Seed quality parameters and optimum pre-sowing treatments for <i>Adansonia digitata</i> L. seed germination in Northwest Ethiopia

Adansonia digitata L. is a large tree with diverse socioeconomic and ecological benefits in the dryland ecosystems. Despite its significance, the natural habitat and its survival are under threat, particularly manifested by the poor regeneration and lack of juvenile individuals. Domestication and cultivation of this key species requires understanding of its seed germination ecology. This study characterizes the fruit morphology, examines seed quality parameters and determines the best pre-sowing treatments for optimum seed germination of Adansonia digitata. The International Seed Test Association’s (ISTA) standards were used for the seed quality parameter tests. Further, the germination experiment was conducted in a completely randomized design (CRD) with four replications of five pre-sowing treatments (control, H2SO4, nicking, cold water and hot water). Adansonia digitata from the Metema provenance exhibit variations in the fruit morphological traits with mean values of 20.11 ± 3.24cm length, 10.71 ± 1.49cm width, 316.8 ± 112.17g weight, 123.03 ± 53.61g seed weight, 30.49 ± 11.25g pulp weight, and 194.43 ± 102.53 seeds per fruit. Furthermore, the viability, purity, and moisture content of Adansonia digitata seeds were 94 ± 0.02%, 95.5 ± 0.71% and 5.63 ± 0.11%, respectively. Regarding the thousands seed weight, 1978–1995 seeds were contained in a kilogram of pure Adansonia digitata seed. Thus, from 1875 to1919, seedlings could be produced from one kilogram of pure A. digitata seeds. The germination trial revealed that Adansonia digitata seeds have a strong dormancy problem, depicted by no (0%) germination in 45 days with the controlled group and 3.75 ± 2.5% with the cold water pre-sowing treatment. Statistically significant variation (P = 0.001) was observed in Adansonia digitata seed germination percentage, germination index, germination mean time, and germination period among the tested pre-sowing treatments. Nicking resulted in the highest germination (91.25 ± 4.8%), followed by H2SO4 (85 ± 5.8%) and hot water pre-sowing treatment (35 ± 4.1%). However, the cold water pre-sowing treatment gave the lowest germination result. Generally, the study highlighted the strong physical dormancy of Adansonia digitata seeds, which resulted from the hard seed coat. Hence, nicking is recommended as the best pre-sowing treatment for enhanced germination of Adansonia digitata. The findings of the current study have implications for the conservation and domestication efforts of this tree species and consequently, for the promotion of its ecological and economical benefits.