Colletotrichum magnum Species Complex: Emerging Pathogens in Tropical and Subtropical Regions

The Colletotrichum magnum complex includes the species C. brevisporum, C. liaoningense, C. magnum (previously named Glomerella magna), and C. okinawense, among others, which are emerging as hazardous pathogens of cucurbits, tropical fruits, peppers, and legumes. Numerous spreads have been reported in tropical and subtropical areas, including the Yucatan Peninsula of Mexico, Eastern Brazil, Southern China, Thailand, and South Korea. C. magnum complex species cannot be identified by simply observing disease symptoms; GAPDH and TUB2 gene sequencing is strictly necessary for identification to the species level. C. brevisporum can synthesize unique metabolites, including brevianthrones, nalgiovensin, and methoxy-nalgiovensin, and volatile organic compounds, which strongly differ from other Colletotrichum species. C. magnum can secrete a variety of hydrolytic enzymes and oxidoreductases, which may participate in plant tissue degradation. C. magnum complex species have been identified co-infecting crops together with other pathogenic fungi; however, there is no study available regarding how C. magnum complex species interact with other microorganisms. Studies regarding the potential toxicity of C. magnum complex metabolites and their use as bioherbicides are lacking. C. magnum complex control strongly relies on the application of toxic fungicides, such as thiophanate methyl, captan, chlorothalonil, and copper salts. However, various non-commercial alternative agents, including sodium silicate, mango kernel polyphenols, Bonellia flammea extract, and Mentha piperita essential oil-containing chitosan coatings, also provided competitive control efficacies. Overall, accurate information regarding the yield losses caused by C. magnum complex species and their virulence factors is lacking, hindering the advancement of the research field.