Species-dependent effects of border cell and root tip exudates on nematodebehavior

Effects of border cell and root tip exudates on root knot nematode (Meloido gyne incognita) behavior were examined. In whole-plant assays using pea, M. incognita second-stage juveniles (J2) accumulated rapidly around the 1- to 2-mm apical region ensheathed by border cells, but not in the region of el ongation. Within 15 to 30 min, J2 which had accumulated within detached clu mps of border cells lost motility and entered into a quiescent state. When border cells (and associated root tip exudates) were washed from pea roots Drier to challenge with nematodes, no such accumulation and quiescence was induced. Attraction of nematodes by roots was species dependent: no attract ion or accumulation occurred in snap bean. Using a quantitative assay, thre e categories of chemotaxis responses occurred: attraction (pea and alfalfa cv. Thor), repulsion (alfalfa cv. Moapa 69), and no response (snap bean and alfalfa cv. Lahonton). In contrast, total root tip exudates from all three plant species acted as a repellent for M. incognita in the sand assay. An in vitro assay was developed to characterize the induced quiescence respons e. When total root tip exudate from the tested legumes (as well as corn) wa s incubated with J2 populations, >80% of the nematodes lost motility. A sim ilar response occurred in Caenorhabditis elegans. Border cell exudates did not induce or contribute to the induction of quiescence. Cocultivation of p ea border cells with M. incognita resulted in changes in border cell shape similar to those observed in response to exogenous plant hormones. No such changes occurred in snap bean border cells. Understanding the cell- and hos t-specific extracellular recognition that occurs between roots and pathogen ic nematodes in the early stages before infection occurs could lead to new avenues for disease control.