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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. [ABSTRACT FROM AUTHOR]

Kelpak® - a liquid seaweed concentrate made from the kelp Ecklonia maxima (Osbeck) Papenfuss - is used as a natural biostimulantto promote rooting and improve yield in crops. Plant-soil environmental conditions and the chemistry of water used for irrigation may affect the efficiency of Kelpak. The effect of pH (pH 4.5, 6.5 and 8.5) and water hardness (200 mg/L and 400 mg/L Ca2+) on the growth-promoting ability of Kelpak was assessed using the mungbean rooting bioassay and in a pot trial with Swiss chard. Kelpak promoted rooting in all the treatments in the mungbean bioassay with maximum rooting generally achieved with 20% Kelpak. With 20% Kelpak, the addition of 200 mg/L and 400 mg/L Ca2+ decreased rooting at pH 4.5, increased rooting at pH 6.5 and did not affect rooting at pH 8.5. A similar trend was observed in the pot trial with Swiss chard: leaf and root (fresh weight) and pigment content (chl a, chl b and carotenoids) improved with the addition of 200 mg/L Ca2+ + 5% Kelpak at pH 6.5 or pH 8.5, while Kelpak was able to partially mask the negative effect of 200 mg/L Ca2+ at pH 4.5. These results suggest that while Kelpak is most effective in neutral pHs, it can be used to promote plant growth in a wide range of pH and water hardness conditions [ABSTRACT FROM AUTHOR]