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ARS Home » Research » Publications at this Location » Publication #63953
Title: AGRICULTURAL BYPRODUCTS AS SUBSTRATES FOR GROWTH, CONIDIATION AND CHLAMYDOSPORE FORMATION BY A MYCOHERBICIDE, FUSARIUM OXYSPORUM

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

Submitted to: Biocontrol Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/4/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary: Some of the major diseases caused by Fusarium species are the vascular wilt diseases caused by formae speciales of Fusarium oxysporum. Recently, these vascular wilt pathogens, which are highly specific for their 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 large 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 with the mycoherbicidal strains of Fusarium oxysporum. Current methods require at least 3 to 5 weeks before substantial numbers of chlamydospores are obtained. This work describes rapid methods to study and optimize conditions required for the production of chlamydospores. The effects of substrates on the growth and formation of spores, especially chlamydospores by three strains of a mycoherbicidal strain of Fusarium oxysporum is described. Overall, the ideal substrates for optimum conididation and chlamydospore formation was aqueous extracts of inexpensive agricultural by-products such as soybean hull fiber and corn cob. This biomass can be used by scientists and agriculturists as a biocontrol agent for undesirable plants.

Technical Abstract: Characteristics, such as mycelial growth, conidiation and chlamydospore formation of three distinct variants of the mycoherbicide Fusarium oxysporum strain EN4 were studied in liquid cultures using agricultural byproducts as substrates. Mycelial growth, and conidia and chlamydospore formation were different for three strains and it was substrate dependant. The quantity at which they were formed was also substrate-concentration dependent. Irrespective of C/N ratios, chlamydospores were formed readily in liquid media and in greater amount on substrates with lower utilizable carbon content than on those with higher carbon content. In liquid cultures, increases in concentration of substrates low in utilizable carbon affected chlamydospore formation far less than those with higher carbon content. The presence or absence of plant fibers in soybean hull fiber extract medium affected the three variants of F. oxysporum differently. The final pH of the liquid cultures (4.1 to 8.5), after 10 days growth, wa affected by the fungal variant, substrate used and by the substrate concentration. In liquid cultures with 1% soybean hull fiber, chlamydospore formation corresponded with an increase in the pH of the media from 6.0 to 7.7. The interaction between fungal variants, the substrates and concentration at which used was highly significant for all the variables tested indicating that conditions needed to optimize the production of fungal propagules is complex. Overall for all three variants, the ideal substrates for optimum conidiation and chlamydospore formation was aqueous extracts of soy bean hull fiber and corn cob at concentrations of 1 to 2.5%.