The 2010 ASHS Annual Conference

The adoption of sustainable and organic cultural practices in recent years has resulted in an increased use of cover crops.  Cowpea (Vigna unguiculata L.) is an excellent warm season cover crop due to its tolerance of heat and drought stress, ability to grow well in sandy, poor, acidic soils, high biomass production with high nitrogen content, and low fertilizer requirement.  In 1997, field screening trials were initiated to identify cowpea populations suitable for use as a cover crop.  The forty-seven populations in the initial studies included cultivars, germplasm accessions, and land races.  Three populations were identified as having superior characteristics for use as a cover crop.  All three were heterogeneous land races that were collected in South Carolina.  A pure-line selection procedure was initiated to develop homogeneous lines.  In 2006, the land race populations were grown in a field planting and three typical plants from each population were selected.  In a 2007 field planting, the original three land race populations and the progenies of the three plants selected from each of the original populations were carefully evaluated for the following traits: rapid growth, good vigor, indeterminate growth habit, canopy height, and high seed quality.  A single progeny population was selected from each of the original land race populations for release as a germplasm line.  The three lines have relatively short photoperiods; flowering does not begin until day length is approximately 13 hours, and flowering and pod set continues in an indeterminate manner until plants senesce in late autumn or are killed by frost.  The lines are homozygous for all important agronomic traits.  They are resistant to the southern root knot nematode [Meloidogyne incognita (Chitwood) Kofoid and White] (many horticultural type cultivars are susceptible), and grow well without nitrogen fertilization.  Iron Clay and other forage cowpea cultivars produce seeds with an impermeable seed coat.  This trait enables viable seeds to overwinter in the soil, germinate the following spring, and become a weed in subsequent crops.  The newly-released lines produce good quality seeds with high germination rates (>95%) and do not produce seeds with impermeable seed coats.  The adoption of these lines for use as a cover crop will eliminate the weed problem caused by dormant cowpea seeds.  Samples of seeds of US-1136, US-1137, and US-1138 are available for distribution to all interested research personnel.