Asexual propagation of Stackhousia tryonii: a step towards restoration of a rare metallophyte

Abstract

Stackhousia tryonii Bailey is a rare, serpentine-endemic herb, with potential for use in phytoremediation and/or phytomining. This study evaluates the use of herbaceous heel cuttings to propagate S. tryonii on three rooting media [sand, Medium I; a commercial nursery mix, Medium II; and sand : peat moss : perlite (2 : 2 : 1; v/v), Medium III] following the application of plant growth hormones, viz. indole-3-butyric acid and naphthalene acetic acid (both as pure and commercial formulations, viz. Clonex Gel-green, Gel-purple and Gel-red), and honey. Cutting survival, rooting percentage, the number of primary and secondary roots produced, the length of the longest root and the total root length were evaluated after 10 weeks. Results show that there was a positive (P < 0.001) influence of plant growth regulator treatments on cuttings' survival. Medium III failed to support survival of cuttings. Percentage rooting (as a proportion of original number of cuttings) was 10–30% higher in Medium I than in Medium II. Cuttings treated with Clonex Gel-red, IBA at 1000 ppm and NAA at 250 ppm had 60–70% higher percentage rooting in Medium I than in Medium II. Total number of primary roots per rooted cuttings was significantly (P < 0.05) higher in Medium I with Clonex Gel-red and NAA at 1000 ppm. Treatments did not have significant effects on the number of secondary roots, the length of the longest root and the total root length. However, values for these parameters were significantly (P < 0.05) higher in Medium I than in Medium II. We conclude that cuttings from mature plants of S. tryonii could be used effectively to multiply S. tryonii, particularly with sand as rooting medium and prior to treatment of cuttings with Clonex Gel-red.