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400 mill years ago, plants emerged form water and colonised the Earth thanks to the help provided by some fungi. Dependence of plants on helper fungi has been so strong ever since, that currently more than the 95% of the plants in the world live in symbiosis with fungi colonising their root system. This association is very robust and works perfectly because both exchange nutrients with each other. Fungi have an enhanced ability to absorb water and minerals from soil which pass them to plants, while plants contribute with carbohydrates from photosynthesis to fungi. This natural cooperation is called mycorrhizal (myco=fungi, rhiza=root) symbiosis and is really important in plant nutrition, particularly in the frame of climate change in which drought stress will be a limiting factor.
Research on the field of plant mycorrhizal symbiosis has showed a more complex picture, as there are many other organisms involved in the mycorrhization process. These organisms are different species of bacteria named “Mycorrhiza Helper Bacteria”. Symbiotic bacteria are also extremely important for some groups of plants, as some can take nitrogen from the air and pass it to plants. Also, independently from symbiosis, other bacteria benefit plants by making other limiting nutrients more easily available. This is the case for soil phosphorous solubilizing agents.
Walnut, like virtually all tree species, also benefits enormously from partnering with mycorrhizal fungi and other soil microorganisms. However, this important relationship is typically overlooked. It is frequent that soils subjected to intensive agricultural practices tend to have a very low amount and diversity of soil symbiotic microorganisms, so that when walnut trees are planted in such soils, their initial growth is poor and dependent on chemical fertilisers.
In walnut production, it is very important to ensure the best growth during the initial steps of the plantation, so that the maximum potential harvest can be achieved. For this reason, the use of mycorrhizal fungi such as Rhizophagus spp. and other soil microorganisms like Mycorrhiza Helper Bacteria or Plant Growth Promoting Bacteria, may enhance plant growth by optimizing the plant nutrient and water uptake and consequently root and shoot growth in walnut plants. As a consequence, the use of chemical fertilizers and other operating costs will be minimised.
Woodnat partners Bosques Naturales and ECM, have carried out several experiments aiming to enhance the survival and growth of walnut seedling from lab to field using mycorrhizal fungi and bacteria. Plants produced in vitro in the lab need to go through a process of hardening and adaptation to outdoor conditions. Our results show that when they count on the help of mycorrhizal fungi, young plants manage to adapt much better and survival and growth rates significantly increase.