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Rise in samples of new blight genotype despite low blight pressure in 2018

Publication Date: 
21 March 2019

Data from AHDB’s Fight Against Blight service shows an increase in a new blight genotype found in outbreaks from last year, despite the hot and dry conditions experienced.

The warmer weather saw fewer samples submitted to Fight Against Blight compared to last year. However, isolates of the 36_A2 genotype found in the samples increased by 15 percentage points compared with the 2% found in 2017.

Rise in 36_A2

While researchers are still trying to build up a full picture of this genotype, the increase in frequency of 36_A2 in an overall low blight pressure year and its spread in continental Europe suggest it is causing an aggressive form of blight.

Results from INRA (French National Institute for Agricultural Research) which has tested blight isolates for aggressiveness, found that 36_A2 produced the largest lesions, as well as the most spores per lesion of the samples tested. Research at the James Hutton Institute showed that the genotype was more difficult to inhibit than other lineages, producing the largest lesion sizes under the lowest doses with the four key fungicide active ingredients used to combat blight. As the doses applied were well below the rates applied in the field, the data do not give evidence of 36_A2’s resistance to the fungicides used.

So far 36_A2 has established itself in the East of the country but has not yet been found further north than Lincolnshire or in the North or West.

Fall in 37_A2

Last year also saw a drop in the number of samples submitted containing the 37_A2 genotype: from 24% observed in 2017 to 16%.

Originally discovered in 2013 in the Netherlands, 37_A2 is of concern due to its insensitivity to fluazinam, meaning the fungicide will not be effective against the genotype. Laboratory tests conducted on the samples submitted from 2018 provided more evidence of 37_A2’s insensitivity. This means a more holistic approach in managing the crop is required, taking into consideration methods such as: removing susceptible crops from the rotation and using resistant varieties. The 37_A2 genotype is more widespread than 36_A2 and in 2018 it was detected in a trial site in South Ayrshire, Scotland.

With only a limited range of samples submitted from 2018 - lower than in an average year for the Fight Against Blight service – it is somewhat difficult to build up a full picture of the changes in blight lineages. This is because the data could be subject to sample size errors, rendering it difficult to compare the data with previous years.

Continuing the fight against blight

A new contract has been put out to tender in order to continue the Fight Against Blight service. Once approved, the funding will enable growers to continue submitting samples for analysis as well as fungicide testing to follow on from the work conducted in 2018.The new research proposal contains provisions for in-season genotyping: currently growers must wait until the end of the season, and after implementing a blight spray programme, to receive results from any samples submitted. If successful, the new project will report back earlier, enabling growers to use the genotyping data to inform their blight management decisions.

Getting blight strain results faster - Outline of new research:

  • Starting 1st April 2019, ending 31st March 2022.

  • Continues previous Fight Against Blight outbreak and genotyping work, and also includes fungicide sensitivity testing throughout the season.

  • Samples of potato tissue infected with late blight will be collected via the existing AHDB Fight Against Blight (FAB) scheme.

  • Additionally this year, blight lesions will be pressed onto DNA storage FTA cards.

  • The FTA cards allow more rapid sample processing and the contractors aim to return genotype results submitted as cards within a week which will allow individual scouts, and the wider FAB campaign, to influence within-season management advice.

  • Samples of Phytophthora infestans will be purified and subject to DNA fingerprinting. Data will be matched to national and international (EuroBlight) databases and the pathogen genotype determined.

  • The sensitivity of a representative selection of isolates of key pathogen genotypes to important fungicide active ingredients will be tested.

  • The fungicide sensitivity testing will extend the lifespan of active ingredients and minimise the risk of blight management failures that would occur if incorrect fungicide choices are made.

  • Results will continue to build on data from previous seasons.

  • Existing close links will be maintained between the contractors on this project and representatives across the potato industry from field staff such as FAB scouts and advisors to breeders and the agrochemical industry.

The wider impact of this study will be to identify changes in fungicide sensitivity or new virulence that overcomes key sources of late blight resistance in potato cultivars and report them to key stakeholders to underpin successful Integrated Pest Management (IPM) practices in the GB potato industry.

If you grow potatoes or are an advisor why not support the Fight Against Blight service by registering as a blight scout? Your samples are crucial for understanding the genotypes causing late blight disease and provide a direct benefit to you and the GB industry to improve growers' blight management practices.

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