Assessment of RAPD and ISSR marker systems for establishing distinctiveness of forage Sorghum (Sorghum bicolor L. Moench) varieties as additional descriptors for plant variety protection

Twenty six varieties of forage sorghum which included 20 released or notified and 6 indigenous local varieties were characterized with 40 morphological DUS descriptors as prescribed by DUS guidelines of PPV &FR Authority and ICAR. RAPD and ISSR markers were also studied to complement the morphological DUS descriptors for establishing distinctiveness of a variety. When all the 33 morphological descriptors of PPV & FR Authority and 7 morphological descriptors of ICAR were studied distinct morphological profiles could be obtained only for 11 out of a total of 26 varieties. Thirteen primers out of a total of 14 RAPD primers were able to establish unique molecular identification profiles (MIPs) for a total of 14 varieties. Fourteen primers out of a total of 20 ISSR primers were able to establish distinctiveness of 19 varieties by the amplification of different genotype specific bands in these varieties. Both the molecular markers revealed a very high level of polymorphism, enabling genetic discrimination of the varieties analyzed by using 121 informative RAPD and 178 ISSR bands. UPGMA cluster analysis of both the markers could distinguish all the twenty six varieties. Higher Mean polymorphic information content (PIC), average expected gene diversity, average resolving power (Rp) and diversity index (DI) were higher for ISSR marker as compared to RAPD one which reflected that ISSR marker is more efficient tool to establish distinctiveness amongst the present set of experimental material. Out of a total of 26 varieties unique identification profiles were developed for 25 varieties by a combination of morphological DUS descriptors and both the RAPD and ISSR markers. However, the variety Pusa Chari 121 was not delineated by any of the morphological and molecular markers. Thus from the present study it could be concluded that in situations where the morpho-physiological DUS descriptors are not able to establish distinctiveness of a variety then unique molecular fingerprints generated by molecular markers may be used as additional or complement descriptors for resolving distinctiveness of varieties.