Optimising Ex Vitro Shoot Cutting Propagation of Genetically Verified Pyrethrum for Industry Revitalisation in Kenya

Pyrethrum (Tanacetum cinerariifolium) remains a globally important botanical insecticide crop. However, the once-dominant Kenyan pyrethrum sector has faced prolonged decline associated with genetic erosion, clonal mixing, and limited availability of high-quality planting material. Industry revitalisation requires reliable molecular validation of elite germplasm and scalable propagation systems. Building upon recent molecular profiling, this empirical work provides the propagation pipeline for genotyped elite clones. This study evaluated the effectiveness of ex vitro shoot cutting propagation as a complementary strategy for the multiplication of genetically verified pyrethrum planting material. Ex vitro propagation trials were conducted using commercial cultivars P4 and K218 under factorial combinations of rooting media (peat moss, forest soil, sand), Indole-3-butyric acid (IBA) hormone applications, nutrient supplementation, and season. Propagation success was assessed through greenhouse survival, lateral bud development, rooting, field establishment and flowering. Media had a marginal effect on greenhouse survival, with peat moss yielding the highest survival, followed by forest soil, while sand performed poorly. Cultivar P4 exhibited significantly greater vegetative performance than K218, including higher greenhouse survival (0.74 vs 0.47; p ˂ 0.01) and lateral bud development (1.50 vs 0.42 buds; p = 0.0011). Omitting nutrient solutions improved initial survival. Lateral bud development was also significantly influenced by season (p = 0.046) and media. Root traits were significantly affected by media, with peat moss producing the strongest rooting response. IBA application had no significant effect on rooting. Rooted plantlets exhibited high field establishment (83.9%), where field survival was dictated by the initial rooting media. Flowering time was primarily influenced by transplanting season. These findings demonstrate that ex vitro shoot cutting propagation provides an effective means of multiplying genetically verified pyrethrum planting material and complements molecular genotyping in supporting germplasm conservation, deployment of elite planting material and the sustainable revitalisation of Kenya’s pyrethrum industry.