Effect of seed size and pre-treatment methods of Bauhinia thonningii Schum. on germination and seedling growth

Abstract

Bauhinia thonningii Schum. a multipurpose tree species found in the savanna wood lands is a priority tree species for conservation in Malawi. The different plant parts are used in traditional medicine to treat different ailments. However, the seeds are dormant and the tree species remain undomesticated. A study was conducted to evaluate the effect of pre-sowing seed treatment and seed size on germination and seedling growth of B. thonningii in a nursery at Bunda College. Seeds grouped into two categories: small (1 to 5 mm) and large (>5 to 10 mm) were subjected to five main pre-sowing seed treatment methods namely; soaking in cold water for 12 h, soaking in hot water for 10 min, nicking, soaking in potassium nitrate (0.2%) for 10 min and soaking in concentrated hydrochloric acid (0.3 M) for 5 min, and a control where seeds were sown without any treatment. The results showed that the combination of nicking and large seeds produced the highest (100%) germination and highest height and diameter growth. Hot water treatment was also observed to be effective in both seed sizes producing 40 and 53.3% germination for small and large seeds, respectively. The increased seed germination and height for physically scarified seeds through nicking suggest that seed dormancy in B. thonningii is mainly due to relatively hard seed coat which renders the seed testa impermeable to water and gases required for germination process.

Key words: Bauhinia thonningii, dormancy, germination, pre-sowing treatment, seed size.