Rhizoctonia solani AG2-1 Causing Root Rot of Wasabi (Eutrema japonica) in the United Kingdom

In 2014, glasshouse-grown wasabi (Eutrema japonica) grown in a compost based media displayed symptoms of poor growth and wilting. Visual assessment the roots showed that 25% symptomatic plants sampled had raised black lesions on affecting between 5 20% total root area. To isolate causal agent, affected material (approximately mm3) was surface disinfested sodium hypochlorite (2%) for 30 s, rinsed twice sterile water plated to agar medium amended with penicillin G (0.2 g/liter) streptomycin sulfate (0.8 g/liter). Plates were incubated at 20oC until fungal colonies visible. After three days, Rhizoctonia solani identified presence septate hyphae right-angle branching, pure culture obtained through hyphal tip transfer onto new plate PDA. DNA extracted from 7-day old (WAS1) as described previously (Woodhall et al., 2013). The AG WAS1 determined AG2-1 using subgroup specific real-time PCR assay (Budge 2009b) confirmed by sequencing (Lekuona Gomez 2015). sequence 100% identical (587/587bp) 1971 (GenBank accession FJ435126) (2009a). Pathogenicity inoculating healthy one-year-old loam (John Innes No.3) each four mm fully colonised PDA plugs placed approx. 40 depth soil. Four place control plants. All six greenhouse 21°C, 18h:6h light: dark watered required. 21 multiple typically 3-5mm length observed all inoculated No From per plant, isolations attempted above. recovered resulting cultures tested positive assay. Isolations but not recovered. Here we demonstrate R. is associated necrosis Eutrema japonica. has been reported various Brassica crops UK 2009a) Matthiola incana It also causing disease potatoes widely present field soils Although AG1 AG4 have infect japonica Japan (Takeuchi 2003; 2008), this first finding identifies agent. potential soil and/or plant debris should be considered prior planting susceptible hosts.