Histopathological changes induced by Nacobbus aberrans in resistant and susceptible potato roots.

Histopathological responses to Nacobbus aberrans infection in roots of the susceptible Solanum tuberosum cv. Revolucion, the clone of S. sparsipilum 7601217.7, and the resistant hybrid B-25 from S. tuberosum ssp. andigena were compared. In the compatible response, N. aberrans was able to initiate and maintain the formation of a syncytium and develop to maturity. The syncytia were characterized by dense cytoplasm, hypertrophied nuclei and nucleoli, partial cell wall dissolution, hyperplasia, and accumulation of starch grains in the cells surrounding the syncytial zone. In the roots of the "resistant" (incompatible) hybrid B-25, development was inhibited by the formation of necrotic cells surrounding the invading nematode. The clone 7601217.7 showed the presence of physical barriers that delayed nematode invasion; development of the syncytium and of the nematodes were, however, almost the same as observed in the cultivar Revolucion.