Introduction
From an agricultural point of view, seeds are the starting point of all activities that lead to crop production. Today, agricultural machinery is one of the most important sources of environmental pollutants in mechanized farms and pollution caused by them can disrupt the germination process and plant growth. Therefore, in addition to a variety of environmental challenges, such as salinity and drought stress, contamination from agricultural machinery can also be added to germination and seedling growth as a threat.
 
Materials and Methods
Based on the gray correlation coefficient between the comparison series and the standard series, a relative series can be created. If γ (x_0, x_i) ≥γ (x_0, x_j), which indicates the degree of correlation between x_i and x_0, is greater than x_j and x_0; In this case, the relationship between potential causes and the optimal amounts of decision factors is shown. In the sense that a larger degree of connection has a smaller effect. Therefore, increasing the degree of prioritization of risk indicates the potential reasons that need to be improved. To analyze the risk of gaseous pollutants leaving the tractor exhaust, the treatment with the lowest gray correlation coefficient should show the highest risk priority. So that the highest degree of gray connection determines the best state of seed treatment. The aim of this study was to investigate the effect of pollutants from tractor exhaust in three different initial life, useful life and burn on canola seed germination. This factorial experiment was performed based on a completely randomized design with three replications. Experimental treatments include three different tractor life periods including initial life, useful life and wear as the first factor, and treatment for the duration of seeds exposed to tractor exhaust pollution including zero, 30, 60, 90, and 120 minutes as the factor. The second was considered.
 
Results and Discussion
The results showed that the highest values of root and stem length, germination rate coefficient, germination index, germination rate index and canola seed vigor were obtained from the absence of exhaust pollution; while the lowest amount of these traits was related to the treatment of exposure to contamination for 120 minutes and worn tractor. Conversely, the amount of seed protein and the activity of antioxidant enzymes catalase and peroxidase increased with increasing tractor wear and duration of contamination. Calculations based on gray theory showed that the treatment with a lower rank is the preferred treatment and has a lower risk according to all growth indices considered for rapeseed. In this study, zero time for different tractor lives without treatment, the risk was identified. Therefore, it is likely that increasing the exposure time to the tractor exhaust contaminant will gradually reduce the seed tolerance and poisoning threshold.
 
Conclusion
Gray's theory has shown that the duration of exposure is more important than the amount of contamination. The severity of exposure also varied depending on the degree of infection. Rapeseed seeds were more sensitive to contaminants from worn-out tractors than new tractors. The sensitivity of these seeds doubles the need to replace worn-out machines, service and repair tractors in a timely manner, use clean fuel, and use new or serviceable tractors.