A REVIEW OF POTATO CYST NEMATODES IN PORTUGAL
The potato crop in Portugal is grown on about 120,000 hectares (just over 3% of the total crop area) and, which other vegetables, represents about 20% of the value of agricultural production. The area under potatoes has increased in recent years but total production has remained steady at just over 1 m tones because average yields have declined. Some of this decline may be due to losses caused by potato cyst nematodes (PCN). Between 40 and 75% of potato fields were found to be infested with PCN in the main potato growing areas, with and average infestation level of about 20 eggs per g soil. Vila Real had fewest infested fields and the lowest overall population densities. Identification of the PCN species in 89 populations by isoelectric focusing, and checking the reaction of 60 of these populations to the H[sub1] and a further 20 to both the H[sub1] and H[sub2] resistance genes, showed that more than 50% were pure Globodera rostochiensis and controllable by cultivars containing the H[sub1] gene. Only five populations were pure G. pallida but at least two of these were able to produce only a few cysts on clone P55/7 (containing the H[sub2] gene) so may contain a proportion of pathotype Pal. Almost half the populations produced at least some cysts on Cara (containing the H[sub1] gene), indicating that many populations were mixtures of the two species. Nevertheless, correct deployment of H[sub1] resistant cultivars will play and important role in PCN management in Portugal.