Application of Molecular Techniques for Detection of Disease Resistant Genes in Tomato Breeding Lines for Guatemala

Topics: Polymerase chain reaction, Chromosome, Gene Pages: 5 (1432 words) Published: July 28, 2009
Application of Molecular Techniques for Detection of Disease Resistant Genes in Tomato Breeding Lines for Guatemala Objectives:
1.Evaluate and modify methods for detection of Fusarium Race 2 resistance gene. 2.Evaluation of two step protocol for detection of Mi-1 gene. 3.Verification of marker for Ty-1 and evaluation for marker in Guatemala breeding lines. (This is a Geminivirus that is transmitted by the whitefly) 4.Use of molecular markers to detect geminivirus resistance source for Gu143 (chilense or hirsutum or potentially both).

Many third world country farmers rely on their crops to provide them with food and a small income. The problem that has been becoming more evident is that these farmers must battle viruses, bacteria, fungi, and nematodes while caring for their crops. These pathogens cause great damage by wiping out whole generations of crops leaving the farmers unable to feed their families and no income. With all of these potential pathogens, rapid and inexpensive techniques that offer reliable resistance identification must be developed to assist breeders in their choices of what plants should be used to produce a resistant hybrid. Although there are various wild varieties of plants that are resistant to the different pathogens, these wild varieties have fruits that are usually too small and unrealistic for commercial use. So instead these wilds types are sources of resistant genes that can be introduced into plants that do produce fruits that are marketable. One such fruit that is being attacked by numerous pathogens is the tomato (genus Lycopersicon has 10 different species), and efforts are underway in many countries and by many commercial companies to breed new lines of tomatoes that incorporate resistance to many of these pathogens.

Fusarium oxysporum is a soil borne fungus that infects plants through their roots and colonizes the xylem of the plant causing wilting. Tomato plants are the hosts for Fusarium oxysporum f.sp. lycopersici. Within tomatoes, one of the primary genes that confers resistance to the pathogen F. o. lycopersici race 2 is I-2, this gene is found among a group of seven other homologues on the chromosome (Mes et al., 2000). The I-2 locus is on the long arm of chromosome 11. This gene was introduced from a resistant variety of the wild species, Lycopersicon pimpinellifolium (Buurlage et al., 2001). (Current methods for detection of Fusarium) (Using the Fus primers in the new Fus program on the UW machine along with currently untested primers create a multiplex PCR, the untested primer will serve as a indicator whether the DNA is good, and the Fus primers will serve as a indicator of whether or not the DNA has the Fus resistance gene.) The Fusarium primers that are in use in this experiment were developed by Lebanon and their research is currently unpublished.

Another very important gene that has been introgressed from resistant into non-resistant tomatoes is the Mi-1 gene that is found at the Mi-1 locus on chromosome 6. There have been seven reported homologs of the Mi gene arranged in groups of three and four (Seah et al., 2004). This gene was introgressed from the corresponding region on the short arm of chromosome 6 (6S) in the resistant variety (Seah et al., 2003), and was introduced from the resistant species L. peruvianum. The Mi-1 gene has been found to confer resistance to some nematodes (Meloidogyne sp.) the 3 most common of these nematodes are: Meloidogyne arenaria, M. incognita, and M. jervanica (Llarduya et al., 2003). The Mi-1 has also been observed to confer resistance to potato aphids (Macrosyphum eupharbiae) and whiteflies (Seah et. Al., 2003).

Currently a two step protocol can be used to detect if the gene that codes for resistance to various pathogens (L. peruvianum-Mi-1 gene) resides within the chromosome of a plant by extracting DNA and subjecting it to various polymerase chain reactions (PCRs)(insert web address...
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