An exchange with friends is good – that also applies to plants. Researchers have now succeeded in enabling tomato plants in greenhouse production to live together with their friendly symbiosis partners. These so-called mycorrhizal fungi reduce the fertilization requirements of plants with the deficient nutrient phosphate considerably. In addition, the symbiosis has a positive effect on the taste and health-related ingredients of the tomato fruits, the studies show.
They are actually better known as pathogens in plants, but among fungi there are not only enemies, but also friends: Some soil-living species establish an intimate exchange relationship with certain plants – a so-called mycorrhizal symbiosis. The partners exchange nutrients via a connection between the fungal network in the soil and the plant roots. In the most widespread form of mycorrhizal symbiosis, this “trade” takes place via a fascinating structure: In some cells of the roots, the fungus and the plant jointly form a tree-like structure (arbuscule) through which the nutrient transfer takes place. The fungus primarily supplies the plant with the nutrient phosphate from the soil and, in return, is provided with sugar.
Demanding friends
It is already known that the mycorrhizal symbiosis can significantly promote the growth, health and the content of beneficial ingredients in plants. This is why researchers are trying to develop methods to specifically promote the colonization of plant roots with the fungi. The application of mycorrhizal preparations containing their spores can serve this purpose. But building friendship networks in the root area is often not that simple. Because the different types of mushrooms place special demands on the nature of the substrate and the nutrient content. This is particularly problematic in commercial plant cultivation under glass, in which the plants are often cultivated on artificially produced substrates into which fertilizer solutions are passed. So up to now there was no possibility of mycorrhization in the commercial cultivation of tomatoes.
The “Mycotom” cooperation project should now change this. Under the scientific direction of mycorrhizal expert Bettina Haus from the Institute for Plant Biochemistry in Halle, the team pursued the goal of transferring the findings from mycorrhizal research into practice. The researchers first set out to find tomato-specific mycorrhizal fungi that form a symbiosis with commercial varieties. The species Rhizophagus irregularis proved to be suitable. In their test greenhouses, the scientists then tested the suitability of various substrates for roots and fungus to grow together. Coconut fiber mats are mostly used in commercial cultivation. “But this substrate alone turned out to be completely unsuitable for mycorrhization,” reports home. “We carried out a long series of tests with substrates that had different proportions of coconut and peat before we found a suitable mixture on which the plants could be mycorrhized,” reports the researcher.
Saving opportunities and better tomatoes
Fertilization posed a further challenge. The problem: tomato plants only allow colonization by the mycorrhizal fungus when they are hungry for phosphate. However, a reduced fertilization could in turn lead to yield losses, so the fear. However, as the researchers were able to show, a balance is established with a phosphate supply of 70 percent of the normal supply: the plants allow their roots to colonize through this slight deficiency, which in turn enables the fungus to improve its phosphate supply to such an extent that there is no loss of yield comes. Ultimately, phosphate fertilizer can be saved.
Following the successful mycorrhization under the greenhouse conditions, the researchers investigated the extent to which the symbiosis affects the quality of the fruit. Their analyzes showed that the tomatoes from mycorrhizal plants contained more taste-influencing sugar substances, more antioxidant lycopene and a lot more amino acids compared to controls. Through genetic studies, they found indications that the symbiosis apparently influences certain programs in the development of the fruit, which has a beneficial effect on the formation of these ingredients.
The conclusion of the researchers is thus: If you want to harvest healthy and tasty tomatoes and also want to save fertilizer, you should mycorrhize the plants. As they report, a company is now developing a commercially available mycorrhizal substrate for growing tomatoes under glass on the basis of the results. Since phosphorus fertilizer can be saved, its use for large tomato producers could quickly pay off. Finally, the researchers highlight this aspect again. It is estimated that the natural reserves of inorganic phosphorus for producing fertilizers will be used up in 40 to 70 years. There is already talk of a phosphate crisis threatening the yields of global agriculture.
Source: Institute of Plant Biochemistry, Article: International Journal of Molecular Sciences, doi: 10.3390 / ijms21197029