Characterizing Avr genes of Leptosphaeria maculans and resistance responses among Canadian canola cultivars in western Canada
Date
2017-01-04
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
ORCID
0000-0003-1426-7470
Type
Thesis
Degree Level
Masters
Abstract
Blackleg of canola, caused by Leptosphaeria maculans (Desmaz.) Ces. & de Not, is a serious concern in western Canada. The disease had been managed successfully since 1990s with use of resistant cultivars and extended crop rotations until recent years when both blackleg incidence and severity increased noticeably. This may be attributed to changes in the pathogen population that erodes the resistance of canola cultivars. The resistance associated with Canadian canola (Brassica napus L.) cultivars (CCCs) in Canada is not clearly understood. The current study was conducted to investigate the race structure of L. maculans in commercial canola fields and determine its role in blackleg incidence and severity. In addition, resistance (R) genes in representative CCCs were characterized to understand their role in blackleg control against the current population of L. maculans.
A total of 372 L. maculans isolates collected from 16 canola fields with different levels of blackleg severity in 2012 and 2013 were analysed for the presence or absence of particular avirulence (Avr) alleles by inoculating 12 lines of a host differential set with known R genes. The results indicated that the alleles AvrLm1, AvrLm3, AvrLm9 and AvrLep2 were at very low or undetectable levels in these fields, while AvrLm2, AvrLm4, AvrLm6 and AvrLm7 were generally common. Since only the R genes Rlm1 and Rlm3 are found commonly in CCCs, this result indicates that most of our cultivars are no longer effective against the current pathogen population on the prairies.Variation in Avr gene frequency was observed, depending on the cultivar, field or region studied, but these differences alone appeared insufficient to explain the variability in blackleg severity in these fields, and the erosion of Rlm1 and Rlm3 would unlikely be the primary cause of isolated blackleg outbreaks for most of the fields investigated.
Description
Keywords
Blackleg, Leptospsphaeria maculans quantitative resistance
Citation
Degree
Master of Science (M.Sc.)
Department
Plant Sciences
Program
Pathology