Variation of the first head annule in Canadian populations of Pratylenchus penetrans (Nematoda: Pratylenchidae) from three host plants

Abstract

Configuration of the surface of the first head annule in 80 females of Pratylenchus penetrans from cherry, strawberry, and tobacco in Canada were compared to assess its diagnostic value in species identification. Most significant were structural features of the oral plate, defined collectively as the oral disk, and its dorsal and ventral extensions. The oral plate varied, often markedly, in surface configurations that were representative of different species groups. Of these, the most distinctive were hexaradiate and dumbbell in shape, comprising, respectively, 25 and 35% of the total heads scanned by scanning electron microscope. In one female the oral plate was panduriform, representing another species group, whereas the rest were of iniergrading forms of a hexaradiate symmetry. The relative proportions of these forms in a given population varied with the host, suggesting an external or selective influence. Of those in 25 females from strawberry 25% were hexaradiate, and of 27 from cherry 52% were dumbbell shaped. Also variable, but to a lesser extent, were the size, shape, and position of the amphid apertures. It is concluded that similar studies under more variable conditions may further extend the diversity of forms.