ABSTRACT
Five rates of benomyl, carbendazim, mancozeb, hexaconazole, carbendazim + mancozeb, imidacloprid + metalaxyl-M + tebuconazole and metsulfuron methyl were incorporated into molten potato dextrose agar to determine growth and sporulation of PSM 197 and Foxy 2, which were isolates of Fusarium oxysporum f. sp. strigae used against Striga hermonthica. Two hundred and eighty Petri dishes containing amended and un-amended media were inoculated with 14 day-old cultures of PSM 197 and Foxy 2 using flame-sterile 5 mm cork borer. Petri dishes were arranged on laboratory bench in a Completely Randomized Design (CRD) and observations taken at 24 hours interval. Mycelia growth and development of conidia were completely inhibited in media amended with benomyl, carbendazim, and carbendazim + mancozeb. Increasing mancozeb rate from 6 to 24 g/L resulted in lower mycelia diameter and conidia counts for PSM 197 and Foxy 2. Fourteen days after incubation, mycelia diameter of both isolates were low on media amended with highest rates of hexaconazole (1 ml/L), metsulfuron methyl (4.6 g/L) and imidacloprid + metalaxyl-M + tebuconazole (8 g/L). Metsulfuron methyl was adjudged most compatible with the two isolates of Fusarium oxysporum f. sp. strigae on the basis of their mycelial growth, micro-conidial number and conidia germination. With respect to counts macro-conidia, hexaconazole treatments resulted in least variations while viability of conidia was higher with mancozeb treatments followed by metsulfuron methyl. With respect to all parameters considered, imidacloprid + metalaxyl-M + tebuconazole had the highest percent variations than hexaconazole, mancozeb and metsulfuron methyl. The study therefore shows that metsulfuron methyl at 2.3 g/L is compatible with PSM 197 and Foxy 2 and should be used for the management of S. hermonthica.
TABLE OF CONTENTS
Declaration……………………………………………………………………………………………………… i Certification……………………………………………………………………………………………………..ii Dedication……………………………………………………………………………………………………….iii Acknowledgement…………………………………………………………………………………………….iv Abstract……………………………………………………………………………………………………………v Table of Contents……………………………………………………………………………………………..vi List of Tables……………………………………………………………………………………………………ix List of Figures ………………………………………………………………………………………………….x List of Appendices …………………………………………………………………………………………..xi CHAPTER ONE
1.0 INTRODUCTION ………………………………………………………………………………………1
1.1 Justification ………………………………………………………………………………………………..2 1.2 Objectives of the Study……………………………………………………………………………….3 CHAPTER TWO
2.0 LITERATURE REVIEW……………………………………………………………………………..4
2.1 Striga hermonthica (Del.) Benth. …………………………………………………………………..4 2.1.1 Taxonomy and
distribution ………………………………………………………………………. 4 2.1.2 Biology of Striga hermonthica ……………………………………………………………………5 2.1.3 Management practices against Striga hermonthica ……………………………………….7 2.1.4 Biological control of weeds ………………………………………………………………………10 2.2 Description of Fusarium Species …………………………………………………………………11 2.2.1 Biology of Fusarium oxysporum………………………………………………………………..12
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2.2.2 Life cycle of Fusarium oxysporum…………………………………………………………….13 2.2.3 Formation and germination of conidia………………………………………………………..14 2.2.4 Infection of Striga seedlings by Fusarium oxysporum …………………………………15 2.2.5 Efficacy of Fusarium oxysporum f. sp. strigae as isolates biocontrol agents of Striga hermonthica ………………………………………………………………………………………….16 2.3 Effects of Fungicides on Fungal Pathogens …………………………………………………..18 CHAPTER THREE 3.0 MATERIALS AND METHODS …………………………………………………………………20 3.1 Preparation of Potato Dextrose Agar Media ………………………………………………….20 3.1.1 Determining the effect of pesticides and pesticide rates on isolates of Fusarium oxysporum f. sp. strigae …………………………………………………………………………………..20 3.1.2 Data collection ………………………………………………………………………………………..22 3.2 Data Analysis ……………………………………………………………………………………………24 CHAPTER FOUR 4.0 RESULTS …………………………………………………………………………………………………25 4.1 Cultural and Morphological Characteristics of Fusarium oxysporum f. sp. strigae Isolates PSM 197 and Foxy 2 on PDAs ……………………………………………………………..25 4.1.1 Main effect of pesticides and rate on morphological characteristics and conidia germination of Fusarium oxysporum f. sp. strigae isolates in Zaria, Nigeria……………25 4.3 Compatibility of Pesticides with Fusarium oxysporum f. sp. strigae Isolates……..40 CHAPTER FIVE 5.0 DISCUSSION …………………………………………………………………………………………..42
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CHAPTER SIX 6.0 SUMMARY, CONCLUSION AND RECOMMENDATIONS……………………….47 6.1 Summary ………………………………………………………………………………………………….47 6.2 Conclusion ………………………………………………………………………………………………..48 6.3 Recommendation ……………………………………………………………………………………….48 REFERENCES……………………………………………………………………………………………….49 APPENDICES ……………………………………………………………………………………………….
