MORPHOLOGICAL RESPONSE OF WITCHWEED (STRIGA-ASIATICA) TO IN-VITRO CULTURE

Excised sorghum root segments (5-10 mm in length) were cultured for 50 d in four different liquid media containing mineral salts, vitamins, amino acids, glucose, and IAA. The roots were removed and the remaining medium was solidified with an equal volume of warm 1.6% water agar. Dry unconditioned or conditioned Striga asiatica seeds were transferred to the medium. Some of the seeds germinated and developed into parasitic-type seedlings. These seedlings had haustoria, tubercles, dense root hairs, branched shoots, and multiple shoot-borne adventitious roots. The plumule pole developed into a shoot, but the radicle pole displayed only rudimentary development. On the same media, but which had not previously been used to grow sorghum roots, the seedlings displayed a well-developed radicle-derived root system, but the plumule did not grow. Shoots began to appear on the roots only after 35-50 d of culture. These seedlings had no haustoria, no tubercles, few or scattered root hairs, no shoot-borne adventitious roots and few shoot branches, and appeared to be non-parasitic-type seedlings. Shoots grew in a medium supplemented with IAA and kinetin, but did not in a medium containing NAA plus IBA. On replacement of glucose and IAA with sucrose and 2,4-D, respectively, Striga seeds germinated, and the heart-shaped embryos dedifferentiated into calli. The calli have been maintained by subculturing for over 9 months. The results demonstrated that a host signal, in addition to those for germination and haustorium formation, is required for further development. Moreover, morphogenesis of cultured S. asiatica is influenced by exogenous growth regulators.