Physiological and Morphological Effects of Paclobutrazol Doses on Early Development of Canola (Brassica napus L.) Seedlings

In this study, the effects of different doses of paclobutrazol (PBZ) on early seedling development of rapeseed (Brassica napus L.) were investigated by measuring some physiological and morphological parameters. PBZ, a plant growth regulator known for its ability to inhibit gibberellin biosynthesis, was applied by spraying on the leaf and stem surfaces of plants at five different concentrations (0, 150, 300, 450, 900 ppm) to evaluate the effects on growth parameters, chlorophyll content, relative water content (RWC), leaf area, shoot and root properties, electrolyte leakage and leaf extract properties (pH and electrical conductivity) of rapeseed seedlings. The results showed that PBZ had different dose-dependent effects on rapeseed seedlings, causing significant reductions in leaf area and volume at high doses. Although PBZ had no significant effect on chlorophyll content, an improvement in water retention (RWC) was observed at 300 ppm. Furthermore, PBZ doses of 150–300 ppm enhanced membrane stability, as indicated by reduced electrolyte leakage. In contrast, higher doses caused morphological abnormalities such as leaf thickening and deformation. While doses of 300 ppm and below were found to be appropriate, PBZ application during the seedling stage had minimal impact on overall plant development.However, the effects of PBZ applications during later growth stages on drought and heat stress should be further investigated.