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AHDB Agronomists’ Conference 2016: Potato cyst nematode

16 December 2016

 

AHDB Agronomists’ Conference 2016 – AHDB Potatoes

Potato cyst nematode; Changing dynamics in UK populations

A recent 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.

The 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, Dr Matthew Back of Harper Adams University told the conference.

“The widespread use of varieties with high resistance to G. 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. The remaining 10% were 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 very 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.

Traditional pathotyping, which reflects the ability of a PCN population to multiply on potato varieties based on their resistance genes, is a lengthy process, said Dr Back.

A further process, mitotyping, is being tested. This involves gene sequencing mitochondrial DNA taken from different PCN populations.

“Mitotyping is very new,” said Dr Back. “It is potentially much quicker and more accurate than phenotyping and we hope it will highlight some useful differences.

“There are three mitopypes of G. pallida, and we would like to see these related to virulence and compare this with a population’s interaction with different varieties.

“Once we understand this relationship between mitotype and variety, breeders could then include this in their variety information, helping growers to select the most appropriate varieties for their particular area.”

Much greater emphasis needed to be put on developing varieties for the ware sector that were resistant to G. pallida, said Dr Back.

 

Species testing

Growers also needed to know that levels of G. pallida had increased. “I believe a lot of growers do sample and get soils tested, but they work on the level of infestation as a whole, rather than taking account of species.

“The survey has shown clearly that populations can change, so they need to get a species test done as well or they may be selecting the wrong varieties.” 

That, coupled with options like extended rotations, biofumigants and trap cropping, would help growers cope as chemistry came under increasing pressure from legislators, said Dr Back.

“We are always looking to tackle fractions of the PCN population in as many ways as we can to build overall control, and there is a role for all strategies in that aim.”

 

Egg viability

Another part of the project aims to provide a better assessment of PCN egg viability than the existing hatching and staining tests. The former was lengthy and expensive and the latter potentially misleading, said Dr Back.

A new assessment under test measures the amount of trehalose, a sugar found in the PCN eggshell.

“Trehalose is lost when the permeability of the egg shell changes. This causes a modification in pressure within the egg, which stimulates juvenile nematodes to hatch,” said Dr Back. “We are seeing a nice relationship between trehalose levels and the expected number of viable eggs.

“This could prove particularly useful after biofumigation or soil fumigation. Often eggs can be found after treatment suggesting the treatment hasn’t worked. This test could provide the proof growers need.”

Kasia’s PhD project was supervised by Matthew Back, Ivan Grove and Simon Edwards from Harper Adams University and Vivian Blok at the James Hutton Institute. Staff from SASA provided technical assistance with the survey.

Speaking after the conference, AHDB knowledge exchange manager Anne Stone said PCN greatly reduced the profitability and sustainability of potato production.

“Varietal resistance is the anchor of an integrated strategy and as G. pallida is now a very high proportion of total infections, the shortage of varieties with resistance to this species is the single main obstacle to PCN control.”

Growers had worked hard against this pest, with some success, but those in areas with relatively low infestation should avoid complacency and test fields prior to growing potatoes, she added.

“It may be tempting to think that ignorance is bliss, but any bliss that comes from ignorance of PCN infestation is short lived.”

PCN Survey 2016

- 48% of land infested with PCN
- 89% contained pure G. pallida
- 5% contained pure G. rostochiensis
- 6% contained a mixed population

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