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

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).

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.

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.

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.