Abstract
The infection process of sugar beet flowers and seed balls by Colletotrichum dematium f. spinaciae was studied using light microscope and scanning electron microscope. When infection occurred at early stage of flowering, germ tubes produced appressoria and subsequently infection pegs penetrated the cuticle 3∼4 days after inoculation. Mycelia spread both inter- and intracellularly. Infected cells eventually collapsed, and lesions became visible about 5 days after inoculation. Mycelia were found not only on the surface of blackened seed caps or pericarps, but also in the inner space of the pericarp. In severe infection, mycelia also found between the seed coats and cotyledons. When infection occurred at the late flowering stage, mycelia were frequently observed on the seed surface, but less frequently inside the seed balls. These hyphae were found in the periphery of the apical pore or inside the seed coat. The results indicate that this pathogen is seed-borne.
