Virulence and genetic diversity of Sclerotium rolfsii Sacc., infecting groundnut using nuclear (RAPD & ISSR) markers

Abstract

Aim: Assess the virulence and genetic diversity of Sclerotium rolfsii isolates causing stem rot disease in groundnut collected from different geographical regions of Tamil Nadu using nuclear markers viz., RAPD and ISSR. Methodology: Survey was conducted in major groundnut growing areas of Tamil Nadu and twenty two cultures of S.rolfsii (18 from groundnut and 4 from other crops) were collected and isolated. Subsequently the virulence of S.rolfsii was tested. Genomic DNA was extracted from S.rolfsii isolates and assessed their genetic diversity using nuclear markersviz., RAPD and ISSR. Results: Among the 22 isolates of S. rolfsii, the isolate from Udumalpet (SrUDM) showed higher per cent disease incidence (80.95%) followed byK.G. Savadi (SrKGS) and Tindivanam (SrTVM) isolates (61.90%), whereas the isolate from Madurai recorded lower per cent disease incidence (33.33%). ITS region of rDNA amplification with specific ITS-1 and ITS-4 universal primers produced the amplicon of approximately 650 to 700 bp and confirmed that all the 22 isolates belongs to the genus Sclerotium. Ten different oligonucleotide primers of RAPD and ISSR were used to assess the genetic diversity among 22 isolates of S. rolfsii. The dendrogram results indicated that all the S. rolfsii isolates from Tamil Nadu formed two distinct clusters. A total of 121 and 123 reproducible and scorable polymorphic bands recorded and ranging from 100 to 2500 bp and 250 to 2000 bp were generated with ten numbers of RAPD and ISSR primers, respectively. The ISSR marker recorded anaverage PIC of 0.87 as against 0.86 of RAPD and the effective multiplication ratio was also superior in ISSR (12.21) comparedtoRAPD (12.00). Interpretation: The result of the present study indicated that ISSR markers were suited well for genetic diversity studies of S. rolfsii than RAPD and no correlation was observed between the virulence and genetic diversity of various S. rolfsii isolates using nuclear markers.