RFLP patterns of the PCR-amplified S1 glycoprotein genes from five IBV strains (3 Reference strains and 2 Field isolates) digested with Alu I, Hae III, BstY and Xcm I. Lane 1 to 5, Alu I; Lane 6 to 11, Hae III; Lane 12 to 16, BstY; Lane 17 to 22, Xcm I; Lanes 8, 19 and 23, molecular weight marker l kb DNA step ladder.