SPEAKER: To begin with, we'll talk about technology that has been around for lots of years and has expanded and developed rapidly. And it's had a tremendous impact on plant breeding. This is tissue culture technology. Basically, it's technology that allows you to take a small part of a plant, put it in the culture medium, and accept the conditions and regenerate large numbers of little plantlets.
Tissue culture has been useful in plant breeding in two main ways. It's allowed breeders to produce true breeding species by vegetatively propagating crosses from material that normally would segregate genetically. And it's also allowed breeders to expand the genetic diversity within crop gene pools.
Tissue culture methods that allow breeders to genetically propagate plant materials include anther culture, micropropagation, and grafting. All three technologies very, very useful, and have been used in the successful development of a number of crop species. Tissue culture has also been useful in expanding the genetic diversity within crop species.
Sometimes when you grow these little plant parts on culture media and regenerate plants, you find that genetic mutations occur, resulting in a process known as somaclonal variation. Somaclonal variation has given rise to several very useful new plant types. In addition, you can produce somatic hybrids by literally fusing cells or protoplasts from different plant cultivars. And making crosses through somatic hybridization often allows breeders to make wider crosses than can be done through normal sexual reproduction.
Sometimes when breeders make crosses between widely divergent species, distantly related species, they can produce a seed, but the seed is often sterile. And it will not grow and germinate. So embryo rescue techniques have been used, whereby scientists can go in, make a wide cross, go in, extract the embryo that's produced through the sexual cross, put in a tissue culture medium, and regenerate plants successfully from crosses, which could not be made using traditional sexual recombination.
Another tool of molecular biology that is proving to be more and more useful each year is technology that involves recombinant DNA. DNA is basically the building block of genes. All genes are composed of DNA molecules. These molecules basically replicate and preserve the genetic integrity of any given species. Technology that's been developed over the last 20 years has allowed scientists to go in and cut and splice genes, much the way that a film editor will cut and splice videotapes.
As you can see from this graphic, basically you can go into a plasmid-- or a very, very small form of life-- you can extract the gene or cut out a part of the DNA. You can move that gene that has been cut and extracted into E. coli, the bacteria. And using the proper enzymes and technology, you can get this gene from a plasmid or a viral source incorporated into the DNA of the E. coli. Once in the DNA of E. coli, you grow out that transformed bacterium in a suitable culture media, and you can produce hundreds of thousands of copies of that gene.
Basically, you can clone the gene. We'll talk later about how such cloning technology has been used to take genes out of organisms like bacteria, insert them into plants. And basically giving rise to the transgenic plant technology. If you're interested in this DNA recombinant DNA technology, there are a series of animated video clips that you can find in our Web Links section of the Cyber Tower room.
As you can see, recombinant DNA technology gives us tools for detecting, identifying, actually cutting out and cloning specific strips of DNA which contain genes. This technology has proven very, very useful in the field of plant genomics. Genomics basically means identifying all of the various gene sequences within an entire species. So far today, the entire genome sequence of rabbit arabidopsis and rice have been completed. And the genome sequences of most of our major crops are well underway.
There are a number of applications of this recombinant DNA technology and genomics for plant breeding. Probably the most useful has been using DNA markers to facilitate that crossing of genes from wild, distantly related plant species into domesticated crop varieties. This current slide gives you a very brief timeline, showing that technologies such as tissue culture, anther culture have been around for several years. But as we move towards the year 2000, we've developed more and more recombinant DNA technologies. A more complete timeline for the development of crops from 10,000 years ago through present day can be found in the timeline section of the Cyber Tower room.
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Plant Breeding: Then and Now provides an overview of plant breeding techniques, from early crop domestication to the latest developments in biotechnology methods. Plant breeding is one of the oldest scientific disciplines that has developed over thousands of years. Discover how recent developments in biotechnology are changing the science and methods of plant breeding.
This video is part 3 of 6 in the Plant Breeding: Then and Now series.