Profiling of Rhizoctonia solani population for development of resistance against commonly used fungicides propiconazole and pencycuron in Punjab

To find out development of resistance against commonly used fungicides namely propiconazole and pencycuron, Rhizoctonia solani isolates were tested in vitro at different concentrations ie. 0, 1, 10, 25, 50, 100 and 250 ppm. Eighty five out of total 99 isolates showed sensitive reaction to propiconazole below 50ppm concentration in food poisoning technique, which indicated development of resistance in R. solani rice isolates. Ten R. solani isolates showed growth inhibition at 100 ppm and four isolates were least responsive and showed growth inhibition only at 250 ppm concentration. All isolates collected from different hosts like maize, potato, cotton and chilli were found to be sensitive in their reaction to pencycuron but only a few isolates of R. solani from rice showed inhibition at higher concentration of pencycuron. Pencycuron was found to inhibit large number of R. solani isolates at low doses when compared with propiconazole. The ED₉₀ values for most of the insensitive R. solani isolates were found to be in the range of 14 to 26 ppm for pencycuron and it was in the range of 27 to 78 for propiconazole. These preliminary studies indicated that there was development of fungicide tolerance in R. solani rice sheath blight isolates. Those isolates which were found sensitive to higher concentration of propiconazole (Tilt 25 EC) and pencycuron (Monceren 250SC) were evaluated under artificial inoculated conditions in the field on rice variety PR 114. At 0.1% spray concentration of Tilt 25EC, disease control was recorded in the range of 54.3 to 99.4% in different isolates, but when a double dose ie. 0.2% was applied under field conditions; very effective disease control was achieved in all these R. solani isolates as percentage decrease in sheath blight was above 93 per cent.

Bioefficacy of pencycuron was also tested against black scurf on potato when applied as tuber dip treatment before planting in soils infested with R. solani. This tuber dip treatment at 0.25% for 15 minutes was able to control black scurf of potato very effectively