Resistance to Three Species of Root‐Knot Nematode in Soybean1

Root‐knot nematodes (Meloidogyne spp.) significantly reduce yield of soybean [Glycine max (L.) Merr.] in the southeastern USA. Cultivars with higher levels of resistance than currently available will reduce yield loss in nematode‐infested fields and may eliminate the need for expensive nematicides. Soybean genotypes (2370) in the Southern Germplasm Collection (Maturity Group V, VI, VII, and VIII) were sequentially screened in a greenhouse to identify the highest levels of resistance to M. incognita (Mi), M. arenaria (Ma), and M. javanica (Mj) based on root galling and nematode reproduction. After three levels of screening using an inoculum density of 2000 nematodeggs per plant, 61, 56, and 61 genotypes were identified as resistant to Mi, Ma, and Mj, respectively. In the next two screening levels, two or three inoculum densities were used to differentiate the levels of resistance among these genotypes. The screening for Mi identified ‘Amredo’, PI96354, PI408088, and PI417444 with lower gall indices, fewer eggs per root system, and eggs per gram of root than ‘Forrest’, the resistant check. In the Ma screening PI200538 and PI230977 had lower gall indices and fewer eggs per root system than ‘Jackson’, the resistant check. The Mj screening identified PI230977 with a lower gall index than ‘Gordon’, the resistant check. These new sources of resistance will be useful to soybean breeders in developing cultivars with higher levels of resistance to root‐knot nematodes than currently available in commercial cultivars.