Colletotrichum Species Associated with Citrus: Disease Biology, Global Diversity, Pathogenicity, and Biosecurity Implications

Citrus is an important fruit crop worldwide and Colletotrichum species are important pathogens of this crop. Colletotrichum species infect a wide range of citrus tissue such as leaves, twigs, flower petals, immature and mature fruit, causing substantial losses in yield, fruit quality, and marketability. This review is a critical assessment of the major Colletotrichum species associated with citrus diseases, their global diversity, distribution, and biosecurity implications. This review also identifies areas in need of further research. Thirty-nine Colletotrichum species have been reported in association with citrus globally. Most Colletotrichum species are plant pathogens, while several are saprobes or exhibit endophytic or latent lifestyles. They also vary in host range, aggressiveness, and environmental adaptation. Several species can infect citrus hosts or tissues beyond those from which they were originally isolated, while some also infect plants from other genera. The nature of infection by Colletotrichum species highlights the need to include non-wound inoculation in bioassays designed to assess the ability of Colletotrichum isolates to penetrate the cuticle and epidermis and cause infection. Accurate identification, pathogenicity testing, and rapid molecular detection are therefore important for disease management, quarantine inspection, and plant biosecurity risk assessment.