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Field evaluation of an integrated Striga hermontica management in Sub-Saharan Africa: Synergy between Striga - mycoherbicides (biocontrol) and sorghum and maize resistant varieties

Summary
The root parasite Striga hermontica (Del.) Benth. constitutes a major biotic constraint to staple food production in Africa. Fusarium oxysporum Schlecht. (Foxy 2 & PSM197) proved to be highly virulent against their target weed S. hermonthica , host specific and they can be mass-produced. Thus, the antagonists offers a good prospect for Striga control in the future when incorporated into a long-term integrated Striga control program. This research focused on the development of an appropriate mycoherbicidal formulation, thereby reducing the amount of inoculum required for a practical field application. “Pesta” granules of both isolates were made by encapsulating their chlamydospore-rich biomass in a matrix composed of durum wheat-flour, kaolin and sucrose. Their efficacy in combination with Striga resistant and susceptible sorghum ( Sorghum bicolor (L.) Moench) and maize ( Zea mays L.) cultivars was tested under field conditions at two locations (Samaru & Bagauda) in Nigeria. 2.0 g of “Pesta” granules of each isolate were applied per planting hole in which 5 g of Striga seed-sand (1:20 w/w) were inoculated. Both granular mycoherbicides (Foxy 2 & PSM197) were very effective with same potential, in controlling Striga on both susceptible and resistant maize and sorghum cultivars tested. Cumulatively (on average), they reduced the number of emerged Striga plants per plot by 75.3 %, Striga dry weight by 74.4 %, Striga flowers by 83.6 %, and crop plant infested by 64.8 % compared to the controls. The resistant maize and sorghum cultivars enhanced clearly both mycoherbicides efficacy. For maize, the reduction in all Striga parameters assessed compared to the controls was clear and in most cases significant for both isolates while for sorghum the differences were small. When the different treatment x cultivar combinations were compared, the combination Pesta granules x resistant cultivar had the strongest suppressive effect on Striga Striga emergence and flowering as a result of combining mycoherbicides and host plant resistance is an important feature to prevent further Striga distribution and infestation. These findings are highly relevant to the realization of an integrated Striga control approach adoptable and applicable by subsistence farmers in Africa.

german version

Keywords/Stichworte:Biocontrol; Mycoherbicide; Striga resistance; Fusarium oxysporum; Parasitic weed; Striga hermonthica

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Autor:B. SCHAUB, A. ELZEIN, Institute for Plant production and Agroecology in the Tropics and Subtropics (380), University of Hohenheim, D-70593, Stuttgart, Germany, e-mail: gasim@uni-hohenheim.de;
P. MARLEY, Institute for Agricultural Research (IAR), Ahmadu Bello University, P.M.B.1044, Samaru, Zaria, Nigeria, email: psmarley@yahoo.co.uk;
J. KROSCHEL, Integrated Crop Management Division, International Potato Center (CIP), Av. La Molina 1895, Apartado 1558, Lima 12, Peru, email: j.kroschel@cgiar.org

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