A survey of potato cyst nematode in Great Britain has identified a fall in the area of land affected by the pest, but a significant shift in populations on areas that remain infested.

Since the last assessment was carried out in 1999, a survey conducted by Kasia Dybal, of Harper Adams University, as part of a AHDB Potatoes' PhD Studentship, showed almost half (48%) of the soils tested in 2016 were found to be infested with PCN.

This was lower than the previous figure of 64%, possibly due to the increase in potato varieties carrying the H1 resistance to globodera rostochiensis, according to Harper Adams' Dr Matthew Back at the AHDB's Agronomists' conference, at the end of 2016.

“The widespread use of varieties with high resistance to rostochiensis, possibly combined with the adoption of better management, including longer rotations, adoption of better practices and integrated management techniques, has led to an overall decline in the area infested,” said Dr Back.

Six out of the 10 most popular varieties in the UK, including the most widely grown, Maris Piper, had resistance scores of 8 or 9 to that species, he added. “But it means we are left with more g. pallida as a result.”

In the 1999 survey, pure g. pallida accounted for 67% of infestations, g. rostochiensis for 25% and a mix of the species for 8%. In 2016, almost almost 90% of infested sites contained pure g. pallida and the remaining 10% was split between pure g. rostochiensis and a mix of the two species.

This was potentially bad news for the fresh potato sector, said Dr Back. “Varietal resistance is a key component of PCN management. The processing sector has access to quite a few resistant varieties, but few options are available for the ware sector. Of the top 10 varieties, two score 3 for resistance and the rest just 2.”

The eventual aim is to produce a map of PCN distribution around the country highlighting regional differences in populations to help growers optimise variety selection.

As well as highlighting species distribution, new work is being carried out to determine the virulence of different populations of the same species, important for fine-tuning variety choice.