Co-acquisition of two sugar beet poleroviruses by M. persicae increased the transmission efficiency of both viruses.

Beet mild yellowing virus (BMYV) and beet chlorosis virus (BChV) are two closely related poleroviruses infecting sugar beet plants, which induce leaf yellowing and cause high yield losses. Poleroviruses are phloem-limited and strictly transmitted by aphids in a circulative and persistent manner. In nature, sugar beet plants can be coinfected by these two viruses, but the outcome of BMYV and BChV coexistence in a plant on virus accumulation and aphid transmission has never been addressed before. In this study, we showed that the accumulation of each virus was not affected by the presence of the other, despite coinfecting about 40 % of infected phloem cells. Both viruses crossed the gut epithelium at the same site in Myzus persicae without any evidence of competition for receptor binding. On the contrary, when aphids simultaneously acquired both viruses from an artificial medium containing equal amounts of each virus, the transmission efficiency increased for both viruses. In contrast, only BMYV exhibited enhanced transmission when acquired from a coinfected plant. This suggests a cooperative effect at the inoculation step facilitating virus delivery in sugar beet cells by aphids. Our results shed light on fine-tuned virus-virus and virus-vector interactions, with potential implications for epidemiology and disease management.