Molecular diversity of Fusarium oxysporum causing rot diseases of vanilla in south India

Incidence of root, stem and beans rot of vanilla (Vanilla planifolia Andrews) caused by Fusarium oxysporum Schlecht was surveyed in vanilla growing areas of south India during December 2008. The incidence of the disease varied from 1 to 100% in different locations. A total of 60 isolates of F. oxysporum were obtained from diseased samples, and nine morphologically different isolates were taken for molecular characterization using Randomly Amplified Polymorphic DNA (RAPD) markers to study the genetic variability if any, among them. PCR amplification of total genomic DNA with random oligonucleotide primers generated unique banding patterns depending upon primers and isolates. Nine oligonucleotide primers were selected for the RAPD assays, which resulted in 384 bands for nine isolates of F. oxysporum. The number of bands obtained was entered into a NTSYS and the results showed that the variability among the pathogen isolates was moderate. The nine isolates studied were grouped into single major cluster at 0.66 similarity index. Hence, it is inferred that F. oxysporum infecting vanilla in south India consists of a single clonal lineage with a moderate level of genetic diversification.