Overcoming seed dormancy of Pterocarpus angolensis DC. (umbila) and the evaluation of different substrates in seedling establishment

Abstract

Pterocarpus angolensis DC. is a premium timber from the Fabaceae family, found in the Miombo woodlands of sub-Saharan Africa. This study aimed at evaluating different scarification methods (chemical, mechanical and thermal) of seeds and the establishment of seedlings. To overcome dormancy, the seeds were subjected to nine treatments: immersion in water – control (T0); immersion in 6% hydrogen peroxide (H₂O₂) in three periods, 10 minutes (T1), 15 minutes (T2) and 20 minutes (T3); mechanical scarification with sandpaper (T4); immersion in hot water at 100 °C for 10 minutes (T5); immersion in hydrochloric acid (HCl) for 60 minutes (T6); immersion in sulphuric acid (H₂SO₄) for 25 minutes in three concentrations, 30% (T7), 60% (T8) and 90% (T9). For the establishment of seedlings, four substrates were tested: T1, sand + litter soil; T2, sand + boskompost + litter soil; T3, humus + sand + litter soil and T4, humus + sand + boskompost + litter soil. The results showed that treatments T8 (60% H₂SO₄ for 25 minutes), T1 (6% H₂O₂ for 10 minutes), T3 (6% H₂O₂ for 20 minutes) and T7 (30% H₂SO₄ for 25 minutes) presented the highest germination percentages with 96%, 87%, 86% and 82%, respectively. Treatments T7 (30% H₂SO₄ for 25 minutes), T8 (60% H₂SO₄ for 25 minutes) and T9 (90% H₂SO₄ for 25 minutes) showed higher germination speed. Regarding seedling establishment, substrate T1 (sand + litter soil) promoted the best results in all growth parameters evaluated. This study contributes to a better understanding of the methods of breaking dormancy P. angolensis seeds and those of increasing germination rates, and well as the influence of substrates on the long-term survival of seedlings of this species in forests.