Studies on Citrus Melanose and Citrus Stem-end Rot by Diaporthe citri (Faw.) Wolf

Part 2. Infection Mode of D. citri to Citrus Leaf

Abstract

Pycnospore germination of Diaporthe citri (Faw.) Wolf and its hyphal penetration to host plant (Citrus unshiu) began 5 hr and 8 hr after inoculation, and reached maximum level 10 hr (15%) and 12 hr (7%) after inoculation respectivery. On the lower leaf surface, hyphal penetration occurred through stomata (67%) or cuticle (33%). Penetration trace on the leaf surface was observed as being a hall by etching with ion beam. Sarrowndings of the trace was specifically stained with basic fucsin. On the upper leaf surface, the hyphae penetrated to cuticle layer just above epidermal suture (40%) and of another portion of epidermal cell (60%). After penetrating into cuticle layer, subcuticle hyphae was formed between cuticle layer and epidermal cell wall. The hyphae did further penetrated into cell wall of epidermal cell, and elongated along the cell wall to epidermal suture. After being elongation, the hyphae reached to inside of epidermal cell from suture of epidermis. Most of invaded hypha died in the cell wall, suture and cell of epidermis. These results suggested that an inhibitor (s) against growth of D. citri might be present in the host tissue.