THE EFFECTS OF EXOGENOUS AUXIN AND ROL GENES ON ROOT-FORMATION IN ROSA-HYBRIDA L MONEYWAY

The effect of indole-3-butyric acid (IBA) on the formation of non-tran sformed and rol gene transformed roots on stem slices of in vitro cult ured shoots of Rosa hybrida L. 'Moneyway' was examined. Formation of a dventitious roots on this rootstock was dependent on the IBA dose; it was not affected by the presence of other root primordia on the same e xplant. Application of 0.32 to 1 mu M IBA during 5 days, followed by t ransfer to medium without hormones resulted in maximum root formation (90%) after three weeks. The formation of such untransformed roots was completely inhibited by transfer to medium with 5 mg l(-1) kanamycin two days after excision. Ri roots were formed upon inoculation with A. rhizogenes LBA9402 harbouring two plasmids: pRi1855, comprising the r ol genes and the binary plasmid p 35Sgusintron with the nptII gene for kanamycin resistance and the CaMV 35Sgusintron gene. The formation of these Ri roots on kanamycin-containing medium was independent of the presence of IBA. Stem slices inoculated with a disarmed A. tumefaciens GV3101, harbouring only the nptII gene, formed callus and subsequentl y roots in the presence of kanamycin exclusively on medium with high I BA concentrations (10 or 100 mu M). Root formation at 100 mu M IBA was considerably improved by transformation with the rolB gene under the influence of the strong CaMV 35S promoter. In addition, low IBA (0.1 a nd 1 mu M) stimulated the formation of roots only on stem slices trans formed with A. tumefaciens harbouring the rolA+rolB+rolC genes; the ro oting response at 10 mu M IBA was much improved. It was concluded that the 35SrolB gene and especially a combination of rolA, B and C genes promote the rooting response.