Genetic Determinants of Differential Resistance to Root-Knot Nematode Reproduction and Galling in Lima Bean

Root-knot nematodes (Meloidogyne spp.) are important root parasites that limit lima bean (Phaseolus lunatus L.) production, although genetic resistance is available. In accession L-136, we investigated the apparent independence of genes controlling nematode reproduction and root galling. Segregation of nematode egg production and root-galling phenotypes in F 1 , F 2 , F 2:3 , and F 2:7-9 populations from L-136 x susceptible 'Henderson Bush' was determined in growth pouch, greenhouse pot, and field screenings. Three nuclear genes designated mir-1 (recessive), Mig-1 (dominant), and Mjg-1 (dominant) were found to control M. incognita reproduction, M. incognita galling, and M. javanica galling, respectively. Contrast analysis indicated that gene combinations affected nematode egg production and gene combinations provided comprehensive resistance. This independent resistance to root-knot galling and reproduction, reported for other leguminous crops and cotton (Gossypium spp.), has important implications for breeding broad-based nematode resistance.