Study On The Fermentation Technology Of Nomuraea Rileyi And The Potential Of Field Application

Nomuraea rileyi is one of the most important entomopathogenic fungi, whichsometimes cause natural epizootic in noctuids’ population. Biology, epizoology, and someothers research fields of the fungus were studied in the world, but no registed productswere reported. Based on former researches, technique progress of fermentation includingmorphology observation on liquid culture, optimization of solid medium, and techniqueprogress of solid fermentation, were studied in the present thesis, A strain of N. rileyi withhigh virulence against the target noctuids, Spodoptera litura, Spodoptera exgua, andHelicoverpa armigera, was selected, and further field trial was carried out to test controlefficacy of the target insect pest, S. litura.Poor study on technique progress of solid fermentation baffled mass production of N.rileyi. Optimization of the solid medium for N. rileyi was carried out to improvefermentation efficiency in the present study. Flour, rice, soybean powder, cotton seedpowder, and oatmeal as single factors were tested their fermentation efficiency. Yellowmealworm powder, yeast, and peptone were compared to determine the optimal nitrogensource. Glucose, fructose, maltose, lactose, and sucrose were also compared as addedcarbonate source. The results showed2%yeast powder, and3%sucrose added in cottonseed powder benefited sporulation, and condia could be harvested over3.32±0.38×10~8conidia/cm~2on the medium.Fermentation technique processes of shallow tray fermentation and thin layerfermentation were studied in the present study. Fermentation efficiency on basic mediumof rice and of shattered soybean was compared. SMY fermentation borth cultured for3days at25℃was inoculated into basic medium at a percentage of25%, and then fellowedsolid fermentation with1cm thick layer at25℃. The basic media of rice and of shatteredsoybean reached sporulation of0.4±0.22×10~8conidia/g and6±1.83×10~8conidia/g,respectively.Another special technique progress of solid fermentation known as thin layerfermentation was also studied. An optimal medium including6%cotton seed powder,2%yeast powder, and1.5%agar was autoclaved and sprayed onto plastic plates, whichresulted in formation of a thin layer of medium less than1mm on the plates, and thenfollowed fungal inoculation of conidia suspension of N. rileyi. The inoculated plastic plateswere covered plastic film to avoid water evaporation, and cultured at25±1℃with full-time illumination for10days. The sporulation reached a mount of2.45±0.16×10~8conidia/cm~2.A N. rileyi strain with high virulence against target pests is the key to develop a newfungal insecticide. Based on primary studies,5strains of N. rileyi, Nr03、Nr06、Nr09、Nr11and Nr15were chosen for further laboratory assessment of virulence against the3speciesof noctuids larvae, Prodenia litura, Laphygma exigua and Helicoverpa armigera.Inoculated conidia density varied from188.9～4048.3conidia/mm~2with variation ofconcentrations of conidia suspension, which be adjusted to1×10~5,1×10~6, and1×10~7conidia/mL. Exposed to the different conidia density, motality of P. litura rangedfrom60%~95%in10days after fungal innoculation. The strain Nr15showed the highestvirulence against the insect pest with a LC50of266.7conidia/mm~2, and a LT50of5.81d atthe highest dosage of4048.3conidia/mm~2. The5N. rileyi strains showed hostspecialization resulting in mortalities of L. exigua and H. armigera neither reached to50%. Dosage effect on fungal disease was shown in the bioassay of N. rileyi againstnoctuids’ larvae.A field trial was carried out to control the2ndinstar larvae of P. litura on the cabbageB. chinensis by the N. rileyi strain Nr15. Two dosage treatments were set byultro-low-volume spraying of conidia suspension at concentrations of1×10~8,1×10~7conidia/mL, respectively, and the control plots treated with0.05%tween-80. Fieldobservation continued for several weeks until the larvae pupation. The results showed themortality and the corrected mortality of P. litura larvae reached96.56±5.12%and96.36±5.68%, respectively, in the treated plots of1×10~7conidia/mL. The other plotstreated with the concentration of1×10~8conidia/mL gained the mortality and the correctedmortality of96.3±2.6%and96.09±3.01%. No significant difference showed on mortalityand corrected mortality between the two treatments. The N. rileyi strain showed greatpotential to be developed a wonderful fungal insecticide against P. litura larvae.