Germination and appressorium formation in Colletotrichum gloeosporioides.
Kuo KerChung
Author Affiliation: Pesticide Application Department, Taiwan Agricultural Chemicals and Toxic Substances Research Institute, Taichung, Taiwan.
Proceedings of the National Science Council, Republic of China. Part B, Life Sciences 23 : 126-132
Abstract : A two-step method was established to study conidial germination and appressorium development in the mango anthracnose fungus Colletotrichum gloeosporioides [Glomerella cingulata] during a 9-hour period. At first, mango decoction was added as a supplement to the spore suspension in order to trigger germination, and this was followed by depletion of the mango decoction to induce the formation of appressoria. This method resulted in a high percentage of germination and appressorium formation in a uniform manner. Germination of C. gloeosporioides took place within 2 h after conidia settled on the silanized cover glass. The total time span for germination and appressorium formation was 6-9 h. The first sign of conidial germination was the secretion of the extracellular matrix (ECM), which could be visualized with a hydrophobic, negatively charged gold sol, Protogold, at about 20-30 minutes before germination. The ECM could be traced throughout the whole process of conidial germination and appressorium formation. In total, 7 steps could be identified in the development of the appressorium: (1) ECM secretion; (2) nuclear division; (3) first septum formation; (4) germling emergence; (5) tip swelling; (6) 2nd septum formation; and (7) melanization of the appressorium. Along with appressorium development, 2 rounds of mitosis could be visualized with a DNA specific fluorochrome, DAPI. The first round took place at the beginning of germination, and the second round occurred during the tip swelling stage of the germ tube. In most cases, only one nucleus could be seen inside the appressorium before it heavily melanized but, on rare occasions, 2-5 nuclei could also be found.