Maize plants that have been inoculated with bacteria naturally present in the soil show improved resistance against a pathogenic fungus and a considerable reduction in the number of attacks by a herbivorous moth. It is the first time that such a double effect has been shown in maize. The results of these studies carried out at the University of Neuchâtel under the supervision of Brigitte Mauch-Mani have been presented at the PR-IR 11 congress on plant defences.
A pathogenic fungus responsible for a disease called anthracnose has been causing serious damage to cereal crops on the North American continent, especially during the 1970's. "Colletotrichum graminicola is not limited to crops. It also affects golf courses, parks and private gardens where the grass changes to an unappealing brown colour, states Dirk Balmer, a PhD student in the molecular and cellular biology laboratory and co-author of the research. Luckily, the problem in Europe is not as serious since the cultivated varieties on this continent are naturally less sensitive to this disease."
In order to test a way to improve the resistance of maize to this pathogen, Chantal Planchamp, the other principal co-author of this study and PhD student in the same group, inoculated the plants with a soil bacterium of the genus Pseudomonas. This microorganism is known to easily colonise maize seeds and roots without damaging the plant. The bacterium acts somewhat like a vaccine by halting the pathogenic fungus's proliferation. Furthermore, it seems that the presence of the bacterium helps to limit the herbivorous moth's attacks.
The origin of this double action protection of maize still needs to be clarified, particularly through the analysis of the mechanisms activated by the plant, such as the production of hormones or specific metabolites.
In parallel to the experiments of Chantal Planchamp, Dirk Balmer wanted to know how the plant reacts to a C. Graminicola infection. It turned out that an infection at the root zone triggers important resistance reactions that spread all the way to the leaves. An inverse effect (leaf to root) has also been shown, but not as pronounced. "It's the first time that a study shows the effects of a systemic resistance caused by this infection. This was possible because the fungus attacks both the roots and leaves of maize," adds Dirk Balmer.
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