Fungal Biofertilizer Can Boost Cucumber Crop Health

A UCO study verifies that the FO12 strain of the  Fusarium oxysporum fungus  improves responses to iron deficiency in cucumber plants, promoting their growth without having to resort to products that are harmful to the environment.

Iron is one of the most abundant elements in the earth's crust and a key element for crop nutrition. However, in calcareous soils (very abundant in Spain) it is quite a challenge for plants to be able to obtain iron from the soil, due to its poor solubility and availability. It is then when iron deficiency appears and plants activate different responses, mainly in their roots, to obtain this nutrient.

The research staff of the María de Maeztu Excellence Unit - Department of Agronomy of the University of Córdoba (DAUCO) - who work in the Plant Physiology group have been studying these plant responses for decades and looking for strategies that make iron more available for plants, avoiding iron chlorosis and increasing crop growth.

In the current context of climate change and the search for environmental conservation, it is essential that these solutions come hand in hand with sustainability, avoiding the abuse of chemical synthesis products, which are harmful to the environment.

The latest work led by this group in collaboration with the departments of Agricultural Chemistry, Pedology and Microbiology moves along this line; Genetics; and Plant Botany, Ecology and Physiology, as well as with the Department of Genetic Improvement of the Institute for Sustainable Agriculture (IAS – CSIC), in which the potential of a microorganism (the FO12 strain of the Fusarium oxysporum fungus) as a  biofertilizer and iron biostimulant.

Although the  Fusarium oxysporum fungus  is very harmful to many crops, "the FO12 strain is non-pathogenic (does not cause disease) and has proven to be a biocontrol agent against  Verticillium dahliae ," explains DAUCO professor Javier Romera. The power of this strain to control diseases was already known thanks to previous work by the Agroforestry Pathology group, and it is probably due to the fact that this strain is capable of activating induced systemic resistance (ISR), a kind of immune system that plants have to defend.

Substances such as ethylene and nitric oxide are involved in the regulation of this defensive response, which are also involved in the activation of responses to iron deficiency. "Since this fungus already induced defensive responses, we thought that it could also induce responses to iron deficiency, and that was the idea of ​​the study, to prove that it also induces them," says researcher Carlos Lucena.

Therefore, this study proves that strain FO12 improves responses to iron deficiency in cucumber plants in calcareous soils. Results are already being seen 24 hours after inoculating the roots of cucumber plants with this microorganism: the genes related to the response to iron deficiency are activated and, after several days of cultivation, plant growth increases.

The study has been carried out with cucumber plants grown in nutrient solution, "a more artificial system", and also in pots with calcareous soils, under greenhouse conditions "because the idea is that these microorganisms can be applied as biofertilizers that favor the acquisition of iron in those calcareous soils, where there are more problems”, recalls Romera. In both cultivation methods, the fungus stimulated iron acquisition and plant growth.

The use of this type of microorganism as a biofertilizer, in addition to influencing environmental sustainability, since they are natural elements that avoid the use of chemical synthesis fertilizers, help regulate the communities of soil microorganisms: their mere presence makes them occupy the niches that could occupy other pathogenic fungi that cause diseases

"The ultimate goal would be to develop a biostimulant that allows both protecting crops from attack by possible pathogens, as well as improving the iron nutrition of plants in adverse conditions," says researcher Miguel Ángel Aparicio. The way to make its use in the field a reality is to analyze its effect on other nutrients, such as phosphorus; optimize treatment doses; and to know the most suitable conditions for its application in the field.

Reference: Aparicio MA, Lucena C, García MJ, et al. The nonpathogenic strain of Fusarium oxysporum FO12 induces Fe deficiency responses in cucumber (Cucumis sativus L.) plants. Planta. 2023;257(3):50. doi:10.1007/s00425-023-04079-2

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