Page 66 - Plant Canada 2024 Proceeding

PLANT CANADA 2024

Wednesday, July 10

Dr. Brent McCallum
Agriculture and Agri-Food Canada

“Combating a dynamic wheat rust population in Canada”

Abstract: Wheat is the largest crop in Canada. Wheat leaf
rust, caused by Puccinia triticina Eriks., is one of the most
common and destructive diseases of wheat. The population
of P. triticina primarily arrives each year from the United
States, carried by wind currents. Due to the absence of the alternate host in North
America, which eliminates sexual recombination, the P. triticina population is
characterized by clonally reproducing groups that diversify through step-wise mutations.
All members of each group have the same mating type alleles and are similar in their
genomes and virulence spectra. Two clonal groups are dominant and comprise the
majority of the population in Canada, while many other smaller groups contribute to
diversity. Each growing area in Canada has different compositions of these groups,
which changes annually. To combat this dynamic population genetic resistance has
been effectively deployed in the wheat cultivars grown in Canada. The common
resistance genes in Canadian wheat in order of frequency are Lr2a, Lr34, Lr21, Lr16,
Lr46, and Lr14a. Since 2013 Lr2a, Lr21 and Lr34 were all deployed in over 50% of the
seeded area for the largest wheat class Canadian Western Red Spring. Of these Lr34
has had the biggest impact because of its ability to combine additively with other leaf
rust resistance genes and its multi-pest resistance that contributes to resistance to other
wheat diseases such as stem rust, stripe rust, and Fusarium head blight. Lr34 also
produces leaf tip necrosis, primarily on flag leaves at normal growing temperatures. This
necrosis and leaf rust resistance can be observed on seedling plants when they are
grown at cold temperatures (8 C to 10 C). Both Lr46 and Lr67 have also been shown to
o
o
act similarly to Lr34, in conditioning multi-pest resistance and combining additively with
other resistance genes. While Lr46 is in some Canadian wheat cultivars, Lr67 has not
been deployed to date. Modern Canadian bread wheat cultivars often have
combinations of many resistance genes, such as those found in Carberry (Lr2a, Lr13,
Lr16, Lr23, Lr34, Lr46), which act together to impart the high levels of durable
resistance that characterize these cultivars.

Bio: Dr. Brent McCallum is a research scientist with Agriculture and Agri-Food Canada working
at the Morden Research and Development Centre in Morden Manitoba. He received his Ph.D in
Plant Pathology from the University of Minnesota in 1995 and started working at AAFC in 1996.
His research focus is on wheat leaf rust disease in Canada. He conducts an annual national
virulence survey in Canada to track changes in the pathogen population that could affect the
wheat crop in Canada. He is involved in identifying and developing sources of resistance to use
in future wheat cultivars and to understand the genetics of disease resistance. This includes
mapping and marker development for genes of interest, host-parasite interactions, and
understanding interactions between resistance genes. He is also involved in research projects
on the causal rust, Puccinia triticina, to understand its pathogenesis, diversity and evolution.

65