Societal Impact Statement Infestation by the parasitic plant Striga hermonthica is a severe threat to food security in sub‐Saharan Africa, impacting the production of the major staple crops pearl millet and sorghum, equating to 7–10 billion $ losses. Using Striga seed dependency on host‐released germination stimulants, we have developed and validated a method for addressing the problem of accumulated parasite seedbanks—the major obstacle in combating Striga infestation in African rain‐fed fields. Application of our method promises to alleviate the problem posed by this pernicious weed by increasing crop production for smallholder farmers. Summary The root parasitic plant Striga hermonthica is a major threat to global food security, causing enormous losses in yields of the main staple crops in sub‐Saharan Africa, which include pearl millet, sorghum, maize and rice. Sustainable Striga control should ideally lead to the depletion of the vast, long‐lived Striga seedbank, and this can be achieved by inducing suicidal seed germination through application of strigolactone (SL) analogs in the absence of host plants. However, this “suicidal germination” strategy has not been evaluated under the natural rain‐fed conditions that prevail in Striga‐prone regions. We have developed and validated a protocol for suicidal germination in laboratory and natural conditions in Striga‐infested rain‐fed African fields. Three SL analogs were tested and these resulted to between 65% and 55% reduction in Striga emergence in pearl millet and sorghum fields, respectively. We conclude that suicidal germination is an effective method for reducing the Striga seedbank. Moreover, the minimal demands of our protocol, in terms of water consumption and amount of selected SL analogs, make it affordable and applicable at a large scale in African rain‐fed agriculture, holding promise for sustainable cleaning of heavily Striga‐infested fields in sub‐Saharan Africa.
Strigolactones (SLs) regulate plant development and induce seed germination in obligate root parasitic weeds, e.g. Striga spp. Because organic synthesis of natural SLs is laborious, there is a large need for easy-to-synthesize and efficient analogs. Here, we investigated the effect of a structural modification of the D-ring, a conserved structural element in SLs. We synthesized and investigated the activity of two analogs, MP13 and MP26, which differ from previously published AR8 and AR36 only in the absence of methylation at C-3′. The de-methylated MP13 and MP26 were much more efficient in regulating plant development and inducing Striga seed germination, compared with AR8. Hydrolysis assays performed with purified Striga SL receptor and docking of AR8 and MP13 to the corresponding active site confirmed and explained the higher activity. Field trials performed in a naturally Striga -infested African farmer’s field unraveled MP13 as a promising candidate for combating Striga by inducing germination in host’s absence. Our findings demonstrate that methylation of the C-3′ in D-ring in SL analogs has a negative impact on their activity and identify MP13 and, particularly, MP26 as potent SL analogs with simple structures, which can be employed to control Striga , a major threat to global food security.
Striga hermonthica, a member of the Orobanchaceae family, is an obligate root parasite of staple cereal crops, which poses a tremendous threat to food security, contributing to malnutrition and poverty in many African countries. Depleting Striga seed reservoirs from infested soils is one of the crucial approaches to minimize subterranean damage to crops. The dependency of Striga germination on the host-released strigolactones (SLs) has prompted the development of the “Suicidal Germination” strategy to reduce the accumulated seed bank of Striga. The success of aforementioned strategy depends not only on the activity of the applied SL analogs, but also requires suitable application protocol with simple, efficient, and handy formulation for rain-fed African agriculture. Here, we developed a new formulation “Emulsifiable Concentration (EC)” for the two previously field-assessed SL analogs Methyl phenlactonoate 3 (MP3) and Nijmegen-1. The new EC formulation was evaluated for biological activities under lab, greenhouse, mini-field, and field conditions in comparison to the previously used Atlas G-1086 formulation. The EC formulation of SL analogs showed better activities on Striga germination with lower EC50 and high stability under Lab conditions. Moreover, EC formulated SL analogs at 1.0 µM concentrations reduced 89–99% Striga emergence in greenhouse. The two EC formulated SL analogs showed also a considerable reduction in Striga emergence in mini-field and field experiments. In conclusion, we have successfully developed a desired formulation for applying SL analogs as suicidal agents for large-scale field application. The encouraging results presented in this study pave the way for integrating the suicidal germination approach in sustainable Striga management strategies for African agriculture.
Striga hermonthica is a destructive parasite of cereal crops in the semi-arid tropical zone. Two greenhouse experiments were conducted at Kamboinse´, Burkina Faso, to investigate the effect of inoculum substrate and location of Striga seeds on the ability of 14 indigenous Fusarium isolates to control the parasite. In Expt 1, Fusarium isolates reduced emerged Striga number, Striga vigour and dry biomass. As a result, sorghum dry biomass and grain yield were enhanced. Inoculum substrate did not influence the ability of Fusarium isolates to control Striga. In Expt 2, Fusarium isolates, substrate and their interaction significantly influenced germination of Striga seeds at both 35 and 50 days after sowing. Isolates grown on compost were more effective at reducing germination of Striga seeds than those grown on chopped sorghum straw. The per cent germination of seeds 50 days after sowing, buried at 5 cm depth, was significantly lower than that of seeds buried at 10 cm. At 10 cm depth, Fusarium isolates still reduced Striga seed germination with respect to the control; horizontal planting distance, 5 or 10 cm from sorghum hills, had no effect.
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