Mohan Jain

Strawberry shoot meristem cultures have been used for producing virus-free strawberry plants. Plantlet regneration from leaf mesophyll protoplasts, and Agrobacterium tumefaciens mediated genetic transformation, mark the beginning of strawberry improvement with biotechnologies. The use of biotechnological tools has a greater potential in producing strawberry plants with traits such as early maturation, frost and disease resistance, mite and nematode resistance, high

Tissue culture generates a wide range of genetic variation in plant species which can be incorporated in plant breeding programmes. By in vitro selection, mutants with useful agronomic traits, e.g. salt or drought tolerance or disease resistance, can be isolated in a short duration. The successful use of somaclonal variation is very much dependent on its genetic stability in the subsequent generations for which molecular markers such as RAPDs, AFLPs, SSRs and others can be helpful. The potential of somaclonal variation has yet to be fully exploited by breeders, even though a few cultivars have been developed in crops such as Brassica juncea, rice and others.

The exploration of somaclonal variation is an approach that could provide date palm breeding programs with new genotypes. Naturally occurring or induced variants may have superior agronomic quality and/or enhanced performance but could also harbor new traits such as tolerance to drought and salinity or resistance to major diseases i.e. bayoud. This chapter summarizes recent progress in terms of studying and exploring date palm somaclonal variation, and provides an outlook about future applications of this biotechnology in this socioeconomically important crop.

Under the Joint FAO/IAEA programme, radiation-induced mutations are used for genetic improvement of both seed and vegetatively propagated plants. The FAO/IAEA programme maintains a database of officially released mutant varieties worldwide (http:www-mvd.iaea.org/). Currently, over 2300 mutant varieties are registered in our database. Coordinated Research Projects (CRPs) and Technical Co-operation Projects (TCP) are two major activities at IAEA that serve Member States at the national, regional and interregional levels. This article highlights CRPs on banana, underutilized and neglected crops, and tropical and subtropical fruits. CRPs on banana and underutilized and neglected crops have already been concluded. TCPs in South East Asia (Thailand, and Malaysia), Africa (Algeria, Morocco, Tunisia, Ghana), and the Middle East (Yemen) are discussed. The main projects in South East Asia are on genetic improvement of ornamental plants, fruits and cereals. In Africa, projects are on cassava, date palm, salinity and drought. In the Middle East, funded projects are related to salinity, and drought. In this article, major achievements are highlighted through CRPs and TCPs on low cost tissue culture, banana, underutilised and neglected crops, tropical and subtropical fruits.

Genetic stability of propagules regeneratedvia somatic embryogenesis is of paramount importance for its application to clonal forestry. Random amplified polymorphic DNA (RAPD) markers were used to determine the genetic stability in somatic embryogenesis ofQuercus serrata Thunb. (Japanese white oak). Forty samples from an embryogenic line, consisting of regenerated plantlets, somatic embryos, and embryogenic calli, were examined using 54 decanucleotide primers. A total of 6520 clear reproducible bands obtained from these studies exhibited no aberration in RAPD banding pattern among the tested samples. Our results show that somaclonal variation is absent in our plant propagation system. The genetic stability is discussed in terms of the origin of somatic embryos.

Stress responses are largely conserved in eukaryotic cells, but with plants having certain distinctive reactions to specific stresses, e.g. the induction of pathogenesis-related proteins. General responses to stress involve signaling stress detection via the redox system, checkpoints arresting the cell cycle and DNA repair processes stimulated in response to DNA damage. Specific responses to stress include the induction of protective metabolites, such as betaines, and protective proteins, for example, heat shock proteins. Chemical signals, e.g. reactive oxygen species, Ca2+ and plant hormones, acting through signal transduction cascades activate genomic re-programming. Genome plasticity in plants allows adaptation to environmental conditions and includes genomic or epigenetic changes (histone acetylation, methylation, chromatin remodeling etc.) and possibly directed mutation. In plants, recent research has indicated that intricate stress response mechanisms and `cross talk' between stress responses exist. Here, changes in the plant genome and in genomic expression in development and as a response to environmental stress are reviewed as background to a discussion of the basis of aberrant genomic expression in vitro. Markers are discussed which may be used to characterize the stress exposure of in vitro tissues.