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' .

Using two varieties, their reciprocal hybrids, F8 lines and doubled haploids, results confirmed that three genetic components are involved in wheat anther culture ability, viz embryo induction frequency, regeneration ability and the frequency of albinism. In these experiments, no significant maternal effects were noticed. For embryo yields, transgressive lines were obtained from hybrids between distant genotypes. Regeneration of green plants depended upon two independent traits: regeneration ability and the frequency of albinos. F8 lines and two doubled haploids equaled the 50% regeneration rate of the hybrids, but they only regenerated green plants. Based upon cytological examination and gliadin patterns, it is suggested that genes favoring regeneration ability could be linked to the 1BL-1RS translocated chromosome from Aurora.

Marked effects of genotype on wheat anther culture response have been observed. Genetic factors have been recognised to be one of the major contributors to in vitro responses of cultured wheat tissues. In wheat anther culture, embryo induction, plant regeneration and albina/green ratio have been determined to be heritable traits. Using Chinese Spring (CS) monosomic 1D, single chromosome substitution lines of chromosome 5B or chromosome arm 5BL from Chinese Spring into six varieties, and F1 hybrids heterozygous for the 1B chromosome structure (1BL-1BS/1BL-1RS), the anther culture response was studied: genes on CS1D chromosome and 5BL chromosome arm increases the embryo frequency; gene(s) involved in regeneration ability are located on the 1RS chromosome arm; a gene increasing albina frequency is located on Chinese Spring 5B chromosome. Our results support the fact that without gametic selection, a differential development occurred from the particular classes of microspores carrying genes for higher regeneration ability. Moreover, in some crosses, a few genes with major effects were involved in determination of anther culture response.

The cross from which the doubled haploid wheat variety 'Florin' is derived was made in 1978. As early as October 1985, after two years of official tests for registration, 'Florin' was licensed. The ma)or advantage of anther culture is the time saved in comparison with conventional pedigree breeding. Much research remains to be done to understand the anther culture system and to increase the efficiency of producing doubled haploids.

Experiments on wheat anther culture in liquid media either synthetic or with potato extract show that it is possible to obtain as many embryos as when using solid potato extract medium. In liquid media young embryos or 14-day old induced anthers can differentiate green plants for regeneration. Glutamine is effective in culturing anthers and can replace potato extract in the medium.

Plants have been regenerated from short-and long-term in vitro somatic tissue cultures made from immature embryos of the hexaploid wheat cultivar "Chinese Spring". The mitochondrial genome organization of each regenerated plantlet was studied, after one selfing, by probing Sal I-restricted total DNA with cloned Sal I fragments of wheat mitochondrial DNA derived from a segment of the genome, which displays marked structural changes in response to in vitro culture. Short-term in vitro cultures give rise to regenerated plants whose mitochondrial genome organization is either close to that of the parental cultivar or to that of embryogenic callus cultures, except for a single plant which has an organization resembling that of short-term non-embryogenic cultures. In contrast, all but one of the plants regenerated from long-term cultures exhibited a mitochondrial genome organization similar to that of long-term nonembryogenic cultures. In addition, extra labelled bands were detected in some of the regenerated plants with two of the probes used. These results emphasize the importance of the duration of the in vitro step preceding the regeneration process: the longer it is, the higher the probability is of obtaining mitochondrial DNA variability in regenerated plants. Furthermore, since increasing the duration of the in vitro stetp results in the production of regenerated plants with a mitochondrial genome organization resembling that of non-embryogenic tissue cultures, the question is thus raised as to whether regeneration from long-term cultures is suitable for use in plant breeding.

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A population of thirty-eight doubled haploid lines, developed from the F, between Vfro wheat parents differing m anther culture and somatic tissue culture responses, was used to examine the genetical control of re'sponses to these m vitro systems.During anther culture genetic variation between hnes ' was exhibited for frequencies of callus induction, embryo production and embryo regeneration rates. In addition the relative frequencies of green and albino plants ' was shown to be genotype dependent. Hoivever, there ' (vas no correlation between the frequencies of embr)ro production and i:he regeneration rate of those embryos suggesting an independent genetic control of these two components. Transgressive segregation for performance was obsen'ed for all components indicating that at least two genes are involved in the response of each, and lines for improved performance, combining high embrv'O production rates and good regeneration capacity were identified.No genetic variation for frequencies of callus induction from immature embryos was observed in this cross. However, genetic variation for the regeneration frequencies of plants was observed. Lines with an improved tissue culture response over the two parents were identified.There 'n'as no correlation between the performance of lines in anther culture and somatic tissue culture, indicating separate genetical control, and lines with alternative levels of response to the two systems were identified.