Plants Response to Diseases in Sulphur Dioxide Stressed Environment

Development of plant diseases depends largely on environmental factors besides the host susceptibility. Contamination of air due to release of phytotoxic pollutants such as SO2 may influence the composition of environment and consequently the host parasite relationship. SO2 enters in plants through open stomata, the gas reacts with moisture and is converted into acid. The acidic ions cause toxicity to the plant tissue as well as to pathogenic spores especially those present on the foliage. There are considerable reports, which indicate that plants show varied response to foliar pathogens under SO2 stressed air. In addition, root-attacking pathogens, such as plant nematodes may also be influenced due to host mediated effects of SO2. Generally, suppressive effects of the gas on pathogens have been reported at the concentrations above 200-300 ppb SO2. However, some studies have also revealed greater severity of diseases on plants exposed to lower concentration of the gas in the range of 50-100 ppb. The present paper has critically analyzed the information available on the topic and has attempted to provide explanation to the varied response of plants to pathogens under SO2 polluted environments and the mechanism involved in the interaction.