Combined chemical and biological control of Fusarium and nematode species associated with Eldana saccharina in sugarcane
Introduction
Eldana saccharina Walker (Lepidoptera: Pyralidea) is a serious pest in maize, sorghum and in all sugarcane regions of South Africa. It is an African native with a wide distribution within South Africa and has a number of natural hosts including the water sedges Cyperus dives and Cyperus papyrus (Assefa et al., 2008; Webster et al., 2005; Rutherford, 2015). The pest is estimated to cause the sugarcane industry losses of over a billion rand per annum (Zhou, 2015). This stem borer started becoming a sugarcane pest when its natural hosts were destroyed for sugarcane production through wetland drainage and bringing sugarcane fields very close to wetlands (Rutherford, 2015). Unlike other significant stem-borers (Busseola, Sesamia and Chilo species) Eldana saccharina rarely feeds on ‘fresh’ leaf whorls and immature stems. In mature stems stalk rotting fungi, most notably Fusarium sp, are present in the plant tissue surrounding E. saccharina borings. These fungi can therefore influence the outcome of the plant-insect interaction (McFarlane et al., 2009). A number of researchers have expressed the importance of integrated approach for the effective control of this pest (Conlong and Rutherford, 2009; Kvedaras et al., 2014; Cockburn et al., 2013; Dentinger et al., 2013). Studies on the pest ecology have revealed the limitation of biological, chemical and plant based control of this stem borer due to the fact that the adult spends most of its short life mating and laying eggs on hidden areas of the sugarcane stalk (Conlong, 1997; Horton et al., 2002). Upon hatching the larvae feeds on the stalk and bores into it where it will remain until it pupates (Keeping, 1995). In South Africa chemical control of this pest has been mainly through the use of a pyrethroid insecticide, Fastac, with three more chemicals receiving “emergency registration” only in 2015. This was due to the perceived high numbers of the pest country wide due to the recent drought in all sugarcane growing regions (Rutherford, 2015). Repeated pesticide application targeting neonate larvae can reduce damage by up to 60%, however this may result in significant production costs and environmental pollution (Leslie, 2003). Sometimes these pesticides increase mycotoxin production (Hrubošová-Hrmová et al., 2011) and there is a serious problem of pathogenic microorganisms developing resistance against pesticides (Kozlovsky et al., 1999). There is also concerns with the pesticides’ negative effects on non-target organisms including beneficial bacteria and fungi, plants, animals and even humans Zukerman and Esnard, 1994. There is a demand to develop some environmentally safer methods to cope with damage of plant diseases. The use of silicon to improve the stalk structure showed significant infestation reduction by making the rind to be less penetrable (Keeping and Meyer, 2002; Keeping and Meyer, 2006; Kvedaras and Keeping, 2007; Kvedaras et al., 2014) however this also caused reduction in sugarcane milling quality (Singh and Singh, 2013). Soil borne pathogens always remain a major threat to cultivated plants. Among all types of soil borne pathogens root-infecting fungi and parasitic nematodes are considered as major and widespread problems. Fusarium species mainly Fusarium solani Mart Appel & Wollenw. emend. Snyd. & Hans., Fusarium oxysporum Schltdl., and Fusarium moniliforme Sheld. are major threat to crop plants. They are isolated from soil, roots, aerial plant tissues, plant debris and other organic substrates and are capable of producing wide range of mycotoxins (Aoki et al., 2003; Nelson et al., 1983; Newson and Martin, 1953). These mycotoxins are …show more content…
Production of resistant varieties is time consuming and needs to be supplemented with other control methods. Sometimes varieties of good agronomic properties are not released from breeding trials because of their susceptibility to eldana (Zhou, 2015). Plant growth promoting rhizobacteria have been reported as a safer method against plant pathogens. These rhizobacteria have been isolated from the phyllosphere, rhizosphere and as endophyte from the plant tissue (Glick, 1995). These bacteria not only enhance the growth of plants by solubilizing phosphate, fixing nitrogen but also improve plant resistance against pathogen invasion by activating system acquired resistance (Bloemberg and Lugtenberg, 2001), producing hydrogen cynide and sidrophores (Kloepper et al.,
