Taxonomy, Morphological and Molecular Identification of the Potato Cyst Nematodes, Globodera pallida and G. rostochiensis

Abstract

The scope of this paper is limited to the taxonomy, detection, and reliable morphological and molecular identification of the potato cyst nematodes (PCN) Globodera pallida and G. rostochiensis. It describes the nomenclature, hosts, life cycle, pathotypes, and symptoms of the two species. It also provides detailed instructions for soil sampling and extraction of cysts from soil. The primary focus of the paper is the presentation of accurate and effective methods to identify the two principal PCN species.

Keywords: Globodera; PCN; PCR; detection; molecular identification; morphology; potato cyst nematode; taxonomy.

Figure 1

Illustration of the life cycle of Globodera rostochiensis (modified after Charles S Papp, Exclusion and Detection, Plant Pest Detection Manual 5:1, California Department of Food and Agriculture, Division of Plant Industry, USA).

Figure 2

Stylets of second-stage juveniles of G. pallida (diagrams (A,B)) and G. rostochiensis (diagrams (C,D)) (after Stone [52]).

Figure 3

Vulval-anal ridge patterns for G. pallida and G. rostochiensis (after Stone [52]).

Figure 4

Puncture cyst wall to release pressure.

Figure 5

Cut across base of cyst to retain vulval and anal region.

Figure 6

Make two more cuts to the excised section of cyst wall.

Figure 7

Light microscope image of cuticle surface of perineal region of potato cyst nematode (PCN) (G. rostochiensis) cyst laid flat on glass microscope slide.

Figure 8

(a) Image of perineal region of Globodera, showing the “halo” effect around the vulval basin, the actual diameter of which is marked by an arrow. (b) Measurements taken to calculate Granek’s ratio, where A is the distance from the anus (at the apex of the V-shaped cuticular mark) to the vulval basin, and B is the diameter of the vulval basin.