Impact de la multi-infection de la betterave sucrière sur la transmission des virus de plante par puceron

Little is known about how viral co-infection modifies the transmission of viruses by their vector. We analyzed in sugar beet virus transmission, aphid feeding behavior, virus localization and accumulation of three viral combinations for which virus transmission by Myzus persicae was affected : BChV/BYV, BtMV/BYV/ and BMYV/BChV BChV/BYV co-infection decreased transmission of BChV by 50 %, but had no impact on BYV transmission, BtMV/BYV co-infection induced a lower transmission of BYV and co-infection of the two poleroviruses, BMYV/BChV resulted in mutualVersion septembre 2024 5 /4 transmission synergy. The drastic reduction of BChV or BYV transmission was not due to a lower accumulation of the viruses in co-infected plants, nor to reduced phloem sap ingestion by aphids from these plants. However, for BChV/BYV and BtMV/BYV co-infections, we observed a different intracellular distribution of BYV in co-infected vs mono-infected cells. BYV was observed in intracellular spherical inclusions in mono-infected cells and displayed a rather diffuse distribution in BtMV/BYV and in BChV/BYV co-infected cells. For BMYV/BChV co-infection, about 30 % of infected cells were co-infected, without impacting virus localization. We propose that the decrease aphid transmission of BChV from BChV/BYV co-infected plants or of BYV from BtMV/BYV co-infected plants is due to virus-virus or plant-virus interactions that decrease BYV or BChV release in the phloem sap and consequently acquisition by aphids. The most probable explanation for enhanced BMYV and BChV transmission from co-infected plants is synergy to reduce plant defenses during virus inoculation.