Abstract
The majority of all fungal formulations contain Trichoderma spp., making them effective biological control agents for agriculture. Chitosan, one of the most effective natural biopolymers, was also reported as a plant resistance enhancer and as a biocide against a variety of plant pathogens. An in vitro three-way interaction assay of T. atroviride, chitosan, and important plant pathogens (such as Cercospora beticola and Fusarium oxysporum) revealed a synergistic effect on fungistasis. Furthermore, chitosan coating on Beta vulgaris ssp. vulgaris seeds positively affected the onset and efficiency of germination. We show that priming with T. atroviride spores or chitosan leads to the induced expression of a pathogenesis-related gene (PR-3), but only supplementation of chitosan led to significant upregulation of phytoalexin synthesis (PAL) and oxidative stress-related genes (GST) as a defense response. Repeated foliar application of either agent promoted growth, triggered defense reactions, and reduced incidence of Cercospora leaf spot (CLS) disease in B. vulgaris. Our data suggest that both agents are excellent candidates to replace or assist common fungicides in use. Chitosan triggered the systemic resistance and had a biocidal effect, while T. atroviride mainly induced stress-related defense genes in B. vulgaris. We assume that both agents act synergistically across different signaling pathways, which could be of high relevance for their combinatorial and thus beneficial application on field.
Highlights
The bioactive molecule chitosan (CHSN) is on everyone’s lips and is considered one of the most effective natural antimicrobial agents
We evaluated chitosan with different molecular weights from commercial preparations on growth inhibition of important phytopathogens in crop production, with special emphasis on B. vulgaris cultivation
LMW and high-molecular-weight chitosan solution pH 4.5 (HMW) chitosan were most effective and showed 60 to 80% growth inhibition for C. beticola and B. cinerea and between 80% and nearly 100% inhibition for the investigated Fusarium spp. over a prolonged incubation time of up to 12 days
Summary
The bioactive molecule chitosan (CHSN) is on everyone’s lips and is considered one of the most effective natural antimicrobial agents. Chito-oligosaccharides (n = 2–10) and very-low-molecular-weight chitosans (n ≤ 20). Are mainly produced for therapeutic purposes, while the more viscous molecules (high molecular weight, HMW) are used for food and fiber technology [2]. Chitosan and its derivatives are considered strong antimicrobial and plant-strengthening agents in crop protection (reviewed [1]), comparable to biological control agents (BCAs), but their widespread application in industrial crop production is still pending. Due to the environmentally problematic production routes of chitosan and the poor understanding around cellular mechanism of action, there is a lack of broad applications in which potentially harmful substances, such as synthetic pesticides, could be substituted. A further benefit of using chitosan is its GRAS-status (generally recognized as safe), which would facilitate registration
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