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Virus yellows on sugar beet in the United Kingdom: resistance breeding

A ProMED-mail post <http://www.promedmail.org>
ProMED-mail is a program of the International Society for Infectious Diseases <http://www.isid.org>

Date: Fri 14 Feb 2020

Source: Farmers Weekly [edited]

<https://www.fwi.co.uk/arable/sugar-beet/4-point-plan-to-control-virus-yellows-in-sugar-beet>

Sugar beet growers are urged to follow a four-point plan to help control beet yellows this [2020] season, as aphid populations rise due to a mild winter, and just one active insecticide remains to control virus spread. Good crop hygiene, rapid establishment, monitoring and timely targeted treatments are the key to protecting crops from infections.

After the ban of neonicotinoid seed dressings in 2018, crops have been left vulnerable to aphid attack, with just a single application of flonicamid [insecticide group; see comments below] available to control the disease, which is capable of reducing yields by up to 50%.

Industry cannot rely on just one active [ingredient], as aphids are likely to build up resistance.

Mark Stevens, British Beet Research Organisation (BBRO), warns growers that beet yellows pose the biggest threat to sugar beet crops, and that epidemics are likely to increase due to favourable weather for aphids and losses of key agrochemicals. "In 2019, 55% of fields were infected, compared with just 18% in 2018, and this situation is likely to worsen as aphid populations have been able to build up, with few frosts killing the pests," he says.

39 000 winged peach-potato aphids [were] caught in a BBRO trial across 63 UK sites during a 12-week trapping period in 2019. Of the 10 000 that were tested, 0.4% were carriers of virus. The rise in overwinter crops is creating the perfect environment for aphids, which makes the choice of species in cover crop mixes increasingly important. A 1 degree Celsius [1.8 degree F] temperature increase can cause migration to begin at the end of April instead of the middle of May.

Research into sugar beet varieties that are resistant to beet yellows virus is under way, with varieties expected to be available to growers within 3 years [see links below].

[Byline: Emma Gillbard]

Communicated by: ProMED-mail <promed@promedmail.org>

[Virus yellows is an important disease affecting yield in sugar beet in the UK and elsewhere. The beet yellows complex may include one or several viruses. In the UK, the main viruses involved are _Beet yellows virus_ (BYV; genus _Closterovirus_), _Beet mild yellowing virus_ (BMYV; genus _Polerovirus_) and _Beet chlorosis virus_ (BChV; genus _Polerovirus_). These viruses are transmitted by aphids, including the peach(-potato) aphid (_Myzus persicae_). Disease management usually includes phytosanitation as well as vector control by field applications and seed treatments with insecticides.

Resistance breeding for multiple pathogens is difficult because host susceptibility is likely to involve different genes for the different pathogens.

In the UK, the disease had already been considered a re-emerging threat even with 90% of the crop receiving an effective

(neonicotinoid) seed treatment (ProMED-mail post http://promedmail.org/post/20100220.0582). Banning of neonicotinoids, the emergence of vector resistances to some foliar insecticides, as well as the warming climate favouring an increase in aphid numbers, suggest that integrated management strategies will be required in the future to control the disease.

The resistance trials in the UK mentioned above were carried out using either BYV or BMYV (see links below). Yield losses of up to 42% and 20% were recorded across varieties due to BYV or BMYV, respectively.

Varieties that had less visible damage to the foliage were low yielding, suggesting that foliar symptoms may not necessarily be an indicator of final crop yield in the field. Breeders are working to produce true tolerant or resistant varieties suitable for commercial use.

Flonicamids are systemic insecticides with selective activity against aphids, whiteflies and thrips. They are very effective against aphids, regardless of species or developmental stages.

Maps

UK (with counties):

<http://www.lib.utexas.edu/maps/europe/united_kingdom.gif>

Pictures

Sugar beet virus yellows leaf symptoms:

<https://cropscience.bayer.co.uk/media/102725813/virus-yellows-beet-1200.jpg>,

<http://www.inra.fr/hyp3/images/6030601.jpg> and <https://c8.alamy.com/comp/APFJJ7/sugar-beet-virus-yellows-sbvy-infection-on-mature-sugar-beet-plant-APFJJ7.jpg>

Sugar beet field affected by virus yellows:

<https://bmcontent.affino.com/AcuCustom/Sitename/DAM/147/050517_p12_13_BB_Virus_yellows_Main.jpg>

and

<https://c8.alamy.com/comp/X9TB4J/sugar-beet-virus-yellows-foci-of-infection-in-a-sugar-beet-crop-X9TB4J.jpg>

Aphids: