Abstract
Based on sequence data from ITS rDNA, cox1 and cox2, six Peronospora species are recognised as phylogenetically distinct on various Papaver species. The host ranges of the four already described species P. arborescens, P. argemones, P. cristata and P. meconopsidis are clarified. Based on sequence data and morphology, two new species, P. apula and P. somniferi, are described from Papaver apulum and P. somniferum, respectively. The second Peronospora species parasitizing Papaver somniferum, that was only recently recorded as Peronospora cristata from Tasmania, is shown to represent a distinct taxon, P. meconopsidis, originally described from Meconopsis cambrica. It is shown that P. meconopsidis on Papaver somniferum is also present and widespread in Europe and Asia, but has been overlooked due to confusion with P. somniferi and due to less prominent, localized disease symptoms. Oospores are reported for the first time for P. meconopsidis from Asian collections on Papaver somniferum. Morphological descriptions, illustrations and a key are provided for all described Peronospora species on Papaver. cox1 and cox2 sequence data are confirmed as equally good barcoding loci for reliable Peronospora species identification, whereas ITS rDNA does sometimes not resolve species boundaries. Molecular phylogenetic data reveal high host specificity of Peronospora on Papaver, which has the important phytopathological implication that wild Papaver spp. cannot play any role as primary inoculum source for downy mildew epidemics in cultivated opium poppy crops.
Highlights
The genus Papaver (Papaveraceae) comprises about 80 annual, biennial and perennial herbs distributed in Central and southwestern Asia, Central and Southern Europe and North Africa [1]
Whereas within the Peronospora arborescens clade the ITS did not resolve accessions from the different hosts, in the cox1 - cox2 trees the accessions from Papaver dubium, P. rhoeas and P. somniferum were placed in three distinct monophyletic clades, the former two with high and the latter with medium to high support (Figure 1)
Molecular Phylogenetic Investigations The current investigations clearly show that the biodiversity of Peronospora on Papaver is higher than previously perceived, which is in line with other investigations on Peronosporaceae (e.g. [37,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63]), demonstrating that high biodiversity is commonly the result of high host specificity
Summary
The genus Papaver (Papaveraceae) comprises about 80 annual, biennial and perennial herbs distributed in Central and southwestern Asia, Central and Southern Europe and North Africa [1]. The most well-known species of Peronospora on Papaver and closely related host genera is P. arborescens, which was originally described from Papaver rhoeas by Berkeley [9] It has been reported from numerous other hosts like Argemone mexicana [10], several Meconopsis spp. including M. betonicifolia, M. cambrica, M. latifolia, M. napaulensis, M. polyanthemos and M. simplicifolia [7,11,12,13,14], and Papaver spp. including P. alpinum, P. argemone, P. caucasicum, P. dubium, P. hybridum, P. lecoqii, P. litwinowii, P. nudicaule, P. orientale, P. pavoninum, P. setigerum and P. somniferum [3,4,7,11,12,13,15,16,17,18,19,20,21,22,23]
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