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Ovicidal effect of microfungi on thick-shelled eggs of naimal-parasitic nematodes - an in vitro study

Thapa, Sundar (2012) Ovicidal effect of microfungi on thick-shelled eggs of naimal-parasitic nematodes - an in vitro study. Masters thesis, University of Copenhagen . . [Completed]

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Summary

Thick-shelled eggs of animal-parasitic nematodes are known to survive and remain infective for long periods in contaminated soil. Therefore, the eggs accumulate over time in soil and increase the risk of transmission to their hosts. The present study was conducted to investigate if nematematophagous microfungi Pochonia chlamydosporia (biotype 10) and Paecilomyces lilacinus (strain 251) can reduce the viability of thick-shelled eggs of Ascaris suum, Ascaridia galli, Toxocara canis and Trichuris suis under laboratory conditions. The role of outermost layer of egg shells of the aforementioned nematodes, except T. suis, in protecting the eggs from the microfungi was also investigated by comparing the susceptibility of normal and decoated eggs (outermost shell layer removed with NaOCl) to the microfungi. For these purposes, the fungi were inoculated on the surface of a 2% water agar medium in Petri dishes, followed by an addition of approximately 150 unembryonated normal or decoated eggs of the respective nematodes. The control group contained only eggs on 2% water agar. The plates were placed in dark in an incubator at 23ºC and the viability of the eggs were then evaluated by using a light microscope at days 7, 14, 21, 28, 35 and 42 post experimental setup (destructive sampling).
Compared to the control eggs, P. chlamydosporia reduced the viability of normal A. galli and T. canis eggs by more than 75% and 60%, respectively, after 21 days of exposure to the fungus. The fungus also showed a moderate effect on the viability of normal T. suis eggs. In contrast, P. lilacinus was found far less effective than P. chlamydosporia in reducing the viability of normal A. galli, T. canis and T. suis eggs. Both fungi had only a minor effect on the viability of normal A. suum eggs. These differences in results are likely due to the difference in the virulence of the microfungi and structural differences in the egg shells of the nematode species tested. The major reduction in the viability of the normal A. galli and T. canis eggs appeared to occur between the first 14 to 21 days of exposure to P. chlamydosporia.
Overall, the decoated eggs of A. suum, A. galli and T. canis were found to be more susceptible to the microfungi (particularly P. lilacinus) compared to the respective normal eggs, suggesting that the uterine layer may help protect the eggs from the microfungi.
The present study has shown a great potential of P. chlamydosporia to utilize as a biological control agent in reducing the viability of A. galli, T. canis and probably T. suis eggs. However, further investigations using soil samples are important to confirm the ovicidal effect of the fungus in soil.


EPrint Type:Thesis
Subjects: Animal husbandry > Health and welfare
Research affiliation: Denmark > Organic RDD 1 > PAROL
Denmark > KU - University of Copenhagen
Deposited By: Mejer, Dr Helena
ID Code:22437
Deposited On:13 Mar 2013 08:16
Last Modified:15 Mar 2013 13:18
Document Language:English
Status:Unpublished

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