The algal polysaccharide ulvan induces resistance in apple to Glomerella leaf spot. However, changes in the pre-infectious process of Colletotrichum gloeosporioides have been reported in apple plants previously treated with ulvan. Thus, this study aimed to verify if the polysaccharide interferes directly in the development of pre-infective structures. For this, 10 µL drops of spore suspension (2x10(5) conidia.m L-1) were distributed on cellophane paper segments settled on glass slides. The conidial suspension was prepared with aqueous solution with (10 mg.mL-1) or without ulvan. Samples were incubated at 25ºC and 100% relative humidity. At every two hours of incubation and over a period of 16 hours, 100 conidia per drop were microscopically (200x) examined. The rates of conidia germination, apressoria formation and melanization were quantified. Germination of conidia was not affected. Ulvan stimulated the elongation of the germ tube but retarded the differentiation of the first apressorium (sessile). The polysaccharide accelerated the formation of second apressorium, but inhibited its melanization.
Ulva fasciata; apple tree; apressorium; germination; melanin; polysaccharide
