Difference in germination rate of Baobab (Adansonia digitata L.) provenances contrasting in their seed morphometrics when pretreated with concentrated sulfuric acid

Baobab (Adansonia digitata L.) is considered an under-utilized species even though it is an economically useful tree often used daily in the diet of rural communities in West Africa. Baobab seeds do not germinate immediately after they are released from ripe fruits due to dormancy imposed by hard seed coats. A study was carried out to assess (1) best soaking duration for seed pretreatment in concentrated sulfuric acid (96%) to increase germination rate of baobab seeds; and (2) relationships between seed morphometric traits as varying with provenances and germination rate. Length, width, thickness and weight of baobab seeds collected from seven provenances spread across an agro-climatic gradient of 250 to 1100 mm in Senegal were first measured. Then, seeds were pretreated by soaking them in distilled water (control) and concentrated H2SO4 (96%) for 12 min, 30 min, 1, 3, 6, 8 and 12 h, respectively. Pretreated seeds were placed on moistened filter paper in 16 cm diameter Petri dishes in an incubator at 25°C for germination. Highest germination rates were obtained for seeds that had been soaked for 6, 8, and 12 h in concentrated sulfuric acid as evidenced by germination rates at 3, 7 and 10 days after sowing, respectively, although we did not find any significant differences among these three soaking durations. Significant variation among provenances was observed in seed morphology traits and seed germination rates. Highest seed trait and germination rate values were observed for Sudano-Sahel and Sudan agro-ecological provenances. This study has shown a significant variation in these characters mainly related to geographical origin. Overall, results could be useful for a further domestication and integration of baobab in the agro-productive system in Senegal as knowledge on seed germination requirements is a critical factor in seedling production for subsequent planting and reforestation.   Key words: Agro-ecology, baobab seed, dormancy, germination physiology, germination rate, non-timber forest product (NTFP), under-utilized species.