Auxin application and cutting length affect rooting in Cuphea hyssopifolia stem cuttings

The effect of cutting length and indole-3-buyric acid (IBA) application on adventitious root formation stem cuttings was studied in Cuphea hyssopifolia. Softwood terminal cuttings of a clone grown in Sicily were trimmed to three lengths (2, 4 or 6 cm) and inserted to a 1-cm depth in bottom heated plastic trays containing a humidified peat-vermiculite mixture 1:2 (v/v). To verify the cutting response to different auxin concentrations, cuttings were dipped to a 1.0 cm depth in a 500ppm or 1000 ppm IBA solutions for 10 seconds. Cutting percent survival was 100%. Regardless of cutting length, the highest rooting percentage was obtained with IBA at 1000 ppm (avg. 86.7%), whereas rooting significantly declined to 73% and 81%, in absence of IBA and at 500 ppm IBA, respectively. Percentage rooting averaged over IBA treatment accounted for 93.3% and 90% in 6 and 4 cm long cutting treatments, espectively. The lowest percentage of rooting was recorded with the 2 cm cutting treatments (59%). Cutting length and IBA application significantly interacted as percentage rooting ranged from 43% in 2 cm long cuttings rooted in absence of IBA to 100% in 4 cm long cuttings with 1000 ppm IBA. The highest number of roots was observed from cuttings exposed to IBA at 500 and 1000 ppm (19.7 and 19.6 roots per cutting, respectively). Root number significantly declined in absence of IBA (16.8 roots per cutting). Our results demonstrated that the use of 4 or 6 cm long cuttings and the application of 1000 ppm IBA for 10 seconds could induce optimal adventitious root formation in C. hyssopifolia. The application of the technique described would enhance propagation of this valuable ornamental species.