Histological changes induced by Meloidogyne incognita in roots of Apamate and Saman seedlings in Venezuela

Apamate and Saman seedlings from Nurseries I and II of the experimental sta tion of PROREFOR, Ticoporo, Barinas State, Venezuela, exhibited symptoms of wilting, stunted growth and numerous root galls. The organism associated w ith the galls was identified as M, incognita, which is reported for the fir st time in Venezuela on Saman. A histological study using light and electro n microscopy,vas made to determine the effect of the nematode on infected r oots. The cytoplasm of the giant cells around the head of the nematode was dense and granular, and contains an average of 14-15 irregularly shaped nuc lei, each with a prominent, isodiametric nucleolus. Cell walls between two giant cells are much thickened, and exhibit elongated extensions protruding toward the center of the cell. The middle lamella was almost completely di ssolved. Parenchyma cells in direct contact with the gelatinous matrix are compressed and collapsed and with a much thickened cell wall but those not in direct contact are apparently unaffected. The cell walls of the nematode eggs had three layers, a thin, dark and smooth external layer, a thick, tr ansparent center layer; and a dark internal layer.