Proliferation of the biocontrol agent Fusarium oxysporum f. sp. strigae and its impact on indigenous rhizosphere fungal communities in maize under different agro-ecologies

Judith Zimmermann,Mary K Musyoki,Georg Cadisch,Frank Rasche

doi:10.1016/j.rhisph.2016.06.002

Abstract

Our objectives were to (1) monitor the proliferation of the biocontrol agent (BCA) Fusarium oxysporum f. sp. strigae strain “Foxy-2”, an effective soil-borne BCA against the parasitic weed Striga hermonthica, in the rhizosphere of maize under different agro-ecologies, and (2) investigate its impact on indigenous rhizosphere fungal community abundance and composition. Field experiments were conducted in Busia and Homa Bay districts in western Kenya during two cropping seasons to account for effects of soil type, climate, growth stage and seasonality. Maize seeds were coated with or without “Foxy-2” and soils were artificially infested with S. hermonthica seeds. One treatment with nitrogen rich organic residues (Tithonia diversifolia) was established to compensate hypothesized resource competition between “Foxy-2” and the indigenous fungal community. Rhizosphere soil samples collected at three growth stages (i.e., EC30, EC60, EC90) of maize were subjected to abundance measurement of “Foxy-2” and total indigenous fungi using quantitative polymerase chain reaction (qPCR) analysis. Terminal restriction fragment length polymorphism (TRFLP) analysis was used to assess potential alterations in the fungal community composition in response to “Foxy-2” presence. “Foxy-2” proliferated stronger in the soils with a sandy clay texture (Busia) than in those with a loamy sand texture (Homa Bay) and revealed slightly higher abundance in the second season. “Foxy-2” had, however, only a transient suppressive effect on total indigenous fungal abundance which ceased in the second season and was further markedly compensated after addition of T. diversifolia residues. Likewise, community structure of the indigenous fungal community was mainly altered by maize growth stages, but not by “Foxy-2”. In conclusion, no adverse effects of “Foxy-2” inoculation on indigenous fungal rhizosphere communities were observed corroborating the safety of this BCA under the given agro-ecologies.

Highlights

Striga hermonthica (Del.) Benth. is an endemic parasitic weed of maize (Zea mays L.) and other cereal crops including sorghum (Sorghum bicolor L.), millet (Pennisetum americanum (L.) Leeke) and rice (Oryza sativa L.) which are main staple crops in Sub-Saharan Africa (Ejeta, 2007; Elzein and Kroschel, 2004; Marley et al, 2004)
The present study successfully identified favoured environmental growth conditions of the rhizosphere-acting biocontrol agent (BCA) “Foxy-2” which will contribute to its proliferation in soils increasing its potential to act effectively against the parasite S. hermonthica
Persistence and establishment of “Foxy-2” in crop rhizospheres could be appraised if considering site-specific factors such as soil texture, soil carbon background, soil pH and climatic conditions

Summary

Introduction

Striga hermonthica (Del.) Benth. is an endemic parasitic weed of maize (Zea mays L.) and other cereal crops including sorghum (Sorghum bicolor L.), millet (Pennisetum americanum (L.) Leeke) and rice (Oryza sativa L.) which are main staple crops in Sub-Saharan Africa (Ejeta, 2007; Elzein and Kroschel, 2004; Marley et al, 2004). Field experiments in Burkina Faso, Benin and Nigeria confirmed the combination of “Foxy-2” along with Striga-tolerant crop varieties as an effective integrated control approach against S. hermonthica (Schaub et al, 2006; Venne et al, 2009). A thorough understanding of environmental conditions which promote the proliferation and persistence of the BCA “Foxy-2” is required to ensure consistent and sustained S. hermonthica control.

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