Abstract:

Colletotrichum sp. is a kind of fungus with wide geographical distribution and wide host range. It can infect plants and fruits before and after ripening, especially for mature tropical crops, causing serious economic losses and affecting the export quality of products. The infection process of C. gloeosporioides on mango fruit and the interaction between C. gloeosporioides and mango host were studied to reveal the infection mode and expansion pathway of the pathogen on fruit and leaves. After Inoculating the healthy ‘Sannian mango’ fruits and leaves with the strong pathogenic strain CG16 isolated and screened from the diseased fruit of local variety ‘Sannian mango’ in Yuanjiang, the histopathology and ultrastructure of mango fruits and leaves infected by C. gloeosporioides were studied by light microscope, scanning electron microscope and transmission electron microscopy. C. gloeosporioides formed primary hyphae 12 hours after infection, and the primary hyphae penetrating the host cell wall formed a funnel-shaped hyphal cone. It constricted at the hyphae in contact with the host cell wall, often formed a diaphragm, and expanded rapidly into normal hyphae after passing through the host cell wall. It took about one day from the inoculation of mango to the appearance of symptoms. In the process of infecting mango, C. gloeosporioides first formed the primary infection hyphae, and the host cells gradually disappeared and died with the invasion and expansion of the primary hyphae. The primary hyphae first spread between cells and continuously established new nutritional parasitic relationships in vivo. 2.5 days after inoculation, with the invasion of hyphae, the host cells finally died and dissolved, and the expanded hyphae diffused in the dead host cells gradually became thinner and more branched, and the secondary hyphae was formed. The secondary hyphae propagated and expanded in large numbers dispersing or forming mycelial bundles in the host. Four days after inoculation, a series of pathological changes occurred in host tissues and cells, including deformation of host cells, thinning of cell walls, deformity and partial disappearance of cells, disintegration of protoplasts and other organelles, necrosis and cell death. Five days after inoculation, the secondary hyphae in the vegetative stage of dead body proliferated and expanded in the dead host cells. Six days after inoculation, the conidiophores formed, and the spores began to mature and fall off 8 days after inoculation. In this study, the way of infection and expansion of C. gloeosporioides in fruits and leaves, as well as a series of pathological changes in host tissues in the process of infection were revealed, which would provide a theoretical basis for the prevention and control of the disease in production.

Key words: Colletotrichum gloeosporioides, infection process, mango, ultrastructure