Antifungal activity of volatile and non-volatile metabolites of endophytes of Chloranthus elatior Sw.

Abstract

Agriculture crops that have fungal infections suffer significant economic losses and reduced crop output. Chemical fungicides are used to tackle the problem, although this has additional detrimental side effects. There is an urgent need for safe and novel antifungals. Volatiles from plant-beneficial endophytic fungi are considered promising alternatives for the biological control of fungal pathogens as a sustainable approach in an agroecosystem. In the present investigation, a volatile-emitting sterile endophytic fungus, Diaporthe sp. CEL3 with bio-fumigation activity, was isolated from leaves of the ethnomedicinal plant Chloranthus elatior Sw., collected from the Passighat forest of North-East India. The camphor odor volatiles of CEL3 showed an inhibitory effect against eight fungal pathogens in vitro and minimized the infections of Monilinia fructicola, a causal agent of cherry fruit rot, in VOC-exposed cherry fruits. Rhizoctonia solani, Botrytis cinerea, Pythium ultimum, and M. fructicola were maximally inhibited up to 51.5%, 55.8%, 61.9%, and 78.5%, respectively, in comparison to control by the volatiles. Another isolate, CEL7, identified as Curvularia sp., synthesized non-volatile, soluble antifungal metabolites in its cell-free extracts and exhibited antifungal action. Bioassay-guided fractionation revealed the presence of imidazole compounds- (2-aminoethyl)-1H-imidazole-2-carbaldehyde, Pyrazole 4, 5 imidazole, 1-formyl 3-ethyl, phenol compounds-Phenol, 4-[2-(methylamino) ethyl]-, 6-Nitro-3-chlorophenol, Phenol, 2,4,6-tri-tert-butyl-, etc., in the cell-free extracts, with a MIC value of 250–2,000 µg ml−1. Optimum VOC emission was achieved in a modified PDA medium with instantly smashed potato (150 g L−1), dextrose (20 g L−1), wheat husk (20 g L−1), and yeast extract (20 g L−1), with additional salts. Interestingly, endophytic CEL3 emitted different types of volatiles, and trans-verbenol (32.25%), geraniol (30.32%), trans-ocimenol (12.90%), and mentha-4,8-diene (5.16%) were the prime ones. These VOCs cause lethal leakage of protein and necessary intracellular molecules from the fungal pathogens. Thus, CEL3 could potentially be used as a bio-fumigating agent to control post-harvest infections caused by fungal pathogens. This study opens a new approach to the use of endophytic fungi in biocontrol.

Endophytic Fungi Volatile Organic Compounds as Crucial Biocontrol Agents Used for Controlling Fruit and Vegetable Postharvest Diseases

“…The VOCs of the endogenous fungus Diaporthe sp. CEL3 treat the pathogenic microorganism Monilinia fructicola and Pythium ultimum, causing the intracellular discharge of compounds of pathogenic microorganism, and with the extension of the processing time, the protein discharges also increase [37]. Some endophytic fungal VOCs can also kill pathogenic microorganisms by damaging their DNA.…”

“…Endophytic fungal Diaporthe sp. CEL3 emits a characteristic scent (a fruity, sweet camphor odor) and inhibits the growth of 10 fungal pathogens from wide taxonomic groups like ascomycetes, basidiomycetes, and oomycetes [37]. Primary VOCs were generated by the endophytic fungus Diaporthe apiculatum strain FPYF 3052 and can suppress the growth of phytopathogenic fungi (Alternaria alternata, Botryosphaeria dothidea, B. cinerea, Cercospora asparagi, Colletotrichum gloeosporioides, F. graminearum, Sphaeropsis sapinea, and Valsa sordida), having inhibitory activities in the range of 23.8-66.7% within 24 h. Among the primary VOCs, commercial (−)-4-terpineol stood out as the terpenoid with the strongest inhibitory activity against these phytopathogenic fungi, with up to 100% inhibition [38].…”

Deciphering the mechanisms, hormonal signaling, and potential applications of endophytic microbes to mediate stress tolerance in medicinal plants

“…SMR1 enhanced downy mildew tolerance in Papaver somniferum (L.) via protein modification, differential expression of transcripts related to signal transduction, transcription factors, and SA-dependent defense pathway ( Ray et al., 2021 ). Many researchers showed the ability of both bacterial and fungal endophytes to control diseases and phytopathogens by synthesized volatile and non-volatile compounds, soluble antifungal metabolites and by specific mechanisms including activation of defense enzymes and PR proteins associated with ISR, JA/ET mediated disease resistance, antagonism, antimicrobial, antioxidant, and anti-proliferative properties, production of IAA, siderophores.and β-1,3-glucanase, proteolytic activity, chitinase and cellulose synthesis in diverse medicinal plants including Chloranthus elatior , Taxillus chinensis, Salvia miltiorrhiza, Curcuma longa, Dioscorea bulbifera, Viola odorata, Cremastra appendiculata , Angelica sinensis , Cornus florida, Nicotiana tabacum, Zingiber zerumbet and Piper betle ( Harsha et al., 2023 ; Jiao et al., 2023 ; Manasa et al., 2023 ; Mei et al., 2023 ; Rotich and Mmbaga, 2023 ; Salwan et al., 2023 ; Santra and Banerjee, 2023 ; Sharma et al., 2023 ; Song et al., 2023 ; Thankam and Manuel, 2023 ; Wang et al., 2023 ; Yehia, 2023 ; Zou et al., 2023 ).…”

Cultivable Endophyte Resources in Medicinal Plants and Effects on Hosts

“…Streptomyces dioscori isolated from Glycyrrhiza uralensis exhibited inhibitory effects on three pathogenic fungi: Rhizoctonia solani , Fusarium acuminatum , and Sclerotinia scrotiorum [ 73 ]. An endophytic fungus, Diaporthe sp., was isolated from the leaves of the Indian medicinal plant Chloranthus elator Sw., and its camphor odor volatiles showed inhibitory effects on eight fungal pathogens in vitro [ 86 ]. Burkholderia gladioli , an endophytic bacterium from Crocus sativus Linn., can reduce corm rot and increase endogenous jasmonic acid (JA) level and expression of JA-regulated and other plant defense genes through antibacterial effects and improve the host’s resistance to Fusarium oxysporum [ 87 ].…”