Culture condition and variation in the pathogenicity of Ustilagonoidea virens isolates causing false smut disease of rice

Abstract

False smut of rice caused by Ustilagonoidea virens was previously considered a minor disease of rice or rather a sign of bumper harvest, hence the disease was also known by the name Lakshmi disease. However, the disease is gaining much importance at present and is reported to occur in most of the rice growing areas of world in moderate to severe forms. Rice which is cultivated throughout the year in West Bengal is also observed to produce the symptoms of the disease every year in varying degree of severity. Effect of light and different temperature on mycelial growth of Ustilagonoidea virens in BOD incubator was tested. It was found that temperature of 28^oC and dark condition favors mycelial growth. Twelve different isolates of Ustilagonoidea virens collected from different districts of West Bengal were isolated in laboratory and tested for their variability in Pathogenicity using the susceptible rice variety Swarna (MTU 7029). 2 ml of inoculum suspension of each isolates were injected to rice plant at booting stage with three replications, whereas in control plants 2 ml of sterilized water was injected and percent grain infection was calculated and analyzed. All the inoculated plants were observed to produce typical false disease symptom with varying degree of severity indicating variation in pathogenicity among the isolates. Percent grain infection ranged from 1.461% to 7.936%. Isolate Uv5 from Alipudwar district was found to be significantly more virulent as compared to other isolates with 7.936% grain infection followed by isolate Uv4 (Jalpaiguri district) and Uv3(Nadia district)  with 5.050% and 4.557% grain infection respectively. Significantly lower infection was observed in isolate Uv9 collected from Coochbehar district with 1.461% grain infection followed by isolate Uv2 (North 24 Parganas district) and Uv12 (Hooghly district) with 1.912 and 3.279% grain infection.