Evidence of apple blotch resistance in wild apple germplasm ( Malus spp . ) accessions
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Evidence of apple blotch resistance in wild apple germplasm (Malus spp.) accessions Thomas Wöhner Monika Höfer
&
Ofere Francis Emeriewen &
Accepted: 10 November 2020 # The Author(s) 2020
Abstract Diplocarpon coronariae causes apple blotch, which results in significant economic losses. Resistance to apple blotch in commercial apple cultivars has not been reported in recent literature. The Malus germplasm collection from the Fruit Genebank of the Julius Kühn-Institut that is maintained in Dresden, Germany consists of 516 accessions of about 49 Malus species. This apple gene pool was evaluated for resistance to Diplocarpon coronariae. A four-year field survey was subsequently followed by artificial inoculation of field-selected accessions. Fifteen accessions that represent nine different species and hybrids were confirmed to be highly resistant following a repeated inoculation assay in the laboratory. The results from this investigation is of high interest to breeders for future apple breeding programmes and investigations of resistance to Diplocarpon coronariae. Keywords Diplocarpon coronariae . Malus . Wild species . Germplasm . Resistance . Marssonina coronaria
The genus Malus Mill belonging to the Rosaceae family of plants, is subdivided into six sections including T. Wöhner (*) : O. F. Emeriewen : . Höfer Julius Kühn-Institute, Federal Research Centre for Cultivated Plants, Institute for Breeding Research on Fruit Crops, Pillnitzer Platz 3a, 01326 Dresden, Germany e-mail: [email protected]
between 25 to 47 species, depending on the taxonomic classification (Robinson et al. 2001, Forsline et al. 2003, GRIN, https://npgsweb.ars-grin.gov). The domesticated apple (Malus ×domestica Borkh.), a prominent member of this genus, is one of the most important fruit crops cultivated in the temperate zone (Hanke et al. 2020). The largest apple producers in the world are China, USA and Poland. Although, apple production for 2018 was 86.1 MMT (FAOSTAT 2020), several diseases threaten its production. One of such diseases is apple blotch, caused by the fungus Diplocarpon coronariae ((Ellis and Davis) Wöhner and Rossmann) previously designated as Marssonina coronaria (Crous et al. 2020). The disease has increasingly caused economic losses in apple cultivation in China and in organic cultivation orchards in Europe (Wöhner and Emeriewen 2019). Apple blotches appear on leaves between June and August followed by premature defoliation of the tree crown before fruit harvest. Fruit blotches (Sutton et al. 2014) also cause several losses but are less frequent. Different factors and stages of the fungus lead to typical apple blotch symptoms and occurrence worldwide (Reviewed in Wöhner and Emeriewen 2019). Disease control by fungicide application has been shown to protect commercial apple orchards against apple blotch (Dang et al. 2017; Sharma et al. 2018). Breeding for disease resistance would be another possibility to manage the disease (Aldwinckle et al. 1997), but unfortunately, most apple cultivars are susceptible to
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