Fruit waste-derived extracts as natural biostimulants for seed priming in maize and common beans

Abstract

Seed germination and early seedling vigour are critical for successful crop establishment, particularly in stress-prone, resource-limited semi-arid agroecosystems. This study evaluated aqueous extracts prepared from market-discarded overripe or spoiled fruits of papaya (Carica papaya L.), banana (Musa spp.), lemon (Citrus × limon (L.) Osbeck), and pineapple (Ananas comosus (L.) Merr.) Merr as natural seed priming agents for maize (Zea mays L.) and common bean (Phaseolus vulgaris L.). Certified seeds meeting Tanzania Official Seed Certification Institute (TOSCI) standards were primed for 4–6 h in 1:4 (v/v) diluted extracts and compared with hydropriming (distilled water) and PEG-6000 osmotic control under controlled laboratory conditions (25 ± 2 °C). The extracts were characterized for key physicochemical properties (pH 4.2–5.7 and total soluble solids 4.6–7.0°Brix), with papaya and banana extracts showing qualitative proteolytic enzyme activity. Papaya and banana extracts consistently outperformed other treatments, increasing final germination percentage to 90–94% in both crops (vs. 74–76% in controls) and reducing mean germination time by 48–61%. Banana-primed maize seedlings produced the longest shoots (14.1 cm) and roots (7.9 cm), while papaya-primed common bean seedlings achieved the highest shoot (13.4 cm) and root (8.2 cm) lengths. Seedling vigour indices followed the same ranking (papaya ≈ banana > pineapple > lemon > control). These superior effects are consistent with the documented richness of papaya and banana extracts in phytohormones (gibberellins, auxins, cytokinins) and proteolytic enzymes (papain, bromelain). These findings demonstrate that low-cost, locally abundant fruit-waste extracts can serve as effective, sustainable alternatives to synthetic priming agents. The approach is particularly promising for smallholder farming systems in semi-arid East Africa, as it supports circular bioeconomy principles by valorising market-discarded produce into accessible biostimulants.