Search Results
Demand for locally produced papaya fruit (Carica papaya) far outweighs the supply in the U.S. Virgin Islands. Due to the high incidence of papaya ringspot virus (PRSV), papayas are grown as an annual crop. The need exists in the Virgin Islands for papayas with early production to ensure a marketable crop before being devastated by PRSV. Breeding and selection has been ongoing for 5 years to develop papayas with tolerance to PRSV and fruit production starting at or less than 60 cm from the ground. The height at first fruit set, of 15 papaya cultivars recommended for the Virgin Islands, ranges from 58 cm to 253 cm. Generally, female plants started setting fruit lower on the stem than hermaphroditic plants. Through breeding and selection, three papaya lines have been developed that set the first fruit between 40 and 60 cm from the ground and exhibit tolerance to PRSV. These low-bearing papaya lines produce fruit that are marketable 1 month earlier than other cultivars.
Dyssodia pentacheta, a prostrate-growing perennial Texas wildflower with potential for use in low-maintenance landscapes, was propagated in vitro and by stem cuttings under mist. Optimum rooting for IBA-treated semihardwood terminal stem cuttings (3 to 30 mm IBA) and in vitro-grown nodal segments (30 to 100 mm IBA) occurred after 4 weeks under an intermittent mist system. A 300-mm IBA basal dip was lethal to macroand microcuttings. In vitro, D. pentacheta produced more shoots per nodal explant on Woody Plant Medium (2 g Gelrite/liter) with 1 to 10 μ m BA than with combinations of BA and 0.5 μm NAA. After shoot proliferation, the shoots were subculture twice and grown on growth regulator-free medium. When maintaining D. pentacheta in vitro on media devoid of plant growth regulators, 1% sucrose was more effective than 2% for promoting shoot growth and suppressing apparent production of phenolics. Chemical names used: N-(phenylmethyl) -1H-purin-6-amine (BA); 1H-indole-3-butyric acid (IBA); 1-naphthaleneacetic acid (NAA).
Dyssodia pentacheta, a low growing perennial Texas wild flower with potential for use in low maitenance landscapes, was propagated in vitro and with cuttings under a mist system. Over 80% of both semihardwood terminal cutting from stock plants and in vitro grown nodal segments, dipped in 0, 3, 10, or 30 M-3 IBA, formed roots after 4 weeks under an intermittent mist system. A 300 M-3 IBA basal dip was lethal to the cuttings. Dyssodia produced significantly more shoots per nodal explant in vitro on semisolid (2 g l-1 Gelrite) WPM with 1-10 M-6 BA than combinations of BA and 0.5 M-6 NAA. Shoots were successfully subcultured and grown for two passes on semisolid growth regulator free medium. When maintaining Dyssodia in vitro on WPM, void of plant growth regulators, 1% sucrose promoted shoot growth and suppressed phenolic production better than 2% sucrose.
Tobacco (Nicotiana tabacum cv Wisconsin 38) leaf discs were transformed with the disarmed Agrobacterium tumefaciens strain EHA101 carrying the Rol C gene from A. rhizogenes (Oono et al., Jpn. J. Genet. 62:501-505, 1987), NPT II and GUS. Shoots that regenerated on kanamycin-containing medium were confirmed transgenic through GUS assays, Southern analyses and transmission of foreign genes through the sexual cycle. Transgenic plants were as short as half the height of control plants, earlier flowering by up to 35 days, had smaller leaves, smaller seed capsules, fewer seeds, smaller flowers and reduced pollen viability. The number of seed capsules, leaf number and root density were similar between transgenic and control plants. Transgenic clones varied in the expression of the Rol C gene and transgenic plants similar or only slightly different from controls were identified. Transformation with the Rol C gene presents a potentially useful method of genetically modifying horticultural crops, particularly for flowering date, height, and leaf and flower size.
`Wisconsin 38' tobacco (Nicotiana tabacum L.) leaf discs were transformed with the disarmed Agrobacterium tumefaciens strain EHA101 carrying the rolC gene from A. rhizogenes (Oono et al., 1987) and NPT II and GUS genes. Shoots that regenerated on kanamycin-containing medium were confirmed as transgenic through GUS assays, polymerase chain reaction (PCR), Southern blot analyses, and transmission of the foreign genes through the sexual cycle. Transgenic plants were as short as half the height of control plants; were earlier flowering by up to 35 days; and had smaller leaves, shorter internodes, smaller seed capsules, fewer seeds, smaller flowers, and reduced pollen viability. The number of seed capsules, leaf number, and specific root length were similar between transgenic and control plants. Transgenic clones varied in the expression of the rolC-induced growth alterations as did the first generation of seedlings from these clones. Such differences suggested the potential for selecting for different levels of expression. Transformation with the rolC gene presents a potentially useful method of genetically modifying horticultural crops, particularly for flowering date, height, and leaf and flower size. Chemical names used: neomycin phosphotransferase (NPTII), β-glucuronidase (GUS).