Abstract
The species in genus Melampsora are the causal agents of leaf rust diseases on willows in natural habitats and plantations. However, the classification and recognition of species diversity are challenging because morphological characteristics are scant and morphological variation in Melampsora on willows has not been thoroughly evaluated. Thus, the taxonomy of Melampsora species on willows remains confused, especially in China where 31 species were reported based on either European or Japanese taxonomic systems. To clarify the species boundaries of Melampsora species on willows in China, we tested two approaches for species delimitation inferred from morphological and molecular variations. Morphological species boundaries were determined based on numerical taxonomic analyses of morphological characteristics in the uredinial and telial stages by cluster analysis and one-way analysis of variance. Phylogenetic species boundaries were delineated based on the generalized mixed Yule-coalescent (GMYC) model analysis of the sequences of the internal transcribed spacer (ITS1 and ITS2) regions including the 5.8S and D1/D2 regions of the large nuclear subunit of the ribosomal RNA gene. Numerical taxonomic analyses of 14 morphological characteristics recognized in the uredinial-telial stages revealed 22 morphological species, whereas the GMYC results recovered 29 phylogenetic species. In total, 17 morphological species were in concordance with the phylogenetic species and 5 morphological species were in concordance with 12 phylogenetic species. Both the morphological and molecular data supported 14 morphological characteristics, including 5 newly recognized characteristics and 9 traditionally emphasized characteristics, as effective for the differentiation of Melampsora species on willows in China. Based on the concordance and discordance of the two species delimitation approaches, we concluded that integrative taxonomy by using both morphological and molecular variations was an effective approach for delimitating Melampsora species on willows in China.
Highlights
Fast-growing woody crops are emerging as an attractive source of biomass
Phylogenetic species recognition has been increasingly used for species delimitation in the genus Melampsora, especially cryptic species that are resistant to traditional morphological species concepts [38, 39]
We report the high concordance of species recognition based on morphology and molecular data
Summary
Fast-growing woody crops are emerging as an attractive source of biomass. Among them, willows (especially shrubs) are one of the best candidates for the production of renewable energy and bioproducts [1, 2]. Diseases caused by Melampsora species have emerged as one of the most important factors limiting the development of willow cultivation. Approximately 90 species in the genus Melampsora have been reported worldwide, over 50 species of which have been reported as causal agents of leaf rust diseases on willows [5, 6]. These species were variously described in Asia, Australasia, Europe and North America, and were recorded with either heteroecious or autoecious life cycles [7,8,9,10]
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