Learning from nature: Using plant-soil feedback effects to improve disease control and sustainability in greenhouse cut-flowers

In this post I will look back on our past project (funded by NWO Groen) on using plant-soil feedbacks to improve the growth of Chrysanthemum, an important cut flower crop in The Netherlands. It is furthermore known that soil-borne diseases cause major losses in the yield of Chrysanthemum. In this project we used plant-soil feedback principles to develop soil microbial inocula from natural soils and wild plant species. These inocula were used to “hot-start” disease suppressiveness in horticultural soils. This work was led by Martijn Bezemer and experiments performed mainly by Hai-kun Ma, Ana Pineda and me. 

At first Hai-kun used 37 wild plant species common to local grasslands to condition the soil. This is based on the knowledge that plant species change the microbial communities in soils, and that these changed microbiomes can influence the growth of the following plant – this case Chrysanthemum. She found out in her paper that growing first grasses in the soils led to positive effects on the growth of Chrystanthemum (in presence and absence of a pathogen).

I followed up on this and identified the microbiomes created by these previously grown 37 plants. We show (here!) that plants indeed create unique microbiomes but that these are not conserved at the level of plant family. Furthermore, we could relate some microbiome types to the good performance of Chrysanthemum in presence and absence of a pathogen. We show thus, plant species specific promotion of following plant through changes in microbiome. Interestingly, plant conditioned soils with a legacy of more mycorrhizal fungi led to better performance of Chrysanthemum in the presence of a pathogen – even though Chrystanthemum itself did not seem to form association with the mycorrhizae.

Next, we tested if we can use these plant-created legacies to ‘cure’ a soil with already occurring disease by adding an inoculum of soil with good microbes to this living soil. This seems to not work so well, better results in terms of pathogen suppression are obtained by adding a healthy soil inocula into a sterile soil.

After that Ana with Ian Kaplan (professor visiting from Purdue University in US) designed an experiment in which they tested if these soil legacies created by plants will affect suppression of above-ground pests of Chrysanthemum and how stable these legacies actually are. We showed that indeed, by conditioning the soil with different plants, differences in the pest-suppression are created and this could be related to the microbial communities. We further showed that the community in the inoculum is similar to the community after the growth of chrysanthemum – but also that there is strong selection on the fungi by chrysanthemum. Especially against AMF as seen before.

In summary, we show that growing other plants to change the microbiome in the soil in between cycles of chrysanthemum is a viable strategy – and does increase plant growth and its ability to defend against below-ground and above-ground pests. However, this inoculation should be done shortly after sterilization and one needs to carefully select the plant species used for conditioning.

We are doing further research on how does inoculation affect the microbiome in the leaves and shoots of the plants, so still something to come…