Page 298 - PC2019 Program & Proceedings

PLANT CANADA 2019

P169. A Brevibacillus fortis isolate produces extracellular antibiotics that inhibit the growth of the
onion pathogen Fusarium oxysporum f. sp. cepae and other Fusarium species
Johnson, E.; M. Bowma; C. Dunlap
USDA ARS

Tan spot is an important foliar disease of wheat caused by the fungus Pyrenophora tritici-
rentis (Ptr), which produces at least three necrotrophic effectors. In North America, Ptr ToxA-producing
isolates are predominant (races 1 and 2), while race 3 isolates (Ptr ToxC-producers) are less frequent.
Race 4, which is non-pathogenic and lacks the ability to produce any effectors, is rare. This study aimed
to investigate virulence and effector genotypes in Ptr isolates obtained from different host types. The
virulence of 130 isolates collected from durum and winter wheat, as well as from native grasses, was
evaluated by inoculating four differential wheat genotypes. This was followed by PCR analysis
with ToxA and ToxB-specific primers. The results showed that races 1 and 2 are the most common on
wheat, but interestingly, the non-pathogenic race 4 is dominant on native grasses, and race 3 occurs more
frequently when durum wheat is surveyed. Atypical virulence was reported when isolates were obtained
from winter wheat, with isolates recovered that induced necrosis but did not produce Ptr ToxA, the only
known necrotrophic effector. In conclusion, Ptr races and effector genotypes vary depending on the host,
and this was the first study to investigate the virulence of Ptr collected from native grasses in Canada.
Moreover, additional necrotrophic effector(s) that await further characterization may play an important
role in Ptr pathogenicity.

Bohan Wei (bwei1@ualberta.ca)

P170. Post-harvest root decay of American ginseng (Panax quinquefolious) and the relationship
with ginseng replant disease
*
Samur, I. ; P. Goodwin
University of Guelph

Ilyonectria mors-panacis causes low levels of root rot of American ginseng in soil not previously planted
to ginseng but high levels of root rot when grown again in soil used for ginseng, which results in replant
disease. One explanation for this could be changes due to relatively large amounts of root debris left in
the soil after harvesting, whose decay could increase levels of I. mors-panacis and soil ginsenosides.
After harvest, approximately 10% by fresh weight of roots remained in the field. By 41 days post-harvest
(dph), fibrous root pieces had completely decayed and 80% of the total root debris by fresh weight
remained. By 198 dph, only 5.8% by fresh weight remained. Root decay typically started near the bud of
intact roots. Among ginseng root grades, pencil grade was the least susceptible to decay. By 73 dph, 15%
of the roots had visible lesions, and I. mors-panacis could be detected in 36% of those lesions. These
results indicate that there are relatively large amounts of root debris left after harvesting, and decay of the
roots occurs rapidly increasing I. mors-panacis soil populations. As ginsenosides comprise 3-5% dry
weight of ginseng roots, this decay likely also releases significant amounts of ginsenosides into the soil.
These changes in soil biology and chemistry may be important elements in creating ginseng replant
disease.

Ivan Samur (isamursu@uoguelph.ca)

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