Morphological and molecular characterization of Pratylenchus mediterraneus Corbett, 1983 (Tylenchomorpha: Pratylenchidae) from Iran

The Karkheh protected area is considered as one of the protected areas of Iran, which harbors a remarkable diversity of vegetation. A population belonging to the genus Pratylenchus was recovered and identified as P. mediterraneus during a survey on the biodiversity of the plant-parasitic nematodes in this region of Khuzestan province. This study aims to characterize the population based on the morphological and morphometric characteristics and evaluate its phylogenetic affinities using LSU D2-D3 and ITS rDNA sequences. Moreover, its phylogenetic relationships were investigated with other relevant genera and species.

Several soil samples were collected from the rhizosphere of tamarisk trees in Karkheh protected area. The centrifugal-floatation and tray methods were used for extracting the nematodes from the soil samples. The collected specimens were fixed and transferred to the pure glycerin after extracting the nematodes by using the modified De Grisse method. Then, permanent microscopic slides were prepared from the processed nematodes. The species was identified by using a light microscope equipped with a drawing tube based on the morphological and morphometric characteristics, and valid keys. The molecular phylogenetic analyses were performed by using partial sequences of the D2-D3 expansion segments of  the large subunit, and internal transcribed spacer (LSU D2-D3 and ITS rDNA) regions based on the Bayesian inference under the GTR + G + I model.

A population of the genus Pratylenchus was recovered in the present study. The morphological, morphometric and molecular studies based on the D2-D3 domains of the 28S and ITS rRNA gene indicated that the recovered population belongs to P. mediterraneus. The morphological, morphometric, and molecular data of the Iranian population of the species were presented for the first time in this study. In the phylogenetic tree inferred using the 28S rRNA gene sequences, the newly generated sequence of the Iranian population of P. mediterraneus formed a clade with other sequences of the species, and some sequences assigned to P. thornei. All other sequences of P. thornei occupied a clade, in close phylogenetic relationship with the aforementioned clade. The newly generated sequence of the Iranian population formed a maximally supported clade with other sequences of the species in the phylogenetic tree inferred using the ITS rRNA gene.  

The two species P. thornei and P. mediterraneus are morphologically very similar and can mainly be separated from each other by presence/absence of male and a functional spermatheca. Their separation is further corroborated by using the partial sequences of 28S and ITS rDNA. The sequences of the two species form the separate clades, and the identification of some sequences occupying the same clade with the sequences of P. mediterraneus need further validations in lack of the morphological data.