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Really great question, Hamish Dunsford  !

Yes - there is evidence of host specificity (I'm compiling a list of papers that we'll eventually post on our website). We are very grateful that Dr. John Leslie, director of the Fusarium Lab at Kansas State University, is part of our team. In fact, he'll be training our international team in France in March. His book is the premier manual on Fusarium...and there is a specific chapter on the unique qualities of Fusarium Oxysporum (one of about 70 kinds of fusaria).

We have also worked with Dr. David Geiser from Penn State Fusarium Lab. Additionally, we are having our strains' genome mapped by Dr. Like Fokkens at the University of Amsterdam, UVA. The gene mapping is early - there isn't a lot to compare our strains to right now. But, as more Fusarium are mapped, we'll be able to identify markers that will help clarify host specificity. Once this is done, we'll have a better idea of horizontal gene transfer to other vegetative compatibility groups.

Things We Know:
- Fusarium oxysporum is a group of plant pathogenic (and saprophytic) fungi that can be identified by their spore type and growth on selective media and on certain diagnostic media (by trained plant pathologists).
- These fungi are wide ranging and attack a large number of plants (weeds of crops).
- Each forma speciales of Fusarium attacks a single species of plant (hence highly host specific).
- The fungi can exist for long periods of time as chlamydospores in the soil.The spores can germinate in the presence of non-host plant roots and replenish their population with a new cycle of chlamydospores.
- These fungi (unlike other fusaria), do not produce toxins, but this has to be tested by an independent tocicology lab for verification (we've tested our strains for fusaria toxins at both Virginia Tech and University of Nairobi...none were identified). These are wilt fungi (they cause wilt of plants by clogging the vascular tissue of their host plant).

Current Unknowns:
- Gene markers for f.sp. strigae are not yet known (nor are they known for other f.sp....this is budding research). We are working with Dr. Like Fokkens to map our strains' genomes - she would compare our DNA alignments with other Fusaria alignments.
- The registration procedure for biological controls is slow. There are steps in place to speed up the regulatory policies...but it could be years before we see change.
- It is unknown if the Striga in other sub-saharan countries will be susceptible to Fusarium oxysporum in all countries. This is why we are working locally. 
- We do not know of a more promising control of Striga than this fungus.
- We do not know of the long term survival of this fungus in various soils. Time will requires years/decades of data (there are papers showing it can stay in the soil for at least 30 years, which is an exciting consideration for weed management).

Things to do related to biocontrol more broadly than this Vision Prize in western Kenya:
1) Analyze genome sequences of different Striga-infecting isolates and compare them with Fusarium oxysporum strains that are not pathogenic or that infect other hosts to assess any risk of jumping from Striga to crops that are grown in the targeted areas.
2) Search for marker genes found in successful Striga-colonizers and use those to screen local Fusarium oxysporum strains for possible biocontrols. In this way we can try and manage the disease without introducing completely new microbes. This search can also provide us with information on Fusarium oxysporum population structure in the targeted areas.

There is more on this specificity in this paper: Host specificity of Fusarium oxysporum Schlect (isolate PSM 197), a potential mycoherbicide for controlling Striga spp. in West Africa. PS MARLEY, J KROSCHEL, A ELZIEN ( Marley's strains were effective on two kinds of Striga but saw a diminishing ability on a very closely-related host (Alectra). It is noted that for strains to jump to an entirely different plant feels very rare in the case of Fusarium oxysporum f.sp., and we really don't understand the timeframe of a jump between Striga hermonthica and Striga asiatica (100 years vs. 1,000 years vs. a million years?). There is evidence of horizontal gene transfer in almost everything if you go back far enough.  

Again, thank you for the thoughtful question, Hamish. Host specificity is an exciting component of biocontrol. It can be considered a weakness: unlike a blanket application like glyphosate that will kill all plants in contact, we have to go after one weed at a time. But, we feel that one weed at a time is a more ecological and safer approach than carpet bombing. 


Itika Gupta Is there a way to use line breaks in the narrative? It is hard to read such large blocks of text. Thanks!

Paul Woomer - Thanks for the clarification on IR Maize! I'm glad to hear there haven't been issues with legume companions because that is a practice we (and most farmer NGOs) encourage. BASF's marketing approach is an interesting one...especially at a time when concerns are growing about chemical exposure. It will be hard for them to change that story now that they started it.

I'm going to look into the legume impact on the seed bank because I don't know much about the relationship. I know there is a team funded by the Gates Foundation to look for strigalactone hormones. Their press release said they didn't anticipate having a practical application until around 2027.

We are working hard on a rice replacement (possibly a rice combo, or even better, a non-food substrate like banana stalk). This is part of our agenda for our science team meeting in March (researchers from 12 countries...including IITA-Zambia). Coated seed is also on the agenda.

Our greatest limiting factor is regulation and registration. Pest Control Products Board and KEPHIS have strict requirements and so the earliest I can envision having a new product (coated seed) approved for market is in probably 3 years. The advantage our current product has over a coated seed is that the farmer is placing a live, active inoculum in the soil...Striga strikes within 72 hours of planting the maize so we think the speed of a "live, active" component is important. Farmers also have the flexibility to use a range of seeds, including saved seed.

Thanks for your encouragement, Paul. I've ready your work and really appreciate your Striga efforts!