INVITRO ROOT CULTURE - A NOVEL-APPROACH TO STUDY THE OBLIGATE PARASITE STRIGA-ASIATICA (L) KUNTZE

We report the development of a novel approach to study haustorial formation in Striga asiatica based upon in vitro root culture. Previous studies have used intact radicles of Striga seedlings. The potential advantages of our root culture system over the use of radicles are that more plant material is available for biochemical and molecular genetic analysis and possible confounding effects of other contaminating organisms are eliminated. Striga roots cultured in a Gamborg B5 salts medium containing indole-3-acetic acid (22.8-mu-M) increased in size and proliferated lateral roots. We demonstrate that cultured lateral roots are capable of haustorial formation within 24 h of treatment with a haustorial initiation factor 2,6-dimethoxy-p-benzoquinone (2,6-DMBQ). Cultured root tips developed haustoria when in contact with a solid medium that contained 2,6-DMBQ. The solidity of the medium was observed to influence the extent of haustorial development. Haustoria formed on cultured roots appeared morphologically similar to those formed by Striga radicles within a similar time period and were 5-10-fold larger. We also show that root cultures can be used as an explant source for regeneration studies. Callus, derived from root culture explants, was induced to form either shoots or roots. The optimal concentrations of the growth regulators N6-(2-isopentenyl)adenine and indole-3-acetic acid for shoot formation were 49-mu-M and 2.85-mu-M, respectively, whereas the best root regeneration medium contained 5.4-mu-M 1-naphthaleneacetic acid and 8.8-mu-M 6-benzylaminopurine.