Status and Prospects of Biotechnology Applications to Conservation, Propagation and Genetic Improvement of Yam

Abstract

Sugar beet (Beta vulgaris L.) is the most important industrial crop used for sugar production in Europe and one of only two plant sources from which sucrose (i.e., sugar) can be economically produced in the world. Sugarcane and sugar beet contribute to the total sugar production by 77.6% and 22.4%, respectively. Despite its relatively short period of cultivation (ca. 200 years), yield and quality parameters of sugar beet have been significantly improved by conventional breeding methods. However, during the last three decades or so, advanced biotechnological methods including in vitro culture and genetic transformation technologies have been combined with classical breeding programmes, which has then lead to the creation of previously non-existing genotypes. Widely applied techniques such as micropropagation and induction of somaclonal variability have already added new germplasm of improved quality and diversity to the sugar beet breeding pool. Organelle exchange, through symetric or asymetric protoplast fusion, and conversion of gametic cells to embryos (i.e., haploid plant production) are other techniques that can be expected to play an increasing role in the improvement of sugar beet. In addition, 1 Sugar Institute, Department of Plant Breeding, 06930 Etimesgut, Ankara, Turkey. Email: songul_gurel@yahoo.com 2 Abant Izzet Baysal University, Department of Biology, 14280 Bolu, Turkey. Email: gurel_e@ibu.edu.tr * Corresponding author © 2014 by Taylor & Francis Group, LLC 114 Bulbous Plants: Biotechnology conservation of germplasm materials, production of disease-free plants, development of homozygous diploid lines (i.e., double haploids/ diplohaploids) from haploid plants obtained from pollen or ovary cultures and isolation and culture of highly totipotent protoplasts from guard cells have been achieved. However, regeneration protocols for both shoot organogenesis and somatic embryogenesis of sugar beet are not reproducible, usually resulting in low regeneration frequencies. Also, a high degree of genotypic variation, primarily because of its highly heterozygous nature due to outcrossing, is a serious problem for the regeneration success of several sugar beet materials. Thus, with all these respects sugar beet is known to be a recalcitrant species. In this chapter, the research to date on sugar beet tissue cultures will be presented from a historical point of view, covering the following topics; (i) micropropagation via proliferation of pre-existing (axillary or shoot-tip) meristems, (ii) plant regeneration through development of direct or indirect de novo shoots and somatic embryos from different types of tissues/explants, (iii) haploid plant production via mostly gynogenesis but also androgenesis, (iv) protoplast isolation and culture from leaf mesophyll, guard or cell suspension cells, (v) somaclonal variation incurred during indirect shoot organogenesis and somatic embryogenesis from callus and in vitro cell selection to be specifi cally expolited for abiotic stress tolerance, and (vi) long-term storage of sugar beet genetic resources through low-temperature storage and cryo-preservation techniques.