Abstract
Phytophthora cinnamomi is responsible for radical rot in a wide range of hosts, resulting in large economic and ecological losses worldwide. In Spain, it is responsible for diseases such as the oak decline or the chestnut blight. In this study, different polyphenol-stevioside inclusion compounds dispersed in a hydroalcoholic solution of chitosan oligomers have been investigated, with a view to their application as natural bioactive complexes to replace conventional systemic fungicides against this fungus. The polyphenols tested in vitro were curcumin, ferulic acid, gallic acid and silymarin. Three concentrations (125, 250 and 500 µg·mL−1) were assayed, with and without silver nanoparticles (AgNPs), and notable differences were found in the inhibition of mycelium growth, with EC50 and EC90 values ranging from 171 to 373.6 µg·mL−1, and from 446.2 to 963.7 µg·mL−1, respectively. The results obtained showed that the addition of AgNPs, despite their antimicrobial activity, did not always lead to synergies. In the case of P. cinnamomi, an unexpected antagonistic behavior was found for two of the polyphenols (curcumin and silymarin), while an additive behavior for ferulic acid and a synergistic behavior for gallic acid were attained. In view of their inhibitory power, the preparations based on ferulic acid with AgNPs and on silymarin without AgNPs are proposed for applications in crop and forests protection against P. cinnamomi.
Highlights
Phytophthora cinnamomi is an oomycete that lives on the ground nourishing itself thanks to decomposing matter
The conjugates with chitosan oligomers in hydroalcoholic solution medium were prepared according to the procedure previously reported in Matei et al [14], and were characterized by infrared spectroscopy (FTIR), SEM and TEM microscopy techniques to ensure the reproducibility of the results presented in patent P201731489 [15]
It is worth noting that the addition of AgNPs only resulted in a noticeable enhancement of activity for the conjugates based on gallic acid
Summary
Phytophthora cinnamomi is an oomycete that lives on the ground nourishing itself thanks to decomposing matter. This pathogen, responsible for “root rot” or “regressive death”, is one of the most invasive species worldwide. It infects close to 5000 species of plants [1], affecting a variety of plant families: conifers, grasses, ferns, ornamental plants and food crops such as pineapple or avocado [2]. Its expansion has been attributed to the phenomenon of climate change, given that the potential disease range is influenced by winter temperature (disease development is strongly hampered by cold winters) and other climatic variables, such as summer temperatures and hydrologic variables.
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