Histopathology of the root-knot nematode, Meloidogyne incognita, on ornamental plants (Crassulaceae)

The interaction between ornamental succulents and the root-knot nematode (Meloidogyne spp.) is poorly known. Morpho-anatomical modifications induced by M. incognita to roots of Echeveria cimette and Pachyphytum compactum (Crassulaceae) were analyzed. The affected roots of both taxa showed: numerous galls with egg masses, hyperplastic reactions, cell suberization, disorganized vascular tissues, and development of multinucleated giant cells. Although both hosts were shown to be susceptible, certain characteristics evidenced plant defense reactions. In E. cimette, in those zones of the gall cortex that had great accumulation of tannins no females or egg masses were observed and this compound would be playing a role of a natural defense barrier. Suberized cells surrounding the egg masses could limit the movement of hatched juveniles. In P. compactum, the presence of branched roots with excessive atypical short extensions was noticeable. They were highly suberized and would act as a barrier preventing the loss of water and solutes; they might also be related to a defense mechanism, since they had tannins. Root cell studies of E. cimette and P. compactum parasitized by M. incognita are described for the first time. These results show the importance of commercializing ornamental plants with an adequate sanitary control to avoid the dispersal of this polyphagous nematode. Vegetative propagation of succulents is highlighted, since when they are affected by nematodes, the cuttings can be used as a resource for the conservation of plants.