Biological Characteristics and Anastomosis Groups of Rhizoctonia solani Associated with Chinese Cabbage Brown Rot in Lanzhou

doi:10.11924/j.issn.1000-6850.casb18040138

Abstract

Abstract: To provide information for the disease control, 8 strains of Rhizoctonia solani isolated from diseased mini Chinese cabbage in Honggu and Yongdeng of Lanzhou were used for testing morphology, cardinal temperature, pathogenicity, fungicide sensibility, and anastomosis group identification. The optimal growth temperatures were evaluated by temperature gradient method, and microsclerotia forming status was observed in the meantime. Numbers of nuclei were observed by staining with safranin O and KOH. The pathogenicity was determined by inoculation to detached leaves. Fungicide sensitivity of R. solani strains was assessed by amendment plate method, autoclaved PDA media were amended prior to pouring with 5 different fungicides. Phylogenetic tree was established based on rDNA- ITS (ITS1- 5.8S- ITS2) sequences of test strains. The results showed that: the optimal growth temperature of all other strains was 25℃, except Rh-5, whose was 15-20℃. All tested strains could produce microsclerotia cultured on PDA plate at 5-30℃. Numbers of nuclei of strain Rh-1- Rh-8 was 3-6, 6-14, 3-18, 4-15, 3-10, 4-10, 3-10 and 4-8, respectively. Detached leaves of mini Chinese cabbage inoculated by strain Rh-2-Rh-6, infected in 2 d at 20℃, had the incidence of 75%-100% in 7 d after inoculation; the leaves inoculated by strain Rh-1-Rh-8, infected in 1-3 d at 25℃, had the incidence of 25%- 100% in 7 d after inoculation; the leaves inoculated by strain Rh-1, Rh-7 and Rh-8, infected in 2-3 d at 28℃, had the incidence of 100% in 7 d after inoculation. Under test concentrations, the sensitivity of the eight tested strains of R. solani to five fungicides was successively: carbendazim> mancozeb> procymidone> triadimefon> difenoconazole. Rh- 1 aligned with R. solani AG 4 HG- II, other test strains (except Rh- 6, since sequencing failure) aligned with R. solani AG 2-1. According to rDNA-ITS (ITS1-5.8S-ITS2) sequences analysis of the test strains, the pathogens causing mini Chinese cabbage brown rot in Lanzhou include R. solani AG 2-1 and AG 4 HG-II. Tested strains of R. solani show the diversified characteristics in colony morphology, numbers of nuclei, optimal growth temperatures, growth speeds, infection temperatures, pathogenicity and fungicide sensitivity. At the tested concentrations, all strains show higher sensitivity to carbendazim and mancozeb (inhibition rate≥ 80%), suggesting that these two fungicides could be used in field trials on control of mini Chinese cabbage brown rot disease.

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