Effects of Cercospora leaf spot disease on sugar beet genotypes with contrasting disease susceptibility
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Beschreibung
The fungal pathogen Cercospora beticola causes the most destructive foliar disease
of sugar beet, namely Cercospora leaf spot (CLS), which results in economically
important yield losses. Current breeding efforts aim at developing sugar beet lines
with lower fungal susceptibility as well as high productivity to ensure reduced
fungicide applications in the context of integrated pest management. However, the
main challenge remains to select sugar beet genotypes that produce the required
yield quality and quantity, and to quantify their defense ability. Well-established visual
disease scoring can be supported and supplemented by new techniques that enable
earlier disease detection and genotype resistance classification. In this thesis, visual
disease scoring was combined with novel invasive and non-invasive techniques to
analyze shoot and root disease responses to Cercospora infection.
The fungal growth within the sugar beet leaf tissue was quantified using molecular
analysis of the fungal calmodulin gene. This allows for the pre-selection of resistant
genotypes before disease symptoms were visible. It could be shown that plants with
high susceptibility (HS) allowed a stronger fungal colonization in the leaf tissue than
ones with low susceptibility (LS). These results correlated with the respective disease
severity. The HS genotypes consistently displayed more severe disease symptoms
than LS plants. In particular, the moderately susceptible (MS) genotype seemed to be
a promising candidate according to its variable response indicating a more adaptable
reaction to changing environmental conditions. Therefore, this MS genotype might
produce more yield under low-to-moderate disease pressure compared with HS
plants, which would be comparatively more strongly infected and deliver reduced
yield.
The cuticle forms a barrier between the plant and the environment and therefore
provides resistance against pathogens. Cuticular wax may affect host-pathogen
recognition and conidia adhesion on the leaf surface. In this study, LS plants were
found to contain larger amounts of cuticular waxes. Mature leaves, which showed
reduced fungal colonization, also had higher wax levels than immature leaves.
Further experiments are needed to investigate the precise role of sugar beet cuticular
waxes on C. beticola infections.
Autor*in
Simone Schmittgen