Characterisation of genotypic and tissue specific resistance in oilseed rape (B. napus) against Sclerotinia sclerotiorum

by Antonia Wilch
Doctoral thesis
Date of Examination:2019-01-28
Date of issue:2020-01-03
Advisor:Prof. Dr. Andreas von Tiedemann
Referee:Prof. Dr. Andreas von Tiedemann
Referee:Prof. Dr. Petr Karlovsky
Persistent Address: http://dx.doi.org/10.53846/goediss-7780

 

 

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Abstract

English

Sclerotinia sclerotiorum is a necrotrophic ascomycete and the causal agent of stem rot disease, an economically important constraint in the cultivation of oilseed rape (Brassica napus L.). Since cultivar resistance is a key to control the disease, this study aimed at characterising resistance traits in diverse B. napus genotypes. Investigations were performed comparing two cultivars considered to display contrasting resistance, cv. ‘Loras’ (susceptible) and cv. ‘Zhongyou 821’ (moderately resistant). However, since disease phenotyping experiments did not consistently confirm such cultivar-related contrasts in responses, differential plant responses in stem and root tissues to S. sclerotiorum were studied. A faster lesion development was recorded in stem as compared to root tissues. Histological studies revealed distinct differences in colonisation strategies in the stem and root tissue. Hyphae followed a strictly linear growth pattern in the stem tissue, which may explain the faster longitudinal growth of lesions on stems than on roots. In contrast, root lesions showed a delayed longitudinal growth and hyphae were typically criss-crossing the root tissue. Here, the ray parenchyma was colonised by hyphae using cell pits as points for penetration. While genotypic effects on glucosinolate (GSL) levels were marginal, significant differences in plant tissues were detected with the roots containing higher amounts of total GSL than the stems. While there was no significant correlation between total GSL contents and resistance, specific GSL components may play a role in constitutive and induced defence mechanisms. Aliphatic GSL predominated in the root and might hamper the spread of the pathogen. The infection with S. sclerotiorum caused an increase of indole GSL which therefore might be involved in plant defence mechanisms. Taken together, tissue specificity in response to infection with S. sclerotiorum was observed on the level of symptom development, colonisation pattern and biochemical reaction, and was more pronounced and consistent than due to different cultivars. These findings provide a novel understanding of quantitative resistance traits of B. napus in response to S. sclerotiorum.
Keywords: Brassica napus; Sclerotinia sclerotiorum; Glucosinolates; Infection pattern; CLSM; tissue specificity
 
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