Genetic Diversity of the North American Wild Kidney Bean (Phaseolus polystachios) in the Eastern U.S.

North American wild kidney bean or thicket bean (Phaseolus polystachios (L.) Britton, Sterns, & Poggenb) is a perennial vine found in the eastern United States from Texas to Connecticut. It is the only Phaseolus species native to temperate North America. Its closest cultivated relative is P. lunatus, the lima bean. Urbanization, agricultural development, and habitat destruction have caused a decline in populations, leading to widely varying estimates of conservation status across its distribution: e.g., it was once prevalent in the Detroit River International Wildlife Refuge, but has not been seen there since the late 1800’s. Crop wild relatives are a critical source of genetic diversity, often holding untapped genes for breeding of domesticated plants in agriculture for disease resistance, yield, quality, and adaptation to climate change, as well as ecologically important members of natural habitat. The Western Regional Plant Introduction Station of the National Plant Germplasm System holds over 20,000 accessions of Phaseolus from 47 species but had only 13 accessions of the wild Phaseolus polystachios, 6 of which had recently been collected in Florida. A collection trip throughout the Midwest in 2015 acquired populations from Missouri (1), Indiana (2), Ohio (7), and West Virginia (1). In Missouri, Illinois, and Indiana, information leading to 15 historically collected sites, resulted in finding only four of these populations still existing. Amplified fragment length polymorphism (AFLP) molecular analysis showed each population to be genetically distinct and distinct from the previous populations from Florida. Several of the populations were infested with weevils, reducing seed viability and threatening population survival. Populations are currently being regenerated for distribution for research and breeding. Plans are underway for future testing for resistance to white mold (Sclerotinia scerotiorum). Population diversity from the Eastern states from Florida to New England and the Midwest and coevolution with white mold may have resulted in new sources of resistance for interspecific breeding, especially with P. lunatus.