Organic control of Plasmopara viticola on grapevine with new biofungicide
Lysobacter capsici AZ78 and thiamine, for different reasons, could be two suitable candidates for developing a new biofungicide to be used in combination with copper to control grapevine downy mildew
The bacterial genus Lysobacter represents a still underdeveloped source of biocontrol agents able to protect plants against pathogenic oomycetes.
The L. capsici strain AZ78 was evaluated with regard to the biological control of Plasmopara viticola, the causal agent of grapevine downy mildew.
L. capsici AZ78 is able to resist copper ions and its resistance to this metal is probably due to the presence of genes coding for copper oxidase (copA) and copper exporting PIB-type ATPases (ctpA). The presence of both genes was also detected in other members of the Lysobacter genus. Resistance to copper allowed L. capsici AZ78 to be combined with a low-dose of a copper-based fungicide, leading to more effective control of grapevine downy mildew.
Notably, prophylactic application of L. capsici AZ78 alone to grapevine leaves reduced downy mildew disease to the same degree as a copper-based fungicide. Furthermore, L. capsici AZ78 persists in the phyllosphere of grapevine plants and tolerates environmental stresses such as starvation, freezing, mild heat shock and UV light irradiation.
These traits suggest that L. capsici AZ78 could be a suitable candidate for developing a new biofungicide to be used in combination with copper to control grapevine downy mildew.
Recently, thiamine (VitaminB1) has been shown to induce resistance against Pseudomonas syringae in Arabidopsis plants through priming of defense responses.
Researchers have demonstrated the efficiency of thiamine to induce resistance against downy mildew caused by the oomycete Plasmopara viticola in a susceptible Vitis vinifera cultivar “Chardonnay” under glasshouse controlled conditions by providing a dual mode of action involving direct antifungal activity and elicitation of host–defense responses.
Thiamine-induced defense responses included the generation of hydrogen peroxide (H2O2) in both grapevine suspension cultured cells (SCC) and plant leaves, upregulation of an array of defense-related genes and the induction of other defense responses at subcellular level such as callose deposition in stomata cells, phenolic compounds accumulation and hypersensitive response (HR) like-cell death. Epifluorescence microscopy studies revealed dramatic changes in P. viticola individual developmental stages during its colonization of the intercellular space of the leaf mesophyll in thiamine-treated plants.
Collectively, the report evidenced the efficiency of thiamine in the control of downy mildew in grapevine by direct and indirect effects, suggesting that thiamine could be an attractive alternative to chemical fungicides in disease management in vineyards.
Gerardo Puopolo, Oscar Giovannini, Ilaria Pertot, Lysobacter capsici AZ78 can be combined with copper to effectively control Plasmopara viticola on grapevine, Microbiological Research, Volume 169, Issues 7–8, July–August 2014, Pages 633-642
Hatem Boubakri, Mohamed Ali Wahab, Julie Chong, Christophe Bertsch, Ahmed Mliki, Isabelle Soustre-Gacougnolle, Thiamine induced resistance to Plasmopara viticola in grapevine and elicited host–defense responses, including HR like-cell death, Plant Physiology and Biochemistry, Volume 57, August 2012, Pages 120-133