Forty-eight populations of Rotylenchulus reniformis were obtained from soil and root samples of different crops and inoculated into various host plants grown in microplots at the Departamento de Fitossanidade of the Universidade Estadual Paulista, Campus de Jaboticabal, São Paulo, Brazil. The symptoms of the disease caused by the nematode in cotton (Gossypium hirsutum) plants were documented in field and the parasitic behavior of the nematode in roots of cotton and papaya (Carica papaya) plants were investigated by in situ staining of the nematode with acid fuchsin. All populations were studied with light microscopy in temporary mounts and some were also examined using scanning electron microscopy (SEM). For SEM, mature females attached to roots were fixed in buffered glutaraldehyde and post-fixed in osmium tetroxide. The samples were then dehydrated in ethanol, dried in a critical point dessicator, mounted, coated with a 35-nm layer of gold, examined and electronmicrographed at 15 kV. The data confirm that R. reniformis is the only species of the genus distributed in Brazil and based on data from the literature, the variations of the morphometric characteristics among R. reniformis Brazilian populations, such as stylet length, V % and tail shape are greater than in populations of the same species from other parts of the world. Young females with bifurcated tails were documented in R. reniformis, a morphological feature that had not been previously reported.
