Follow-up funding for microbial fight against parasitic weed in Africa


Follow-up funding for microbial fight against parasitic weed in Africa


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Sorghum is a staple crop for many small African farmers, but a parasitic weed threatens their harvests and their livelihoods. Can micro-organisms in the soil come to the rescue? That's the question that launched the Promise-project six years ago. Initial results have been so promising that the Bill & Melinda Gates Foundation has now announced follow-up funding to the tune of 10 million dollars.

For the past six years, an international team from the Netherlands, Ethiopia and the United States has cooperated intensively to hammer out a successful new approach to what is a persistent and increasingly serious problem. 

Striga has brightly coloured and attractive flowers, but appearances are deceptive as its nickname - 'witchweed' - will attest. It's a parasitic weed that saps some of Sub-Saharan Africa's main food crops - including sorghum, rice and millet - of vital nutrients. 

Poverty and promise

Sorghum is the 5th most important cereal crop in the world. Farmers who grow sorghum are usually self-supporting but have little land. So if Striga causes half - or all - of their crops to fail, the consequences are immediate and disastrous. Hunger and poverty follow in its wake.

Promise stands for Promoting Microbes for Integrated Striga Eradication. The researchers have been looking for micro-organisms occurring naturally in the soil which may help in ingenious ways to prevent and fight against Striga-infestation. Their research shows that micro-organisms can intervene during different stages of the infection-cycle: from the moment the weed's seeds germinate and attach to sorghum roots to the moment it emerges from the ground.

Xavier Pita
The different phases of Striga-infection. The seeds germinate after a chemical signal from the sorghum plant, they attach to the sorghum roots and start sapping vital nutrients, and eventually mature Striga-plants deposit their seeds in the soil and restart the cycle.

The leader of the project is Jos Raaijmakers, the head of NIOO's department of Microbial Ecology. He is elated about the Gates Foundation's decision to award major follow-up funding to Promise. It's something the Foundation would only do if it is confident that a concrete solution to a serious problem is within reach. Raaijmakers explains where the team are now, and what their plans are for the future.

— What were the most interesting outcomes of Promise I?

"We can now intervene during different stages of the Striga infection-cycle, with help from soil micro-organisms. Our research shows that it's quite simple to activate these micro-organisms so that they produce specific volatile substances. These substances have proved very effective at slowing down the germination process.

We have also identified specific fungi and bacteria that can disrupt the chemical communications between the parasite and its host. This disruption results in the germinating Striga-plants being thrown off track so to speak. In addition, some micro-organisms are able to alter the internal cell structure of sorghum roots, in a way that slows down the Striga-infection when the seeds attach to the roots."

— What are your plans for Promise II? And why is a follow-up important?

"We will translate our scientific findings into effective control methods that are affordable and accessible to small farmers. Affordability could be a deal breaker here, as the farmers' financial means are very limited. More specifically, we are going to study the ability of local soils to stimulate volatile substances that slow down Striga in the soil microbiome (i.e. the microbial community in the soil). We'll also develop microbial products that have a direct impact on the germination and survival of Striga-seeds, or an indirect impact through the sorghum plant.

Together with other projects funded by the Gates Foundation, we will look into effective ways to integrate our approach with other control measures. We're talking about Striga-resistant sorghum crops here, as well as synthetic substances that stimulate the germination of Striga-seeds without crop plants.

Our follow-up research will broaden the fight by including two Striga-species in Ethopia, Senegal and Tanzania. Promise II will start after the summer."

— What are you most looking forward to?

“My dream is to have a working, integrated strategy ready in five years' time with our international research team and ten partners from seven countries, improving the livelihoods of smallholder farmers in sub-Saharan Africa by protecting some of their key main food crops."

Jos Raaijmakers
Project leader Jos Raaijmakers (NIOO-KNAW)