مطالعه كاريوتايپي توده‌هاي سير (Allium sativum) شمال ايران

Karyotypic Analysis of Garlic (Allium sativum) Accessions in the North of Iran

ويژگي‌هاي كاريوتايپي توده‌هاي محلي سير شمال ايران (سير سفيد گرگان، صورتي ساري و ارغواني رشت) در سال 1397 در دانشگاه علوم كشاورزي و منابع طبيعي گرگان مورد بررسي قرار گرفت. براي انجام آزمايش مريستم انتهايي نوك ريشه با 002/0 مول 8-هيدروكسي كينولين به‌مدت چهار ساعت در دماي چهار درجه سانتي‌گراد تيمار شد و با استفاده از اورسيين دو درصد رنگ‌آميزي گرديد. سلول‌ها در مرحله متافاز ميتوز عكس‌برداري و شاخص‌هاي كروموزومي محاسبه شدند. تعداد كروموزوم پايه هشتx=8 (2n=2x=16)و ديپلوئيد مورد تأييد قرار گرفت. بزرگترين طول كروموزوم (169/51 ميكرومتر) متعلق به توده گرگان و كوچك‌ترين طول كروموزوم در توده رشت (136/57 ميكرومتر) ثبت گرديدند. آناليز كاريوتايپ متافاز نشان داد كه سانترومرها به‌طور عمده در وسط (متاسنتريك) يا نزديك وسط (ساب‌متاسنتريك) كروموزوم قرار دارند. كروموزوم‌ها در جهت كاهش طول بازوي كوتاه مرتب شدند و فرمول كاريوتايپ12m+4sm براي تمام توده‌ها به‌دست‌آمد. كروموزوم‌هاي 13 تا 16 براي دو توده گرگان و رشت ساب­متاسنتريك بود. كروموزوم‌هاي ساب‌متاسنتريك روي كروموزوم‌هاي شماره 11-12 و 15-16 براي توده ساري مشاهده شد. با توجه شاخص‌هاي عدم تقارن از نظر تيپ كروموزوم، درصد شكل كلي و قرارگيري در كلاس 2Bطبقه‌بندي استبينز، سه توده مورد بررسي از نظر تكاملي در يك سطح قرار مي‌گيرند. داده‌هاي كاريوتايپي، منبع جامع از اطلاعات سيتوژنتيكي فراهم مي‌كند كه در برنامه­هاي اصلاحي براي درك بهتر طبقه‌بندي، تكامل و شكل‌گيري در جنس آليوم استفاده مي ­شود.

Background and Objectives Allium sativum is one of the most important, mostly used economical vegetable plants in Iran. Chromosome analysis or karyotyping is a test that evaluates the number and structure of chromosomes to study evolution. The present study was carried out to explore the cytological features, including chromosome number and karyotypic characteristics in a local cultivar of Allium sativum L., north of Iran (Gorgan, Sari, and Rasht accessions). Materials and Methods The root tip cells were treated first with 0.002 mol·L−1 8-hydroxyquinoline for 4 h at 4°C and then fixed for 24 h in fixative (1:3 glacial acetic acid/absolute alcohol) at 4°C. Finally, the root tips were softened with 1 M hydrochloric acid at room temperature for 8 min and stained for 10 min with acceto orcein 2% before being squashed between a glass slide and a coverslip. Root tip cells photographed at mitosis metaphase, which had well-separated chromosomes and a clear centromere. Long arm, short arm, the ratio of long arm to short arm, and chromosome index of mitotic chromosomes were calculated from metaphase plates. Figures summarized the idiogram for the three garlic accessions, based on the eight pairs of chromosomes’ short arm order length. Results Basic chromosome number was confirmed as x = 8 (2n = 2x = 16). All the studied accessions cytotypes were diploid. The largest chromosome length belonged to Gorgan accesion as amount 169.51 micrometers, and the smallest chromosome length was obtained in Rasht accesion as amount 136.57 micrometers. The long arm of the chromosome was recorded between 4.85 to 6 micrometers. The short arm of the chromosome was measured between 3.18 to 3.80 micrometers. The Metaphase karyotype analysis revealed that centromeres were mainly located at the middle (metacentric - m) or near the middle (submetacentric - sm) of chromosomes. The chromosomes are arranged in decreasing order for short arm length, and the karyotype formula was obtained 12m+4sm for all accessions. Chromosomes 13 to 16 were submetacentric for both Gorgan and Rasht accessions. Submetacenteric Chromosomes were observed on chromosomes number 11-12 and 15-16 for Sari accesion. Three of the studied accessions were evolutionary located in one level according to asymmetrical karyotype, the value of TF% and separating to 2B classes based on Stebbins categories. Discussion Regarding asymmetric karyotype and according to interchromosomal asymmetry (A2) as well as difference between the range of relative length (DRL), the most were found in Rasht accession (A2=0.34; DRL=6.99). A2 and DRL are two aspects of karyotype asymmetry related to shifts of the centromere position from the median to terminal or subterminal. The karyological data provide a comprehensive cytogenetic resource useful in cytotaxonomic research and assessment of their role in the evolution of Garlic. This resource can help better understand the taxonomy, evolution, and speciation in the genus Allium and identify candidate species for breeding programs.