Heterokaryosis is not
required for virulence of Heterobasidion annosum
Matteo M. Garbelotto1
Hoon K. Lee, Garey Slaughter, Tina Popenuck, Fields W. Cobb,
Thomas D. Bruns
Department of Environmental Science, Policy and Management
University of California
Berkeley, California 94720
Mycologia 89(1):92-102 (1997)
Intensive sampling of the pathogenic fungus Heterobasidion
annosum in white fir stands yielded a large percentage of
homokaryotic isolates. To assess the stability and virulence of
homokaryotic isolates, four homokaryons and four heterokaryons
were inoculated on 200 roots from 50 mature trees. Roots were
sampled after 4 and 12 months. Eighty-three percent of the
inoculated roots were infected, and 95% of the isolates retrieved
were identified as the isolates originally inoculated. Homokaryons
were not heterokaryotized and no significant colonization difference
was observed between homokaryons and heterokaryons. One year
after the removal of inoculated roots and the subsequent creation of
large basal wounds, fungal isolates that had reached the root collar
and colonized the main stem of the tree could still be isolated. Eight
putative heterokaryons and six putative homokaryons were obtained
from stems of a subsample of the inoculated trees and were grown in
the laboratory. Six of eight heterokaryons remained unchanged,
whereas all six homokaryons had been heterokaryotized.
Key Words: Homokaryons, heterokaryons, inoculation,
mating, root pathogen.
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