A ‘growing’ role for phosphites in promoting plant growth and development

There is some on-going controversy about the role of phosphites in plant development. Little or no evidence is available that phosphites can be converted to phosphates, and thus directly enhance plant nutrition. Some phosphite-based products have been reported to have 'fungicidal' activity against certain soil-borne oomycetes. However, in the work reported here no direct activity against true fungi was detected. Moreover, phosphites tested were also found to be ineffective as elicitors of plant defence compounds, phytoalexins. So what do they do? We have shown that foliar application of phosphites consistently enhances root growth and development. This has been shown in glasshouse experiments, carried out in axenic culture, using wheat, oilseed rape, sugar beet and ryegrass. Our findings have been supported by parallel field evaluations conducted by Omex Ltd. Phosphites therefore appear not to act as pesticides or fertilisers, but rather as biostimulants of root growth. On-going work, using the model plant Arabidopsis thaliana, has also observed that phosphites stimulate root growth. This will allow us to identify the molecular mechanism(s) through which phosphite promotes root growth and development in the near future