Fumonisin B1 production by Fusarium moniliforme and Fusarium proliferatum as affected by cycling temperatures.

The effects of temperatures cycling between 5 and 20 degrees C, 10 and 25 degrees C, and 15 and 30 degrees C on the production of fumonisin B1 (FB1) and ergosterol by Fusarium moniliforme and Fusarium proliferatum on rice was studied. Temperatures were cycled at 12-h intervals by manually moving cultures from one temperature to another. Constant temperature incubation at 25 degrees C and a low temperature stress were compared with the cycling temperature incubations. Low temperature stress was achieved by incubating rice cultures at 25 degrees C for 2 weeks followed by 15 degrees C for 4 weeks. The maximum yields of FB1 were found to be 247 microg/g by F. moniliforme at temperatures that cycled between 10 and 25 degrees C after 2 weeks and 284 microg/g by F. proliferatum when the temperatures cycled between 5 and 20 degrees C after 6 weeks. Ergosterol content of the rice cultures was also monitored. Overall, the two Fusarium species showed differences in production of FB1 and ergosterol under the various temperature treatments. The most notable differences were that the temperature treatments that stimulated greatest FB1 production were different for each species: cycling temperatures between 10 and 25 degrees C for F. moniliforme and cycling temperatures between 5 and 25 degrees C for F. proliferatum. At most temperatures, F. proliferatum produced more ergosterol than F. moniliforme. Maximum production of ergosterol by F. proliferatum occurred at 6 weeks, with temperatures that cycled between 10 and 25 degrees C, whereas F. moniliforme produced maximum amounts of ergosterol at 6 weeks, with temperatures that cycled between 15 and 30 degrees C.