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Infectivity of the propagules associated with extraradical
mycelia of two VAM fungi following winter freezing
Talk: "Mycorrhizae in Stressed Ecosystems" session on Monday
afternoon
ADDY, HEATHER1, MURRAY MILLER2 & LARRY
PETERSON3
1Dept. of Horticulture, The Pennsylvania State
University, University Park, PA 16802 USA
2Dept. of Land Resource Science and
3Dept. of Botany, University of Guelph, Guelph,
Ont., Canada N1G 2W1
ICOM1 Abstract
VAM fungi have been thought to survive adverse environmental
conditions primarily as spores. However, evidence from
previous research in our laboratory suggested that infective
extraradical mycelia survived in frozen soil over winter. We
conducted two experiments to investigate the infectivity of
mycelia of two Glomus species after prolonged periods in
frozen soil. Extraradical mycelia were produced in pouches
made of fine nylon mesh, which excluded roots but not hyphae.
Mycelia in these pouches were exposed to freezing conditions
both in the field and in a controlled-temperature chamber.
Following freezing, soil in half of the pouches was disturbed
by sieving. In the second experiment, an additional treatment
was included such that a third set of pouches contained only
isolated spores. The relative infectivity of mycelia and
spores following freezing was determined by growing bioassay
plants directly in the pouches. Spores were not an effective
inoculum in any of the bioassays, regardless of freezing.
Soil disturbance following freezing reduced subsequent
colonisation of bioassay plants, indicating that mycelia were
responsible for mycorrhizal formation following freezing.
These results are consistent with the hypothesis that mycelia
remain infective in frozen soil over winter. The persistence
of mycelia in frozen soil was not dependent on connection to
root systems nor on the presence of root pieces. The presence
of the hyphal network in soil in spring has important
implications for the early phosphorous nutrition of
seedlings.