Breeding of Vegetable, Spice and Tuber crops (2+1)

Genetic engineering in plants

Meristem and bud culture

• Zygotic embryo culture, Anther and microspore culture, Cell and tissue culture,Chromosome engineering, Protoplast culture, Genetic engineering, Molecular markers, Monoclonal antibodies, micro propagation for commercial purposes, genetic conservation, and exchange of material, inter specific crosses, haploid production, in vitro selection, somaclonal variation, somatic embryogenesis, artificial seeds 2n gametes for inter specific crosses, fusion for somatic hybridization gene transfer, aid to breeding programmes to develop resistant varieties to plant diseases.

• In vitro culture of zygotic embryos (embryo rescue) has enabled us to overcome barriers to a number of inter specific crosses from zygotic failure. Several interspecific hybrids have been obtained in this way-for example, between Lycopersicon species and Solanum species, among cucurbits, and among legumes. In vitro culture of anthers allows the regeneration of large number of haploid plants, from which, by chromosome doubling via colchicine treatment or via further in vitro culture, diploid plants, homozygous at all loci, can be obtained.
  

• Lines produced from anther culture of hybrids are obtained in less time and show greater variability than those obtained by self-pollination; several varieties produced using this method have already been released. Direct culture of microspore has proved to be efficient in Brassica species.

Agrobacterium-mediated genetic engineering

• Recombinant DNA procedures can be used to make discrete changes in the genetic make up of plants.
  
• Transgenic plants of over 50 species that contain genes from other plant species, bacteria, viruses, and animals, are currently available.
• The foreign genes expressed in transgenic plants confer on them a variety of important agronomic traits including: insect resistance, virus resistance, microbial resistance, herbicide resistance, altered macromolecular composition, modified reproductive capacity, and .delayed senescence.
• Alien genes from organisms that cannot hybridize with AVRDC mandate crops can be introduced through genetic engineering. Such gene transfers are impossible with conventional breeding methods.
  
• Genetic engineering also allows introduction of only one or two well-characterized genes at a time, unlike hybridization where extensive backcrossing is needed to remove undesirable genes.
• Efforts have been made at AVRDC in producing transgenic mungbean, hotpepper(chilli), tomato, and vegetable soybean plants via the Agrobacterium-mediated uptake of marker genes.
• Bacterial genes that conferred antibiotic resistance "marked" transformed cells.
  
• These selectable marker genes permitted the transformed cells to be grown in antibiotic that would kill non-transformed cells. Such marker genes have been used to optimize the transformation protocol and to study the inheritance and stability of introduced genes.
• Cucumber mosaic virus (CMV) causes large yield losses in pepper and tomato.
  
• Since there are no resistant sources in germplasm and no effective way to prevent the infection, the novel approach of genetic engineering becomes new solution to problems.
• The truncated CMV RNA-2 replicase and coat protein genes were transferred to pepper and tomato.
  
• The detection of certain nucleotides had resulted in a truncated translation product about 75% of the full length protein.
  
• The AVRDC scientists have observed a high degree of CMV resistance in the RO and R1 lines of the transgenic chilli pepper and tomato plants.
• Once a gene is successfully transferred, transgenic plants need to be grown and tested in a newly-constructed, special confinement facility — a greenhouse for transgenic plants — in order to establish the stability and effectiveness of the gene, and to further produce transgenic plants.
• The movement of transgenic plant materials from the laboratory or greenhouse to the field is highly regulated in many countries.
  
• The regulations state that field tests of transgenic material can only be done under a permit that is granted on a case by case basis.
  
• However, the results from many studies in the last five years indicate that the use of genetic engineering does not impose extraordinary risks on environment and society.
• It is obvious from the level of activity in this area that the pipeline is full with a large variety of potential products.