Impact of volatile organic compounds of Bacillus mycoides on tomato plant development and defenses

The industrialization of the agricultural sector has increased the chemical burden on natural ecosystems and it is recognized that this is no longer sustainable. On the other hand, the world population is growing and solutions need to be found to produce the needed food in a sustainable and ecological manner. One solution might be to build upon and foster the positive interaction between plants and their natural ecosystem. For example, plant growth promoting rhizobacteria (PGPR) play a key role in these interactions maintaining plants in optimal physiological state. More recently, it has been discovered that certain soil-borne bacteria trigger plant growth promotion and stimulate plant defenses via production of volatile organic compounds (VOCs). This research work is aiming at understanding and describing these interactions. For this purpose, we studied the impact of VOCs emitted by B. mycoides on tomato plant development and defenses against infection. Our objectives were to define the activity of VOCs produced by different strains of B. mycoides on the tomato development in order to identify particularly interesting strains in the framework of biocontrol settings. We studied the impact of the VOCs of B. mycoides on seeds germination, the ability of those VOCs to promote plant growth and their ability to trigger an induced systemic resistance against P. infestans, responsible for tomato and potato late blight, a devastating plant pathology, in particular in Belgium. To achieve these goals, experimental setups were used, whereby B. mycoides was put in presence, but not in contact with the plants. The experiments confirmed that plants have the ability to detect and respond to microbial VOCs in their environment. This present work demonstrated the plant growth promoting activity of VOCs emitted by B. mycoides in tomato seedlings, as well as the plant defenses stimulating action against late blight development. The complex impact of VOCs emitted by B. mycoides on tomato seed germination remains to be further characterized. These findings provide new insights into the interactions between VOCs emitted by bacteria and plants, which can lead to the development of new ways to ensure adequate yield in agriculture, but also lead to further considerations, as there is a considerable step between experiments in controlled condition and the safe and effective implementation of biocontrol in the fields.