Effect of Growing Substrate, Season, and Genotype on Vegetative Propagation (Division) of the Wetland Rush, Juncus lomatophyllus

Juncus lomatophyllus, an indigenous South African aquatic plant with reported tyrosinase-inhibitory activity and potential cosmeceutical value, remains poorly studied regarding large-scale propagation. This study established the first documented vegetative propagation protocol for the species using division under outdoor conditions. Two genotypes from Mpumalanga (MP) and the Western Cape (WC) were evaluated in a 2 × 5 × 3 factorial experiment arranged in a randomised complete block design. Five growing substrates were assessed for their effects on sprouting, survival, rooting percentage, root development, and sprout production over three months under constant water conditions. Growing substrate, genotype, and trial period significantly influenced propagation success. The substrate composed of red soil, bark, and compost (2:1:1, v/v) produced the most favourable rooting and sprouting responses. Overall, the MP genotype outperformed the WC genotype across most growth parameters. A further 11-month evaluation confirmed distinct phenotypic differences, with the MP genotype exhibiting greater cold tolerance and earlier reproductive development. These findings highlight the importance of substrate selection, genotype choice, and seasonal conditions in successful cultivation. The superior performance of the MP genotype suggests strong potential for commercial biomass production, cosmeceutical applications, and future breeding and biotechnological improvement programmes targeting J. lomatophyllus and other indigenous aquatic species.