Increased penetration of host roots by nematodes after recovery from quiescence induced by root cap exudate

Fourteen of 20 plant species surveyed produced root cap exudates that induced a state of reversible quiescence in Meloidogyne incognita and Caenorhabditis elegans. Exudate from six species failed to induce quiescence in either nematode species. Root cap exudates from pea were found to trigger quiescence in populations of plant-parasitic, animal-parasitic, insect-pathogenic, and free-living nematode species. One animal parasite was resistant. Caenorhabditis elegans strains with defects in known metabolic pathways also were screened to explore the potential for using this model system to examine the genetic basis for exudates-induced quiescence (EIQ). All 62 lines tested exhibited wild type sensitivity to root cap exudates and preliminary efforts to obtain viable EIQ-resistant strains by ethyl methanesulphonate (EMS) mutagenesis were unsuccessful. After recovery from EIQ, penetration of alfalfa roots by second-stage juveniles of M. incognita more than doubled within 24 h, compared with controls, and the number of nematodes per root remained high for a week but long-term development and maturation was similar to that of untreated control inoculum. In cucumber, penetration after recovery from EIQ increased by several fold but returned to control levels within 4 days post-inoculation.