Improving germination and early seedling growth of marula (Sclerocaya birrea (A.Rich.) Hochst.) through hydro-priming

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Introduction Despite the socio-economic and nutritional significance of marula ( Sclerocarya birrea (A.Rich.) Hochst.) in sub-Saharan Africa, its domestication and commercial cultivation are constrained by poor seed germination due to a hard, impermeable seed coat. This study aimed to determine the most effective hydro-priming duration for enhancing germination and early seedling growth of marula under controlled and field conditions. Methods Separate pot (laboratory) and field experiments were conducted using a completely randomised design (CRD) with four replications. Mature marula seeds were subjected to four hydro-priming durations: no soaking (control), soaking for 24 h, 48 h, or 60 h in distilled water. Data were collected on germination percentage, germination index, seedling height, root length, number of secondary roots, and vigour index. Two-way analysis of variance (ANOVA) was performed, and means were separated using Fisher’s protected least significant difference (LSD) test at p < 0.05. Results Hydro-priming duration had a highly significant (p < 0.001) effect on germination percentage in both experiments. In the pot experiment, the highest germination (45%) was achieved after 70 days with 48 h of priming, while in the field experiment, 60 h of priming produced the highest germination (77.5%) after 45 days. Germination index and root length were also significantly (p < 0.05) affected by priming duration. The longest roots were recorded from seeds primed for 60 h in both the pot (9.46 cm) and field (16 cm) experiments. Significant method × treatment interactions (p < 0.01) were observed for final germination, secondary root number, germination index, and vigour index, indicating environment-specific optimal priming durations. Discussion Extended hydro-priming (48–60 h) consistently enhanced metabolic activation, resource mobilisation, and subsequent seedling vigour, particularly under field conditions. The superior performance of field-sown seeds was attributed to both the longer storage duration (15 months) and favourable summer growing conditions. The contrasting proliferation of secondary roots under pot conditions suggests a phenotypic adaptive response to resource limitation. It is concluded that hydro-priming is an effective, low-cost technique to improve marula seed germination and early seedling establishment. For direct field seeding, a 60-h hydro-priming treatment is recommended, whereas 48 h is optimal for containerised nursery production. Planting during the summer months (October–November) is advised to maximise germination potential.

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