Project description:Relict species play an important role in understanding the biogeography of intercontinental disjunctions. Pterocarya (a relict genus) is the valuable model taxon for studying the biogeography of East Asian versus southern European/West Asian disjunct patterns. This disjunction has not been as well studied as others (e.g., between Eastern Asia and North America). Several phylogenetic studies on Pterocarya have been conducted, but none have provided a satisfactory phylogenetic resolution. Here, we report the first well-resolved phylogeny of Pterocarya using restriction site-associated DNA sequencing data based on the sampling of all taxa across the entire distribution area of the genus. Taxonomic treatments were also clarified by combining morphological traits. Furthermore, fossil-calibrated phylogeny was used to explore the biogeography of Pterocarya. Our results support the existence of two sections in Pterocarya, which is in accordance with morphological taxonomy. Section Platyptera comprises three species: P. rhoifolia, P. macroptera, and P. delavayi. Section Pterocarya also comprises three species: P. fraxinifolia, P. hupehensis, and P. stenoptera. The divergence between the two sections took place during the early Miocene (20.5 Ma). The formation of the Gobi Desert and climate cooling of northern Siberia in the Middle Miocene (15.7 Ma) might have caused the split of the continuous distribution of this genus and the formation of the East Asian versus southern European/West Asian disjunct pattern. Lastly, the divergence between P. hupehensis and P. stenoptera as well as between P. rhoifolia and P. macroptera/P. delavayi (10.0 Ma) supports the late Miocene diversification hypothesis in East Asia.
Project description:Based on molecular phylogenetic analyses of a multigene matrix of partial nuSSU-ITS-LSU rDNA, cal, his, ms204, rpb1, rpb2, tef1 and tub2 sequences, recent European and Iranian collections of Melanconium pterocaryae from the type host, Pterocarya fraxinifolia, are shown to be distinct from the Japanese Melanconis pterocaryae from Pterocarya rhoifolia, and both are confirmed as closely related members of the recently described genus Juglanconis. Therefore, the new name Juglanconis japonica is proposed for Melanconis pterocaryae. As no type collection could be traced, Melanconium pterocaryae (syn. J. pterocaryae) is neotypified, described and illustrated, and it is recorded for Europe for the first time. During field surveys in natural stands of P. fraxinifolia in Guilan province (Iran), Juglanconis pterocaryae was consistently isolated from tissues affected by branch and trunk cankers, twig dieback and wood necrosis, indicating that it is the causal agent of these diseases. The external and internal symptoms associated with these trunk diseases are described and illustrated.