Comparative Evaluation of Paclobutrazol and Rhizobacterium Variovorax sp. YNA59 Effects on Mitigating Drought Stress in Chinese Cabbage (Brassica rapa ssp. Pekinensis)

Drought has severely impacted worldwide agricultural land, resulting in substantial yield loss and abiotic pressures in crops such as Chinese cabbage. Paclobutrazol (PBZ) and plant growth-stimulating bacteria have been extensively recommended to reduce a variety of stresses in crops. Considering these facts, we used PBZ and rhizobacterium Variovorax sp. YNA59, a microbe with potential plant growth-stimulating qualities, in Chinese cabbage under drought stress and non-stressed conditions, and we observed their impacts on morphological and physiological attributes. Our findings revealed a considerable improvement in total plant biomass growth after treatment with YNA59 (28%) and PBZ (8%) under drought conditions. In contrast, negative results of PBZ were observed under normal conditions, suppressing plant growth and reducing plant biomass. The increase in physiological parameters, such as chlorophyll content, relative water content, and photochemical efficiencies of PS II, were observed in YNA59-treated plants, followed by PBZ, especially under drought. Furthermore, drought stress significantly increased the endogenous phytohormone abscisic acid level, whereas PBZ and YNA59 inoculations significantly decreased it. Antioxidant analysis revealed that PBZ and YNA increased glutathione and catalase and decreased polyphenol oxidase and peroxidase levels. These findings suggested that rhizobacterium YNA59 could be more significant for conferring water stress in the Chinese cabbage plant than PBZ.