Eldur Balla Zahran Biological control of Striga hermonthica (Del.) Benth. using formulated mycoherbicides under Sudan field conditions Institute for Plant Production and Agroecology in the Tropics and Subtropics University of Hohenheim Prof. Dr. J. Sauerborn Biological control of Striga hermonthica (Del.) Benth. using formulated mycoherbicides under Sudan field conditions Dissertation submitted in fulfillment of the requirements for the degree ″Doctor der Agrarwissenschaften″ (Dr.sc.agr. / Ph.D. in Agricultural Sciences) to the Faculty Agricultural Sciences Presented by Eldur Zahran Sudan 2008 This thesis accepted as a doctoral dissertation in fulfillment of the requirements for the degree ″Doctor der Agrarwissenschaften″ (Dr.sc.agr. / Ph.D. in Agricultural Sciences) by the Faculty Agricultural Sciences at University of Hohenheim on 17.12.2007. Date of oral examination: 08.01.2008 Examination committee: Supervisor and Reviewer Prof. Dr. J. Sauerborn Institute for Plant Production and Agroecology in the Tropics and Subtropics University of Hohenheim Co-Reviewer Prof. Dr. Gehards Institute of Phytomedicine, Dep. of Weed Science, University of Hohenheim Additional examiner Prof. Dr. H. Piepho Institute of Plant Production and Grassland Research Vice-Dean and Head of the Prof. Dr. W. Bessei Committee Dean of the Faculty Agricultural Sciences Dedication To the soul of my father and sisters: Khalda and Magda To all who contribute to the success of this work Table of content 1 Introduction 1 1.1 Sorghum as an important food crop 1 1.2 Striga problem 2 1.3 Objectives of the study 4 2 Literature review 6 2.1 Biological control of weeds 6 2.2 Achievements on bological control of Striga 8 2.2.1 Biological control using insects 9 2.2.2 Biological control using microorganisms 10 2.3 Mycoherbicide formulation 14 2.3.1 Inoculum production 15 2.3.2 Types of mycoherbicide formulations 16 2.3.2.1 Liquid formulations 17 2.3.2.2 Solid formulations 18 2.3.3 Application of bioherbicides 22 2.3.3.1 Soil application 22 2.3.3.2 Seed treatment 22 2.3.3.3 Arial application 23 2.4 Phytoxins and mycotoxins production 24 3 Materials and methods 26 3.1 Laboratory experiments 26 3.1.1 Fungal cultures 26 3.1.2 Inoculum production 26 3.1.3 Preparation of durum wheat flour – kaolin granules 27 3.1.4 Preparation of alginate pellets 28 3.1.5 Comparison between the stability of alginate and “Pesta” formulations in the soil 28 3.1.6 Seed treatment experiments 29 3.1.6.1 Seed soaking 29 3.1.6.2 Seed coating 30 3.1.7 Production of chlamydospores by Fusarium species 31 3.1.8 Identification of trichothecene mycotoxins 33 3.2 Field experiments 34 3.2.1 Site description 34 3.2.2 First season experiments 34 3.2.2.1 Screening for the optimum dose of formulated bioagents and testing the seed coating technique for Striga control under field conditions 34 3.2.2.2 Testing the stability of the formulated bioagents in the soil 36 3.2.3 Second season experiments 37 3.2.3.1 Evaluation of “Pesta” and alginate formulations and seed coating technique to control Striga 37 3.2.3.2 Testing the stability of the formulated biocontrol agents in the soil 38 3.2.4 Pot experiment to evaluate the efficacy of “Pesta” and alginate formulations and seed coating technique in Striga control 39 3.3 Statistical analysis 39 4 Results 41 4.1 Laboratory experiments 41 4.1.1 Inoculum production 41 4.1.2 Formulation of fungal isolates in “Pesta” granules 42 4.1.3 Formulation of fungal isolates in alginate granules 42 4.1.4 Comparison between the development of fungal populations after the application of different formulations in the soil 43 4.1.5 Seed treatment experiments 44 4.1.5.1 Seed soaking 44 4.1.5.2 Seed coating 45 4.1.6 Media for chlamydospore production by F. nygamai 49 4.1.7 Media for chlamydospore production by F. Abuharaz 50 4.1.8 Identification of trichothecene mycotoxins 51 4.2 Field experiment first season 52 4.2.1 Effect of Fusarium species on Striga incidence 52 4.2.2 Effect of Fusarium isolates on the total number of Striga shoots 56 4.2.3 Effect of Fusarium spp. on Striga growth 61 4.2.4 Effect of Fusarium species on sorghum growth 63 4.3 Field experiment second season 66 4.3.1 Effect of “Pesta” and alginate formulations and the Fusarium- coated seeds on Striga incidence 66 4.3.2 Effect of “Pesta” and alginate formulations and the Fusarium- coated seeds on the total number of Striga shoots 68 4.3.3 Effect of Fusarium spp. on Striga growth 70 4.3.4 Effect of Fusarium spp. on sorghum growth 73 4.3.5 Development of the fungal populations after the application of “Pesta” and alginate granules to the soil 75 4.4 Pot experiment 77 4.4.1 Effect of “Pesta” and alginate