The Pathogenic Mechanism On Pieris Rapae And Liquid Culture Of Acremonium Hansfordii

This paper was studied on the virulence,pathologic changes of the infected Pieris rapae,sperating toxin matter and the liquid culture of Acremonium hansfordii.The results were as follows:1. The Acremonium hansfordii was bioassayed on the Brevicoryne brassicae,Pieris rapae,Pultella xylostella,Mythimna separate by the ways of spray and dipping. The result showed that the Brevicoryne brassicae and Pieris rapae were most susceptible.The infection was obviously increased with the increasing concentration.The values of LC50 was1.62×10⁶conidia/mL,1.25×10⁷conidia/mL,1.13×10⁸conidia/mL,1.01×10⁹conidia/mL against the Brevicoryne brassicae,Pieris rapae,Pultella xylostella,Mythimna separate, respectively.2. The fungus,Acremonium hansfordii, was bioassayed on the insect by physiology, researched pathologic changes and intrusion mechanism of the infected Pieris rapae. The result indicated that the appetite,body weight,excretion quantity and digestion rate of the infected 3rd instar Pieris rapae were obviously influenced.After infected 2 days, the appetite,body weight and excretion quantity were obviously lighter than CK.Digestion rate of the infected 3rd instar Pieris rapae reduced by 40.5%⁸6.1%,however,CK was reduced by 88.5%⁹4.5%.The results showed, the content of protein in infected 3rd instar Pieris rapae was reduced.In addition, the invasion of Acremonium hansfordii destroyed the protection enzyme system of insects. The activities of SOD and POD of the infected 3rd instar Pieris rapae were lower than CK. There was no difference between the activity of CAT of the infected 3rd instar Pieris rapae and uninfected before 2 hours.However, after 4 hours the activity of CAT of the infected 3rd instar Pieris rapae was lower than CK,descending from 9.277U·mg^-1·min^-1 at the time of 2 hours to 1.531 U·mg^-1·min^-1 at the time of 48 hours, respectively.3. The crude toxin sperated from the liquid cultural medium of Acremonium hansfordii by the way of liquid-extract, researched its virulence to four insects. The results showed Acremonium hansfordii possibly produced insecticidal activity in Fries liquid culture. The crude toxin from Acremonium hansfordii by different solvent was bioassayed on Brevicoryne brassicae,Pieris rapae,Pultella xylostella and Mythimna separata.The test revealed there were some discrepancies between different insects and extracts from different solvent.The activity of extracts from ligroin was best,its final adjusted mortality was 36.47%,35.84%,29.80%,11.11%, respectively. There was no insecticidal activity in the extract from ethyl acetate, its final adjusted mortality was 6.25%,2.22%,3.85%,5.56%.Its pathogenicity test against Brevicoryne brassicae was best in the same conditions(concentration and time), its mortality was 36.47%,Pieris rapae was more susceptible, its mortality was 35.84%.4. The effects of C-Source, N-Source, C/N nutritive medium and different time on mycelian growth and sporulation yields in liquid culture of Acremonium hansfordii were tested. The result indicated that the optimal C-Source for mycelium growth and conidia yields of Acremonium hansfordii was xylose. The optimal N-Source was nitrogen. The ratio of optimal C-Source and N-Source was 10:1. It was favourable for the growth and sporulation yields under 20℃.Under the vibration condition (20℃, 130rpm) the mycelium growth and conidia yields of the fungus were respectively 1.40 times and 1.25 times under static condition.The mycelia biomass and conidia yields of Acremonium hansfordii reached the peak after 6 to 7 days. Therefore, 6 to 7 days was the best inoculation time as the terminal of liquid fermentation.