Submitted to: Mycologia
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 4, 2013
Publication Date: September 19, 2013
Citation: Amaradasa, B., Horvath, B., Lakshman, D.K., Warnke, S.E. 2013. DNA fingerprinting and anastomosis grouping reveal similar genetic diversity in Rhizoctonia species infecting turfgrasses in the transition zone of USA. Mycologia. 105(5):1190-1201. Interpretive Summary: Rhizoctonia blight is a common and serious disease of many turfgrass species. Conventional biological approaches to pathogen identification are inconvenient, often imprecise, and time-consuming. For surveying the epidemiology of pathogenic species and races of Rhizoctonia and developing efficient disease management practices with pesticides and breeding for disease resistance, precise molecular identification processes are essential. We have evaluated two molecular approaches to identify and characterize Rhizoctonia isolates of turfgrasses from Maryland and Virginia to species, group, and subgroup levels and demonstrated that several Rhizoctonia species and groups are responsible for causing patch diseases on cool-season turfgrasses. Our results also indicated that more than one Rhizoctonia species or groups could be present in the same turfgrass site.
Technical Abstract: Rhizoctonia blight (sensu lato) is a common and serious disease of many turfgrass species. The most widespread causal agent, R. solani, consists of several genetically different subpopulations. Though hyphal anastomosis reactions have been used to group Rhizoctonia species, they are time consuming and sometimes difficult to interpret. Isolates of different subgroups within an anastomosis group (AG) are not distinguishable based on anastomosis reactions since they anastomose each other. This study evaluated molecular techniques in comparison with traditional anastomosis grouping to identify and group isolates of Rhizoctonia. More than 400 Rhizoctonia isolates were collected from diseased turfgrass leaves from eight locations in Virginia and Maryland. A random sample of 86 isolates was selected and initially characterized by colony morphology, nuclei staining and anastomosis grouping. Molecular identification was performed by analysis of ribosomal DNA internal transcribed spacer (rDNA-ITS) region and the DNA fingerprinting technique, universally primed PCR (UP-PCR). The cladistic analysis of ITS sequences and UP-PCR fragments supported seven clusters. Isolates of R. solani AG 1-IB (n=18), AG 2-2IIIB (n=30) and AG 5 (n=1) clustered separately. Waitea circinata var. zeae (n=11), and var. circinata (n=4) grouped separately. A cluster of six isolates (UWC) did not fall into any known Waitea group. Most of the binucleate Rhizoctonia-like fungi (BNR) (n=16) grouped separately. Our study indicated that several Rhizoctonia species and AGs are responsible for causing patch diseases on cool-season turfgrasses. Results of the molecular analysis also suggest that more than one Rhizoctonia species or AG could be present in the same turfgrass site. There was no relationship between the geographic origin of the isolates and the clusters formed.