Plant regeneration through somatic embryogenesis from immature and mature zygotic embryos of Musa acuminata ssp.

Banana and plantains (Musa spp.) form a major staple food for millions of people living in the tropics and subtropics. The two wild progenitors of edible bananas viz., Musa acuminata and Musa balbisiana produce seeds freely while most of the edible clones are seedless, with a few notable exceptions such as ‘Pisang Awak’ sub-group (ABB; Simmonds 1966). Owing to the parthenocarpic and sterile nature of edible bananas, strategies aimed at banana improvement are extremely complex and time consuming. Therefore, to complement conventional breeding programs new strategies need to be developed utilizing tissue culture and genetic engineering technologies. Limited and variable seed germination exhibited by Musa spp. (Simmonds 1952 and 1959) may be due to seed mortality caused by lack of endosperm. Embryo culture prior to embryo abortion has the potential to rescue many useful crosses. Therefore, in vitro embryo culture represents a convenient tool for improving recovery of hybrid germplasm in a short time (Cox et al.1960).A simple and efficient protocol has been developed for in vitro regeneration of M. acuminata ssp. burmannica (AA) plants. Somatic embryos were produced when immature and mature zygotic embryo explants were cultured on Murashige and Skoog medium supplemented with plant growth regulators 2,4-dichlorophenoxyacetic acid; (2,4-D), picloram or benzyl adenine and indole acetic acid. In general, immature embryos responded better than mature embryos. Callus proliferation was highest in medium supplemented with 2,4-D (4.5 μM). Subsequent transfer of callus to fresh medium produced rapidly proliferating embryogenic calli. Embryogenic calli were maintained in complete darkness for 15 d followed by cycles of 8 h dark and 16 h light, under white fluorescent lamps with a light intensity of 3,000 lm/m2 and at temperature of 28 ± 2°C. Regeneration of embryogenic calli into plantlets was higher for immature embryos (76.6%) than for mature embryos (50.6%). This plant regeneration protocol using mature or immature zygotic embryos, via somatic embryogenesis, has significant potential to improve germination efficiencies of hybrid progenies used in conventional breeding strategies. Furthermore, tests on seed storage showed that seed viability rapidly decline after harvesting and was negligible after 9 mo of storage. This indicates using freshly harvested seeds as explant material is necessary for maximizing the tissue culture response