CALLUS FRIABILITY AND SOMATIC EMBRYOGENESIS IN HEVEA-BRASILIENSIS

The influence of plant growth regulators, sucrose, calcium and various macronutrient media on callus friability and somatic embryogenesis wa s investigated in Hevea brasiliensis Mull. Arg. Friable and embryogeni c calli were spontaneously formed in two rubber tree clones (PR 107 an d RRIM 600) on the Medium for Hevea (MH), with 3,4-dichlorophenoxyacet ic acid (3,4-D), kinetin and sucrose, while compact embryogenic calli were enhanced in three other clones (PB 260, PB 235 and GT1). Callus f riability was enhanced in clone PB 260 when the concentration of one g rowth factor (3,4-D or kinetin) was reduced from 4.5 muM to 0.45 muM d uring the first culture, or when high sucrose or calcium levels 351 mM and 12 mM, respectively) were maintained during subcultures. The diff erent macronutrient media did not alter callus texture but only use of MH and Murashige and Skoog (MS) media led to somatic embryogenesis. F riable calli obtained by modifying the auxin/cytokinin balance lost th eir embryogenic potential. In contrast, those obtained on media with h igh sucrose or calcium concentrations were mainly composed of embryoge nic cells embedded in a mucilaginous matrix. Such calli could be of po tential interest for establishing embryogenic cell suspension cultures .