تعيين مشخصات ريخت‌شناسي و مولكولي Pratylenchus mediterraneus Corbett, 1983 (Tylenchomorpha: Pratylenchidae) از ايران

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

در اين مطالعه، جمعيتي از جنس Pratylenchus در ارتباط با درختان گز از منطقه حفاظت شده كرخه بدست آمد. مطالعات ريخت‌شناسي، ريخت‌سنجي و مولكولي اين جمعيت بر اساس توالي دو ناحيه D2-D3 از ژن 28S rRNA و ژن ITS rRNA نشان داد اين جمعيت متعلق به گونهP. mediterraneus مي‌‌باشد. اين جمعيت داراي ماده‌هايي به طول 431 تا 551 ميكرومتر با كيسه ذخيره اسپرم پُر و استايلت به طول 15 تا 16/5 ميكرومتر مي‌باشد. نرهاي جمعيت به دست آمده فعال بوده و داراي بدن به طول 331 تا 485، استايلت به طول 14/8 تا 15 و اسپيكول به طول 16/2 تا 19 ميكرومتر مي‌‌باشند. در آناليز فيلوژني با استفاده از توالي‌هاي ناحيه D2-D3 ژن 28S rRNA، توالي‌ جمعيت ايراني به همراه توالي‌هاي ديگري از گونه P. mediterraneus و تعدادي از توالي‌هايي كه به گونه P. thornei تخصيص داده شده‌اند، در يك كلاد قرار گرفتند. اين كلاد در ارتباط خويشاوندي نزديك با كلادي است كه توالي­‌هاي متعددي از گونه P. thornei را در بر‌گرفته است. در آناليز فيلوژني با استفاده از توالي­‌هاي ژن ITS rRNA، توالي‌ جمعيت ايراني به همراه توالي‌هاي ديگري از گونه P. mediterraneus در يك كلاد قرار گرفتند. اين كلاد در ارتباط خويشاوندي نزديك با كلادي است كه توالي‌هاي متعددي از گونه P. thornei را در بر‌گرفته است. ويژگي‌هاي ريخت‌شناسي، ريخت‌سنجي و توصيف جمعيت ايراني اين گونه در تحقيق حاضر براي اولين بار ارائه گرديد.

Background and Objectives 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. Materials and Methods 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. Results 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. Discussion 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.