Mechanical Scarification and Sucrose Priming Overcome Physical Dormancy in Caesalpinia spinosa (Tara) Seeds from the Peruvian Highlands

Abstract

Caesalpinia spinose (tara) is a leguminous tree native to the Peruvian Andes-Amazon region, valued for soil restoration and high tannin content. However, its large-scale propagation is constrained by physical seed dormancy caused by a hard and impermeable seed coat. This study evaluated six pre-germination treatments to break dormancy and enhance early seedling development under local agroclimatic conditions in Magdalena District, Chachapoyas, Peru. A completely randomized block design with three replicates was used. Treatments included mechanical scarification (seed coat incision with nail clippers) followed by soaking in a 10% sucrose solution for 2, 4, or 6 days (T1, T2, T3); mechanical dehulling with a mill followed by sucrose soaking (T4); hot water shock (T5); and an untreated control soaked in cold water (T6). Germination percentage, plant height, leaf number, and root length were recorded over approximately 8 weeks. Treatments T2 and T3 achieved the highest germination rates (90.7-92.5%), significantly outperforming all other treatments (p<0.001). These treatments also produced the tallest seedlings (up to 8.2 cm), the highest number of true leaves (nearly four per plant), and the longest roots (>15 cm). In contrast, hot water shock (T5) and mechanical dehulling (T4) resulted in low germination (~20%), while the control (T6) had only 5.15% germination. The combination of controlled seed coat incision and osmotic priming with 10% sucrose effectively overcomes physical dormancy, promotes vigorous seedling growth, and offers a simple, low-cost method suitable for nursery propagation and reforestation programs in the Peruvian Andes.