Four potato varieties not known to be resistant to white potato cyst nematode (Globodera pallida) have given much better yields than eight others in the first year of a two-season SARIC-funded research project*.
Andrew Blake reports....
The latest work aims to improve AHDB’s potato cyst nematode population advisory tool (potatoes.ahdb.org.uk/online-toolbox/pcn-calculator), explains Matthew Back, of Harper Adams University.
“We’re working with the University of Leeds and Barworth Agriculture to overcome issues which relate to the accuracy of yield benefits from chemical control and tolerance values,” he says.
Five of the top 10 UK varieties are missing from the PCN calculator, notes colleague William Watts.
They are Markies, Melody, Nectar, Royal and Taurus.
“New management practices such as trap cropping and biofumigation aren’t yet built into it,” he adds.
“And it doesn’t currently incorporate summer temperatures into PCN decline rates over time.”
Field experiments on PCN-infested land were carried out last season on the top 10 most widely grown varieties plus two PCN-tolerant varieties – Cara and Maris Piper.
“We determined the PCN population densities before planting and after harvest,” says Dr Back. “This gives us a greater understanding of population dynamics, particularly multiplication rates.
“We’re also assessing the invasion of potato roots by PCN juveniles six weeks after planting as well as monitoring potato growth and yield development.”
The varieties’ tolerances are judged by comparing their untreated yields with their output when protected by granular nematicide – in this work oxamyl (as in Vydate) applied via a bedtiller.
“The field experiments have been carefully set up to account for the patchiness of PCN populations.
They’re in four blocks on about 0.5ha in a stratified randomised block design based on PCN density. The crop was planted in May and harvested in September.”
The PCN egg density at the site ranged from 28 to 304 eggs/g soil – previous commercial tests suggested only 18-109.
One of the project’s aims is to find out more accurately how soil type influences the rate of PCN decline.
“We’re providing PCN populations to the University of Leeds for this aspect,” says Dr Back. “Many of these populations came from an AHDB-funded survey of PCN in England and Wales conducted by Katarzyna Dybal.”
Preliminary results from the 2017 work found no significant differences between the nematicide-treated and untreated plots.
“That may have been due to the high initial PCN population densities. However, Cara, Maris Piper, Melody and Nectar produced significantly higher yields than the other varieties in the experiment.
“Interestingly, none of these varieties possess resistance to Globodera pallida – it was a pallida site – although Cara and Maris Piper have been reported to be tolerant in other published studies.
“We’re in the process of assessing the final post-harvest PCN samples. These results should allow us to interpret the PCN population dynamics throughout the experiment.”
Potato cyst nematodes, especially Globodera pallida, are important soil pests causing potato growers significant economic losses, says project leader Peter Urwin, of Leeds University.
In its 2015 research and development strategy document AHDB Potatoes estimated the pest caused losses of £26 million which could rise to £50m if nematicides became unavailable.
“Pallida is the most prevalent species in the UK and its control is the most problematic,” says Prof Urwin.
“The AHDB acknowledges that the PCN advisory tool needs improving and updating. While offering valuable advice, in certain scenarios the model could reflect outcomes more accurately.”
The lack of commercially favoured PCN-resistant varieties and concerns surrounding the use of chemical control measures mean Globodera pallida has become an intractable problem for farmers in the UK and in many other countries, he adds.
“The potato cyst nematode advisory tool developed by AHDB, and being enhanced with SARIC funding for the UK, could be modified as a pest management tool for the central Andes.
“Improvements should consider the greater altitudinal range in central Andes than the UK and future-proofing added for changes in temperature and precipitation which are predicted by IPCC climate change models.”
The potato industry definitely needs a model to help growers and agronomists assess and measure their adopted strategies for tackling the PCN problems of their own crops, says Lincolnshire-based Barworth Agriculture agronomist Andy Barker.
“Every grower’s situation is different as is every field,” says Dr Barker. “So there’s no single answer, and having a model against which to compare potential management approaches will be invaluable.
“We would hope that the final product is sufficiently flexible to allow novel approaches and new varieties to be included as they become available.
“An important part of the current project is the work on the potential decline rates of PCN in field situations.
“Clearly this is a crucial component of long-term strategic management; and with the emphasis on sustainability, any contribution to field rotation planning will greatly improve the economic robustness of a whole farm enterprise.
“Previous assessments of PCN decline rates have relied on repeated and targeted sampling methods, and this will continue to be part of the exercise.
“However, examining the ‘status’ of cyst contents promises to offer a more direct and immediate indication of PCN decline, albeit not an absolute measure.”
AHDB project: SARIC-funded project: Development of a PCN population advisory tool that provides robust advice and management
July 2016–March 2019
Funding: University of Leeds (Principal Investigator): £100,050
Harper Adams University: £83,844
Industry partner: Barworth Agriculture