Lipids stimulate spore germination in the entomopathogenic ascomycete <Emphasis Type="Italic">Ascosphaera aggregata</Emphasis> |
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Authors: | Email author" target="_blank">R?R?JamesEmail author J?S?Buckner |
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Institution: | (1) USDA-ARS Bee Biology and Systematics Laboratory, Department of Biology, Utah State University, UMC 5310, Logan, UT 84322-5310, USA;(2) USDA-ARS Red River Valley Agricultural. Research Center, Biosciences Research Laboratory, P.O. Box 5674, Fargo, ND 58105-5674, USA |
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Abstract: | The alfalfa leafcutting bee (Megachile rotundata) is solitary and managed on a large scale for pollination of alfalfa seed crops. The bees nest in holes drilled in wood or
polystyrene blocks, and their larvae are highly prone to a fungal disease called chalkbrood. The most prevalent form of chalkbrood
is caused by Ascosphaera aggregata, but this ascomycete is difficult to culture. Hyphae will grow on standard fungal media, but spore germination is difficult
to achieve and highly variable. We found that germination can be enhanced with oils. Lipids derived from plants and bee larvae
increased germination from 50% (without oil) to 75–85% (with oil). Percent germination was significantly greater in the presence
of lipids but germination was not significantly different when different oils, including mineral oil, were used. A. aggregata spores oriented along the oil--aqueous interface in the broth in a polar fashion, with swelling and germ tube formation always
occurring into the aqueous portion of the broth. The other half of the spore tended to attach to a lipid droplet, where it
remained, without swelling, during germ tube formation. The physical attachment of spores to the oil--aqueous interface is
what most probably stimulates spore germination, as opposed to some nutritional stimulation. However, further research is
needed to determine if and where the spores encounter such an interface when germinating in the host gut, where germination
normally occurs. |
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Keywords: | alfalfa leafcutting bee chalkbrood fatty acids lipids Megachile rotundata spore germination |
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