Frequency and pathogenicity distribution of Rhizoctonia spp. causing sheath blight on rice and banded leaf disease on maize in Yunnan, Chin

摘要

Sheath blight on rice and banded leaf disease on maize are epidemic in Yunnan, China, causing severe losses of both crops. Isolates from maize sheaths showing symptoms of sheath blight, were collected from five representative counties in Yunnan. These isolates were identified as Rhizoctonia spp. based on their morphological characteristics. Four anastomosis groups (AGs) of R. solani were identified: AG-1 IA (10 isolates, 28.3% of the total), AG-1 IC (8.3%), AG-4 (11.4%) and AG-5 (11.4%). The binucleate isolates of Rhizoctonia spp. belonged to AG-A. Thirteen multinudeate isolates failed to anastomose with the AG testers of R. solani, but they possessed morphological characteristics of Rhizoctonia zeae and anastomosed with the tester isolate of anastomosis group Z of the Waitea spp. (WAG-Z). Isolates of AG-1 IA were highly pathogenic at heading stage on maize, while isolates of AG-5, AG-1 IC, and WAG-Z were considerably less pathogenic. Isolates of AG-4 and AG-A were the least pathogenic. Among the sheath samples of rice with sheath blight symptoms, forty-nine isolates from 15 counties in Yunnan were collected. They were identified as four AGs of R. solani, AG-1 IA (31 isolates, 65.3% of the total), AG-1 IB (6.1%), AG-1 IC (6.1%) and AG-4 (2.1%). Binucleate isolates belonged to AG-Bb. Tested isolates of AG-1 IA, AG-Bb, and AG-4 were highly pathogenic at the heading stage on rice; isolates of AG-1 IC were moderately pathogenic, whereas isolates of AG-1 IB were non-pathogenic on rice.