Cowpea is an important grain legume crop used as a feed for livestock and as a green vegetable, and its dry beans provide 22% to 25% protein (Goenaga et al., 2008; Murillo-Amador et al., 2006). Because of its versatility, high nutrition, and self-pollinating nature, cowpea has been advocated as a candidate crop for space agriculture (Nelson et al., 2008). World production of cowpea was 5.63 million tons in 2010 with 95% of total production originating in African nations (Food and Agriculture Organization of the United Nations, 2012).
Calcareous soils, where cowpea is often grown, cover more than 30% of the earth’s soil surface (George et al., 2012). When grown at pH >7.5, cowpea develops severe leaf chlorosis caused by deficiencies of iron (Fe), zinc (Zn), and often manganese (Mn). To our knowledge, there are no commercial cowpea cultivars possessing alkaline soil tolerance, but evidence of genotypic differences has been observed (R. Goenaga, unpublished data). For over 10 years, seeds of photoperiod-sensitive accessions in the U.S. Department of Agriculture (USDA) cowpea collection has been regenerated at the USDA-Agricultural Research Service (ARS) facilities in St. Croix, U.S. Virgin Islands (Gillaspie et al., 1999), in part because incidence of pests and diseases of cowpea at this site are minimal because of the absence of large plantings of this or related crops. Genetic diversity for tolerance to alkaline soil conditions, such as those encountered at St. Croix, has been observed by the authors during these regeneration cycles in field plots with pH >8.0. Tolerance is defined in this study as the ability of a PI to produce a good crop (seed yield over 1000 kg·ha−1) when field grown at a pH >7.5.
The present study was conducted with the objective of determining yield potential of selected cowpea PIs that have shown alkaline soil tolerance in unreplicated seed regeneration plots as an effort to identify PIs that could be used in areas where agricultural production may be limited by high soil alkalinity of calcareous soils.
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