Variations in relative humidity modulate Leptosphaeria spp. pathogenicity and interfere with canola mechanisms of defence

• Published in: European journal of plant pathology Vol. 126; no. 2; pp. 187 - 202
• Main Authors: El Hadrami, Abdelbasset, Fernando, W. G. Dilantha, Daayf, Fouad
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer Netherlands 01-02-2010; Springer; Springer Nature B.V
• Subjects: Agriculture; Biological and medical sciences; Biomedical and Life Sciences; Blackleg; Brassica napus; Cultivars; Ecology; Fundamental and applied biological sciences. Psychology; Fungal plant pathogens; Humidity; Life Sciences; Pathogens; Phytopathology. Animal pests. Plant and forest protection; Plant diseases; Plant Pathology; Plant Sciences; Relative humidity; Relative humidity; Lignin; Temperature; Canola (oilseed rape); Blackleg; Phoma canker; Hypersensitive reaction; Phenolics; Ascomycota; Plant pathology; Plant pathogen; L; Mechanism; Fungi; Pathogenicity; Plant; Phoma; Leptosphaeria maculans; Fungi Imperfecti; biglobosa
• ISSN: 0929-1873; 1573-8469
• DOI: 10.1007/s10658-009-9532-1

Blackleg (phoma stem canker), caused by
Leptosphaeria
spp., is an important disease of canola (oilseed rape,
Brassica napus
). Control strategies rely on the use of resistant cultivars, chemical and disease-reducing cropping practices. In Canada, the pathogen population is represented by
L. maculans
and
L. biglobosa
, which are considered to be highly and weakly aggressive, respectively. It is largely admitted that
L. biglobosa
isolates are not able to cause a significant amount of stem canker and develop on the plant only when it becomes senescent, late in the season. The prevalence of
L. maculans
over
L. biglobosa
has been considered to be linked to the low aggressiveness of the latter. However, in this study, we show that
L. biglobosa
isolates could become highly aggressive in terms of lesion appearance on cotyledons, if the right conditions of temperature and relative humidity (RH) are provided. Percent germination of inoculated pycnidiospores was not affected by the RH regimes tested. This is the first study to show the importance of RH as a factor conditioning the pathogenicity of
L. biglobosa
isolates on canola cotyledons. Concurrent changes in the host defence mechanisms against
L. biglobosa
isolates in response to variations in the RH were also investigated. Under high RH, the increase in disease caused by the weakly aggressive isolates coincided with a reduced accumulation of lignin at the early stages of infection.