Yellow (Cyperus esculentus) and purple nutsedge (Cyperus rotundus) are notinjured by increasing root-knot nematode (Meloidogyne incognita) population density

Greenhouse studies in 1995 and 1996 examined the response of yellow and pur ple nutsedge to inoculation with increasing densities of southern root-knot nematodes. Yellow and purple nutsedge root and shoot weight, numbers of le aves and tubers produced, and tuber weight were unaffected across 17 nemato de inoculum densities that ranged from 0 to 20,000 eggs per 15-cm pot, four times the maximum nematode density recorded under field conditions in New Mexico. Hence, yellow and purple nutsedge do nor exhibit a classic threshol d response to root-knot nematodes. Moreover, the results suggest that the r elationship between these nematodes and perennial nutsedges is an example o f a positive biological interaction. The relationship between root-knot: ne matodes and purple nutsedge appears to be one of commensalism, because whil e the nematodes reproduced effectively, purple nutsedge reproduction was no t related to final nematode populations. The relationship between yellow nu tsedge and root-knot nematodes appears to be a mutually beneficial one, bec ause yellow nutsedge tuber number and weight and root weight increased as f inal nematode populations increased. However, while both nutsedges were una ffected in the absence of the association, root-knot nematodes cannot survi ve without a host plant.