Diagnosis and Molecular Variability of an Argentinean Population of Nacobbus aberrans with Some Observations on Histopathology in Tomato.

Diagnosis of an Argentinean population of Nacobbus sp. infecting sweet pepper (lamuyo) was carried out including morphology, scanning electron microscopy, and molecular studies. In light of our morphometric, molecular and host-range results, we consider the studied population to belong to N. aberrans s. l., and by host range tests the population is assigned to the "sugar beet group." ITS-PCR analysis on individual male and immature female specimens of this population yielded amplification products of approximately 922 bp. RFLP profiles and sequencing of the ITS region revealed that, in addition to the host group, the present population can be assigned to the "Argentina 2" group. Disease development and histopathology were investigated with glasshouse observations using tomato, pepper, sugar beet and potato seedlings exposed to nematode infection for 45 days at 28 +/- 2 degrees C. Histopathology of tomato roots confirmed that all immature stages and young females and males are migratory, whereas mature females are obligate sedentary endoparasites. Rather than syncytia, large regions of cortical necrosis and cavities were detected in tomato swellings infected by juveniles. However, syncytia were associated only with adult females. Large root galls, hyperplasia, abnormal proliferation of lateral roots and asymmetry of root structure were common anatomical changes induced by the nematode feeding in tomato roots.