Effect of IBA Treatments, Bottom Heat, Stock Plant Location, and Cutting Type on the Rooting of Spigelia marilandica Cuttings

Abstract

Abstract Spigelia marilandica (India pink, pinkroot), a herbaceous perennial native to the United States, is underused in the nursery trade, in part because it is difficult to propagate. We found from the first of two studies conducted during winter 2007 that stem-tip cuttings collected from greenhouse-grown stock plants submersed in 3000 or 6000 ppm (mg·liter−1) potassium salt of indole-3-butyric acid (IBA) for one minute had greater percentage rooting (average 76.6) than cuttings not treated with IBA (46.9). Bottom heat [average 27.2C (81F)] compared to no bottom heat [23C (73F)] increased rooting percentage from 48 to 85%. The second winter 2007 study determined that rooting percentage according to method of application of 3000 ppm IBA was in the order: solution dip (60.1) > powder dip (49.8) ≥ solution submersion (46.6) ≥ control (42.7). During summer 2009, bottom heat and the same methods of application of 3000 ppm IBA described above were applied to terminal (stem tip) or subterminal cuttings collected from greenhouse-or field-grown stock plants. While IBA application method had no effect on rooting of cuttings from greenhouse-grown stock plants (average 54.1%), it affected cuttings from field-grown stock plants in the order: solution submersion (80.1%) > solution dip (54.4%) > powder dip = control (average 29.5%). Solution submersion cuttings from field-grown stock plants had much greater rooting (80.1%) than those from greenhouse-grown stock plants (47.2%). Control and powder dip cuttings from greenhouse-grown stock plants had greater rooting percentage than those from field-grown stock plants. Cutting type had no effect on rooting of field-grown cuttings (average 48.4%). Terminal cuttings from greenhouse-grown stock plants had greater rooting (73.3%) than subterminal cuttings (34.8%).