The DNA was quantitative against lambda standards on agarose gels stained with ethidium bromide, and the concentration of DNA was then diluted to 10 ng • μL-1. Resistant and susceptible bulks for bulk segregant analysis (BSA) were made by pooling equal amount of genomic DNA from 10 resistant F2 plant and 10 susceptible F2 plant, respectively, and both bulks were used along with the parents to identify markers showing polymorphisms between these samples.