Polyploidy is widely acknowledged as a major mechanism of adaptation and speciation in plants (Ramsey and Schemske, 1998). Polyploidy is such a common component of plant evolution that it must be part of any general theory of the evolutionary ecology and genetics of plants. Furthermore, artificial polyploidization is an effective method for the generation of innovative germplasm resources suitable for selective breeding (Ye et al., 2010). Polyploid plants often possess superior agronomic traits over their diploid counterparts. For example, polyploids may have larger leaves and flowers, thicker stems and roots, darker green leaves, an increased width-to-length ratio of the leaves, and increased cell size; these characteristics lead to larger reproductive and vegetative organs, a more compact growth habit and a higher tolerance to environmental stress (Grouh et al., 2011). Moreover, polyploidy has been used in horticulture as a breeding tool to enhance ornamental characteristics, and to increase resistance to environment stresses and diseases; and it can also cause variations in secondary metabolite content (Abdoli et al., 2013).
Amongst the many applicable methods for the induction of polyploidy, the use of chemicals to induce changes in chromosome number is well established (Sajjad et al., 2013). Colchicine is a compound that effectively arrests mitosis at the anaphase stage, and it is widely used to induce polyploidy in plants (Rego et al., 2011). The treatment of shoots, smaller axillary or subaxillary meristems, seeds or seedlings with colchicine is the approach traditionally used to produce polyploid plants. For example, tetraploidy in Mitracarpus hirtus L. was successfully induced by immersing leafless shoots in colchicine solution (Pansuksan et al., 2014) and tetraploidy of Crocosmia aurea was induced by treating seeds with colchicine (Hannweg et al., 2013).
Lobularia maritima (L.) Desv., a small white-flowered plant known as alyssum or sweet alyssum, is a diploid (2n = 24) herbaceous perennial belonging to the family Brassicaceae. It is native to southern Europe, northern Africa, the Azores, the Madeira Islands and the Canary Islands. The plant bears many branches and small fragrant flowers which appear from March to June on long raceme inflorescences. It is an important ornamental plant, planted primarily in pots and hanging baskets, at the front of flower borders, and in rock gardens; it is also highly effective as groundcover. In Spain, Alyssum is commonly used as a diuretic and antiscorbutic (Chopra et al., 1986). It is also highly regarded as an astringent in the treatment of gonorrhoea. In the Amalfi Coast, Campania (Southern Italy), Lobularia maritima subsp. maritima is used in folk phytotherapy to treat abdominal pains, cold and coughs (Savo et al., 2011). L. maritima (L.) Desv. is also recognized as a Ni-hyperaccumulator plant, able to tolerate 1% Ni2+, and hence it has been developed for commercial application in detecting and removing heavy metals from contaminated soils (Yuan et al., 2010). Overall, however, only a limited amount of research has so far been undertaken on this species. Researches of L. maritima (L.) Desv. are mainly focused on cultivation and management, rapid propagation in vitro. Few researches have been conducted on the breeding of L. maritima (L.) Desv. However, Alyssum as an ornamental plant, the flowers of diploid plant are small and the leaves of diploid plant are linear-lanceolate to lanceolate. To improve ornamental characteristics, it is important to do researches on breeding of L. maritima (L.) Desv.
In this study, we aimed to develop an efficient method to induce tetraploid plants by treating germinating seeds and the apical growing points of seedlings with colchicine. In addition, the chromosomal, morphological and stomatal characteristics of the tetraploid plants were assessed.
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