Page 165 - Plant Canada 2024 Proceeding

PLANT CANADA 2024

had greater weed seedbank density and species richness; however, this did not result in greater in-
season weed biomass. Manure application resulted in a gradual decline in weed seedbank density over
time regardless of cover crop treatment. Further, manure application increased the in-season competitive
ability of cover crops, resulting in greater weed suppression per unit of cover crop biomass. In contrast, in
the absence of manure, weed seedbank density remained largely unchanged through time regardless of
cover crop treatment. We found that management practices associated with annual and perennial cover
crops had distinct ecological filtering effects throughout the rotation on the weed community and
prevented the dominance of any particular species. Together, our results demonstrate that combining the
cultural practices of annual or perennial cover cropping and manure application contributes to weed
suppression and should be considered an important component of sustainable potato production.

[O124] GLOBAL REGULATION OF PLANT PATHOGENICITY IN THE COMMON SCAB PATHOGEN
STREPTOMYCES SCABIEI. Wanyue Li, Aaron Rees, and Dawn R. D. Bignell. Department of Biology,
Memorial University of Newfoundland, 45 Arctic Avenue, St. John’s, NL, Canada, A1C 5S7
Correspondence to: dbignell@mun.ca

Common scab (CS) is a plant disease caused by soilborne bacteria belonging to the genus
Streptomyces. The disease affects the quality and market value of root and tuber crops such as potato,
beet, carrot and radish. At least a dozen or so Streptomyces species are responsible for CS worldwide, of
which Streptomyces scabiei is the best characterized. This organism produces several phytotoxic
specialized metabolites as well as secreted proteins and phytohormones that are known or suspected to
contribute to plant host colonization and disease development. While there has been much effort in
understanding how these known or potential virulence factors contribute to CS disease, there is less
known regarding the genetic factors that control the onset of pathogenicity in S. scabiei.

Most studies on virulence gene regulation in S. scabiei have focused on the thaxtomin A (ThxA)
phytotoxin, which is a critical for the development of CS. ThxA biosynthesis is stimulated by plant-derived
molecules such as cello-oligosaccharides and suberin and is controlled at the molecular level by the
transcriptional activator TxtR and the cellulose utilization repressor CebR. In addition, several members of
the bld (bald) gene family of global regulators, as well as a member of the leucine-responsive regulatory
protein family, have been shown to modulate ThxA production and virulence in S. scabiei. Given that
there are more than 800 predicted regulatory genes in the S. scabiei genome, it is likely there are
additional regulators that control the production of ThxA and other virulence factors in S. scabiei.

This study focuses on afsR, which is highly conserved in Streptomyces species and is a known global
regulator of specialized metabolite production in non-pathogenic species. Given that deletion of afsR in
the acid scab pathogen Streptomyces acidiscabies resulted in reduced ThxA production, we predict that
ThxA production in S. scabiei is also under control of afsR, and that afsR may additionally be required for
production of other virulence factors in this organism. To address this, S. scabiei strains that overexpress
or carry a deletion of the afsR gene were constructed, and the strains were assessed for the production of
ThxA and other phytotoxic specialized metabolites. In addition, plant bioassays were conducted to
investigate the impact of afsR gene deletion and overexpression on the virulence phenotype of S. scabiei.
Overall, this work advances our understanding of the genetic factors that control virulence factor
production and CS disease development by S. scabiei.

[O125] DROUGHT-RESILIENT DIPLOID POTATOES FOR SHORT AND LONG GROWING SEASON
AGROCLIMATES AS DEPICTED THROUGH GENOME-WIDE ASSOCIATION STUDIES. Bourlaye
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Fofana , David Main , Moshin Zaidi , and Benoit Bizimungu . Charlottetown Research and Development
Centre, Agriculture and Agri-Food Canada, 440 University Avenue, Charlottetown, Prince Edward Island,
2
C1A 4N6, Canada; and Fredericton Research and Development Centre, Agriculture and Agri-Food
Canada, 95 Innovation Road, PO Box 20280, Fredericton, NB E3B 4Z7
Correspondence to: Bourlaye.fofana@agr.gc.ca

In the context of climate change, crops production has become a challenge in most agrosystems due to
drought. Using a panel of 384 diploid potato clones, we recently conducted a genome-wide association
study on maturity and drought tolerance traits. A wide phenotypic diversity was observed in the collection,
and drought-tolerant potato clones that are early or late maturing were detected. Using genotype-to-
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