Role of plant-microbe interactions in host resistance and emergence of virulent races
M. RASHID (1), S. Liban (2), X. Zhang (1), P. Park (1), M. Borhan (3), W. Fernando (1) (1) University of Manitoba, Canada; (2) DL seeds, Canada; (3) Agriculture and Agri-Food Canada, Canada

Brassica napus is susceptible host to a few major plant pathogens including blackleg caused by Leptosphaeria maculans. A number of single dominant resistance (R)-genes have been identified in different Brassica species but single R-gene may not offer durable resistance to the disease indicating the need for integrated management strategies. A 4-year study was initiated to generate the required data to implement a canola cultivar rotation strategy based on an understanding of R-gene durability and the nature of emergence of virulent isolates. Five near isogenic lines (NILs) carrying single blackleg resistance genes along with the susceptible parent were used in this study. Each plot was sprayed with either 90% avirulent isolates for durability or 100% avirulent isolates for emergence. A 2-year canola-wheat-canola rotation was used. The pathogen isolates collected from either infected stubble or a 7-day Burkard spore trap were subjected to differential testing as well as PCR identification for the presence of avirulence genes to monitor changes in the pathogen virulence. Disease incidence significantly varied among the NILs as well as between years in both the durability and emergence trials. However, similar trends of disease reduction were observed among the NILs in each year at both trials. The disease severity scores of Rlm3 plots in the emergence trial in 2014 and 2015 were 2.5 and 1.5 respectively. The rest of the cultivars showed ≤ 1.0 disease severity irrespective of trial and year. Differential phenotyping as well as PCR analysis of L. maculans isolates obtained from infected-stubble indicated the frequency of isolates carrying AvrLm1, AvrLm2, AvrLm3, AvrLm4, AvrLm5, AvrLm6, AvrLm7 and AvrLm11. The second year data indicates the efficacy of crop rotation in rducing disease severity and gaining back of avirulence gene. The study will continue for four years to observe the likelihood and timeline for the durability of R-genes and the emergence of new isolates. 

Abstract Number: P17-595
Session Type: Poster