Ultrastructural response of potato roots susceptible to cyst nematode Globodera pallida pathotype Pa3

Syncytia were examined by light and electron microscopy in the roots of three susceptible potato cultivars four and twelve days after inoculation with juveniles of Globodera pallida pathotype Pa 3. The syncytia formed in cv. Diamant developed into the stele, occupying most part of the central cylinder. The nematodes established their feeding site in the endodermal cells. In cv. Anosta the syncytia developed particularly in the cortical region and ultimately involved only the outer region of the vascular cylinder. The nematodes were localized in the cortical cells. In cv. Irene the syncytia were formed outside the-stele. The only major difference observed between the syncytia was, apart from the larger area in Diamant, in the metabolic activity of the cells involved. Syncytial cells in cv. Diamant roots showed considerable proliferation of smooth endoplasmic reticulum, less in cv. Anosta and almost none in cv. Irene. Differences in cytoplasmic activity may be indicative of a variation in the susceptibility of the plant due to the nutritional quality of the food. No Wall ingrowths were observed in the three syncytia examined.