عنوان مقاله [English]
Background and objectives
Allium sativum is one of the most important, most used and economical vegetable plants in Iran. Chromosome analysis or karyotyping is a test that evaluates the number and structure of chromosomes in order to study the evolution. The present study was carried out to study the cytological features including chromosome number and karyotypic characteristics in a local cultivar of Allium sativum L., from 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 temprature 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, that had well-separated chromosomes and a clear centromere. Long arm, short arm, 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 short arm order lenght of eight pairs of chromosomes.
Basic chromosome number was confirmed as x = 8 (2n = 2x = 16). All studied accessions cytotypes were diploid. The largest chromosome length was belonged to Gorgan accesion as amount 169.51 micrometer and the smallest chromosome length was obtained in Rasht accesion as amount 136.57 micrometer. The long arm of chromosome was recorded between 4.85 to 6 micrometer. The short arm of chromosome was measured between 3.18 to 3.80 micrometer. Metaphase karyotype analysis revealed that centromeres were mainly located at the middle (metacentric - m) or near the middle (submethacentric - sm) of chromosomes. The chromosomes are arranged in decreasing order for short arm length, and karyotype formula were obtained 12m+4sm for all accessions. Chromosomes 13 to 16 were submetacenteric 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, value of TF% and separating to 2B classes based on Stebbins categories.
Regarding asymmetric karyotype according interchromosomal asymmetry (A2) and difference of range of relative length (DRL), the most was 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 which useful in cytotaxonomic research for assessing their role in the evolution of Garlic, that can be used to better understand the taxonomy, evolution, and speciation in the genus Allium and to identify candidate species for breeding programs.