Page 221 - Plant Canada 2024 Proceeding

PLANT CANADA 2024

forecasting model DOWNCAST to predict the risk of sporulation and infection as sporulation infection
periods (SIPs), based on daily air temperature, relative humidity, leaf wetness duration and temperature,
plus temperature in the days following potential infection. Fungicide sprays are also recommended if
downy mildew lesions are found on onions in the region, or if sporangia of P. destructor are found on
spore traps. Rotorod spore traps are assessed three times a week throughout the growing season. From
2012 to 2023, the forecasting program was accurate in 10 of the 12 years. This included two years where
DOWNCAST was accurate in predicting no disease risk and no downy mildew developed in the Holland
Marsh. In 2022, DOWNCAST forecasted SIPs and airborne sporangia were later found, but the disease
did not develop in grower fields, likely due to appropriately timed fungicide applications predicted by
DOWNCAST. Weather conditions were very favourable for onion downy mildew development throughout
the 2023 growing season. DOWNCAST predicted multiple SIPs and there were high numbers of
sporangia found in spore traps. In a fungicide trial, a SIP was identified on 14 July and the first lesions
found on 27 July. Disease was assessed on 1, 10 and 15 Aug as lesions per m of plot. In the 15 Aug
2
assessment, the treatment receiving the fungicide mefenoxam S (Ridomil) alternated with oxathiapiprolin
2
plus mandipropamid (Orondis Gold) had 2 lesions, compared to 79 lesions m in the nontreated check. In
most years, onion downy mildew developed 14 – 17 days after sporangia were found. While the model
alone is mostly effective, spore trapping can improve DOWNCAST to confirm disease risk. DOWNCAST
continues to be a useful tool for onion growers in the Holland Marsh and other regions in Ontario.

[P36] GENETIC DIVERSITY IN VIRULENCE OF POPULATIONS OF PUCCINIA CORONATA VAR
AVENAE F. SP. AVENAE COLLECTED USING EXTENSIVE SAMPLING TECHNIQUES COMPARED
1
1
TO INTENSIVE SAMPLING TECHNIQUES. James Menzies , Sharon Deceuninck , and Henry Klein-
Gebbinck . Morden Research and Development Centre, Agriculture and Agri-Food Canada, 101 Route
2 1
100, Morden, Manitoba, R6M 1Y5, Canada; and Beaverlodge Research Farm, Agriculture and Agri-Food
2
Canada, Beaverlodge, Alberta, T0H 0C0, Canada
Correspondence to: jim.menzies@agr.gc.ca

Puccinia coronata var avenae f. sp. avenae (Pcaa), the causal agent of crown rust, is a significant threat
to oat production in Canada. The development and use of crown rust resistant oat varieties in Canada
has helped mitigate the effects of this disease on oat yield and quality. A knowledge of the virulence
characteristics of the pathogen population is essential to identify effective resistance genes to be
incorporated into new oat varieties. This, in turn, requires the proper sampling of the pathogen population
to determine its virulence characteristics and genetic diversity. Traditionally, collections have been made
in Manitoba and eastern Saskatchewan by sampling one isolate of Pcaa per field from many fields over a
large area, or by extensive sampling. Extensive sampling involves access to many fields in which there
are Pcaa infected plants, as well as the physical and human resources to conduct the work, which are not
always readily available. Alternatively, intensive sampling could be practiced in which many isolates of
Pcaa are sampled from a few fields, reducing the number of fields in which access is required, and the
resources necessary to conduct the work. The objective of this work was to compare extensive sampling
and intensive sampling methods of natural populations of Pcaa in Manitoba in 2018, 2019 and 2020 to
obtain genetically diverse collections, as determined using virulence. Difference between the two
sampling methods were determined using the Shannon diversity index, followed by Hutcheson’s t test.
Extensive sampling collections of Pcaa were observed to be more genetically diverse than intensive
sampling collections in 2018 and 2020, but there were no significant differences between the collections
in 2019. A greater percentage of the races identified in the extensive sampling collections each year were
represented by a single isolate as compared to the intensive sampling collections. Common or dominant
races were observed as a greater proportion of the isolates collected in the intensive sampling collections
as compared to the extensive sampling collections in 2018 and 2020. The extensive sampling method
and the intensive sampling method achieved similar results in 2019, but considering the results obtained
in 2018 and 2020, a more genetically diverse collection of isolates of Pcaa can be obtained using the
extensive sampling method.

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