Use of Endophytic and Rhizosphere Actinobacteria from Grapevine Plants To Reduce Nursery Fungal Graft Infections That Lead to Young Grapevine Decline

Abstract

Endophytic and rhizosphere actinobacteria isolated from the root system of 1-year-old grafted Vitis vinifera plants were evaluated for their activities against fungi that cause grapevine trunk diseases. A total of 58 endophytic and 94 rhizosphere isolates were tested. Based on an in vitro bioassay, 15.5% of the endophytic isolates and 30.8% of the rhizosphere isolates exhibited antifungal activity against the fungal pathogen Diplodia seriata, whereas 13.8% of the endophytic isolates and 16.0% of the rhizosphere isolates showed antifungal activity against Dactylonectria macrodidyma (formerly Ilyonectria macrodidyma). The strains which showed the greatest in vitro efficacy against both pathogens were further analyzed for their ability to inhibit the growth of Phaeomoniella chlamydospora and Phaeoacremonium minimum (formerly Phaeoacremonium aleophilum). Based on their antifungal activity, three rhizosphere isolates and three endophytic isolates were applied on grafts in an open-root field nursery in a 3-year trial. The field trial led to the identification of one endophytic strain, Streptomyces sp. VV/E1, and two rhizosphere isolates, Streptomyces sp. VV/R1 and Streptomyces sp. VV/R4, which significantly reduced the infection rates produced by the fungal pathogens Dactylonectria sp., Ilyonectria sp., P. chlamydospora, and P. minimum, all of which cause young grapevine decline. The VV/R1 and VV/R4 isolates also significantly reduced the mortality level of grafted plants in the nursery. This study shows that certain actinobacteria could represent a promising new tool for controlling fungal trunk pathogens that infect grapevine plants through the root system in nurseries. IMPORTANCE Grapevine trunk diseases are a major threat to the wine and grape industry worldwide. They cause a significant reduction in yields as well as in grape quality, and they can even cause plant death. Trunk diseases are caused by fungal pathogens that enter through pruning wounds and/or the root system. Although different strategies have recently been developed to protect pruning wounds using antifungal compounds (natural or synthetic) or biocontrol agents, no tools are yet available for controlling soil pathogens that infect plants through their root system. This study shows that different actinobacterial isolates, when applied to grafts in a nursery, can significantly reduce the infection rate caused by fungal pathogens that enter through the root system. This is a new, promising, and green alternative for preventing the decline of young grapevines in nurseries and vineyards.

Effect of white mustard cover crop residue, soil chemical fumigation andTrichodermaspp. root treatment on black‐foot disease control in grapevine

“…More recently, Halleen and Fourie concluded that T. harzianum performed better against natural black‐foot infections in an integrated strategy in the propagation process combined with chemical treatment and/or HWT than in repeat treatments of the same product. Other BCAs have been tested against black‐foot disease pathogens with promising results . Inoculation of roots with the mycorrhizal fungus Rhizophagus irregularis (syn.…”

“…Glomus intraradices ) reduced the disease severity caused by black‐foot disease pathogens . Also, application of actinobacteria to grafted plant roots, selected for their in vitro antifungal properties against black‐foot disease pathogens, resulted in a significant decrease in fungal infection in nursery fields …”

“…Other BCAs have been tested against black-foot disease pathogens with promising results. 23,62 Inoculation of roots with the mycorrhizal fungus Rhizophagus irregularis (syn. Glomus intraradices) reduced the disease severity caused by black-foot disease pathogens.…”

“…Successful biological control of black-foot disease with antagonistic micro-organisms is practised to a rather limited extent, and research to date has shown variable results for preventing fungal infections. [19][20][21][22][23] The standard HWT of 50 ∘ C for 30 min provides 100% control of black-foot, with no reduction in budding or growth rate. 20,21,24,25 However, HWT of dormant nursery plants has not yet been embraced as a standard treatment in most European nurseries, because of the confusion in the industry about its efficacy and safety.…”

Qualitative and quantitative molecular analysis indicate the presence of Phaeomoniella chlamydospora in vineyard soils

“…Many attempts have been made to understand the origin of the Pch inoculum, and numerous potential sources of the fungus have been suggested, but its epidemiology is still unclear. This fungus is considered an air-borne and water-splashed pathogen , and its main infection of grapevine is reported to occur through wounds caused by intensive pruning, hydric stress, frost or other mechanical injuries such as grafting (Agustí-Brisach, León, Garcia-Jimenez, & Armengol, 2015;Larignon & Dubos, 2000).…”