Identification of AG-V, a new anastomosis group of binucleate Rhizoctonia spp. from taro and ginger in Yunnan province

Binucleate Rhizoctonia (BNR) spp. isolates were collected from taro (Colocasia esculenta (L.) Schott) and ginger (Zingiber officinale (Willd.) Roscoe) (Yunnanxiaojiang cv.) in Yunnan province. These Yunnan (YN) isolates did not anastomose with any of the tester isolates of the known AGs of binucleate Rhizoctonia spp. The growth of YN cultures on PDA was appressed, mealy and matlike after 4 days of incubation, then turned white brown, producing brown to dark brown, irregularly shaped sclerotia were embedded in the PDA medium after 14 days. All attempts to induce basidiospore production were unsuccessful, but the length and sequence of the internal transcribed spacer (ITS1 + 5.8S rDNA + ITS2) regions of 5.8S rDNA from the YN isolates were identical in length and sequence to isolates of all the other AGs of binucleate Rhizoctonia /Ceratobasidium spp. The sequences of 5.8S rDNA-ITS from the YN isolates were unique among AGs of BNR. The YN isolates had sequence similarities of 94% with isolates of AG Fb and P, 93% with AG E, 91% with AG R, 79-94% with AG S, and 74-87% with AG A, Ba, Bb, Bo, C, DI, DII, DIII, Fa, G, H, I, K, L, O, and Q. Four isolates of AG YN caused minor virulence (lesions ae broken vertical bar 1mm(2)) to ginger or taro in growth chamber studies. It was concluded that the YN isolates belong to a new anastomosis group AG-V of the Ceratobasidium spp..