Propagation daily light integral and root-zone temperature influence rooting of single-internode Pennisetum × dadvena culm cuttings

Crown division, tissue culture, and culm cuttings are methods for propagating purple fountain grass [Pennisetum ×advena Wipff and Veldkamp (formerly known as Pennisetum setaceum Forsk. Chiov. ‘Rubrum’)]. However, propagation by culm cuttings is becoming an economically attractive method for quick liner production. Our objective was to quantify the impact of propagation daily light integral (PDLI) and root-zone temperature (RZT) on root and culm development of single-internode purple fountain grass culm cuttings. Before insertion into the rooting substrate, cuttings were treated with a basal rooting hormone solution containing 1000 mg•L⁻¹indole-3-butyric acid (IBA) + 500 mg•L⁻¹1-naphthaleneacetic acid (NAA). The cuttings were placed in a glass-glazed greenhouse with an air temperature of 23 °C and benches with RZT set points of 21, 23, 25, or 27 °C. PDLIs of 4 and 10 mol•m⁻²•d⁻¹(Expt. 1) or 8 and 16 mol•m⁻²•d⁻¹(Expt. 2) were provided. After 28 d, culm and root densities (number) increased as the RZT increased from 21 to 27 °C, regardless of PDLI during Expt. 1. Compared with 4 mol•m⁻²•d⁻¹, a PDLI of 10 mol•m⁻²•d⁻¹generally resulted in the greatest root biomass accumulation. For example, as PDLI increased from 4 to 10 mol•m⁻²•d⁻¹, root dry mass increased by 105%, 152%, and 183% at RZTs of 21, 25, and 27 °C, respectively. In Expt. 2, as the RZT increased from 21 to 23 °C, root dry mass increased by 70% under a PDLI of 8 mol•m⁻²•d⁻¹. However, root dry mass was similar among all RZTs under a PDLI of 16 mol•m⁻²•d⁻¹. Our results indicate that single-internode culm cuttings of purple fountain grass can be most efficiently propagated under PDLIs of 8–10 mol•m⁻²•d⁻¹together with RZT set points of 23 to 25 °C for quick liner production.