Dr. Karen O’Hanlon discusses biological organisms position as a plant growth promoter within a chemically regulated environment
Plant Growth Promoting Bacteria (PGPB) are naturally occurring reproducible organisms which are used as fertilisers and pesticides. These bacterial strains are used routinely and effectively in many developing countries for plant growth promotion. In Europe, where agricultural chemicals remain relatively inexpensive compared to the cost of food, the use of PGPB occupies a small, but growing, niche in the development of organic agriculture.
The microbial inoculum has several advantages over artificial agricultural chemicals. They are environmentally friendly, renewable sources of nutrients and phytohormones that can restore soil fertility, ultimately improving plant growth and also alleviate abiotic stresses.
PGPB – as anti-fungal agents – are highly targeted to particular species, while chemicals have a broad-spectrum mode of action. For example, chemical fungicides target all or most fungi, which can result in variable quality and efficacy of PGPB under field conditions.
Currently, there are also challenges with PGPB product registration. However, due to the probable lower toxicity and ecotoxicity of these environmentally available strains of bacteria, it is probable that the registration process will speed up once the regulatory bodies establish a clear framework among all EU member states for registering these biological products.
Many companies are commercialising these organisms as products for use as soil conditioners and fertilisers; circumventing the need to register them as plant protection products (PPPs). Other long-established agrichemical companies are registering these PGPB under the PPP legislative framework. Bayer Crop Science, for instance, has commercialised Serenade ASO (Bacilus subtilis) in Europe as an anti-fungal agent containing the spore-forming micro-organism. Agrichemical companies have registered approximately 30 fungi and bacteria as PPP for use in the EU. This list encompasses strains of Trichoderma, Bacillus, Pseudomonas, and Azotobacter amongst many and enables the company to write PPP claims on the label that non-registered products cannot.
The PGPB field is growing as other smaller commercial companies are entering from various sectors. Progressive seed companies have purchased nitrogen-fixing bacterial strains to coat legume seeds for some time now. Because of these partnerships, soya, lupine, clover, alfalfa and bean seeds have also been successfully coated and used in Europe. No regulations on the use of Rhizobium strains are enforced in Ireland, Germany or Italy currently; however, France, a large legume producer, requires registration as a PPP.
The long-awaited draft EU fertiliser Regulation published in July 2019 – and due to come into force in 2022 – includes Rhizobium, Azotobacter, Azospirillium (three nitrogen-fixing bacteria) and Mycorrhizal fungi. Products containing these named organisms will be handled under this fertiliser regulation (including France). They will not have to be registered under PPP regulations to make an efficacy claim on the label. It is hoped that this biological list in the fertiliser regulation will extend to include other beneficial organisms in time.
Efficacy trials need to demonstrate the benefits of their use to improve yields in order to approve the use of PGPB by commercial growers and farmers. The environmental sustainability and long-term soil conditioning benefits are unquestionable, however many farmers are mainly interested in the potential percentage yield increases. One of the significant problems with the long-term benefits is that many farmers in Ireland occupy rented land and cannot justify the costs of using PGPB for the long-term improvement in soil quality when they may not be using the land the following season. This is one challenge that needs to be addressed by integrated pest management (IPM), including the framework Directive on the sustainable use of pesticides (EU DG Environment) and member states should incentivise farmers to think of the long-term sustainability of land rather than short-term measures.