Level and geographical distribution of resistance to Meloidogyne arenaria in the US peanut germplasm collection

The peanut root-knot nematode [Meloidogyne arenaria (Neal) Chitwood race 1] causes significant economic losses in many peanut (Arachis hypogaea L.) pr oduction areas of the world. The objectives of this study were (i) to exami ne the peanut core collection to identify sources of resistance, (ii) to es timate the level of resistance that occurs in the U.S. germplasm collection , and (iii) to examine the geographical distribution for resistance in pean ut germplasm. Seven hundred forty-one accessions from the core collection s ere tested in greenhouse trials. The egg-mass rating for cultivar Florunner , the susceptible check, was 4.0 on a 1.0 to 5.0 state with a nematode repr oduction rate of 15 496 eggs per gram of fresh root weight. Fifty-six acces sions exhibited an egg-mass rating of less than or equal to 2.5. Thirty-six core accessions showed a reduction in root galling, egg-miss rating, egg c ount per root system, and egg count per gram of root in comparison to Floru nner. Twenty-one accessions showed a 70% reduction in egg count per root sy stem and per gram of root, and two accessions showed a 90% reduction of the se variables in comparison with Florunner. The 56 resistant indicators from screening the core collection identified 39 clusters in the entire germpla sm collection that should be examined more thoroughly. China and Japan appe ar to be valuable geographical sources for resistance to this nematode.