The sexual stage (Glomerella cingulata) of Colletotrichum gloeosporioides from mango, and effect of temperature and light on its reproduction.
Ann P. J.
Author Affiliation: Chiayi Agricultural Experiment Station, Chiayi, Taiwan.
Plant Pathology Bulletin 4 : 173-179
Abstract : The sexual stage G. cingulata was detected in mango orchards in Taiwan. The frequency of distribution of the homothallic perithecial strains was relatively low, with an isolation rate of c. 0.3-0.95%. The perithecial strains produced both ascospores and conidia on potato dextrose agar (PDA) while the conidial strains produced only conidia. On PDA under light treatment, the perithecial strains required 8-10 d, 10-11 d and 10-12 d for perithecial, ascus and ascospore formation, respectively. Abundant ascospores were produced and released in/from asci after incubation for 20-30 d on the same medium. Only empty perithecia without asci or ascospores could be detected after 50-60 d. The sexual organs produced on/in PDA medium were similar to those formed in diseased mango leaves in the fields. Ostiolate perithecia were dark brown, obpyriform or subglobose with an av. range of 114.3-117.8 × 91.8-108 µm. Each perithecium contained between 7 and 56 asci with an av. of 17.5. Asci were hyaline, clavate, 8-spored and the mean size was 56.6-77.4 × 11.7-12.2 µm. Ascospores were hyaline and slightly curved and sizes were 14.3-18.6 × 6.6-6.8 µm. The perithecial strains produced ascospores from 15-30°C with the opt. temp. around 25°. While the opt. temp. for conidial formation was c. 30°. Light was essential for sexual reproduction and also enhanced conidial formation. Formation and production of ascospores under cool fluorescent light with light intensity of 2000 Lux for 24 h/d was significantly earlier and higher than those produced under 1000 Lux for 12 h/d, 1000 Lux for 24 h/d or 3000 Lux for 24 h/d. In darkness ascospores were either not produced or rarely produced.