Scanning Electron Microscopy of Vulval Cones of Heterodera glycines and Three Related Cyst Nematode Species.

Vulval cones of four closely related Heterodera species - H. glycines (races 1-5), H. lespedezae, H. schachtii, and H. trifolii - were examined using scanning electron microscopy. Numbers of dorsal and ventral radial ridges, total radial ridges, perineal ridges, and preanal ridges were useful in differentiating the five races of H. glycines and the other three species. Most of the populations differed significantly (P < 0.01) using the Waller-Duncan k-ratio t-test for mean separation of the five characters. H. glycines races 2, 4, and 5 were most similar. H. schachtii and H. trifolii were most dissimilar to each other and to H. lespedezae and H. glycines. Two additional qualitative characters were also useful in differentiating the populations. The shallower, shorter radial ridges of H. glycines provided a basis for separation from the other three species. Width and smoothness of the perineal ridges were useful in differentiating both races and species.