CHAPTER ONE
1.0 INTRODUCTION Parasitic weeds of the genus Striga (Orobanchaceae) pose a major threat to cereal production in the African savannahs. To this effect, these weeds are important limitations to the attainment of regional food security (Parker and Riches, 1993). Kuchinda et al. (2003), Marley et al. (2004), Marley and Shebayan (2005) and Ejeta (2007) reported independently, that Striga hermonthica (Del.) Benth is the most economically important parasitic weed of cereals, especially maize (Zea mays L.) and sorghum (Sorghum bicolor (L.) Moench) in the African Savannah, causing 40 – 100 % grain yield losses. Management approaches for Striga control in Nigeria are generally based on cultural practices such as land preparation, hand pulling, hoe weeding, use of trap and catch-crops, seed treatment, application of appropriate rate of nitrogen fertilizer, herbicide spray, use of biological control and host plant resistance (Lagoke et al., 1988; Marley et al., 1999; Nekoum and Marley, 2002; Menkir et al., 2006). Control of Striga is particularly difficult due to its biology and intimate physiological interaction with its hosts. The parasite attaches its roots to the host, thereby withdrawing water, mineral nutrients, carbohydrates and amino-acids for its growth and development. These consequently cause stunted shoot growth, leaf chlorosis and reduced photosynthesis in the host (Ejeta and Butler, 2000; Frost et al., 1997).
Damage is done to the host before parasite shoots emerge above soil level. So far, effective control of Striga has not been achieved through any single measure, and therefore, the integrated approach of which bio-control is a crucial component, is the
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most promising strategy for reducing Striga infestations. The potential of using fungi for biological control of Striga was proposed by Musselman and Hepper (1983) and has since generated research interest. Adeoti (1993) and Weber et al. (1995) showed that Fusarium spp., Cercospora spp., Phoma spp., Alternaria spp. and Macrophomina spp. were associated with Striga spp. Abbasher et al. (1995) first reported Fusarium oxysporum f. sp. strigae as pathogenic on Striga spp. This fungus infects Striga at all developmental stages from seeds to flowering (Fravel et al., 2003). From diseased Striga hermonthica in northern Ghana, Foxy 2 was isolated (Abbasher et al., 1999). Elzein et al. (2006) reported between 75 and 81 % reduction of healthy emerged Striga shoots when Sorghum seeds were coated with Foxy 2 using 40 % gum Arabic. PSM 197 isolated from diseased Striga hermonthica plants in northern Nigeria, is aggressive isolate which reduce S. hermonthica emergence by 89.1 and 100 % through foliar application and soil incorporation of the fungus respectively (Marley et al., 1999). 1.1 Justification The application of biocontrol agent (Fusarium oxysporum f. sp. strigae) coated with maize seeds has been found effective in controlling Striga hermonthica (Ciotola et a., 2000; Ndambi, 2011). However, many farmers use imidacloprid + metalaxyl-M + tebuconazole, benomyl dressed seeds to manage seedling diseases, metsulfuron methyl to manage weeds and application of carbendazim, mancozeb and hexaconazole for managing fungal diseases. The efficacy of PSM 197 and Foxy 2 as a biological control agent (BCA) can be affected by pesticides usage. Therefore, the need to test some of these pesticides on growth and conidia of F. oxysporum isolates obtained in West Africa in vitro became imperative.
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1.2 Objectives of the Study The objectives of the study were to:
1. evaluate effect of pesticides on the two Fusarium oxysporum f. sp. strigae isolates
2. determine the most appropriate rate of pesticides for application with Fusarium oxysporum f. sp. strigae isolates
3. determine the compatibility of pesticides with Fusarium oxysporum f. sp. strigae isolates
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