ANATOMICAL, GERMINATION AND IN VITRO STUDIES ON SHEA TREE (Vitellaria paradoxa C.F.Gaertn.) SEED

ABSTRACT In vivo and in vitro germination and regeneration studies were conducted on the development of Vitellaria paradoxa seedlings as an initial effort towards its domestication. However, to achieve this objective, the morphology and anatomy of the seeds were first studied because they influence germination. Although a smooth, brown coat encloses a V. paradoxa seed, it did not impose dormancy on the embryo. Transverse and longitudinal sections through the seed showed that the embryo is surrounded by latex- and fat-containing tissues which made its identification difficult. Thus, the embryo was identified by immersing transversely cut seeds in 1.0 % tetrazolium chloride (TTC) solution for 24 hours which stained it red. When V. paradoxa seeds of similar size were sown on nursery beds, the resulting seedlings developed through seven stages namely sprouting, pseudoradicle elongation, bulging, appearance of the shoot on the pseudoradicle, shoot elongation, emergence and seedling establishment. The pseudoradicle is the fused petioles of the two cotyledons and a transverse section through it revealed an outer sheath and lactiferous vessels surrounding a central hollow tube. Longitudinal section also showed the lactiferous vessels surrounding the central hollow tube in which the plumule moves through until it reaches the bulge of the pseudoradicle where it develops into a rudimentary shoot. The rudimentary shoot then protrudes from the pseudoradicle and grows upwards. Classifying seeds into three groups based on sizes and sowing them on nursery beds showed that seed size significantly affected days to germination and the morphology of the resulting seedlings. Large seeds germinated within one week after sowing with vigorous growth compared to small and medium seeds. Although the seedcoat of V. paradoxa never imposed dormancy, deshelling (removal of the seedcoat) significantly led to early germination and synchronous seedling emergence compared to those for intact seeds (control). In vitro culture of intact and deshelled seeds on Murashige and Skoog (1962) basal salts modified with 6-benzylaminopurine (BAP) produced no plantlets although 80 % of the deshelled seeds developed long pseudoradicles on a medium supplemented with lower concentration of BAP (1.0 or 2.0 mg/l). Similarly, the culture of TTC identified embryonic axes did not produce plantlets, but rather significantly long pseudoradicles were produced with BAP having significant effect on pseudoradicle development. Contrastingly, in vitro culture of excised rudimentary shoots on the same MS medium modified with BAP and naphthaleneacetic acid (NAA) produced plantlets with distinct shoots and leaves. Significant reduction in days to emergence of seedlings from deshelled seeds and successful in vitro plantlet development using rudimentary shoot explants will enhance nursery establishment of this economically important tree species for domestication and reafforestation programmes in sub-Saharan Africa.