The in vitro development of a whole plant from a single cell (eg microspore or somatic cells) is a characteristic feature of plants. The amenability of a plant to in vitro culture is influenced by the genotype, which is thus of major importance in the plant tissue culture response. The differences observed between different cultivars during in vitro tissue culture with respect to embryogenesis and regeneration result from quantitative or qualitative genetic differences. We describe results obtained from quantitative genetic studies, from Mendelian genetic analysis and from gene mapping. It is less easy to study the influence of cytoplasmic genomes. Moreover, it is necessary to discriminate between maternal effects and cytoplasmic inheritance. A conclusion from this review is that the choice of parental strains for a breeding program should be realized on agronomic criteria rather than on compatibility with the tissue culture technique used. Fortunately, it is relatively easy to incorporate short-term tissue culture capacity into agronomically valuable genotypes. This is of major interest since tissue culture remains necessary for most aspects of crop plants biotechnology. Very little is known about the molecular events that trigger in vitro embryogenesis and regeneration. It is clear that genes involved in the tissue culture response are not specialised ‘tissue culture genes’.

Genetic analysis of in vitro plant tissue culture responses and regeneration capacities

The seed is the primary organ for the perpetuation of germplasm and propagation in all flowering plants. It contains the embryo which develops from the zygote following the fertilization of the egg cell by one of the male gametes. Gene recombination during the formation, as well as the fusion, of the gametes plays a critical role in the evolution of the angiosperms. During its development the embryo is nourished by the endosperm, which itself is formed as a result of the fusion of the second male gamete with two nuclei (in most of the angiosperms) of the central cell of the embryo sac. During the course of evolution many species have developed special means of propagation to overcome physical, environmental and genetic factors that prevent flowering and seed formation. These include the formation of perennial structures such as tubers, rhizomes, bulbs, stolons, etc (see Sharma and Thorpe, this volume). An advanced form of perennation is found in many apomictic species which produce embryos from unfertilized gametic or somatic cells. Like the zygotic embryos, the apomictic embryos develop within the seed and are protected and dispersed like natural seed. Apomictic embryos of all genotypes — irrespective of heterozygosity — developing from unreduced and unfertilized somatic or gametic cells (agamospermy, adventive embryony, apospory, diplospory) breed true and give rise to clonal populations. Apomixis is known to be under genetic control, but environmental conditions such as temperature and photoperiod may also promote a switch from sexual to apomictic development [1,2].

https://link.springer.com/content/pdf/10.1007/978-94-011-0485-2_10

Somatic Embryogenesis in Herbaceous Dicots

Role of Artificial Seeds in Alfalfa Breeding

Legumes are members of the third largest family (Leguminosae) of flowering plants, and are globally distributed, with as many as 19,000 species. Several species have the ability to undergo a symbiotic association with nitrogen-fixing bacteria of the genera Rhizobium or Bradyrhizobium. Consequently, legumes tend to have high protein contents, and are an essential source of food, feed, and forage. They are also used as ornamentals, or valued for green manure, timber, gums, and other compounds.

Somatic Embryogenesis in Legumes

Agronomic crops are responsible for the majority of the world’s food supply, either through direct consumption or as animal feed. Until recently, however, the importance of these crops has not been reflected by research efforts and progress in biotechnology. Many agronomic crops have been difficult to manipulate in vitro, and regeneration has been problematic. Currently, progress in regeneration has been significant, such that most crops can now be regenerated. For example, it is estimated that over 130 species of angiosperms and gymnosperms have been induced to form somatic embryos (Thorpe, 1988). As a result of progress in regeneration, a number of laboratories have reported success in stable transformation of many important agronomic crops (Deak et al., 1986; Everett et al., 1987; Firoozabady et al., 1987; Chabaud et al., 1988; Hinchee et al., 1988; Zhang et al., 1988; Gasser & Fraley, 1989). There are numerous applications of biotechnology to crop improvement, such as production of doubled haploids to produce homozygous plants rapidly, propagation of genetic marker stocks, clonal propagation for genetic and physiological studies, induction of variation, mutagenesis and cell selection for specific traits, protoplast fusion for wide hybridization, and genetic transformation. For this review, the focus is micropropagation.

Applications of micropropagation for agronomic crops

Genotypes from twelve accessions of five wild species from the genusMedicago were screened for callus formation and somatic embryogenesis using two tissue culture protocols. These wild species were compared with two highly regenerable genotypes ofMedicago saliva. Embryogenesis for the wild types was very low. Wild species genotypes, which gave some callus production, were isolated.

P. D. Walton

Papers

Screening ofMedicago wild species for callus formation and the genetics of somatic embryogenesis