Bioprotection and alternative fertilisation of petunia using mycorrhiza in a soilless production system

Ornamental crop production is increasing worldwide and petunia is nowadays a major bedding plant with high economic impact. To meet growing demands, a high production of quality nursery plants is needed. However, production in greenhouses is confronted by two main problems: fertiliser-induced salinity and pathogen attack like by Thielaviopsis basicola which both cause high losses. Moreover, there is increasing consumer demand for crops produced by environment-friendly practices. The application of arbuscular mycorrhizal (AM) fungi can present an appropriate approach to avoid excessive use of fertilisers and pesticides. Here, we report studies of the interaction between Petunia hybrida and the AM fungus Glomus mosseae in abiotic and biotic stress situations. Root colonisation by G. mosseae, although very low, was able to compensate phosphate deficiency in the substrate and resulted in increased plant dry matter, water and phosphorus content in the shoots. However, these positive effects were attenuated at high salt concentrations (abiotic stress). In contrast, disease symptoms caused by the root pathogen T. basicola (biotic stress) were significantly reduced in G. mosseae-colonised plants. Such protective effects were not achieved with the AM fungi Glomus intraradices and Gigaspora rosea, and a negative effect of the pathogen on root colonisation by G. intraradices was observed. This shows for the first time under nursery practice conditions that G. mosseae can compensate the negative impact of lower levels of phosphate fertilisation on plant growth in a soilless production system and induce bioprotection of petunia against T. basicola. Based on the different effects observed with the three AM fungi, petunia can provide an experimental system to define the molecular mechanisms underlying mycorrhiza-induced resistance against root pathogens.