Abstract
Cytospora species are destructive canker and dieback pathogens of woody hosts in natural and agroecosystems around the world. In this genus, molecular identification has been limited due to the paucity of multi-locus sequence typing studies and the lack of sequence data from type specimens in public repositories, stalling robust phylogenetic reconstructions. In most cases a morphological species concept could not be applied due to the plasticity of characters and significant overlap of morphological features such as spore dimensions and fruiting body characters. In this study, we employed a molecular phylogenetic framework with the inclusion of four nuclear loci (ITS, translation elongation factor 1-alpha, actin, and beta-tubulin) to unveil the biodiversity and taxonomy of this understudied important genus of plant pathogens. Phylogenetic inferences based on 150 Californian isolates revealed 15 Cytospora species associated with branch and twig cankers and dieback of almond, apricot, cherry, cottonwood, olive, peach, pistachio, plum, pomegranate, and walnut trees in California. Of the 15 species recovered in this study, 10 are newly described and typified, in addition to one new combination. The pathogenic status of the newly described Cytospora species requires further investigation as most species were associated with severe dieback and decline of diverse and economically important fruit and nut crops in California.
Highlights
The generic name Cytospora (Sordariomycetes, Diaporthales, Cytosporaceae) was introduced in 1818 and includes seemingly innocuous endophytes isolated from the bark, xylem, and leaves of asymptomatic woody plants (Spielman 1983, Bills 1996), saprobes that colonize and degrade the wood of dead or dying trees (Christensen 1940), and destructive canker pathogens that cause dieback of more than 85 woody plant species (Sinclair et al 1987, Adams et al 2005, 2006)
The pycnidia arise in a stroma embedded in host tissues (Grove 1923), and possess either a single locule or a complex of invaginated walls producing labyrinthine ORFXOHV ZLWK ¿ODPHQWRXV FRQLGLRSKRUHV ZKLFK may be reduced to conidiogenous cells that bear hyaline, allantoid conidia (Adams et al 2006)
92 samples were obtained from symptomatic trees in 70 orchards of various fruit and nut crops including almond (Prunus dulcis), apricot (Prunus armeniaca), cherry
Summary
The generic name Cytospora (Sordariomycetes, Diaporthales, Cytosporaceae) was introduced in 1818 and includes seemingly innocuous endophytes isolated from the bark, xylem, and leaves of asymptomatic woody plants (Spielman 1983, Bills 1996), saprobes that colonize and degrade the wood of dead or dying trees (Christensen 1940), and destructive canker pathogens (known as Cytospora-, Leucostoma-, Valsa-, or perennial canker) that cause dieback of more than 85 woody plant species (Sinclair et al 1987, Adams et al 2005, 2006). Conidia oozing from pycnidia embedded in dead or dying host cortical tissues during humid or wet conditions are considered the infectious propagules potentially initiating new infections; the role of ascospores has not been determined. Conidia are dispersed to new plant tissues by rain-splash, where they germinate and infect the host plant via cracks and wounds to the bark created by pruning wounds, leaf scars, insect injuries, You are free to share - to copy, distribute and transmit the work, under the following conditions: Attribution:
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