AGRICULTURAL BY-PRODUCTS AS SUBSTRATES FOR GROWTH, CONIDIATION AND CHLAMYDOSPORE FORMATION BY A POTENTIAL MYCOHERBICIDE, FUSARIUM-OXYSPORUMSTRAIN EN4

Characteristics, such as mycelial growth, conidiation and chlamydospor e formation, of three distinct variants (EN4-FT, EN4-FF and EN4-S), of the potential mycoherbicide, Fusarium oxysporum, strain EN4 were stud ied in liquid cultures. Agricultural by-products, such as cornmeal, co rn cob, soya bean hull fiber (Dietfiber-Soyfiber), cotton seed embryo pour (Pharmamedia), cane molasses yeast extract and potato dextrose me dium were used as substrates. The mycelial growth and conidia and chla mydospore formation were different for the thr-ee strains and varied w ith the substrate used. The quantity of conidia and chlamydospores pro duced depended on the concentration of the substrates. Irrespective of carbon:nitrogen ratios, chlamydospores were formed readily in liquid media and in greater amount on substrates with low utilizable carbon c ontent (aqueous extracts of soya bean hull fiber and corn cob) than on those with higher utilizable carbon content (potato dextrose broth, a queous extracts of cotton seeds and molasses yeast extract broth). In liquid cultures, increases ill the concentration of substrates high in utilizable carbon resulted in reduced chlamydospore formation; howeve r this was far less in those with a lo,ver carbon content. The effect oil fungal growth characteristics due to the presence or absence of pl ant fibers in various concentrations of unfiltered and filtered extrac ts of soya bean hull fiber depended on the fungal variant tested. Howe ver, it had a gi-eater effect on viable and microconidial counts than on chlamydospore and macroconidial counts. The viable and microconidia l counts were significantly higher in unfiltered than in filtered extr acts. The final pH of the liquid cultures (4.1-8.5), after 10 days of growth, was affected by the fungal variant, the substrate used and by the substrate concentration. In liquid cultures with 1% soya bean hull fiber, chlamydospore formation corresponded to an increase iii the pH of the medium from 6.0 to 7.7. The interaction between fungal variant s, the substrate used and the substrate concentration was highly signi ficant for all the variables tested indicating that optimization of th e production of fungal propagules is complex. Overall, for all three v ariants, the best substrates for optimum conidiation and chlamydospore formation were aqueous extracts of soya bean hull fiber and corn cob al concentrations of 1-2.5%.