ON THE EFFECTS OF EXPOSURE TO REALISTIC SULFUR-DIOXIDE LEVELS ON 6 HOST PATHOGEN COMBINATIONS

The effects of long-term exposure to a gradient of realistic concentrations of sulfur dioxide (up to 135 ppb) on six host/pathogen combinations were investigated under experimental conditions. No visible symptoms of injury were induced by the treatments on the host plants. The results obtained were quite conflicting and did not show an overall trend in the interactions. No significant effect of the pollutant gas was detected on Alternaria raphani on Raphanus sativus (radish) and Rhizoctonia solani on radish and Cucumis sativus (cucumber). A linear inhibition of parasitism was observed in Oidium tuckeri on Vitis vinifera (grape); a mixed effect (stimulation in the range 0-75 ppb, followed by an inversion of this effect in the 75-135 ppb range) was observed for the rust fungus Puccinia recondita on Triticum aestivum (wheat); a linear stimulation of Colletotrichum trifolii was assessed on Trifolium repens (clover). The mechanisms responsible for these interactions and the practical implications of these findings are briefly discussed