Germination and appressorium development of Phyllosticta ampelicida pycnidiospores

Germination of Phyllosticta ampelicida pycnidiospores was followed from attachment through development of mature, highly melanized appressoria. Using time-lapsed video microscopy, it was determined that mature appressoria formed within 6 hours of attachment of the spores on hydrophobic substrata, Pycnidiospores germinated in the presence of tricyclazole did not produce pigmented appressoria indicating that the darkening agent is melanin, which in normal appressoria reached maximum levels within 6 hours following germination. Pycnidiospores were binucleate. Prior to development of the septum separating the pycnidiospore and germ tube from the appressorium, the two nuclei divided mitotically and three of the four resulting nuclei migrated into the appressorium. The fourth nucleus remained in the pycnidiospore where it degraded ultimately. Mature appressoria formed penetration pegs capable of penetrating polycarbonate.