Rhizoctonia Blight of Azolla japonica Caused by Rhizoctonia solani

Azolla Lam. is a small aquatic fern with deeply bilobed leaves, which are consisted of a thick greenish, withchlorophyll, upper (dorsal) lobe and a thinner, translucent lower (ventral) lobe, without chlorophyll,submerged in the water. Azolla blight was observed at a lotus pond. Mycological characteristics of the fungusassociated with Azolla blight was immediately determined as Rhizoctonia sp. by the thickness and branchingof hypha at right angles at the point toward the distal end of septa, with branching hypha is constricted. Thefungus produced brown mycelia and dark brown sclerotia on PDA. The optimum temperature for mycelialgrowth and sclerotia formation were 25oC and 30oC, respectively. The optimum temperature for fungalinfection was 30oC, when spray inoculated. Phylogenetic analysis of rDNA-ITS revealed that the fungus wasidentified as Rhizoctonia solani (AG-1 IA) closest to one causing rice sheath blight disease. This is the firstreport on the blight disease of Azolla caused by R. solani in Korea.