Fungal endophytes are microorganisms that colonize living, internal tissues of plants without causing any immediate, overtly negative effects. Many fungal endophytes produce secondary metabolites and some of these compounds exhibit antifungal and antibacterial activity that strongly inhibits the growth of other microorganisms. Antimicrobial strains are widely distributed among endophytic fungi and do not cause any obvious symptoms on host plants. Infected hosts usually grow quickly, have strong resistance to adverse conditions and diseases, and are immune to herbivory in comparison with uninfected plants. Endophyte-infected plants thus have competitive advantage. Endophytes act as biological control agents by inhibiting pathogen growth by the production of antibiotics, hydrolases, plant growth regulators and alkaloids. They also compete with pathogens for nutrition, enhancing resistance of host plants to diseases and inducing systemic resistance. Endophytic fungi are therefore biological control agents with great potential for applied use.
We investigated the antimicrobial properties of an endophytic fungus Chaetomium globosum L18 from a traditional Chinese medicinal plant Curcuma wenyujin Y. H. Chen et C. Ling (Zingiberaceae), on several conventional plant pathogens, using in vitro culturing methods. We thus present a preliminary discussion of the antimicrobial spectrum and antagonistic mechanisms of Chaetomium globosum L18. This fungus had different inhibitory actions on plant pathogenic fungi and bacteria, and wide-ranging inhibitory effects. There was significant difference (P<0.05) on inhibition of different plant pathogenic bacteria; and the inhibition rate was up to 92.9%. Our inhibition experiment showed that competition and mycoparasitism were the main antagonistic mechanisms. When two strains intersected with pathogenic fungi on co-culturing plates, plant pathogens were surrounded, and the margins of colonies gradually collapsed and shriveled. The pathogens stopped growing and began to die; and Chaetomium globosum L18 colonized the nutritious space. Chaetomium globosum L18 parasitized pathogens by parallel intergrowth, intertwining, and even penetrating their mycelia. Our fermented product test showed that Chaetomium globosum L18 was able to strongly inhibit mycelial growth and spore germination. Its presence resulted in mycelia that were twisted and inflated, with increased abnormal branching, broken mycelial walls, and cell contents released. Spores were reduced in number and deformed; germination rate and germination tube length were decreased.