Effects of chemical substances on melanin formation of Rhizoctonia solani AG-1 IA

Objective  Rice sheath blight, caused by Rhizoctonia solaniAG-1 IA, is an important fungal disease. The purpose of this study was to determine the relationship between external culture conditions and melanin formation of R. solani AG-1 IA.

Method  The effects of four different treatment groups, i. e. chemical fertilizer group 500 μg/mL K₂SO₄, NaH₂PO₄, CO(NH₂)₂, metal ion compound group(5 μg/mL CuSO₄, FeSO₄, ZnSO₄), antioxidant group (5 μg/mL quercetin, morin, vitamin C) and control group (300 μg/mL hyoscyamine, 50 μg/mL catechol, water), on the mycelial growth rate, sclerotia number, sclerotial fresh weight and dry weight as well as melanin content of R. solani AG-1 IA were determined by measuring mycelial growth rate and ultraviolet spectrophotometry.

Result  Chemical fertilizer 500 μg/mL K₂SO₄, NaH₂PO₄, CO(NH₂)₂, metal ion compound (5 μg/mL CuSO₄, ZnSO₄), antioxidant(5 μg/mL quercetin, morin, vitamin C) and catechol(50 μg/mL) could promote the formation of melanin. Under the treatment of 500 μg/mL CO(NH₂)₂, the melanin content of R. solani AG-1 IA was the highest (113.2 mg), while under the treatment of 300 μg/mL hyoscyamine, the melanin content of R. solani AG-1 IA was the lowest (37.4 mg).

Conclusion  Melanin formation is not necessarily related to mycelial growth and sclerotial development, i.e. the chemical substances, which have inhibitory effect on mycelial growth and sclerotial development, might have no inhibition on melanin formation. The results of this study provide a basis for understanding the mechanism for prevention and control of rice sheath blight.