Population dynamics of potato cyst nematodes (PCN) in relation to temperature
In temperate countries it has been generally accepted that PCN undergoes a single generation during the potato crop followed by an obligate dormant stage (diapause) which is not broken until the nematode has experienced a winter. However, partial and complete second generations have also been reported and this has significant implications for the control of PCN.
If the second generation is completed this could lead to large increases in population sizes as well as applying strong selection for PCN genotypes with faster life cycles and/or increased virulence. Alternatively, a partially completed second generation might lead to lower final population levels if the egg content of the first generation is significantly reduced while the second generation is not completed at harvest.
Lab and field studies were carried out to examine the rate and amount of hatching of the two PCN species.
The population of G. pallida tested hatched more at lower temperatures than the G. rostochiensis populations and G. rostochiensis hatched more at higher temperatures than G. pallida. A model was developed describing the relationship between temperature and hatching for both species.
The occurrence of a second peak of juvenile nematodes was observed in pot experiments and is consistent with the start of a second generation. This implies that entry into dormancy at the end of the first generation is not obligatory. The amount of juveniles in the second peak increased with increasing temperatures. The start of the second peak occurred earlier with G. rostochiensis.
In field trials at Harper Adams, England and Luffness, Scotland, the G. pallida populations were monitored monthly. At Harper Adams, which had an average soil temperature of 14.85ºC there was evidence of a second generation based on the presence of juveniles and females in the roots in the latter part of the growing season. Luffness had an average soil temperature of 14.15°C and was cooler in the latter part of the growing season and there was little evidence of a second generation