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Journal of Biological Sciences
Year: 2006  |  Volume: 6  |  Issue: 2  |  Page No.: 305 - 315

Variation in Germination, Virulence and Conidial Production of Single Spore Isolatesof Entomopathogenic Fungi in Response to Environmental Heterogeneity

Mohammed El Damir    

Abstract: The objectives of this study were to evaluate spore germination, virulence against a surrogate host [the western flower thrips, Frankliniella occidentalis (Pergande)] and spore production capabilities at different temperatures and RH combinations of 6 single spore isolates newly obtained from multispore isolates of Beauveria bassiana (Balsamo) Vuillemin (5672) and Metarhizium anisopliae (Metschnikoff) (1080). We found that temperature and RH influenced conidial germination, spore production and virulence of 5672 and 1080 and their single spore isolates tested. At =98% RH, 20 and 30 °C, single spore isolates from 5672 had higher %germination than their multispore isolate, while at 100% RH and all temperature tested, the single spore isolates (1080-1 and 1080-2) had higher germination than their multispore isolate 1080. At 95% RH, the conidial germination was poor and only occurred at 20 °C for two single spore isolates (5672-4 and 5672-5) as well as for the multispore isolates 5672 and 1080. Metarhizium anisopliae isolates were more virulent against western flower thrips than the B. bassiana isolates tested. At 100% RH, mortality of western flower thrips was more obvious than at other %RH levels tested. Single spore isolates 5672-1 and 5672-3 were less virulent than other isolates tested, whereas 1080-3 and 1080-1 were more virulent than all tested isolates. Conidial production at 100% RH and 20 °C was higher than other %RH and temperatures tested. At 95% RH and temperatures of 30 and 15 °C, conidial production was limited to few isolates. Only 5672-5 produced conidia at 30 °C, and 5672-1, 5672-4, 5672-5 and the multispore isolate 5672 produced conidia at 15 °C, but no production of conidia was found for the multispore 1080 and its single spore isolates at these temperature and RH combinations. No conidial production was found at <95% RH. Variability in conidial germination, spore production and virulence of 5672 and 1080 and their single spore isolates tested will help in selection and development of these fungi for Sunn Pest, Eurygaster integriceps Puton management under temperatures and RH levels occurring in the Sunn Pest overwintering sites.

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