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Title: Influence of nutrition on the virulence and stability of the insect pathogenic fungus Metarhizium anisopliae
Author: Shah, Syed Farooq Abbas
Awarding Body: University of Wales Swansea
Current Institution: Swansea University
Date of Award: 2005
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Nutrition influenced growth, sporulation, phenotypic stability and virulence of the insect pathogenic fungus, Metarhizium anisopliae. Virulent conidia were produced on nutrient poor or osmotic stress media, while least virulent conidia were produced on nutrient rich media. Repeated subculturing on nutrient rich media caused further attenuation of virulence, however, attenuation was strain dependent. Several strain independent parameters were identified that could be used to monitor the virulence of M. anisopliae conidia during normal production or when developing new inexpensive culture media. Virulent conidia typically had high levels of spore bound Pr1, a CN ratio below 5.2:1 and high germination rates. RT-PCR revealed that virulent conidia from insects contained high levels of transcripts of pr1 A and other pathogenicity-related genes (e.g. ste 1, try 1 and chy 1). Virulent conidia from 1% yeast extract media had higher level of transcripts of these pathogenicity-related genes than the least virulent conidia from CN 35:1 medium (=SDA), however, levels were significantly lower than those in insect-derived conidia. This study shows for the first time that passaged inoculum is virulent irrespective of the original culture medium or insect host suggesting that starvation conditions, whether in vivo or in vitro, results in de-repression of Pr1 and that elevated levels of this enzyme enhance fungal virulence. Nutrition also influenced expression of other pathogenicity determinants e.g. adhesive properties of conidia (hydrophobicity, surface charge) and destruxins production, however, inconclusive relationship between these pathogenicity determinants and nutrition was observed. Nutrition also influenced fungal stability independent of strain.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available