en Environmental Health, Sciences, and Engineering Environmental Health, Sciences, and Engineering پژوهشي Original Article <div style="text-align: justify;"><span style="font-size:14px;"><span style="font-family:Times New Roman;"><strong>Background:</strong> This research was conducted to evaluate the effect of <em>Piriformospora indica</em> (<em>P.indica</em>), drought, and soil salinity stress on diesel oil biodegradation in a soil that was polluted with Pb and Cd.<br> <strong>Methods:</strong> Treatments consisted of corn inoculated with <em>P.indica</em> and white clover intercropping system under the salinity (3.1 and 6 dS/m) and drought (normal and intensive) stress which cultivated in the Pb and Cd polluted (naturally) soil which simultaneously contaminated with diesel oil at the rates of 0 and 4 % (W/W). After 10 weeks, plants were harvested and the diesel oil biodegradation in the soil was determined. In addition, the soil microbial activity, the APX and POX enzyme activates were measured.<br> <strong>Results:</strong> Diesel oil biodegradation significantly increased in the soil under cultivation of plants inoculated with <em>P.indica</em>, while it significantly decreased under salinity and drought stress by 12.9 and 9.8%. However, the intercropping system had positive effects on increasing the soil microbial activity and biodegradation of diesel oil in the soil.<br> <strong>Conclusion:</strong> Corn inoculation with <em>P.indica</em> significantly affected the biodegradation of diesel oil in the heavy metals and petroleum hydrocarbon polluted soil that is under salinity and drought stress.</span></span></div> Diesel oil, P.indica, Salinity, Drought, Biodegradation, 173 181 http://jhehp.zums.ac.ir/browse.php?a_code=A-10-230-8&slc_lang=en&sid=1 Amir Hossein Baghaie ambaghaie@yahoo.com 100319475328460011484 100319475328460011484 Yes Department of Soil Science, Arak Branch, Islamic Azad University, Arak, Iran.