Potato cyst nematode: 1 species or 2?

Abstract

THE potato or golden cyst nematode, Heterodera rostochiensis Woll., is an important pest of potatoes and tomatoes but has never been fully described. It belongs to the group of species of Heterodera1,2 which have round cysts and do not produce an egg sac3, for which the sub-generic name Globodera was suggested4. This group includes H. tabacum Lownsbery and Lownsbery, H. virginiae Miller and Gray, H. mexicana Compos Vela, and the undescribed Osborne's cyst nematode, all with host ranges in the Solanaceae. The females of H. rostochiensis turn golden yellow after fertilization; hence the name “golden nematode”. Mean larval lengths2,5,6 range from 450 to 470 µm. In the past, control depended on rotations with infrequent susceptible crops, but recently potato varieties (Maris Piper and Ulster Glade) have been bred with a dominant gene for resistance, derived from Solanum tuberosum ssp. andigena. These resist pathotype A but not pathotype B or E populations of H. rostochiensis7. Guile8,9 showed that pathotype E females remain white until they die and become cysts, whereas pathotype B females, which produce few cysts on H. multidissectum (Hawkes), have a prolonged cream and a very short yellow phase. Webley10 showed that larvae of pathotypes B and E were longer, and had longer stylets and a greater distance between the crescentic valves of the median pharyngeal bulb and the excretory pore than larvae of pathotype A.