Abstract
Grapevine trunk diseases (GTDs) are a serious and growing threat to vineyards worldwide. The need for innovative control tools persists since pesticides used against some GTDs have been banned and only methods to prevent infections or to reduce foliar symptoms have been developed so far. In this context, the application of imaging methods, already applied to study plant–microbe interactions, represents an interesting approach to understand the effect of experimental treatments applied to reduce fungal colonization, on GTD-related pathogens activity. To this aim, trials were carried out to evaluate the efficacy of copper-based treatments, formulated with hydroxyapatite (HA) as co-adjuvant with innovative delivery properties, loaded with two different copper(II) compounds (tribasic sulfate and sulfate pentahydrate), and applied to grapevine propagation material to inhibit fungal wood colonization. The treated rootstock (Vitis berlandieri × Vitis riparia cv. K5BB) and scion cuttings (Vitis vinifera L., cv. Chardonnay) had been inoculated with a strain of Phaeoacremonium minimum (Pmi) compared to uninoculated rootstocks. Experimental treatments were applied during the water-soaking process, comparing the copper(II) compounds pure or formulated with HA, to hydrate the cuttings. After callusing, grafted vines were grown under greenhouse conditions in a nursery and inoculated with Pmi::gfp7 or with Pmi wild-type. Fifteen weeks post-inoculation, woody tissues close to the inoculation site were sampled to evaluate the efficiency of the treatments by studying the plant–microbe interaction by confocal laser scanning microscopy (CLSM). Copper and further elements were also quantified in the same tissues immediately after the treatments and on the CLSM samples. Finally, the grapevine defense responses were studied in the leaves of cuttings treated with the same formulations. The present investigation confirmed the relevant interaction of Pmi and the related transformed strain on the vascular tissues of grafted vines. Furthermore, in vitro assay revealed (i) the fungistatic effect of HA and the reduced effect of Cu fungicide when combined with HA. In planta assays showed (ii) the reduction of Pmi infection in propagation material treated with HA-Cu formulations, (iii) the movement of HA-Cu formulations inside the plant tissues and their persistence over time, and (iv) the plant defense reaction following the treatment with pure HA or Cu, or combined.
Highlights
During the last decades, grapevine trunk diseases (GTDs), including Petri disease and esca complex disease (Esca), have become serious and destructive diseases in young and mature vineyards and currently represent a major issue in viticulture
Control plates did not reveal any inhibition of the mycelial growth of Phaeoacremonium minimum (Pmi)::gfp7 (Figure 2A) and Pmi wild-type (Figure 2B), and no differences in growth between the gfp transformant and the wildtype were observed after fungi were grown on MEA
The integrated application of an approach based on imaging–analytical–biomolecular methods was tested as a key tool to understand the effect of experimental treatments on controlling the GTD pathogen colonization and the plant responses
Summary
Grapevine trunk diseases (GTDs), including Petri disease and esca complex disease (Esca), have become serious and destructive diseases in young and mature vineyards and currently represent a major issue in viticulture. The main difficulty is linked to the location of the GTD pathogens in the xylem vessels. This limits the efficiency of a control treatment as it is difficult to get it into contact with the pathogen within the vascular system. Uninjured grapevine roots and shoots can be infected by Pmi (Feliciano and Gubler, 2001). This fungus colonizes the plant by occupying the intercellular spaces of the epidermis. The cortex, the pith, the rays, and xylem vessels are colonized, but the latter more extensively (Feliciano and Gubler, 2001; Valtaud et al, 2009; Fleurat-Lessard et al, 2014)
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