Page 217 - Plant Canada 2024 Proceeding

PLANT CANADA 2024

possible resistance biomarkers for rapid screening of additional breeding families—a necessary
component of safeguarding Canada’s forest sector.

[P28] FUNGICIDE INSENSITIVE IN COLLETOTRICHUM LENTIS ON LENTIL IN SASKATCHEWAN,
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2020-2022. Michelle Hubbard , Zakir Hossain , Merek Wigness , and Bruce D. Gossen . Swift Current
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Research and Development Centre, Agriculture and Agri-Food Canada, 1 Airport Rd, Swift Current, SK,
Canada, S9H 3X2; and Saskatoon Research and Development Centre, Agriculture and Agri-Food
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Canada, 107 Science Place, Saskatoon, SK, Canada, S7N 0X2
Correspondence to: michelle.hubbard@agr.gc.ca

Anthracnose caused by Colletotrichum lentis is currently the most important foliar disease of lentil in
Saskatchewan. Fungicides belonging to FRAC groups 11 (strobilurins), 7 (succinate dehydrogenase
inhibitors) and 3 (demethylation inhibitors) are routinely used to manage this disease. Through field
surveys in 2020, 2021 and 2022, we explored the insensitivity of C. lentis to fungicides in FRAC groups
11, 7 and 3 using radial growth and molecular methods. The distribution of anthracnose, its severity and
group 11 insensitivity within fields as well as the impact of group 11 insensitivity on isolate growth and
disease severity were investigated. Anthracnose symptoms were consistently more severe in low spots
within fields relative to hilltops. Hot, dry conditions in 2021 suppressed anthracnose development such
that only a few samples were available for assessment. Overall, insensitivity to strobilurins was
widespread but there was little or no insensitivity to groups 3 and 7. The distribution of strobilurin
insensitivity was often patchy and uneven within a single field. This patchy distribution likely occurs
because C. lentis is transmitted primarily by rain-splash and lacks a air-borne phase to distribute spores
across a region or even a single field. In these patches, insensitivity to strobilurins was correlated with
lower anthracnose severity in 2020, but not in 2022. Strobilurin sensitivity status had no impact on isolate
growth in the absence of a strobilurin, which is an indication that the mutation to insensitivity has not
affected isolate fitness. Lentil growers in Saskatchewan should use fungicides with active ingredients
other than, or in addition to, strobilurins for management of anthracnose.

*[P29] IDENTIFICATION OF PYTHIUM SPECIES ASSOCIATED WITH CAVITY SPOT LESIONS ON
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CARROTS IN THE HOLLAND MARSH, ONTARIO. Umbrin Ilyas , Lindsey J. du Toit , and Mary Ruth
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McDonald . Department of Plant Agriculture, University of Guelph, Guelph, Ontario, Canada, N1G 2W1;
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and Department of Plant Pathology, Washington State University, Mount Vernon, WA, USA, 98273
Correspondence to: uilyas@uoguelph.ca

Cavity spot is caused by several species of soilborne Pythium categorized as slow (< 20 mm/day) or fast-
growing (>20 mm/day) based on their growth rate on agar media. Some Pythium species are now
classified as Globisporangium based on phylogenetic studies. However, for consistency, the term
"Pythium" is used throughout this abstract. The objectives of this study were to (1) identify Pythium
species associated with cavity spot lesions, and (2) determine if the diversity of Pythium isolates varies
with lesion size, applications of the fungicide mefenoxam, or between fields with a history of low or high-
risk of cavity spot. Lesions were cut from carrots sampled from eighteen commercial fields in the Holland
Marsh, Ontario, Canada. Lesions were categorized as small (0.1 cm), medium (0.2–0.5 cm), large (0.6–1
cm), or very large (> 1 cm) based on the horizontal lesion length. Lesions were plated on a semi-selective
agar medium to isolate Pythium. The isolates were identified using microscopy and Sanger sequencing of
internal transcribed spacer on 18S r RNA gene, cytochrome c oxidase-I, and NADH dehydrogenase
subunit 1 gene. In 2020–21, 220 medium-sized lesions from eight fields yielded 260 Pythium isolates,
nearly all were P. sulcatum, except eight isolates that were P. intermedium. In 2022–23, 242 lesions of
four different sizes were collected from ten carrot fields, including low and high-risk fields, and those with
and without mefenoxam application. The 929 Pythium isolates belonged to seven species. Three were
slow-growing: P. sulcatum (71% of all isolates), P. violae (18%), and P. rostratifingens (1%). Four were
fast-growing: P. intermedium (5%), P. sylvaticum (3%), P. irregulare (1%), and P. ultimum (1%). There
were no significant effects of mefenoxam or history of cavity spot risk on the diversity of Pythium isolates.
The number of isolates of P. violae was 21% lower in fields in which mefenoxam had been applied vs no
mefenoxam applications. There was a significant association of lesion size with the frequency of slow and
fast-growing isolates based on chi-square test (χ = 50, P = 0.0001). Slow-growing species were isolated
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