Cuticle Structure in the Genus Heterodera

Abstract

The cuticle structure of H. rostochiensis males and of the females of fourteen species or pathotypes of Heterodera was examined with light and electron microscopes. The layers of the male cuticle resemble those of the 2nd-stage larva and other vermiform Tylenchida so far described. The cuticle of females differs from this basic pattern in ways that fit their swollen form and sedentary habit, and their ultimate function as a protective cyst enclosing the quiescent eggs. The outer and inner layers, A and B, of males and larvae are supplemented by a third, fibrous layer, C, in lemon-shaped and round-cyst nematodes and by a fourth layer, D, in round-cyst nematodes only. The fibres in D are arranged helicoidally as in the chitin of insect endocuticle. The B layer of larvae and males is crystalloid, with disjunctions in the regular pattern at every half-annule. The periodicity of the pattern is 18-20 nm, similar to one of the forms of collagen. In females, the B layer ruptures as the body swells and ultimately occurs as separate islands at the junction of the A and C layers. Stained sections observed with bright field, phase, polarised light or interference microscopy, suggested that the thick fibre layers C and D are collagenous and that the A and C layers contain lipid. The composition and function of the various layers and the role of collagen are discussed. The differences in cuticle structure between the species with lemon-shaped and round cysts supports placing the round-cyst species (possibly excluding H. punctata) into the separate genus Globodera, already suggested by Skarbilovich as a subgenus.