Milder autumns may increase risk for infection of crops with turnip yellows virus.

Abstract

Climate change has increased the risk for infection of crops with insect-transmitted viruses. Mild autumns provide prolonged active periods to insects, which may spread viruses to winter crops. In autumn 2018, green peach aphids (Myzus persicae) were found in suction traps in southern Sweden that presented infection risk for winter oilseed rape (OSR; Brassica napus) with turnip yellows virus (TuYV). A survey was carried out in spring 2019 with random leaf samples from 46 OSR fields in southern and central Sweden using DAS-ELISA resulting in TuYV being detected in all fields except one. In the counties of Skåne, Kalmar and Östergötland, the average incidence of TuYV-infected plants was 75% and the incidence reached 100% for nine fields. Sequence analyses of the coat protein gene revealed a close relationship between TuYV isolates from Sweden and other parts of the world. High-throughput sequencing for one of the OSR samples confirmed the presence of TuYV and revealed co-infection with TuYV-associated RNAs. Molecular analyses of seven sugar beet (Beta vulgaris) plants with yellowing, collected in 2019, revealed that two of them were infected by TuYV together with two other poleroviruses: beet mild yellowing virus and beet chlorosis virus. The presence of TuYV in sugar beet suggests a spillover from other hosts. Poleroviruses are prone to recombination, and mixed infection with three poleroviruses in the same plant poses a risk for the emergence of new polerovirus genotypes.