Seed age and PEG priming enhance germination and seedling development of <i>Solanum torvum</i>

Abstract Solanum torvum (turkey berry) is an underutilized vegetable with nutritional, medicinal and agronomic importance. Its fruits are rich in iron, calcium, fibre and antioxidants, while the plant serves as a rootstock in grafting for tomato and eggplant due to its resistance to soil-borne pathogens and tolerance to abiotic stresses. Despite these benefits, large-scale cultivation is constrained by poor and inconsistent seed germination, largely attributed to seed dormancy and uncertainty regarding optimal seed maturity. This study aimed to identify the ideal physiological maturity stage for seed extraction and evaluate priming treatments to enhance germination and seedling development. A completely randomized design (CRD) with a 3 × 5 factorial arrangement was used. Fruits were harvested at 12, 14 and 16 weeks after-flower opening (WAF) for seed extraction. Seeds were extracted and subjected to priming with polyethylene glycol (PEG 6000), potassium nitrate (KNO ₃ ), gibberellic acid (GA ₃ ), sodium chloride (NaCl) or distilled water. Germination indices (percentage, mean germination time, rate, synchrony and uncertainty) and seedling growth parameters (height, chlorophyll content and biomass) were assessed. Seed maturity and priming significantly influenced germination and seedling vigour. Seeds harvested at 12 WAF and primed with 15% PEG were among the treatments with the highest germination percentage (100%), while seeds harvested at 16 WAF and primed with 0.5% KNO ₃ improved germination and synchrony, while GA₃ enhanced germination rate and vegetative growth. In contrast, NaCl treatments consistently resulted in low germination. PEG and GA₃ priming also improved root biomass and shoot elongation. This study demonstrates that both seed age and priming treatments are critical for overcoming dormancy and improving S. torvum propagation. While 12 WAF combined with 15% PEG produced the highest germination, 16 WAF is identified as the optimal harvest stage overall, as seeds at this stage exhibited consistently high germinability across the broadest range of priming treatments, whereas the 12 WAF response was achieved only under a specific, narrow osmopriming regime. Together with PEG priming as the most broadly effective treatment, these findings provide practical strategies to support domestication, enhance cultivation and expand the horticultural and medicinal use of S. torvum . Significance of the Study What is already known on this subject? Solanum torvum (turkey berry) is valued as a nutritionally rich fruit crop and as a disease-resistant rootstock for grafting tomato and eggplant. Despite this recognized value, the crop remains underutilized because of poor and erratic seed germination linked to physiological dormancy. Growers lack clear guidance on optimal seed harvest timing or effective priming protocols, even though such techniques are well established in related Solanaceae crops like tomato and pepper. What are the new findings? This study shows that seeds harvested at 16 weeks after flower opening gave the most consistent germination across a broad range of priming treatments. Seeds harvested earlier, at 12 weeks, can achieve exceptionally high germination, but only under a narrow, precisely calibrated PEG osmopriming regime. Priming agents were also found to act through distinct mechanisms, with GA₃ best for germination speed and growth, KNO ₃ best for synchrony, and PEG best for breaking dormancy in early-harvested seed, while NaCl was consistently detrimental. What are the expected impacts on horticulture? Collectively, this work strengthens the foundation for broader domestication and cultivation of this nutritionally and medicinally valuable but currently underutilized crop.