CONIDIUM GERMINATION AND APPRESSORIUM PENETRATION OF COLLETOTRICHUM-GLOEOSPORIOIDES ON STYLOSANTHES-GUIANENSIS

Pre-penetration and early penetration phases of two pathogenic strains of Colletotrichum gloeosporioides (HM 502, HM 514)from Zaire were inv estigated quantitatively on four Stylosanthes guianensis genotypes (cv . Schofield, cv. Graham, CIAT 184 and CIAT 10136) of various levels of susceptibility. The results demonstrated control of the rates and typ e of conidial germination by the fungus, influenced to a lesser extent by the host genotype. Cell reactions were visible as papillae and cyt oplasmic aggregations closely associated with the penetration peg. No fungal growth was observed when deposits of papillae occurred under ap pressoria-forming infection pegs, whereas the effect of the cytoplasmi c aggregations varied according to the host genotype. In the interacti ons with strain HM 502, the highest rates of plant reaction were recor ded on the resistant CIAT 184 genotype, while the highest level of pen etration without reaction was observed on the most susceptible cv. Sch ofield. Cytoplasmic aggregations were also observed under a few ungerm inated appressoria on this genotype. Differences were thus detected in the rates and types of conidial germination, in the rates and types o f cell reactions under appressoria and in the appressorial penetration rates without cell reactions. However, these differences did not comp letely explain the range of macroscopic symptoms observed on the vario us genotypes.