Comparative Effects of Polyalthia longifolia Leaf Extract and Synthetic Growth Hormones on the Nursery Development of Cocoa (Theobroma cacao L.) Seedlings

Background: Quality seedling production is fundamental to sustainable cocoa (Theobroma cacao L.) establishment, yet the cost and environmental burden of synthetic hormones have renewed interest in botanical alternatives. Aim: The study investigated the comparative effects of Masquerade tree (Polyalthia longifolia) leaf extract (MLE), indole-3-acetic acid (IAA) and a commercial synthetic auxin on the emergence and early nursery growth of cocoa seedlings. Study Design: A 2 × 3 factorial experiment (hormone source × application rate), plus an untreated control, was laid out in a completely randomised design with three replications. The treatment sources were indole-3-acetic acid and a synthetic auxin (each at 100 mg/L and 50 mg/L) and Polyalthia longifolia leaf extract (1 kg/3 L and 1 kg/5 L water), giving seven treatments: A100, A50, I100, I50, M5L, M3L and control (Cn). Place and Duration of Study: The study was conducted at the screen house of the Cocoa Research Institute of Nigeria (CRIN), Ibadan, south-western Nigeria, for three months. Methodology: Freshly harvested F3 Amazon cocoa beans (18 per treatment) were soaked in the respective hormone or extract solution for 24 hours before sowing; control beans were sown untreated. One bean was sown per bag, with six seedlings per treatment per replicate (42 per replicate; 126 total). Emergence was recorded at 14, 18, 22, 26 and 30 days after sowing (% of beans sown). Plant height, leaf number, stem diameter and leaf area were measured every four weeks from 4 to 12 weeks after sowing (WAS). At 12 WAS, seedlings were destructively sampled: taproot length and shoot and root dry weights (oven-dried at 70°C to constant weight) were recorded. Results: Synthetic auxin consistently depressed emergence (as low as 11.1% at 14 days after sowing) and suppressed vegetative growth relative to the control, indicating supra-optimal auxin stress. MLE and IAA produced growth comparable to, and at several stages exceeding, those of the control, with MLE giving the highest leaf area (83.65 cm²) and dry shoot weight (4.07 g) at 12 weeks. Root traits were largely unresponsive to treatment. Conclusion: These findings indicate that Polyalthia longifolia leaf extract is an effective, low-cost organic alternative to synthetic auxin for raising vigorous cocoa nursery seedlings, and its use at 1 kg/3 L is recommended over high-concentration synthetic auxin.