Histological characterization of resistance to Meloidogyne incognita in Avena sativa

Root-knot nematodes, especially Meloidogyne incognita, are recognized by expressive damages on important agronomic crops worldwide. White oat (Avena sativa) is an excellent alternative to sustainable management of nematodes especially when used in crop rotation with another plant species. In this context, the aim of the present work was to study the resistance of IPR Afrodite oat cultivar to M. incognita, using histopathological methods in a comparative approach with the susceptible cultivar URSFAPA Slava. Experiments were done under greenhouse conditions, with 6 replicates for each cultivar and evaluation time. Observations of fuchsin-stained roots at 3, 9, 15 and 30 days after inoculation (DAI) revealed that the resistant cultivar did not suppress nematode penetration but caused a delay in the nematode development compared with the susceptible cultivar. Moreover, mature, egg-laying females were not found in the roots of the resistant cultivar. Hypersensitive reaction (HR) was observed at 18 DAI. The HR was characterized by the formation of few giant cells of reduced size on the resistant cultivar, associated with collapsed M. incognita specimens. In most specimens, light blue fluorescence indicated lignified cells, an active plant response to nematode penetration or establishment. Intercellular spaces were of dark yellow color, indicating the presence of phenols, often associated with plant defense mechanisms to nematodes and other pathogens. Our results suggest that resistance of IPR Afrodite to M. incognita is mediated by a HR response and studies are needed to clarify the nature of compounds produced by the plant involved in the resistance.