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Background:The objective of this study was to develop instrumental protocols for evaluating physicochemical characteristics of plant biostimulant/biofertiliser formulations. Six formulations (Rygex, Algavyt, Ryzoset, Manek, Ecoryg and Algavyt Zn/Mn) containing algal/plant extracts, humic and amino acids, lipids and inorganic components were assessed for particle size distribution and zeta potential (ZP) by dynamic light scattering (DLS) and gross compositional differences by thermogravimetric analysis (TGA), Fourier transform infrared (FTIR), and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). Results:The six commercial formulations were assessed by mung bean root and wheat leaf senescence bioassays to determine auxin-and cytokinin-like activities. Among them, Rygex, Manek and Ecoryg showed significant auxin-like activities compared to the other formulations. Only Manek showed very low cytokinin-like activity. In combination, the four instrumental techniques highlighted gross differences in the particle sizes, ZP and compositions of the products, and provided key results on the physicochemical characteristics of the formulations including potential stability of the products. Conclusion:The three techniques (TGA, FTIR and Py-GC/MS) require no sample preparation beyond drying of the materials. The activities of the plant growth hormones have been compared to show advantages of the growth hormone bioassay methods for selecting better formulations.

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SUMMARYOnion callus was exposed to high concentrations of a number of intermediates involved in the synthesis of S-fraw5-prop-l-enyl-L-cysteine sulphoxide, the major flavour precursor in the intact onion plant. The intermediates were sodium sulphate, L-valine, methacr\'lic acid and S-(2-carboxypropyl)-L-cysteine. Growth was reduced or totally inhibited at the highest concentration (50 to 100 mM) of all the intermediates but, except for methacrylic acid which was inhibitory at all concentrations, a limited growth occurred at the lower concentrations (10 to 20 HIM) of the other compounds. The only treatment which caused the callus to produce an onion odour on crushing the tissue was when S-(2-carboxypropyl)-L-cysteine was incorporated in the culture medium; this result indicated that the callus was capable of the final stages in the synthesis of S-fr<2W5-prop-l-enyl-L-cysteine sulphoxide. The presence of this pathway was confirmed by feeding smaller amounts of L-cysteine, L-valine and S-(2-carboxy-propyl)-Lcysteine (1 and 3 mM) and separating the amino acids and flavour precursors by t.l.c. electrophoresis. 5-^ram-prop-l -enyl-L-cysteine sulphoxide was found only when S-(2-carboxypropyl)-L-cysteine was present in the medium. When S-ethyl and S-propyl-L-cysteine were fed to the callus these compounds were oxidized to their sulphoxides showing that an oxidase system for the S-alkyl cysteines was present in the callus.