Effect of environmental factors on rust disease severity and rate of spread of bach (Acorus calamus L.) in West Bengal, India

Bach (Acorus calamus L.) is an important medicinal plant found predominantly in the Himalayan and sub-Himalayan regions of India, generally known to cure several diseases like fever, asthma, and bronchitis (Reddy et al., 2018). Like other crops, bach is also affected by several biotic and abiotic factors leading to a decline in the yield, out of which rust disease caused by Uromyces spp is one of the major biotic factors. The effect of weather factors like temperature, relative humidity, rainfall and bright sunshine hours on the incidence and development of rust disease was studied under field condition in West Bengal, to correlate the rust disease severity with weather parameters. Stepwise multiple regression analyses for prediction of the rust disease severity of bach revealed that maximum temperature exhibited highly significant positive contribution on the Percent Disease Index (PDI) increment and was identified as critical while the minimum temperature exhibited highly significant contribution on the rate of spread (ROS) and was identified as critical. Comparison of weather parameters with the rate of spread of disease revealed that the range of maximum temperature 23-26 °C, minimum temperature 8-10 °C, maximum relative humidity 93-97%, minimum relative humidity-50-68%, followed by low rainfall and bright sunshine hour of 8-9 hours were suitable for higher rate of disease spread.