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Jameel M. Al-Khayri, Feng H. Huang and Teddy E. Morelock

Callus, induced in the dark from leaf tissue of spinach (Spinacia oleracea L. cv. Fall Green) on Murashige and Skoog (MS) medium supplemented with (in mg·liter -1) 2 kinetin and 0.5 2,4-D regenerated shoots upon transfer to a medium containing 2 kinetin, 0.01 2,4-D, and 1 GA3. Complete plants were established by stimulating rooting of the shoots with 1 mg IBA/liter and transferring them to potting soil; survival was 60%. Chemical names used: N-(2-furanylmethyl)-1H-purin-6-amine (kinetin); 2;4-dichlorophenoxy acetic acid (2,4-D); gibberellic acid (GA3); 1H-indole-3-butanoic acid (IBA).

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Jameel M. Al-Khayri, Teddy E. Morelock and Edwin J. Anderson

Cowpea, or southernpea, is an important food legume that provides a source of high-quality protein, especially in the mature seeds. In the United States, industries exist to supply dry and processed seeds. Our aim is to develop a regeneration system for cowpea as a prerequisite for genetic engineering. Our objective was to examine the in vitro responses of shoot tips to growth regulators. Shoot tips isolated from in vitro-germinated seedlings (`Coronet') were cultured on MS medium containing 2,4-D at 0, 0.01, 0.1, or 1 mg·liter–1 and kinetin at 2.5, 5, 10, or 20 mg·liter–1. Cultures were maintained at 12-hour photoperiods and 24C. Callus, shoots, and roots or combinations thereof developed depending on the treatment. Callus formed on 1 mg 2,4-D/liter, regardless of the kinetin level, but at 0.1 mg 2,4-D/liter and 5 or 10 mg kinetin/liter, shoots also grew. Callus, shoots, and roots developed on 2,4-D lower than 0.1 mg·liter–1. Callus induced on 5 mg kinetin/liter and 0.01 mg 2,4-D/liter regenerated shoots on transfer to 5 mg kinetin/liter and 0.1 mg NAA/liter. This work may assist in the development of a micropropagation system for cowpea.

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Misty J. Moore, Mohanjeet S. Brar, Jameel M. Al-Khayri, Teddy E. Morelock and Edwin J. Anderson

Cowpea (Vigna unguiculata L.) is an important grain legume that is grown extensively in Africa, South America, India, and in the United States. This study investigated the effects of silver nitrate (AgNO3) on regeneration of cowpea cotyledon explants. Silver nitrate at 50 μm significantly increased percent regeneration in comparison to the control. The effect of duration of exposure was also determined with the ethylene inhibitor AgNO3. By exposing explants to 59 μm AgNO3 during different stages of culture, significant increases were actualized in percent regeneration and shoot number. The greatest percent regeneration was obtained when 59 μm AgNO3 was augmented to both the initiation and regeneration media or to only the regeneration media. These results indicate that the low percentage of regeneration of this genotype may be related to ethylene biosynthesis or metabolism. This study resulted in an improved regeneration system for the commercial cowpea cultivar Early Scarlet, and will be useful in developing a cowpea transformation system.

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Mohanjeet S. Brar, Jameel M. Al-Khayri, Teddy E. Morelock and Edwin J. Anderson

Cowpea (Vigna unguiculata L.) is an important grain legume, which in developing countries provides much of the protein in human diets. A plant regeneration system for cowpea was developed. Cotyledons were initiated on MS medium containing 15 to 35 mg·L-1 benzylaminopurine (BAP) for 5 to 15 days. For shoot regeneration, the explants were transferred to a medium containing 1 mg·L-1 BAP. Regeneration percentage (1% to 11%) and the number of shoots (4 to 12 shoots per explant) were significantly influenced by genotype. The duration of culturing and BAP concentration in the initiation stage significantly affected the regeneration capacity. Explants initiated on 15 mg·L-1 BAP for 5 days resulted in the highest regeneration percentage. Conversely, the highest number of shoots was obtained from explants initiated on 35 mg·L-1 BAP. This is the first report of plant regeneration of U.S. cowpea cultivars.

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Jameel M. Al-Khayri, Feng H. Huang, Teddy E. Morelock and Tahani A. Busharar

A preliminary study has shown that the addition of 15% (v/v) coconut water (CW) to the culture medium significantly improved callus growth, shoot-regenerative capacity, and shoot growth in leaf disk cultures of spinach (Spinacia oleracea L.). Subsequently, the influence of a range of CW concentrations, 0%, 5%, 10%, 15%, or 20% (v/v), was examined. Callus weight obtained after 5 weeks showed direct relationship to the concentration of CW. This stimulator action was observed in both cultivars tested in this study, `High Pack' and `Baker'. On CW-containing medium, shoot regeneration was expedited to 4 to 5 weeks compared with 8 to 12 weeks on a CW-free medium. Callus of `Baker' induced on a CW-free medium exhibited a significant increase in shoot regeneration frequency when transferred to a regeneration medium enriched with CW, suggesting that the addition of CW to the regeneration medium only is sufficient to achieve improved regeneration.

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Jameel M. Al-Khayri, Feng H. Huang, Teddy E. Morelock and Forrest E. Lane