Potential control of forest diseases by solutions of chitosan oligomers, propolis and nanosilver

Abstract

23There is a growing necessity to replace chemical agents with ecofriendly materials, arising from 24 their impact on the environment and/or human health, which calls for the design of new broad-25 spectrum fungicides. In this work, chitosan oligomers (COs), propolis (Ps) and silver nanoparticles 26 (AgNPs) mixtures in solution were assessed to control the growth of different phytopathogenic fungi 27 and oomycetes in vitro. Binary solutions of COs-Ps and COs-AgNPs evinced the highest antifungal 28 effect against Fusarium circinatum and Diplodia pinea fungi, respectively, with a ca. 80% reduction 29 in their mycelial growth. The COs solution by itself also proved to be greatly effective against 30Gremmeniella abietina, Cryphonectria parasitica and Heterobasidion annosum fungi, causing a 31 reduction of 78%, 86% and 93% in their growth rate, respectively. Likewise, COs also attained a 32 100% growth inhibition on the oomycete Phytophthora cambivora. On the other hand, Ps inhibited 33 totally the growth of Phytophthora ×alni and Phytophthora plurivora. The application of AgNPs 34 reduced the mycelial growth of F. circinatum and D. pinea. However, the AgNPs in some binary and 35 ternary mixtures had a counter-productive effect on the anti-fungal/oomycete activity. In spite of the 36 fact that the anti-fungal/oomycete activity of the different treatments showed a dependence on the 37 particular type of microorganism, these solutions based on natural compounds can be deemed as a 38 promising tool for control of tree diseases. 39

Chitosan-Based Coatings to Prevent the Decay of Populus spp. Wood Caused by Trametes Versicolor

“…According to Rabea et al [46], the MIC value depends on factors such as the type of chitosan, the fungus under study, the chemical or nutrient composition of the substrate and the environmental conditions. Another work on Sphaeropsis sapinea and Trichoderma harzianum wood-degrading fungi suggested that the application of 1 mg·mL −1 of low-molecular weight chitosan reduced growth rate by a factor of 3 with respect to the control [47], in line with the results reported by Silva-Castro et al [40], who found that 1 mg·mL −1 of CO inhibited 86% of the mycelial growth of Heterobasidium annosum basidiomycete fungus. Thus, in view of aforementioned MIC values, it may be inferred that T. versicolor would show an intermediate sensitivity (i.e., would be moderately sensitive) to chitosan/CO alone, albeit such resistance would not be as high as that of, for example, Macrophomina phaseolina (for which MIC values of water-soluble chitosan as high as 12.5 mg·mL −1 were found [48]).…”

“…Subsequently, oligo-chitosan was prepared by oxidative degradation of the solubilized MMWC by addition of hydrogen peroxide (0.3 M), obtaining a MW of 2 kDa [39]. Propolis constituents soluble in ethanol were extracted by grinding the resin and adding it to a hydroalcoholic solution (ethanol 30%), followed by stirring for 72 h at room temperature, and by filtration with a stainless steel 220 mesh to remove insoluble particles [40]. Silver nanoparticles were synthetized by a sonication method: 50 mL of silver nitrate (50 mM) were first mixed with 50 mL of sodium citrate (30 mM) as a reducing agent, and the solution was heated up to 90 • C until it turned from colourless to pale yellow, which then became more intense.…”

Environmentally friendly methods for controlling pine pitch canker

“…The effects of chitosan and phosphite may result from IR and/or a fungistatic effect. This conclusion is consistent with the findings of Silva-Castro et al (2018b) and Cerqueira et al (2017) who demonstrated that chitosan oligomers and phosphite salts were able to inhibit mycelial growth of F. circinatum in vitro. As noted above, pine rhizobacterial isolates of E. billingiae and P. fluorescens protected young P. radiata seedlings against F. circinatum (Iturritxa et al, 2017), probably as a consequence of a combined effect of mycelial growth inhibition and induced resistance.…”

“…Another natural compound widely used in plant protection for its antiseptic properties is propolis (Özcan et al ., ), which effectively inhibited mycelial growth (68%) of F. circinatum (Silva‐Castro et al ., ). Moreover, coating of propolis on seeds enhanced survival by approx.…”

“…This conclusion is consistent with the findings of Silva‐Castro et al . () and Cerqueira et al . () who demonstrated that chitosan oligomers and phosphite salts were able to inhibit mycelial growth of F. circinatum in vitro .…”