**5. Conclusion**

Much research is still needed to fully understand the role that rhizosphere competent fungal entomopathogenic *Lecanicillium* hybrid strains play in regulating SCN populations and how we can use this knowledge to design and implement more effective SCN biological control programs. Questions of particular importance to consider are highlighted by Vega et al. (2009) and include the following: (1) Do plants benefit from a rhizosphere association with

*Lecanicillium* spp. have activity against numerous phytopathogenic fungi including powdery mildews (Verhaar et al., 1997, 1998; Askary et al., 1997, 1998, 1999; Dik et al., 1998; Miller et al., 2004), rusts (Spencer and Atkey, 1981; Leinhos and Buchenauer, 1992) green molds (Benhamou and Brodeur, 2000) and *Pythium* (Benhamou and Brodeur, 2001). Fungi that may control phytopathogenic fungi can act through antibiosis and mycoparasitism (Kiss, 2003). Some *Lecanicillium* isolates act as mycoparasites, attaching to powdery mildew mycelia and conidia, producing enzymes such as chitinase, that allow penetration of the mildew spores and hyphae, killing the pathogen (Askary et al., 1997). Leinhos and Buchenauer (1992) demonstrated that several *Lecanicillium* spp. were able to penetrate and colonize uredial sori of *Puccinia coronata*. In *Penicillium digitatum*, the mode of action was attributed to changes in host cells prior to contact by the *Lecanicillium* spp. (Benhamou and Brodeur, 2000) while in *P. ultimatum*, in addition to mycoparasitism of the plant pathogen, the mode of action was linked to colonization of host plant tissues, triggering a plant defense reaction (Benhamou and Brodeur, 2001). Hirano et al. (2008) found that applying *L. muscarium* blastospores to cucumber roots induced systemic resistance. *L. muscarium* pre-inoculated plants suffered significantly fewer lesions and reduced disease severity compared with non-inoculated plants. Kusunoki et al. (2006) and Koike et al. (2007b) found that root treatment with *L. muscarium* reduced disease incidence and wilting score in other soil-borne disease combinations such as tomato—*Verticillium dahliae*, Japanese radish—*V. dahliae*, and melon—

In the case of soilborne pathogens, further opportunities exist for interactions with other microorganisms occupying the same ecological niche. The significant role of nematodes in the development of diseases caused by soilborne pathogens has been demonstrated in many crops throughout the world. In many cases, such nematode–fungus disease complexes involve root-knot nematodes (*Meloidogyne* spp.), although several other endoparasitic (*Globodera* spp., *Heterodera* spp., *Rotylenchulus* spp., *Pratylenchus* spp.) and ectoparasitic (*Xiphinema* spp., *Longidorus* spp.) nematodes have been associated with diseases caused by soilborne fungal pathogens (Back et al., 2002). In the case of SCN, Sudden Death Syndrome (SDS) caused by *F. solani* is a major disease of soybean which, among other symptoms, induces root rot, crown necrosis, interveinal chlorosis, defoliation and abortion of pods (Rupe, 1989; Nakajima *et al*., 1996). Recent research on SDS has focused on identifying genes for dual resistance against both nematode and fungus (Chang *et al*., 1997; Meksem

It is known that entomopathogenic *Lecanicillium* spp. have antagonistic effects to soil-borne fungi such as *Fusarium oxysporum*, *F. solany*, *Pythium* spp. and *Verticillium dahlia* (Koike et al., 2006, Goettel et al., 2008). Therefore, it might be possible to develop *Lecanicillium* hybrid strains with potential for biological control of a complex of plant diseases, plant parasitic

Much research is still needed to fully understand the role that rhizosphere competent fungal entomopathogenic *Lecanicillium* hybrid strains play in regulating SCN populations and how we can use this knowledge to design and implement more effective SCN biological control programs. Questions of particular importance to consider are highlighted by Vega et al. (2009) and include the following: (1) Do plants benefit from a rhizosphere association with

*Fusarium oxysporum* f.sp. *melonis.* 

*et al*., 1999; Prabhu *et al*., 1999).

nematodes and insect pests.

**5. Conclusion** 

fungal entomopathogens? (2) Is the 'bodyguard' concept relevant in soil? If so, what is the signaling mechanism between trophic levels? (3) Do different phylogenetic groups of fungal entomopathogens display different strategies in their association with plants? (4) How do soil-borne fungal entomopathogens interact between above and below ground ecosystems? (5) What is the mechanism of yield increases in biological control target plant? (6) Does plant diversity impact fungal entompathogen diversity at the landscape or local level, and what is its impact on natural pest control? In addition to the basic scientific questions posed above, there are a number of questions that require further investigation as well: (1) What is the most effective approach for inoculating roots with rhizosphere competent isolates? Approaches will need to be identified for plants propagated via seed treatment, because there are a lot of problems in the direct treatment of soil such as costs & labor requirements. (2) How long do rhizosphere competent isolates persist on the root system of soybean or other host plants of plant parasitic nematodes? (3)Will the use of rhizosphere competent isolates provide consistent and acceptable levels of pest including plant parasitic nematode control?

At present there has been only limited success with field applications of biological controls against SCN. Chen (2004) pointed out factors involved in their biological control, 1) stage of nematode infected, 2) ability to colonize soil, roots, cysts and gelatinous matrices, 3) competition with other fungi, 4) cropping systems and tillage, and 5) edaphic and environmental factors. In our research, all experiments were done *in vitro* and in glasshouses. Although there is still much to be learned at the field level, it has been demonstrated that *Lecanicillium* hybrid strains have multiple effects (toxic and parasitism) for SCN and soybean plant roots (as root colonizer and endophyte) as well as on plant pathogens and insect pests, making these strains promising for development as broad spectrum biopesticides that include SCN.

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