INFLUENCE OF EXOGENOUS HORMONES ON SOMATIC EMBRYOGENESIS IN HEVEA-BRASILIENSIS

Generating somatic embryos from the inner teguments of Hevea seeds is difficult. Like other ligneous plants, the rubber-tree is generally considered to be recalcitrant with regard to somatic embryogenesis. In this paper we show that when conventionally used amounts of both 3, 4-dichlorophenoxyacetic acid (3, 4-D) and benzylaminopurine (BAP) are reduced by 2-4 times and when the length of exposure to these hormones is also reduced, the embryogenic capacity of calli increases without affecting callogenesis. The germination of several embryos and plantlets was obtained. We conclude that an excess of auxin and cytokinin in the medium, even of a weak auxin such as 3, 4-D, and the prolonged exposure to these hormones suppress the embryogenic capacity of the callus. © 1991 Annals of Botany Company.