Cultural studies on two cercospora species of sesame and their interactions with some sesamum germplasm in Kenya

Abstract

Conditions influencing in vitro growth and sporulation of Cercospora sesami and C. sesamicola were investigated to determine appropriate techniques for producing adequate quantities of inocula for use in the creation of epiphytotics of the white and angular leaf spots of sesame during resistance screening programs. Both fungi produced the largest colonies, and most abundant quantities of conidia on carrot leaf decoction potato dextrose agar, and sesame stem meal agar, respectively. Optimum media quantity for growth of both fungi was 35-ml per 9-cm diameter petri-plate. C. sesami sporulated most abundantly in plates holding 15-ml of media, but maximum conidial production by C. sesamicola was in those carrying 35-ml. Greatest mycelial and conidia! production by the two fungi occurred between pH 6-7. However, prolonged incubation widened the optimum pH range for growth and sporulation of both fungi. Prolonged incubation of C. sesami also improved sporulation but only until the 21st day. For C. sesamicola, every increase in the duration of incubation enhanced sporulation. Optimum temperature for culturing both fungi was 25 0 C. Growth of both fungi was stimulated, and depressed by continuous light at all temperatures below and including 30° C, and at 35° C, respectively. Sporulation of C. sesami was greater under continuous dark and alternating light/dark cycles at temperatures below and including 25° C. At higher temperatures, illumination treatments did not produce significant effects on conidial production. For C. sesamicola, the largest number of conidia was observed under continuous light at all the tested temperatures …