SHOOT ORGANOGENESIS AND PLANT-REGENERATION IN MULBERRY (MORUS-BOMBYCIS KOIDZ) - FACTORS INFLUENCING MORPHOGENETIC POTENTIAL IN CALLUS-CULTURES

Regeneration of multiple shoots via callus induction and organogenesis was achieved in mulberry (Morus bombycis). Pre-soaked internodal expl ants in 4.4-8.9-mu-M benzyladenine (BA) formed callus on Linsmaier and Skoog's medium containing 2,4-dichlorophenoxyacetic acid (9.05-mu-M), alpha-naphthaleneacetic acid (2.85-mu-M) and BA (2.2-mu-M). Explants soaked for 48 to 72 h in low levels of BA produced loose and nodular c allus that showed regeneration ability. Calluses developed adventitiou s shoot buds within 3-4 weeks on medium containing BA (8.9-mu-M). Fift een-week-old calluses developed fewer shoot buds than five-week-old ca lluses, indicating a decrease in morphogenetic potential with increasi ng duration of callus cultures. Semi-thin section microscopy was used to evaluate incapability of sustained regeneration. Development of nor mal shoot bud primordia, due to sub-surface reorganisation, was high i n young calluses. The decline in the frequency of shoot bud primordia formation with callus ageing is due to reduced cell division activity in epidermal as well as sub-epidermal layers.