Comparative Effects of Externally Applied Glycinebetaine and Neem (Azadirachta indica) Leaf Extract on Plant Growth, Physio-Biochemical Characteristics and Yield Production of Canola (Brassica napus L.) Subjected to Drought Stress

A pot experiment was performed using two canola (Brassica napus L.) cultivars, cv. Super and cv. Sandal. The study was arranged in a randomized design with two different water deficit treatments [control (100% field capacity) and 60% field capacity], each replicated three times. After 30 days of water stress, plants were sprayed with 100 mM glycinebetaine (GB) and 5% neem (Azadirachta indica) leaf extract (NLE). Results showed that plant growth, measured by shoot and root lengths and weights, as well as leaf chlorophyll pigments, relative water content (RWC), total phenolics, soluble proteins, and ascorbic acid (AsA), decreased under water deficit stress. Conversely, chlorophyll a/b ratio, free proline, relative membrane permeability (RMP), GB, malondialdehyde (MDA), hydrogen peroxide (H2O2), and the activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) increased significantly. Foliar application of GB and NLE reduced MDA and H2O2 levels, while enhancing plant growth, chlorophyll content, soluble proteins, GB, phenolics, AsA, and enzyme activities in both cultivars. Among the two, cv. Super performed better than cv. Sandal under drought stress for most observed attributes. Therefore, although both GB and NLE effectively promoted growth and vital metabolic processes, NLE, being cost-effective and efficient, could be widely used to mitigate drought’s negative effects on various crop aspects, including canola.