Arbuscular mycorrhiza affects grapevine fanleaf virus transmission by the nematode vector Xiphinema index

The soil-borne nepovirus Grapevine fanleaf virus (GFLV), causal agent of grapevine fanleaf degeneration disease, spreads mainly via the nematode vector Xiphinema index. Since the arbuscular mycorrhizal (AM) fungus Rhizophagus intraradices can induce local and systemic protection against X. index (Hao et al., 2012), therefore, the objective of the present study was to investigate if AM may represent a means for limiting GFLV infection by reducing nematode vector attack. Three-week-old mycorrhizal or nonmycorrhizal grapevine rootstock SO4 (Vitis berlandieri x V. riparia) plants were inoculated with 10 or 100 viruliferous nematodes per plant under glasshouse conditions. Plants were harvested 35 and 90 days after inoculation with X. index (DAIN), prior to and after the appearance of fanleaf degeneration symptoms, respectively. Both levels of viruliferous X. index inhibited root growth of nonmycorrhizal plants at 90 DAIN, while the presence of arbuscular mycorrhizal colonization significantly decreased gall formation on roots at both time points and reduced nematode reproduction in soil at 90 DAIN. GFLV was not detected by one-step reverse transcription PCR in the roots of any plant at 35 DAIN after viruliferous X. index inoculation. At 90 DAIN with 10 viruliferous nematodes per plant, the virus was present in nonmycorrhizal roots but absent from mycorrhizal grapevine. The virus was detected in both mycorrhizal and nonmycorrhizal plants 90 DAIN. It is suggested that inhibition of X. index proliferation and penetration by AM may protect grapevine against GFLV at a low abundance of the viruliferous nematode in soils and so contribute to virus control under these conditions.