CHARACTERIZATION OF THE ROLE OF PHASEOLINONE PRODUCED BY MACROPHOMINA PHASEOLINA IN THE DEVELOPMENT OF CHARCOAL ROT ON SOYBEAN

Macrophomina phaseolina (Tassi) Goid is a soil-borne and seed-born pathogen that causes charcoal rot in soybean and 500 different plant species. Charcoal rot is one of the most destructive diseases of soybean in the United States. Little is known about the mechanisms governing the interaction between soybeans and M. phaseolina that result in charcoal rot development. The ability of M. phaseolina to cause charcoal rot may be associated with the production of the phytotoxin phaseolinone by the fungus. There are different methods suggested by previous works that can be used to control the disease such as irrigation, tillage, biological control, fungicide and plant resistance. However, none of these techniques were effective to completely combat the disease. The objective of our study was to find new tools and new ways of finding resistant lines of soybean to charcoal rot and to find some of the genes that we believe are involved in phaseolinone production. In my research I used a cDNA-AFLP (Amplified Fragment Length Polymorphism) approach as a qualitative and quantitative tool to identify M. phaseolina genes involved in the production of phaseolinone. I also did an assay with the toxin extracted from the fungus on soybean plants. By using this toxin assay, I was able to screen for susceptible and resistant genotypes of soybean to M.phaseolina. Scientists have been trying for years to find the best way to combat the disease and to find some soybean varieties, which are resistant to this fungus. There are different technics that can be used to quantify the amount of pathogen in plant and screen for resistant lines. One of these methods to differentiate between soybean genotypes according to their reaction to M.phaseolina is colony-forming unit index (CFUI) and intensity of internal root and stem discoloration (Mengistu, Ray et al. 2007). I used q-PCR techniques as a faster and more efficient way to quantify the amount of fungus in soybean roots and detect the most resistant soybean lines to this pathogen