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

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.