Charles H. Opperman, and David M. Bird.
The Center for the Biology of Nematode Parasitism, North Carolina State University, Raleigh, NC, USA.
Plant parasitic nematodes collectively cause over $100 billion in crop losses, with most of the damage caused by Meloidogyne spp (root-knot nematode [RKN]) and Globodera/Heterodera spp. (cyst nematodes). Root-knot and cyst nematodes both are significant parasites of legumi-nous crops, including soybean, alfalfa and other forage legumes, pea. bean, and peanut, The most economical and environmentally friendly method for management is to deploy nematode resis-tant cultivars. However, genetic resistance is either not available or not complete in many leg-umes. We have established Medicago truncatula as a system to study host-nematode interac-tions. Screening of >100 accesions from the Medicago truncatula germplasm collection has re-vealed variation in susceptibility to both RKN, including M. incognita, M. arenaria, and M. hapla, and clover cyst nematode, H. trifolii. Additionally, we have recently identified a soybean cyst nematode, H. glycines, strain which is able to infect and reproduce upon M. trunca-tula.Some accessions are resistant to all species, while others have varying combinations of resistance. Because accession DZA045 is resistant, and accession F83005 susceptible to all three RKN species, we chose them for genetic analysis. We examined responses from Recombinant Inbred Lines (RILs) generated by crossing these two accessions, results obtained from 212 RILs demonstrate that two unlinked loci control resistance to M. incognita. These genes are additive, and the inheritance of only one of the two results in an intermediate phenotype. Although resistance in DZA045 is temperature sensitive, we do not observe a hypersensitive response, com-monly seen in Solanaceous hosts. Instead, most of the infected nematodes develop as males and leave the root. Examination of gene expression in the susceptible interaction has revealed that many genes involved in feeding site formation also appear to be expressed during nodulation. Models for the shared signal transduction pathways have been developed.