The optimisation of spore production by the potential fungal biological control agent for aphids, Erynia neoaphidis Remaudiere and Hennebert (Zygomycetes: Entomophthoraceae) was studied. The fungus was able to grow in semi-defined Frynia medium (SDEM) containing glucose, yeast extract, mycological peptone, and 0.02% oleic acid buffered to a pH 6. Oleic acid was fungicidal at 0.1 % (v/v) while 0.02% (v/v) oleic acid was the optimum for radial grovvth. Plugs cut 5-10 mm from the margin ofa colony produced more conidia than plugs cut 13-20 mm from the colony margin. Renewed grovvth continued through two subcultures on solid SDEM lacking yeast extract (SDEML YE), and SDEM lacking mycological peptone (SDEMLMP). The continued growth was attributed to the carry over of nutrient in the inoculum. Growth was supported on SDEMNH4S04 when ammonium sulphate was used as the nitrogen source instead of mycological peptone suggesting that the fungus could obtain the growth factors it required from yeast extract. When chitin was added to SDEM in insoluble powder form instead ofglucose (SDEMC 1 & SDEMC2), the absence of a clearing zone around the developing colony suggested that chitin was not metabolised by E. neoaphidis. Biomass grown on SEMA and on SDEMDG (containing double the original concentration ofglucose 3 2grl), resulted in production of fewer conidia oflarger volume compared to SDEMDMP containing double and half the original concentration of mycological peptone (SDEMHP), SDEM containing halfthe original concentration ofglucose (SDEMHG). Increasing the glucose to double the original concentration resulted to an increase in biomass. Erynia neoaphidis grown on aphid cadavers produced many, smaller conidia. Mycelial mats harvested from biomass grown in fed-batch liquid fermenter culture in SDEMDG at the end ofthe exponential phase and placed on water agar discharged conidia at a rate of 6,700 conidia mm -2 h-1which persisted for approximately 3 days. When E. neoaphidis was subcultured onto SDEM from SEMA medium, the colony growth rate increased on the second subculture on SDEM where more lipases and aminopeptidases were detected at higher concentrations using the API ZYM system. This shows that attenuation might have taken place by either a phenotypic or genotypic (eg mutation) change or both when E. neoaphidis was grown on SDEM from SEMA medium. Growth in GASP medium resulted in the production of more biomass and a delay in the onset of decline phase compared to cultures grown in SDEM. Fewer enzymes were detected at a lower concentration in cultures grown in GASP compared to cultures grown in SDEM, this difference might be more likely to relate to the balance of nutrients and the fact that GASP medium is more similar in composition to the nutrients found in the haemocoel of an aphid. Based on this research. It is recommend that E. neoaphidis be grown in SDEM liquid cultures containing 32 grl glucose instead of 16 grl glucose. Biomass for field applications should be harvested at the end ofthe exponential growth and mycelial mats made. The mycelial mats should be maintained at high relative humidity and can be expected to discharge conidia for 3 days.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:619297 |
| Date | January 2003 |
| Creators | Mukiibi, Joy Lois Nalweyiso |
| Publisher | University of Bedfordshire |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/10547/324344 |
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