Estimation of genetic divergence among elite cotton cultivars-genotypes by DNA fingerprinting technology

Epidemics of cotton leaf curl virus disease (CLCD) was the compelling factor in the decision to devise new strategies for cotton breeding programs of Pakistan. The genetic similarity among the elite cotton (Gossypium spp.) cultivars released before the advent of CLCD epidemics was in the range of 81.5 to 93.41%. New cultivars were developed by crossing the exotic resistant germplasm (LRA-5166, CP-15/2, and Cedix) with adapted varieties highly susceptible to CLCD. A study was designed to assess the genetic relatedness or diversity among the newly released, extremely resistant and resistant cultivars. After screening 27 cotton genotypes by different diagnostic methods such as field evaluation, whitefly-transmission studies, grafting, dot-blot hybridization, and multiplex PCR using conserved primers sequences, 20 extremely resistant and resistant cultivars were selected for a random amplified polymorphic DNA (RAPD) analysis. The genetic similarity of the exotic germplasm with the elite cultivars was in the range of 81.45 to 90.59%. Similarly, the genetic relatedness among the elite cultivars was in the range of 81.58 to 94.90%. The average genetic similarity among all studied genotypes was 89.55%. We have demonstrated that only cultivar VH-137 possesses a diverse genetic background. Our study suggests the need to breed for high genetic diversity to serve as a buffer against potential epidemics.