Modification of the exogenous carbon and nitrogen requirements for chlamydospore germination of Fusarium solani by contact with soil

Abstract

After exogenous carbon-independent macroconidium germination by Fusarium solani at 1 × 104 conidia/ml in axenic culture, chlamydospores were formed terminally on germ tubes. Low chlamydospore germination was supported under axenic conditions by 0.004 ng C/spore (calculated value), supplied as ethanol, or by 0.04 ng C/spore, supplied as glucose or several other sugars. Chlamydospores in direct contact with a nonsterile loamy fine sand soil (6.2 μg NH4+-N and 7.1 μg NO3−-N/g soil) had a greater exogenous carbon requirement and did not germinate until 2.0 ng glucose-C/spore was supplied. Supplemental exogenous nitrogen, added as NH4Cl, had little or no influence on percentage of germination at the levels of exogenous carbon supporting low germination, both in soil and in axenic culture. However, increasing the amounts of glucose plus NH4Cl supplied per spore increased percentage of chlamydospore germination more than increasing the amount of glucose alone for both soil and axenic systems. In axenic culture, complete germination was observed at 2.0 ng C plus 0.13 ng N/spore. Greater than 90% germination occurred for chlamydospores in contact with soil at the highest glucose plus NH4Cl level examined (200 ng C plus 13 ng N/spore), but not in glucose alone. Sterile acid-washed sand did not have a similar adverse effect on chlamydospore germination. Chlamydospores were nearly 100% germinable after 1 year of incubation in an inorganic salts medium under axenic conditions.