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Waltram Second Ravelombola, Ainong Shi, Yuejin Weng, John Clark, Dennis Motes, Pengyin Chen and Vibha Srivastava

Cowpea [ Vigna unguiculata (L.) Walp] (2 n = 2 x = 22) is a legume of economic importance worldwide. It is widely grown in Central and West Africa with a production estimated at 5.4 million tons of dry seed ( Olufajo, 2012 ) and also grown in

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Waltram Ravelombola, Jun Qin, Yuejin Weng, Beiquan Mou and Ainong Shi

Induction of salt stress tolerance in cowpea [ Vigna unguiculata (L.) Walp.] by arbuscular mycorrhizal fungi Legume Res. 38 579 588 Agbicodo, E. M. Fatokun, C. A. Muranaka, S. Visser, R.G.F. van der Linden, C.G. 2009 Breeding drought tolerant cowpea

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Lurline Marsh

Explants (cotyledon, cotyledonary node, second node, hypocotyl, epicotyl, and leaf) of cowpea (Vigna unguiculata) genotypes MN13 and Pinkeye Purple Hull were cultured on Murashige and Skoog basal nutrient medium. The medium was supplemented with 1 mg·L–1 benzyladenine (BA) or 1 mg·L–1 benzyladenine plus naphthalene acetic acid (BA + NAA) or 2 mg·L–1 2,4-dichlorophenoxy acetic acid (2,4-D). Cultures were maintained at 22°C for 1 month, after which they were transferred to 1 mg·L–1 BA + NAA. Cotyledons, hypocotyl, epicotyl, and leaf segments produced only calli after subculturing in BA + NAA. The second node and cotyledonary node explants cultured on the BA or BA + NAA followed by subculture on BA + NAA produced calli, shoots, and roots. The plants were then transplanted to promix but later died.

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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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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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John C. Alleyne, Teddy E. Morelock and Clay H. Sneller

Genotype by environment (G × E) effects in Regional Cooperative Southernpea trials for the southeastern United States were investigated to characterize the extent, pattern, and potential impact of G × E on seed yield of southernpea [Vigna unguiculata (L.) Walp] genotypes. The structure of G × E effects was investigated using the Additive Main Effect and Multiplicative Interaction (AMMI) method. AMMI analyses revealed a highly significant genotype × environment interaction, most of which was partitioned into a genotype × location component of variance. AMMI first principal component axis scores stratified environments into two groups that minimized variation within groups. Biological interpretation of groupings and visual assessment of the AMMI biplot, revealed high-yielding genotypes interacting positively with one group of environments and conversely, low-yielding genotypes interacting positively with the other group. There were some significant rank changes of genotypes as yield potential varied across environments. Some environments showed similar main effects and interaction patterns indicating that most of the G × E effects could be captured with fewer testing sites, and consequently redundancy of some testing environments over years.

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Timon K. Moi and Craig R. Andersen

Southernpea [Vigna unguiculata (L.) Walp.] is the main source of protein in humid and subhumid tropics, but production is limited by low and erratic rainfalls. This potential calls for greater management of water deficit stress through timely irrigation and greater understanding of crop response to adverse environmental conditions. The objectives of this study were to: identify growth stages of southernpea sensitive to water deficit, estimate critical length of water deficit detrimental to southernpea during each stage, and describe physiological and morphological responses of southernpea to water deficit stress. In this study, two southernpea cultivars, `AR.91-285' and `Coronet', were used to examine the effect of water deficit stress on seed yield, number of pods per plant, number of seeds per pod, pod length, and hundred seed weight during three stages of growth. The greenhouse and field results for these parameters indicated that the vegetative stage was the least sensitive to water deficit stress, followed by podfilling and flowering stages. However, pod filling stage was found to be less sensitive than vegetative stage beyond 21 days of stress. The critical length of water deficit causing yield reduction appeared to be 7 days for flowering and pod filling stages and 14 days for vegetative stage. `Coronet' was less sensitive to water deficit stress than `AR.91-285'. Reduced plant size, change in leaf color, and wilting were plant responses during the vegetative stage. Leaf senescence, flower abscision, fewer and shorter pods, and early pod maturity were observed plant responses during the reproductive stages. We observed a general decline in stomatal conductance and net CO2 assimilation with increasing days of stress. After 7 and 14 days of water-deficit-stress vegetative growth, stomatal conductance and net CO2 assimilation returned to the levels of control.

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Abe Shegro Gerrano, Patrick Olusanmi Adebola, Willem Sternberg Jansen van Rensburg and Sonja Louise Venter

. Adebola, P. 2015 Genetic variability in cowpea [ Vigna unguiculata (L.) Walp.] genotypes. S. Afr. J. Soil and Plant 32:165–174 Girish, G. Viswanatha, K.P. Manjunath, A. Yogeesh, L.N. 2006 Genetic variability, heritability and genetic advance analysis in

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Pei Xu, Tingting Hu, Yuejian Yang, Xiaohua Wu, Baogen Wang, Yonghua Liu, Dehui Qin, Jeffrey Ehlers, Timothy Close, Zhongfu Lu and Guojing Li

Cowpea ( Vigna unguiculata L. Walp.) (2n = 2x = 22), a self-pollinating diploid species belonging to the genus Vigna of the Phaseoleae tribe, is an important food legume worldwide. Two main cultivated divisions of cowpea are the ssp. unguiculata

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Erin C. Hill and Mathieu Ngouajio

Hairy vetch (Vicia villosa Roth) (HV) and cowpea [Vigna unguiculata (L.) Walp.] (CP) are two leguminous cover crops used in vegetable production systems. The residues of both species have been shown to suppress weeds via allelopathic interactions; however, they may also carry a risk of crop injury. A laboratory experiment was designed to study the dose response of carrot, sweet corn, cucumber, lettuce, onion, pepper, and tomato germination and radicle elongation to the aqueous extracts of both HV and CP. Aqueous extracts of fresh, whole plants were lyophilized to obtain a dry powder. Treatments of 0.00, 0.25, 0.50, 1.00, 2.00, 4.00, and 8.00 g dry extract/L of distilled water were applied to 10 seeds on filter paper in petri dishes. The petri dishes were then sealed and placed in the dark at 21 °C for 4 to 7 days, depending on the species germination. After the incubation period, germination rates and radicle lengths were recorded. Each treatment had 4 replications and the full experiment was executed twice. Pepper germination was reduced by increasing concentrations of HV extract; however, all other crops were not affected by HV or CP extracts. The HV extract had a significant effect on radicle elongation in carrot, corn, cucumber, lettuce, onion, and tomato. Inhibition of radical growth at 8 g·L-1 ranged from 42% in cucumber to as high as 81% in carrot. The CP extract had a negative effect on the radicle elongation of carrot, corn, lettuce, and tomato. Inhibition at 8 g·L-1 ranged from 42% in carrot to 67% in tomato. This study shows that both HV and CP extracts hold the potential to negatively affect the listed crops. Therefore, studies need to be done on the persistence of these effects in the field to maximize weed control while avoiding crop injury.