Leaf Rot and Leaf Ring Spot Caused by Rhizoctonia solani in Chinese Cabbage

Research in Plant Disease 2013;19(4):300-307.
Published online December 30, 2013.

Chang-Ki Shim, Min-Jeong Kim*, Yong-Ki Kim, Hyeong-Jin Jee, Sung-Jun Hong, Jong-Ho Park, Eun-Jung Han and Jong-Chul Yun

Organic Agriculture Division, National Academy of Agricultural Science, Rural Development Administration, Suwon 441-707, Korea

Received: November 15, 2013 Revised: November 25, 2013 Accepted: November 26, 2013

Abstract

This study was conducted to determine the occurrence of leaf rot and leaf ring spot, caused by Rhizoctonia solani in Chinese cabbage under seedling nursery and cultivation greenhouses. Symptoms of leaf rot and leaf ring spot were found in three Chinese cabbage cultivars, Brassica campestris subsp. pekinensis, ‘Ryeokgwang’, ‘Daetong’, and ‘CR mat’. In Hwacheon, the disease incidence was 73.8% in the seedling stage of the Chinese cabbage. In Icheon, the symptoms were observed on the upper leaves of the Chinese cabbage cultivar, ‘Norangmini’ with 20.5% of disease incidence. The symptoms appeared as primary lesions consisting of small, circular necrotic ring spots with gray color, 1.4?3.0 mm in diameter, accompanied by secondary rot lesions with large irregular borders of leaves. The color of mycelial mat of 20 isolates was dark brown and light brown. The average hyphal diameter of all the isolates was within 5.01?11.12 μm. Among the 20 strains isolated from Chinese cabbage, 16 isolates and four isolates anastomosed with the AG-1 (IB) and AG-1 (IC), respectively. Twenty isolates tested were only virulent on foliage parts of Chinese cabbage leaves but were avirulent on stem parts of the plants. Based on the mycological characteristics and pathogenicity test on host plants, the fungus was identified as Rhizoctonia solani.

Key Words: Anastomosis group, Bottom rot, Brassica campestris subsp. pekinensis, Rhizoctonia solani