Development and validation of a quantitative assay for viability testing of potato cyst nematodes

The potato cyst nematodes (PCN) can be managed by a series of integrated management practices. However, knowledge of the survival of the nematodes in the field would make the evaluation of management strategies more accurate. This study aimed to develop and optimize a quantitative method to determine the number of viable eggs of PCN based on trehalose present in live eggs. Trehalose was extracted from cysts and from a dilution series of eggs and quantified. Results showed that more trehalose was detected when cysts were crushed than when left intact. Reaction volumes needed to be adapted to the number of eggs because small reaction volumes hampered an accurate quantitative extraction of trehalose; maximum 11 eggs per µl reaction volume can be used. The detection limit was defined as 5 viable eggs. I compared the performance of this trehalose method with visual assessment and the hatching test, commonly used methods to determine cyst viability. The three methods were compared using cysts recovered from soil after exposure to soil amendments (pig slurry, cattle slurry, farmyard manure, chitin compost, nitrogen fertilizer, wood chip compost alone and in combination with biochar) which had different nematicidal properties. There was no difference between the visual assessment and the trehalose method. The visual assessment, however, is time consuming, requires trained people and could involve subjectivity. Less viable eggs were measured with the hatching test than with the other methods. Hence, the viability assessment method based on trehalose seems to be a practical, sensitive, fast and cheap technique.