Wild prose millet (Panicum miliaceum) is genetically variable and distinct from crop varieties of proso millet

Prose miller occurs both as a crop and a weed in North America. In 1970, an olive-black seeded biotype called ''wild prose miller'' was found as an aggressive weed in row crops in Minnesota and Wisconsin and has since spread over a large area. We used Random Amplified Polymorphic DNA (RAPD) to assess genetic relationships among biotypes, measure genetic variation within wild prose miller across its range, and detect hybridization between wild prose miller and crop biotypes of proso miller. We found 97 RAPD genotypes among 398 individuals: 69 wild prose miller genotypes, 26 crop and crop-like weed genotypes, and two hybrid genotypes. Five RAPD markers consistently differentiated wild prose millet from crop cultivars and crop-like weeds. About 10% of the genotypes had at least one marker of the other type, suggesting possible hybridization between wild prose miller and crop biotypes. Most genotypes occurred in only one or two of the over 100 populations rested. The most widespread wild prose miller genotype occurred in 12 populations distributed in North Dakota, Minnesota, Illinois, and Wisconsin. More genetic variation exists among populations of wild prose millet than expected for a plant that presumably experienced a severe genetic bottleneck only 20 generations ago. Hypermutation rates and crossing between wild prose miller and crop cultivars could not account for the degree of genetic variation found in wild prose miller. The pattern of generic variation among wild prose miller populations suggests multiple introductions of wild prose miller to North America.