Influence of abiotic factors, inoculum source, and cultivar susceptibility on the potato tuber blemish diseases black dot (Colletotrichum coccodes) and silver scurf (Helminthosporium solani).
Black dot and silver scurf are potato blemish diseases whose economic impact has
increased in recent years. Because their symptomatology on tubers is visually similar,
disease assessment does not usually differentiate between the two pathogens, which
share the same ecological niche. The epidemiology of black dot has been extensively
studied, especially in the UK, but the factors that influence silver scurf have been less
investigated. In this study, the influence of cultivar, source of inoculum, and environmental
conditions on both diseases was studied in field trials over a three-year
period
(2016–2018)
in Switzerland. Planting minitubers did not prevent either disease in
daughter tubers, indicating the contribution of soil as an inoculum reservoir. An arbitrary
threshold of Colletotrichum coccodes soil inoculum could be set to discriminate
between low and high disease risk. For the first time, Helminthosporium solani DNA
was detected in stolons, and infections appeared earlier in stolons than in tubers. H.
solani stolon and tuber infections usually appeared later in the season than those of
C. coccodes. Black dot severity correlated positively with precipitation, while silver
scurf severity correlated positively with temperature. Table potato cultivars commonly
grown in Switzerland exhibited significant differences in susceptibility to both
diseases, and cultivars with low susceptibility to both silver scurf and black dot were
identified. These results gave new insights into understanding the factors driving the
epidemiology of potato blemish diseases and may contribute to building a risk assessment
scheme to manage both diseases simultaneously.