoal these globular embryos underwent further stages of embryo development. In a period of 30-40 days embryogenic tissues turned into clumps of somatic embryos displaying different stages of development Cotyledonary stage embryos were separated and transferred to basal medium. These embryos developed into complete plants. Cold and desiccation treatment of somatic embryos significantly enhanced the rate of plant conversion. Hypocotyl segments of elongated somatic embryos were good source explant for induction of shoot organogenesis. The hypocotyl-length and the proximity to-shoot-apex were found to influence the rate of shoot induction from hypotyl segments. Multiple shoot complexes which formed on hypocotyl segments were separated and individual shoots were grown on a root induction medium resulting in complete plant development. The possibility of both embryogenic and organogenic modes of plant regeneration make somatic embryos a highly versatile explant source for experiments on genetic manipulation.

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Raspberry has very cultivar specific requirements for proliferation. Plant regeneration rates from isolated explants are inconsistent and vary widely among cultivars. As a step towards developing a viable transgenic system in red raspberry (Rubus idaeus L.) we first developed an efficient and consistent protocol for plant regeneration from isolated explants. A modified MS medium with cytokinin BA gave vigorous shoots with an average proliferation rate of 3-5 depending on the cultivar. These vigorous shoot proliferants served as an ideal explant source for plant regeneration experiments. The average rate of shoot regeneration from leaf explants was 72, 32, 68. and 72% for cvs. Canby, Chilliwack, Meeker and Heritage respectively. In addition to leaf, petiole explants were equally good sources for inducing shoot organogenesis. In all the above-mentioned cultivars, 44-57% of the petiole explants gave rise lo healthy and vigorous shoot regenerants in culture. The regenerated shoots were induced lo root on a rooting medium and were successfully transplanted to the greenhouse. This regeneration system was successfully applied in our laboratory for developing gene transfer system in red raspberry (see abstract by Mathews, et al).

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Seven hybrid tomato rootstocks with possible resistance to bacterial wilt caused by Ralstonia solanacearum and a known resistant cultivar were tested as grafting rootstocks to impart resistance to a bacterial wilt-susceptible cultivar, BHN 602. Greenhouse studies showed resistance of all the rootstocks to bacterial wilt. The disease incidence and yield of ‘BHN 602’ grafted to these rootstocks were evaluated in open-field tomato production in Florida and Virginia over four seasons. Significant differences in bacterial wilt incidence were observed between grafted entries in three of the four trials. In these three trials, grafted entries consistently exhibited the least bacterial wilt incidence compared with the controls; the self-graft, and non-grafted entries. Over all the trials, tomato plants grafted onto ‘Cheong Gang’, ‘BHN 1054’, and ‘BHN 998’ displayed the least bacterial wilt incidence. Rootstocks had a significant effect on total marketable yield in all the trials with certain grafted entries yielding significantly greater than non-grafted ‘BHN 602’. Field studies show that grafting holds promise for decreasing the impact of bacterial wilt on tomato cultivars as well as increasing the overall productivity of tomato cultivars.

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Improved in vitro clonal propagation methods are valuable tools for nurseries and growers, and are essential for manipulation and improvement of tree fruit germplasm using the tools and techniques of biotechnology. We have developed a rapid shoot multiplication procedure for clonal propagation of apple, Malus ×domestica cv. Gale Gala and pear, Pyrus communis L. cv. Bartlett. Rapid clonal multiplication was achieved after the following series of steps: pre-conditioning of micropropagated shoots, sectioning pre-treated stems into thin slices, placing slices onto shoot induction medium and incubating directly under cool-white fluorescent lights or after a brief dark incubation. Multiple induction of shoots recovered from stem slice explants within three weeks of culture. A maximum of 37% of cultured apple stem slices, and 97% of pear stem slices, showed induction of shoots. More shoots were recovered on phytagel solidified shoot induction medium than on agar. Cultured stem slices of both apple and pear showed maximum recovery of shoots from shoot induction medium supplemented with thidiazuron (TDZ) compared to medium supplemented with BAP and kinetin. Under ideal conditions, pear stems generated four times the shoots as the same quantity or length of apple shoots. Micropropagated shoots were rooted and transferred to the greenhouse and field nursery for further evaluation. Chemical names used: N-phenyl-N′-1,2,3-thidiazol-5-ylurea (thidiazuron or TDZ); 6-benzylaminopurine (BAP).

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Ten broccoli [Brassica oleracea L. (Botrytis Group)] accessions were grown in several environments to estimate glucosinolate (GS) variability associated with genotype, environment, and genotype × environment interaction and to identify differences in the stability of GSs in broccoli florets. Significant differences in genetic variability were identified for aliphatic GSs but not for indolyl GSs. The percentage of GS variability attributable to genotype for individual aliphatic compounds ranged from 54.2% for glucoraphanin to 71.0% for progoitrin. For total indolyl GSs, the percentage of variability attributable to genotype was only 12%. Both qualitative and quantitative differences in GSs were detected among the genotypes. Ten-fold differences in progoitrin, glucoraphanin, and total aliphatic GS levels were observed between the highest and lowest genotypes. Only two lines, Eu8-1 and VI-158, produced aliphatic GSs other than glucoraphanin in appreciable amounts. Differences in stability of these compounds among the cultivars were also observed between fall and spring plantings. Results suggest that genetic factors necessary for altering the qualitative and quantitative aliphatic GS profiles are present within existing broccoli germplasm, which makes breeding for enhanced cancer chemoprotectant activity feasible.

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The eriophyid mite, Phyllocoptes fructiphilus, vectors the causal agent, Rose rosette virus (RRV), that results in rose rosette disease. Parts of the southeastern United States have remained free of the disease, except for infected plant material introductions that were eradicated. A survey of sampling points through Alabama, Georgia, and Mississippi (n = 204) revealed the southeastern border of RRV. The presence of RRV in symptomatic plant tissue samples (n = 39) was confirmed by TaqMan-quantitative reverse transcription polymerase chain reaction (RT-qPCR). Samples were also collected at every plot for detection of eriophyid mites, specifically for P. fructiphilus. Three different species of eriophyid mites were found to be generally distributed throughout Alabama, Georgia, and Mississippi. Most of these sites (n = 60) contained P. fructiphilus, found further south than previously thought, but in low populations (<10 mites/gram of tissue) south of the RRV line of incidence. Latitude was found to be significantly correlated with the probability of detecting RRV-positive plants, but plant hardiness zones were not. Plot factors such as plant size, wind barriers, and sun exposure were found to have no effect on P. fructiphilus or the presence of RRV. The reason for the absence of RRV and low populations of P. fructiphilus in this southeast region of the United States are unclear.

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