Characterization of Heterodera avenae in Spain1

Several types of Heterodera spp. belonging to the ? avenae ? group have been found in Spain on cereal crops and wild Gramineae. The morphological differences between them relate to the colour of the cysts, presence or absence and consistency of the subcrystalline layer, presence or absence and shape of the ? underbridge ? in the vulvar cone, length of the 2nd-stage larvae and shape of their stylet knobs. The value of these characters in the diagnosis of these species is discussed together with the identity of the types.