Abstract
Rhizoctonia isolates obtained from maize grown in commercial fields in 33 representative counties (or cities) in Sichuan province in China were characterized according to colony morphology, hyphal anastomosis and pathogenicity. Of 141 isolates, 116 were identified as R. solani, 23 as R. zeae and two as binucleate Rhizoctonia. The isolates of R. solani were assigned to four anastomosis groups (AG): AG‐1‐IA (101 isolates, accounting for 71.6% of the total), AG‐1‐IB (2, 1.4%), AG‐4 (9, 6.4%) and AG‐5 (4, 2.8%). The two isolates of binucleate Rhizoctonia belonged to AG‐K. On maize, isolates of AG‐1‐IA caused typical sheath blight symptoms. Lesions produced by isolates of AG‐4, AG‐5, AG‐1‐IB and AG‐K were darker than those of AG‐1‐IA. Rhizoctonia zeae usually caused discontinuous lesions with a dark brown margin and a brown centre on the leaf sheaths, as well as ear rot. Isolates of AG‐1‐IA were the most virulent to maize, with an average lesion length of approximately 15 cm. Isolates of R. zeae produced lesions approximately 12 cm long, while those of AG‐4, AG‐5, AG‐1‐IB and AG‐K were progressively shorter. On potato dextrose agar (PDA; pH 6.4), the minimum temperature for mycelial growth of R. zeae isolates was 14–18°C, the maximum 38–40°C and optimum 30°C. Isolates of R. zeae did not grow on PDA (28°C) at pH 2.0, the optimum for growth being pH 6.4.
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