Microbial helpers
Striga, a parasitic weed, causes large cereal production losses in Sub-Sharan Africa. Preventing striga infections is therefore important. Now a group of international researchers discovered that microbes may hold the key to preventing striga infections.
Striga infects many cereals. As they are dependent on their host, striga seeds wait with germinating till they know that their host is nearby. For this they have a lot of patience, sometimes they wait up to 20 years. The recognition of a suitable host occurs on basis of the signalling molecules plants excrete when they are short on phosphate. After germination striga grows towards its host, which it enters to siphon off its nutrients. This makes that infected plants grow less well and have a lower yield.
Searching for an effective method to prevent striga infection, the researchers decided to analyse the effect of microbes on a striga infection. Doing so they germinated sorghum seeds on soil from a Dutch field that either was or wasn’t heated first. After germination the researchers transplanted the seedlings to sandy soil with striga seeds. After a couple of weeks the researchers studied the number of striga infections. Noticing that plants grown in soil that was heated first had more infections that plants growing in natural soil.
Striga seeds can wait up to 20 years for a suitable host
In order to find out why, the researchers studied striga growth. While striga seeds germinated just as well in heated soil as in natural soil. Just germinated striga developed less well in natural soil. With as result that they could not reach their host.
Subsequently the researchers analysed the striga growth inducing molecules the host plant excrete. In natural soil, with microbes, the researchers found more breakdown products of those striga growth inducing molecules than in heated soil. Suggesting that the microbes breakdown striga growth inducing molecules, which in turn disrupts the development of just germinated striga plants.
The researchers furthermore studied the effect of striga disrupting bacteria on the host plants. While doing this the researchers discovered that striga disrupting bacteria promote the production of a protective layer. Which probably is making it more difficult for striga to enter the sorghum plants.
A cocktail of striga inhibiting bacteria
Lastly the researchers analysed which microbes inhibit the striga infections. For this the researchers catalogued the microbes that were present up and around the sorghum plants. Subsequently they tested potential candidate bacterial isolates. From this they observed that Pseudomonas isolate VK46 disrupts striga development through breaking down striga growth inducing molecules. In addition, Arthrobacter isolate VK49 stimulated the production of the extra protection layer.
Sorghum plants benefit from the presence of striga disrupting microbes. Each bacteria inhibits striga a little bit. With an optimal microbial cocktail it should be possible to protect sorghum plants and other crops against striga infection.
Literature
Kawa et al., (2024) The soil microbiome modulates the sorghum root metabolome and cellular traits with a concomitant reduction of Striga infection, Cell Reports, https://doi.org/10.1016/j.celrep.2024.113971
Plant en Zo 