I have tried following several protocols to extract DNA for PCR amplification (Lodhi et al. 1994; Doyle & Doyle1987), from Quercus leaves.  Interestingly, some samples showing good and clear band , however, other samples are not showing sharp band on my Agarose gel electrophoresis. Does anybody know what is the problem with my samples or which protocol to follow for good quality DNA isolation? I would very thank full for any comments and guidance