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

Abstract

Organic Agriculture Division, National Academy of Agricultural Science, Rural Development Administration, Suwon 441-707, Korea(Received on November 15, 2013; Revised on November 25, 2013; Accepted on November 26, 2013)This study was conducted to determine the occurrence of leaf rot and leaf ring spot, caused by Rhizoctoniasolani in Chinese cabbage under seedling nursery and cultivation greenhouses. Symptoms of leaf rot and leafring 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 Chinesecabbage. 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 ofsmall, circular necrotic ring spots with gray color, 1.4 −3.0 mm in diameter, accompanied by secondary rotlesions with large irregular borders of leaves. The color of mycelial mat of 20 isolates was dark brown andlight brown. The average hyphal diameter of all the isolates was within 5.01 −11.12 µm. Among the 20 strainsisolated 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 wereavirulent on stem parts of the plants. Based on the mycological characteristics and pathogenicity test on hostplants, the fungus was identified as Rhizoctonia solani. Keywords : Anastomosis group, Bottom rot, Brassica campestris subsp. pekinensis, Rhizoctonia solani