Fungal species associated with apple Valsa canker in East Asia
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Wang et al. Phytopathology Research (2020) 2:35 https://doi.org/10.1186/s42483-020-00076-5
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Fungal species associated with apple Valsa canker in East Asia Xuli Wang1,2, Cheng-Min Shi3, Mark L. Gleason4 and Lili Huang1*
Abstract Since its discovery more than 110 years ago, Valsa canker has emerged as a devastating disease of apple in East Asia. However, our understanding of this disease, particularly the identity of the causative agents, has been in a state of confusion. Here we provide a synopsis for the current understanding of Valsa canker and the taxonomy of its causal agents. We highlight the major changes concerning the identity of pathogens and the conflicting viewpoints in moving to “One Fungus = One Name” system for this group of fungal species. We compiled a list of 21 Cytospora species associated with Malus hosts worldwide and curated 12 of them with rDNA-ITS sequences. The inadequacy of rDNA-ITS in discriminating Cytospora species suggests that additional molecular markers, more intraspecific samples and robust methods are required to achieve reliable species recognition. Keywords: Perennial canker, Cytospora, Species recognition, Nomenclature, Malus
Background Apple (Malus domestica Borkh) is one of the most widely planted and nutritionally important fruit crops in the world (Cornille et al. 2014; Duan et al. 2017). At one time nearly each area had its own local apple cultivars (Janick et al. 1996). As of 2018, the overall apple plantation area was close to 5 million ha and the total apple production exceeded 86 million ton, ranking the third in worldwide fruit production (http://www.fao.org/faostat/). The nutritional value of apple makes this fruit particularly beneficial to human health as being highlighted by a famous aphorism: “An apple a day keeps the doctor away”. With the increase of people’s income and public awareness for balanced nutrition, apple consumption continues to grow beyond its global production capacity. In the meanwhile, apple production, and global food security in general, faces a tremendous threat from fungal diseases (Fisher et al. 2012). It has been estimated that 12–25% of annual apple harvest was lost due to abiotic and biotic stresses, including those caused by fungal diseases (Forte et al. 2002). * Correspondence: [email protected] 1 State Key Laboratory of Crop Stress Biology for Arid Areas and College of Plant Protection, Northwest A&F University, Yangling 712100, Shaanxi, China Full list of author information is available at the end of the article
Valsa canker has emerged as a global threat to apple industry (CABI and EPPO 2005; EPPO 2020), and is particularly destructive in East Asia (Togashi 1925; Uhm and Sohn 1995; Abe et al. 2007; Wang et al. 2011). Its causative fungus, Valsa mali (Ideta 1909; Tanaka 1919; Togashi 1925; Tai 1979), was once synonymized with V. ceratosperma (Kobayashi 1970), and has recently been resurrected (Adams et al. 2005; Wang et al. 2011, 2014). It is critically important to have pathogens be settled in a stable tax
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