Effect of Genotype, Explant Type and 2,4-D on Cell Dedifferentiation and Callus Induction in Cumin (Cuminum cyminum L.) Medicinal Plant

Introduction Cumin (Cuminum cyminum L.) is a commercial plant which is valued for its aroma and its medicinal and therapeutic properties. Although India has been the primary exporter of cumin seeds and cumin oil in the world. However Turkey and Iran are providing stiff competition now. India, Turkey, Syria, China, the US, Iran, Indonesia, Sudan, Egypt, Morocco, Algeria, and Libya are the leading producers of cumin in the world. Iran produces 15,000 to 20,000 tons of cumin seeds and stands third in the leading producer’s list [1]. Callus culture plays a special role in plant biotechnology area for producing medicinal compounds in large-scale [2]. Moreover, callus masses derived from plant tissues can sometimes produce high amounts of secondary metabolites [3]. Callus production from roots, shoots, and leaves are generally applied to determine the conditions required for the explants to survive and grow, exploit products coming from primary and secondary metabolism, study cell development and obtain cell suspension in propagation [2]. Callus culture of cumin has been previously reported by some researchers using leaf [4-7], embryo [8-10] hypocotyl and cotyledon [5, 6] but there is no comparative study on callus induction of this plant in various explants especially in root and seed explants. Jha et al., [11] published the first study on the callus induction of cumin. They used the hypocotyl and leaf explants in B5 medium complemented with various plant growth regulators (PGRs). Beiki et al., [12] studied callus induction of three Iranian landraces with the use of embryo explant. Gupta et al., [13] produced embryogenic and nonembryogenic callus in cumin on Murashige and Skoog (MS) supplemented with 0.5 mg/L 2,4dichlorophenoxyacetic acid (2,4-D) after 35 days of inoculation from all the four explants viz., root, hypocotyl, cotyledon and shoot apex, and organogenic and non-organogenic callus on MS medium supplemented with 0.1 mg/L TDZ after 40 days of inoculation from hypocotyl explants. Mansouri et al., [14] studied the effect of length and position of cumin hypocotyl explants on physical and morphological properties of callus were analyzed by machine vision. In spite of cumin importance in numerous industries such as medical industry, there are a few studies on rapid and efficient callus induction in the world. Therefore, the present experiment was conducted to achieve the various objectives such as large-scale production of callus to ge erate somaclonal variation, application in genetic engineering strategies and extraction of valuable materials from this medicinal plant. Cumin (Cuminum cyminum L.), a member of the Apiaceae family, is one of the most important medicinal plants in the world. An experiment was conducted for the evaluation of callus induction optimization in cumin accessions from four different regions: Shahdad, Koohbanan, Badrood, and Afghanistan. A factorial experiment based on completely randomized design was conducted on MS medium supplemented with different concentrations of 2,4-D (0, 0.5, 1 and 2 mg/L) plus 0.1 mg/L Kinetin in different explants (Root, Shoot, Leaf, Embryo and Seed) of cumin accessions. In this experiment the evaluated traits were days to callus induction, callus induction percentage, and callus growth rate. Statistical analysis showed that seed (as the latest) and root (as the earliest) explants require 54 and 11 days for the initiation of callus induction, respectively. Results showed that accession, explant, accession × explant and 2,4-D × explant interactions had statistically significant effects (P<0.01) on callus induction percentage and callus growth rate. Furthermore, 2,4-D had a significant effect on callus induction percentage. According to the results of this study, in plants of some regions the root explant is an appropriate explant for large production of callus in some accessions of Cuminum cyminum. Also, Koohbananian accession produced callus in shorter time and the Afghanian one produced high number of callus.