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Tropentag, September 17 - 19, 2013 in Stuttgart-Hohenheim

"Agricultural development within the rural-urban continuum"

Effects of Contrasting Soil Types, Organic Fertilisation and Striga Presence on the Abundance of the Biocontrol Agent Fusarium oxysporum F.sp. strigae in Soils

Judith Zimmermann1, Alan Watson2, Markus Gorfer3, Georg Cadisch1, Frank Rasche1

1University of Hohenheim, Institute of Plant Production and Agroecology in the Tropics and Subtropics, Germany
2McGill University Canada, Department of Plant Science, Canada
3University of Natural Resources and Life Sciences (BOKU), Fungal Genetics and Genomics Unit, Austria


The parasitic weed species Striga hermonthica is one of the major constraints to cereal production in sub-Saharan Africa affecting the livelihood of about 100 million people. Striga lives parasitically on cereal crops such as millet, sorghum, maize, rice and sugar cane where it can lead to up to 100% crop loss in the field. The soil-borne biocontrol agent (BCA) Fusarium oxysporum f.sp. strigae (acronym: Foxy 2) has shown superior suppression ability of all growing stages of the weed Striga and seems to be a promising control tool for the African farmers. For the wide spread application in the field it is necessary to assess the control stability and therefore the persistence of the BCA under contrasting environmental conditions to investigate necessary re-inoculation times. Therefore a molecular detection tool based on quantitative polymerase chain reaction (qPCR) was developed to specifically quantify Foxy 2 in soil samples. In the presented study, a rhizobox experiment was performed with a Striga tolerant maize variety under controlled conditions in a climate chamber. Since the persistence of Foxy 2 can vary under different soil conditions and with presence or absence of the weed Striga we have included two contrasting tropical soil types, organic fertilisation with Tithonia diversifolia and Striga presence and absence in the experimental design. Foxy 2 was introduced via seed coating of the maize seed with 1.15*105 colony forming units per seed. Rhizosphere soil samples were obtained 14, 28 and 42 days after planting and further analysed on the abundance of Foxy 2.
The rhizobox experiment clearly showed that soil type and organic fertilisation have significant effects on the abundance of Foxy 2. The propagation ability of the BCA was significant higher in the sandy soil type compared to the clayey soil. The organic fertilisation treatment was clearly promoting the abundance of Foxy 2 in both soils and can therefore increase the effectiveness of the BCA which is particularly important under non favoured soil conditions of the BCA to provide stable control ability against Striga.

Keywords: Biological control agents, Fusarium oxysporum f.sp. strigae, Striga hermonthica

Contact Address: Judith Zimmermann, University of Hohenheim, Institute of Plant Production and Agroecology in the Tropics and Subtropics, Stuttgart, Germany, e-mail: judith.zimmermann2@gmx.de

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