formulations and seed coating technique on the total number of Striga shoots 77 4.4.2 Effect of Fusarium species on Striga growth 79 4.4.3 Effect of Fusarium species on sorghum growth 82 5 Discussion 85 5.1 Inoculum production 85 5.2 Efficacy of “Pesta” granules in controlling Striga 87 5.3 Efficacy of seed treatment in controlling Striga 93 5.4 Efficacy of alginate pellets in controlling Striga 97 5.5 Persistence of F. nygamai and F. Abuharaz in the soil 99 5.6 Chemical control vs. bioherbicides 101 5.7 Mycotoxins 103 5.8 Conclusions and prospective 105 6 References 107 7 Summary 127 8 Zusammenfassung 132 Acknowledgements 138 Appendices 140 Appendix I: Metrological data 140 Curriculum Vitae 141 Erklärung 143 1 Introduction 1 1 Introduction 1.1 Sorghum as an important food crop Sorghum (Sorghum bicolor (L.) Moench, Poaceae) is an important food crop in Africa, South Asia and Central America. It is the fifth major cereal crop in the world after maize (Zea mays L.), wheat (Triticum vulgare L.), rice (Oryza sativa L.), and barley (Hordeum vulgare L.). Worldwide, the area under sorghum is estimated to about 44 million hectares in 99 countries in Africa, Asia, Oceania, and the Americas. Sorghum main producers (in million metric tons) are: USA (11.5), Nigeria (8.0), India (7.5), Mexico (6.3), China (3.1) and Sudan (2.6) (FAO, 2006). Sorghum is the second most important cereal crop after maize in Sub-Saharan Africa (Haussmann et al., 2000). It is the main staple food for about 300 million people who live in the semi-arid tropics (Chantereau and Nicou, 1994). In many parts of the world sorghum is traditionally being used in food production and various food items are made from this versatile cereal: kisra, injera, porridge, unleavened bread, cookies, cakes, couscous, and malted beverages. Sorghum grains are also major components of feed in livestock and poultry production (Doggett, 1988). Sorghum stover is an important source of dry season maintenance rations for livestock especially in India and Sudan (Doggett, 1988). In many African countries sorghum stems are used for fencing, construction of temporary buildings in the villages, as well as an important source of energy for cooking. In developed countries sorghum is mainly used for animal feed. Recent work has shown that sorghum and millet (Pennisetum glaucum (L.) R. Br) are rich in antioxidants and gluten-free, which make them an attractive alternative for wheat allergy sufferers (Dahlbert et al., 2004). In Sudan, sorghum is the most important cereal crop in terms of production and consumption (Ibrahim et al, 1995). It is cultivated all over the country, either under rainfed or under supplementary irrigation. Despite the crop’s importance and the long experience in its cultivation, sorghum yield is very low (0.4 t/ha, FAO, 2006) compared to its potential. The low productivity can be attributed mainly to the use of traditional low-yielding varieties, limited or no use of fertilizers, and poor management practices (Ibrahim et al., 1995). 1 Introduction 2 1.2 Striga problem Witchweeds (Striga spp.), root-parasitic plants belonging to the family Orobanchaceae (Olmstead et al., 2001), are considered the most serious biotic factor that threatens cereal (sorghum, maize, pearl millet and rice) production in the rainfed agriculture of the semi-arid tropics (SAT) including Sudan (Doggett, 1988; Obilana and Ramaiah, 1992, Parker and Richer, 1993). About 21 million hectares of the cereal production area in Africa are estimated to be infested by Striga, causing an annual grain loss of about 4.1 million tons (Sauerborn, 1991). Losses in grain yield due to Striga infestation vary from 5 to 75%, depending on the level of infestation, susceptibility of the crop, climatic conditions and nature of the soil (Lagoke et al. 1991; Sallè et al. 1987). Grain yield losses can reach 100% in susceptible cultivars under a high infestation level and drought conditions (Haussmann et al., 2000). In Sudan, more than 500,000 hectares under rainfed cultivation are heavily infested with Striga, which commonly results in significant yield losses of 70-100% (Babiker, 2002). Severe infestation by Striga may force farmers to shift to less economic crops such as millet, to abandon the land when infestation is too heavy (Sallè et al. 1987) or even to migrate from their location to other locations (Obilana and Ramaiah, 1992). Striga hermonthica (Del.) Benth. and S. asiatica (L.) Kuntze are the major biotic constrains to crop production, especially in the non fertile semi-arid region of Africa, whereas S. aspera (Willd.) Benth. and S. forbesii Benth. are of lower economic importance (Haussmann et al., 2000).