Currently, many of the most widely grown potato varieties have strong resistance to Globodera rostochiensis, but not for one or more of the three major G. pallida variants.
to an unforeseen issue. Mr Prentice tells that several new IPM seedlings have dual resistance and are achieving high resistance scores for G. pallida in its own assessments. Two of those have also received some encouraging feedback from packers on suitability for the fresh market, with good taste and skin finish. He says while not everyone has issues with G. pallida on their land, it is promising fresh growers may soon have a handful of varieties with resistance and a significant end market for their potatoes. “These can then be targeted on the land where the problems are, potentially helping to bring land back into fresh production where it hasn’t been possible due to PCN,” he adds.
Selection pressure The question is how to use a future highly dual resistant variety on a farm. A single H1 resist- ance gene is enough to give a variety strong resistance to the Ro1 pathotype of G ros- tochiensis found in the UK. However, with G. pallida the situation is much more complex, with multiple pathotypes present in the UK: Pa 1 and Pa 2/3. Populations of G. pallida Pa 2/3 are known to have significant genetic diversity, according to Harper Adams University nema- tologist Matthew Back, and potentially makes variety choice and use complex.
Resistance to G. pallida is typically polygenic (made up of multiple genes) or quantitative (quantitative trait loci) if the resistance derived from the wild solanum species, Solanum vernei. The resistance conferred is typically partial. There is some concern that with insufficient in- formation on the resistance a variety has, or on the PCN population present in the soil, certain varieties may be used in the wrong situation. “Ideally, it would be useful to characterise pallida populations for given fields. And then select va- rieties with suitable resistance,” explains Dr Back.
Integrated management AHDB Potatoes knowledge transfer manager Anne Stone says in starch production in the Netherlands, growers have planted G. pallida resistant varieties on tight rotations and seen genetic variants emerge. She doesn’t believe British potato producers will shorten rotations as more resistant varieties become available, but says the selection risk must be acknowl- edged and negated through integrated pest management. This includes maintaining long rotations, practicing good cross-rotational vol- unteer control, using biofumigation or trap crops and appropriate use of chemical nemati- cides. Dr Stone also notes a good information flow between breeders and growers and
NEED TO KNOW
▶ Significant breeding efforts to find G. pallida resistant potato varieties are ongoing
▶ Encouraging feedback from packers on new fresh varieties with dual PCN resistance
▶ Risk of selecting for different G. pallida pathotypes when using highly resistant and tolerant varieties
▶ More info on resistance, combined with accurate PCN speciation, will help making a choice
▶ Resistance should be combined with other control measures
▶ Improved information flow between breeders and growers required
agronomists will be required to make sure vari- eties are used in the appropriate situations and in a responsible way. To do this, growers will need to speak to breeders about the pedigree
▶ FUTURE FARMING | 22 February 2019 19
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