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The seaweed concentrate (SWC) Kelpak® is made from Ecklonia maxima (Osbeck) Papenfuss and is used as a biostimulant in agriculture. Cytokinins and auxins have been identified in Kelpak® and are partly responsible for the growth-promoting effects observed. Other biologically active compounds such as polyamines (PAs) might also be present in the SWC. A study was carried out to investigate the PA levels in E. maxima and Kelpak®. The stipes, fronds, and SWC prepared from E. maxima were collected monthly over a 2-year period. Extracts were benzoylated, and endogenous PAs were quantified using high-performance liquid chromatography. Putrescine concentrations ranged from 6.10 to 40.40 μg g-1 dry weight (dw), from 15.98 to 54.46 μg g-1 dw, and from 0.98 to 5.51 μg ml-1 in the stipe, fronds, and SWC, respectively. Spermine concentrations ranged from 1.02 to 35.44 μg g-1 dw, from 1.05 to 27.35 μg g-1 dw, and from 1.27 to 4.95 μg ml-1 in the stipe, fronds, and SWC, respectively. Spermidine concentrations fell below the detection threshold. This is the first report of PAs being detected in a SWC. The seasonal pattern established for the stipe, frond, and SWC followed the same trend over a biennial cycle, with PAs accumulating in the seaweed tissue during periods of active growth and during periods of rough wave action (stress response).

Plant growth‐promoting rhizobacteria (PGPR) are used in agriculture to improve crop yield. Crude smoke–water (made by bubbling plant‐derived smoke through water) stimulates germination and improves seedling growth. Some active compounds have been isolated from smoke with karrikinolide (KAR1) stimulating plant growth and trimethylbutenolide (TMB) being inhibitory. These smoke compounds have great potential in agriculture but their interaction with PGPR is unknown. In the present study, a two‐factorial pot trial with three replicates per treatment was designed to investigate the interactions between Bacillus licheniformis and two concentrations each of smoke–water, KAR1, and TMB on okra (Abelmoschus esculentus). Growth and physiological parameters (chlorophyll, carotenoid, protein, sugar and α‐amylase) of okra as well as bacterial abundance in the rhizosphere were measured after 5 weeks. Application of B. licheniformis and 10−7 M KAR1 significantly improved the shoot biomass and 10−7 M KAR1 also significantly improved leaf area of okra. However, when 10−7 M KAR1 was applied in combination with B. licheniformis, there was an antagonistic effect on plant growth. While TMB had a negative effect on plant growth, a combination treatment of TMB and B. licheniformis overcame the inhibitory effect of TMB resulting in plant growth similar to the control plants. All treatments had no effect on chlorophyll, carotenoid, protein and sugar concentrations, while α‐amylase activity was significantly elevated in okra root treated with 1:500 (v/v) smoke–water. Determining the rhizobacteria populations at harvest showed that all treatments had no significant effect on the rhizosphere microbial abundance. The modes of interaction between PGPR and smoke‐derived compounds need to be further elucidated.

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