Genetic base of major conmercial soybean cultivars is very narrow. The top 10 most widely grown cultivars in the U.S. have been developed from 17 parent lines (Hartwig, 1973). Recently three soybean Plant Introductions, namely, PI 171.451, PI 227.687 and PI 229.358, have been found to have good leaf-feeding resistance to Mexican bean beetle (Epilachna varivestis Mulsant) (Van Duyn et al., 1972) and corn earworm (Heliothis zea Boddie) (Hatchett et al., 1976; Joshi and Wutoh, 1976).
Joshi, J. M.
"Research Notes: Field screening of soybean gerrnplasm (Maturity Group 00
to IV) against H. zea damage,"
Soybean Genetics Newsletter: Vol. 4
, Article 19.
Available at: http://lib.dr.iastate.edu/soybeangenetics/vol4/iss1/19