Abstract
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.
Highlights
Baobab (Adansonia digitata L.) is an African fruit tree species belonging to Malvaceae family
The present study suggests that concentrated sulfuric acid (96%) disrupts the seed coat and facilitates rapid germination
Seed germination increased with increasing soaking durations while the highest germination rates were recorded for provenances of the more humid zones (Sudano-Sahel and Sudan) and were obtained when baobab seeds were soaked in concentrated sulfuric acid for 6, 8 and 12 h
Summary
Baobab (Adansonia digitata L.) is an African fruit tree species belonging to Malvaceae family. Under adequate aeration and temperature conditions, nondormant plant seeds need only access to water to be able to germinate after putting them in the soil. Even in such optimal conditions, baobab seeds often remain several weeks in the soil before germinating (Gebauer et al, 2002; ICUC, 2006, 2010). Genetic variation among and within baobab (A. digitata L.) provenances in seed germination and seedling growth has been reported in selected natural populations in Malawi (Munthali et al., 2012). For reforestation and enhancement of A. digitata seedling production, there is a need to understand the basic requirements for promotion of baobab seed germination in general and from different provenances. We report results on variations in seed morphometric characteristics and seed germination related parameters among seven provenances of A. digitata and their mutual relationships with climatic and environmental factors such as temperature, altitude, and humidity
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