Abstract
In a context in which the incidence and severity of grapevine fungal diseases is increasing as a result of both climate change and modern management culture practices, reducing the excessive use of phytosanitary products in viticulture represents a major challenge. Specifically, grapevine trunk diseases (GTDs), caused by several complexes of wood decay or xylem-inhabiting fungi, pose a major challenge to vineyard sustainability. In this study, the efficacy of chitosan oligomers (COS)–amino acid conjugate complexes against three fungal species belonging to the Botryosphaeriaceae family (Neofusicoccum parvum, Diplodia seriata, and Botryosphaeria dothidea) was investigated both in vitro and in planta. In vitro tests led to EC50 and EC90 effective concentrations in the 254.6−448.5 and 672.1−1498.5 µg·mL−1 range, respectively, depending on the amino acid involved in the conjugate complex (viz. cysteine, glycine, proline or tyrosine) and on the pathogen assayed. A synergistic effect between COS and the amino acids was observed against D. seriata and B. dothidea (synergy factors of up to 2.5 and 2.8, respectively, according to Wadley’s method). The formulations based on COS and on the conjugate complex that showed the best inhibition rates, COS−tyrosine, were further investigated in a greenhouse trial on grafted vines of two varieties (”Tempranillo” on 775P and “Garnacha” on 110R rootstock), artificially inoculated with the mentioned three Botryosphaeriaceae species. The in planta bioassay revealed that the chosen formulations induced a significant decrease in disease severity against N. parvum and B. dothidea. In summary, the reported conjugate complexes may be promising enough to be worthy of additional examination in larger field trials.
Highlights
The so-called grapevine trunk diseases (GTDs) represent one of the greatest threats to vineyards in the last 20–25 years, as a consequence of changes in the management and intensification of the crop, the increase in the production of propagating plant material, the banning of chemicals or the existence of a climate change scenario
Are shown the results of the assays carried out to test the antifungal capacity of a series of conjugates based on chitosan polymers and certain amino acids, for the control, both in vitro and in plant, of some taxa of the Botrysphaeriaceae family involved in the so-called wood diseases in young grapevine plants
For D. seriata and B. dothidea, a synergistic effect was observed for all the chitosan oligomers (COS)−amino acid conjugate complexes, evident for COS-Tyr, with estimated synergy factors (SF) of 2.03 and 2.29 in the EC50 values and SF of 2.48 and 2.84 in the EC90 values, respectively
Summary
The so-called grapevine trunk diseases (GTDs) represent one of the greatest threats to vineyards in the last 20–25 years, as a consequence of changes in the management and intensification of the crop, the increase in the production of propagating plant material, the banning of chemicals or the existence of a climate change scenario. External symptoms produced by this pathogenic complex include death of the cordons, canes, shoots and buds, stunting, bud necrosis, bleached canes, reduced bunch set and bunch rots, while internal symptoms like brown wood streaking and wedge-shaped discolorations are very frequent [4,5]. Together with these disease symptoms, these and other related GTD fungi are known to produce toxic metabolites [6], some of them well characterized by chemical methods, whose toxicity has been proven on different organs and tissues of several Vitis vinifera L. cultivars [7]
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