Effect of paclobutrazol and priformospora indica inoculation on antioxidant enzymes activity and morphological characteristics of green beans (Phaseoluse vulgaris L.) in chilling stress

To study the effect of Piriformospora indica and paclobutrazol (PBZ) as a plant growth regulator for inducing cold stress tolerance in green beans plant (Phaseolus vulgaris L.), a greenhouse experiment was performed as a factorial arrangement based on completely randomized design with three replications. Treatments consisted of three cold stress levels (control, three and six days cold stress at 5°C), two levels of fungi inoculation (non-inoculated and inoculated with P. indica) and three levels of PBZ (0, 40 and 80 ppm). P. indica was inoculated prior to planting and PBZ was sprayed five and six weeks after planting. Eight weeks after planting, green bean plants exposur to cold stress and some morphological and physiological growth characteristics and activity of antioxidant enzymes consist of catalase (CAT) and guaicol peroxidase (GPX) were measured. The results showed that the six days of cold stress particularly reduced aboveground shoot morphological traits such as height (approximately 2%) and GPX enzyme activity, but CAT activity was increased (about 1.3 times). Also CAT activity increased up to 2.16 times and 34% in three and six days cold stress compared to control and ameliorate the damage of chilling stress.. In all cold stress levels, 80 ppm of PBZ increased the CAT activity (50, 159 and 87). The results of this study confirmed the positive role of P. indica and PBZ on growth and improving plant resistance to cold stress in green beans.