Genomic DNA extraction and primer selection
Total genomic DNA was also extracted from dried seeds according to the method described by Kang et al. (1998). After isolation of DNA, its quantity was determined spectrophotometrically at a wavelength of 260 and 280 nm using NanoDrop ND-1000 Spectrophotometer. The ratio between absorbance at 260 and 280 nm (260/280) was used to estimate DNA purity. DNA of each cultivar was diluted to a working concentration of 20 ng/μl for PCR/RAPD analysis.
Initially, three cultivars, one each from aromatic, non-aromatic and japonica type was used to optimize the RAPD protocols and select the suitable primers which exhibit polymorphisms between the three cultivars. Overall, 40 arbitrary decamer oligonucleotides, belonging to kit OPA and OPB from Operon Technologies Inc. (Alameda, California, USA), were tested as single primers to identify the most promising ones for detecting polymorphism. After an initial screen, 14 primers were ultimately chosen for further use on the basis of their ability to detect the polymorphism and produce the reliable and easily scorable banding patterns in rice cultivars. Among them, three primers could not amplify the DNA from some of the cultivars used. Therefore, finally the data of 11 primers were used and compiled to look at the genetic diversity and relationship among 35 commercial varieties and primitive cultivars of Pakistani rice.