Introduction
Eldana saccharina Walker (Lepidoptera: Pyralidea) is a serious pest in maize, sorghum and in all sugarcane regions of South Africa. It is an African native with a wide distribution within South Africa and has a number of natural hosts including the water sedges Cyperus dives and Cyperus papyrus (Assefa et al., 2008; Webster et al., 2005; Rutherford, 2015). The pest is estimated to cause the sugarcane industry losses of over a billion rand per annum (Zhou, 2015). This stem borer started becoming a sugarcane pest when its natural hosts were destroyed for sugarcane production through wetland drainage and bringing sugarcane fields very close to wetlands (Rutherford, 2015). Unlike other significant stem-borers (Busseola, Sesamia and Chilo species) Eldana saccharina rarely feeds on ‘fresh’ leaf whorls and immature stems. In mature stems stalk rotting fungi, most notably Fusarium sp, are present in the plant tissue surrounding E. saccharina borings. These fungi can therefore influence the outcome of the plant-insect interaction (McFarlane et al., 2009). A number of researchers have expressed the importance of integrated approach for the effective control of this pest (Conlong and Rutherford, 2009; Kvedaras et al., 2014; Cockburn et al., 2013; Dentinger et al., 2013). Studies on the pest ecology have revealed the limitation of biological, chemical and plant based control of this stem borer due to the fact that the adult spends most of its short life mating and laying eggs on hidden areas of the sugarcane stalk (Conlong, 1997; Horton et al., 2002). Upon hatching the larvae feeds on the stalk and bores into it where it will remain until it pupates (Keeping, 1995). In South Africa chemical control of this pest has been mainly through the use of a pyrethroid insecticide, Fastac, with three more chemicals receiving “emergency registration” only in 2015. This was due to the perceived high numbers of the pest country wide due to the recent drought in all sugarcane growing regions (Rutherford, 2015). Repeated pesticide application targeting neonate larvae can reduce damage by up to 60%, however this may result in significant production costs and environmental pollution (Leslie, 2003). Sometimes these pesticides increase mycotoxin production (Hrubošová-Hrmová et al., 2011) and there is a serious problem of pathogenic microorganisms developing resistance against pesticides (Kozlovsky et al., 1999). There is also concerns with the pesticides’ negative effects on non-target organisms including beneficial bacteria and fungi, plants, animals and even humans Zukerman and Esnard, 1994. There is a demand to develop some environmentally safer methods to cope with damage of plant diseases. The use of silicon to improve the stalk structure showed significant infestation reduction by making the rind to be less penetrable (Keeping and Meyer, 2002; Keeping and Meyer, 2006; Kvedaras and Keeping, 2007; Kvedaras et al., 2014) however this also caused reduction in sugarcane milling quality (Singh and Singh, 2013). Soil borne pathogens always remain a major threat to cultivated plants. Among all types of soil borne pathogens root-infecting fungi and parasitic nematodes are considered as major and widespread problems. Fusarium species mainly Fusarium solani Mart Appel & Wollenw. emend. Snyd. & Hans., Fusarium oxysporum Schltdl., and Fusarium moniliforme Sheld. are major threat to crop plants. They are isolated from soil, roots, aerial plant tissues, plant debris and other organic substrates and are capable of producing wide range of mycotoxins (Aoki et al., 2003; Nelson et al., 1983; Newson and Martin, 1953). These mycotoxins are …show more content…
Production of resistant varieties is time consuming and needs to be supplemented with other control methods. Sometimes varieties of good agronomic properties are not released from breeding trials because of their susceptibility to eldana (Zhou, 2015). Plant growth promoting rhizobacteria have been reported as a safer method against plant pathogens. These rhizobacteria have been isolated from the phyllosphere, rhizosphere and as endophyte from the plant tissue (Glick, 1995). These bacteria not only enhance the growth of plants by solubilizing phosphate, fixing nitrogen but also improve plant resistance against pathogen invasion by activating system acquired resistance (Bloemberg and Lugtenberg, 2001), producing hydrogen cynide and sidrophores (Kloepper et al.,