Skip to main content
ARS Home » Research » Publications at this Location » Publication #70641
Title: LIQUID FERMENTATION TO PRODUCE BIOMASS OF MYCOHERBICIDAL STRAINS OF FUSARIUM OXYSPORUM

Author
item HEBBAR, K - OICD
item Lumsden, Robert
item Lewis, Jack
item Poch, Stephen

Submitted to: Biocontrol Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/29/1997
Publication Date: N/A
Citation: N/A

Interpretive Summary: Some of the major diseases caused by Fusarium are the vascular wilt diseases caused by formae speciales of Fusarium oxysporum. recently these vascular wilt pathogens, which are highly specific hosts, have been suggested for use as mycoherbicides of weeds and narcotic plants. One of the major requirements for successful application of a mycoherbicide is the elarge scale production of fungal propagules resistant to desiccation and temperature extremes. In nature, chlamydospores, resting and survival spore structures produced by several species of fungi including Fusarium, serve a similar function, and play an important role in the long term survival of the pathogen, and in their subsequent infection of host plants. Very little research has been done on chlamydospore formation in the mycoherbicidal strains of Fusarium oxysporum. Current methods require 3 to 5 weeks before substantial numbers of chlamydospores are obtained, This work describes a rapid (2 week) liquid fermentation method to optimize conditions required for the production of chlamydospores. The optimum fermentor conditions for growth and formation of chlamydospores was low dissolved oxygen (DO) with a final increase in fermentor pH from 7.0 to between 9.0-10.0. This procedure will be used by scientists and industrial microbiologists for production of Fusarium chlamydospores.

Technical Abstract: Filtered extracts (1%) of soybean hull fiber were utilized in 2.5 l fermentors as growth medium to optimize conditions for spore production by mycoherbicidal strains of Fusarium oxysporum. Spore production was affected by dissolved oxygen (DO), controlled by sparging air into the fermentor, and pH of the fermentor medium, regulated by adding 1 N NaOH. The treatments had a significant effect on the growth characteristics of strains pathogenic to coca (Erythroxylum coca) and poppy (Papaver somniferum). The effect of fungal strain, however, was not significant for most of the variables studied except the chlamydospore formation. After 14 d, the spore types produced in the medium were microconidia (log 6.4-7.6) ml**-1), and chlamydospores (log 5.7-6.6 ml**-1), with very little production of macroconidia (log 1.7-4.5 ml**-1). Microconidial and viable counts were significantly higher (log 0.5) under sparged than under non-sparged treatment. Chlamydospore yields were significantly higher (log 0.5) under non-sparged the under sparged conditions. Chlamydospore numbers increased as the pH of the medium changed from 5.5 to 7.0. Higher numbers could not be achieved by adding 1 N NaOH at 4 d and increasing the fermentor pH above 7.0 to between 9.0 and 10.0. However, the % of chlamydospores, as a proportion of total viable (cfu) were significantly higher when the pH was increased. Scaling up fermentation to 20 l yielded log 6.8 chlamydospores ml**-1 after 14 d. Viable counts from air dried biomass were approximately log 8.0 g**-1 dry weight.