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Seedlings of Capsicum annuum L. cv. San Luis were grown in pots containing a pasteurized mixture of sand and sandy loam soil inoculated or noninoculated with the V-A mycorrhizal (VAM) fungus Glomus intraradices Schenck et Smith. Long Ashton nutrient solution (LANS) was modified to supply P at 0, 11 or 44 μg·ml–1. Diurnal gas exchange measurements were taken 15, 30 and 50 days after the experiment was initiated. Plant growth, leaf elemental content, and mycorrhizal development were assessed 52 days after transplanting. Gas exchange and net photosynthesis were enhanced by mycorrhiza and full strength LANS fertilization (44 μg·ml–1). The symbiosis increased leaf nutrient content of P, K, Mg, S, Fe, Mn, Zn, Cu, B, Mo, and Al. Mycorrhizal plants had higher shoot dry weights, leaf number, leaf area, and fruit primordia than nonmycorrhizal plants with P at 0 and 11 μg·ml–1. Root colonization (arbuscules, vesicles, and internal and extraradical hyphae development) were higher with P at 0 and 11 μg·ml–1. The quantity of spores recovered in soil was independent of P treatments.
Citrus Tristeza Closterovirus (CTV) induces mild and/or severe symptoms on Citrus species. It may cause death of trees if the rootstock-scion combination is susceptible. It has been found in other plant/virus combinations that transformation with partial or complete viral genes (e.g., coat protein genes) can confer resistance to the resulting transgenic plants. We previously reported A. tumefaciens mediated transformation and production of two sour orange (C. aurantium L.) plants expressing the coat protein gene of CTV, which was the first report of production of transgenic Citrus using a viral gene. However, in order to properly evaluate resistance, it is necessary to obtain as many transgenic Citrus plants from single transformation events as possible. Therefore, we are currently transforming grapefruit (Citrus paradisi) `Marsh' and `Star Ruby' and sweet orange (C. sinensis) `Valencia' with CTV coat protein genes. These species are susceptible to CTV and more amenable to transformation than sour orange. Epicotyl segments of etiolated seedlings were inoculated with A. tumefaciens strain EHA101 harboring binary plasmid pGA482GG containing the coat protein gene of mild Florida CTV strain T30 (CP-T30) or severe Florida strain T36 (CP-T36). Putatively transformed shoots were regenerated on selection medium containing kanamycin. Regenerated shoots were evaluated with GUS assays; those shoots positively identified by GUS were then evaluated with PCR. We have currently identified 17 `Marsh' grapefruit, 20 `Star Ruby' grapefruit, and seven sweet orange putatively transformed plants.