Turnip yellows virus (syn Beet western yellows virus), an emerging threat to European oilseed rape production

Nomenclature:  The International Committee for the Taxonomy of Viruses (ICTV) approved the proposal to reclassify the European non-sugar beet infecting strains of Beet western yellows virus (BWYV) as an independent species within the genus Polerovirus, with the name Turnip yellows virus (TuYV) being accepted. Recent molecular evidence  supported the separation of the beet-infecting and non-beet infecting isolates as two distinct viruses. European strains of Beet western yellows virus (BWYV) that infect oilseed rape in the UK should now be referred to as Turnip yellows virus(TuYV).

Turnip yellows virus (TuYV) is probably the most important, yet least understood, viral disease of oilseed rape in the United Kingdom. It is likely that TuYV is one of the principal reasons why commercial oilseed rape crops do not reach their genetic yield potential. The virus is probably present throughout the UK and at high levels in southern England. Virus symptoms, which are not readily recognisable, are usually not expressed before stem extension and can easily be confused with other stress symptoms and nutritional deficiencies.

The main virus vector is the peach-potato aphid, Myzus persicae. Annual sampling of M. persicaepopulations have shown that up to 72% of winged M. persicae carry TuYV. Studies in the 1980s and early 1990s showed that TuYV could be widely present in oilseed rape crops throughout the UK. Work at Broom's Barn Research Centre in the 90s showed that TuYV could decrease yields by up to 26%. All yield parameters including the number of primary branches, numbers of seeds per pod and percentage oil per seed were affected; the glucosinolate concentration in the oil was also significantly increased in infected plants. Recent work in Australia showed seed yield losses up to 46%. Estimates of yield loss indicate that at an individual crop level, control of TuYV could raise average yields from 3.3 t/ha to between 4.4 and 6.0 t/ha. If only half of those losses could be prevented (10-15%) by controlling TuYV, then the value of the yield improvement would be in the order of £100-150/ha (equivalent to £60-90 million per year to UK OSR growers).

Milder autumn and winter conditions favour the development of the aphid vectors and encourage virus spread. Climate change will exacerbate the situation as warmer conditions will encourage the survival and multiplication of M. persicae throughout the winter.

Strategies are required to decrease the impact of TuYV and its aphid vectors on the yield of oilseed rape. Cultural practices, seed treatments and foliar sprays provide an opportunity to limit the impact of TuYV in a responsible and sustainable manner. The levels of resistance to TuYV in current UK varieties are not known. The identification and exploitation of potential resistance genes provides an alternative strategy to control this important viral disease. Recent work in Germany identified a potential resistance gene that could be exploited to provide resistance to TuYV. Identification and exploitation of other sources of resistance to TuYV are required.