Agrobacterium rhizogenes induced rooting of in vitro regenerated shoots of the hybrid Helianthus annuus x Helianthus tuberosus

Difficulty in rooting of in vitro regenerated shoots of the hybrid Helianthus annuus x Helianthus tuberosus was overcome by trans formation with an Agrobacterium rhizogenes strain carrying an Ri plasmid with functional T-DNA. Whereas rooting of control shoots (in vitro regenerated hybrid shoots) could not be induced on MS basal medium, only sparse, and unbranched roots were produced on the MS medium supplemented with indole-3-butyric acid (IBA). However, the bacterial inoculated shoots produced sparse, and unbranched roots on MS basal medium and extensively branched hairy roots on the MS medium supplemented with IBA. Paper electrophoresis of crude tissue extracts of the putatively transformed roots confirmed the transformation by A. rhizogenes. The results of the present study therefore confirm that the T-DNA of the Ri plasmid of A. rhizogenes strain AR 532 is able to elicit the transformed root phenotype thus facilitating efficient rooting of the in vitro regenerated hybrid shoots. This also indicates that transformation with A. rhizogenes can help in the establishment of a well-developed root system in difficult-to-root genotypes of sunflower hybrids. (C) 2002 Elsevier Science B.V. All rights reserved.