LIQUID FERMENTATION TO PRODUCE BIOMASS OF MYCOHERBICIDAL STRAINS OF FUSARIUM-OXYSPORUM

Conditions for optimizing spore production, especially chlamydospores, by host-specific mycoherbicidal strains of Fusarium oxysporum causing vascular wilts in coca (Erythroxylum coca) and poppy (Papaver somnife rum) were studied in 2.5-1 fermenters. The fermentor dissolved oxygen and pH had significant effects on the growth characteristics of F. oxy sporum strains. The effect of the fungal strain, however was not signi ficant for most of the variables studied except for chlamvdospore form ation. After 14 days of fermentation, the spore types produced were mi croconidia and chlamydospores, with very little production of macrocon idia. While the total viable counts were significantly higher under hi gh than under low dissolved O-2, the chlamydospore counts were signifi cantly higher under low than under high dissolved O-2 The percentage o f chlamydospores obtained, as a proportion of total viable was signifi cantly higher when the fermenter pH was increased, than when it was no t. Scaling-up the liquid fermentation to 20 1, yielded log(10) c = 6.5 (where c = chlamydospores ml(-1)) after 14 days' fermentation, with b iomass viable counts of log(10)v similar to 8.0 (where v = viable coun ts g(-1) air-dried biomass). A single-step liquid fermentation reporte d in this study increased chlamydospore yields and reduced the time re quired for their production with techniques currently available from 5 weeks to less than 2 weeks.