Somatic embryogenesis and organogenesis in callus cultures of a tree legume--Albizia richardiana King

Hypocotyl explants of 1 and 10 mm lengths were excised from 12-day-old in vitro-grown seedlings of Albizia richardiana. The larger pieces, after 40 days of culture, developed shoots along with green calli on B5 + BAP (10(-7)-10(-5)M), while the smaller segments produced only green calli on B5+BAP (10(-7)-10(-4)M) medium. Some of the green calli turned morphogenic and started producing somatic embryos with the 2nd sub-culture and shoots from 7th sub-culture onwards. Calli retained the morphogenic potential even after repeated sub-culturing for over two years. The number of embryos in an embryogenic culture varied from 2 to 20 per callus mass of 5-6.5 cm(3). Sucrose at the 2% level in MS medium was optimal for embryogenesis while 4% was optimal for shoot bud differentiation. Higher levels of sucrose (6-10%) caused browning of green calli and also inhibited differentiation into embryos and shoot buds. By selective sub-culturing of 0.1 cm(3) pieces of embryogenic calli on MS+10(-5)M BAP, 46% of the cultures produced somatic embryos. The latter germinated into plantlets on Knop's medium.