Factors influencing physical dormancy and its elimination in two legumes

Introduction: Prosopis laevigata (Humb. & Bonpl. ex Willd.) M. C. Johnst, P. glandulosa Torr., Vachellia schaffneri (S. Watson) Seigler & Eibinger, V. pennatula (S. Watson) Seigler & Eibinger and V. farnesiana (L.) Wight & Arn. are characteristic species of semi-arid areas. Their seeds show physical dormancy and are naturally scarified by chewing, trampling, digestive tract of fauna, fire, or washing away during rains. Objective: To describe the morphology of the seed coat of three species of Vachellia and two of Prosopis, and to assess the chemical, mechanical and thermal scarification of seeds. Materials and methods: Chemical (HCl for 30, 120, 150 and 180 min), thermal (80, 100, 120 and 140 °C for 3 min) and mechanical (sanding) scarification were applied. Resistance to breaking by compression was measured. The experimental design was randomized complete blocks per species. Results and discussion: Seeds showed a layer of lignified and impermeable macrosclereids, but the aleurone layer could not be detected. Sanding allowed germination from 81.2 to 100 %. Chemical and thermal treatments showed no differences, only in the case of P. laevigata, chemical scarification for 180 min caused higher germination (72.5 %) compared to the control. Vachellia schaffneri seeds were more resistant to compression (669 N) and had more intense dormancy (0.83), while P. glandulosa had the lowest dormancy (0.42). Conclusions: Mechanical scarification was the best method to eliminate dormancy in Vachellia and Prosopis seeds.