Evaluation of mycoparasitic efficacy of nematode-trapping fungi against Rhizoctonia solani inciting sheath blight disease in rice (Oryza sativa L.)
Graphical abstract
Introduction
Rice sheath blight caused by soil borne Basidiomycete fungus Rhizoctonia solani Kühn (teleomorph: Thanatephorus cucumeris) is most damaging disease that greatly reduces yield in upland and rain-fed lowland rice worldwide (Ou, 1985, Prot and Matias, 1995, Sariano et al., 2000, Sariano and Reversat, 2003). Management of R. solani infecting rice is largely reliant on the use of fungicides (Chin and Bhandhufalck, 1990, Damicone et al., 1993). However, fungicidal management causes various undesirable effects such as phytotoxicity to plants, soil and water pollution and unavoidable natural imbalance in the soil affecting the whole ecosystem adversely (Groth et al., 1990, Dehne and Oerke, 1998, Anand et al., 2010). Hazardous effect of pesticides on humans and other non-target organisms have led to search on ecofriendly methods for management of plant diseases among which management through utilization of naturally occurring enemies of phytopathogens has emerged as one of the most possible approach within the integrated pest management context (Oka, 2010, Niu and Zhang, 2011).
Some fungi are known to establish interrelationships whereby a fungus parasitic on another fungal species. This kind of relationship is referred as mycoparasitism (Butler, 1957) and fungus causing mycotrophic life style on other fungi represents a useful tool in biological control due to the fact that many of their host are fungal plant pathogens of agricultural crops (Papavizas, 1985, Chet et al., 1997). In recent past, several studies have been conducted in the search for mycoparasitic fungi acting as biological control agents against a number of important soil borne plant pathogens (Kumar et al., 2011, Consolo et al., 2012, Kumar et al., 2012, Singh et al., 2012a, Singh et al., 2012b). Nematode-trapping fungi are a unique group of microorganisms broadly distributed in terrestrial and aquatic ecosystems (Pramer, 1964, Kumar and Singh, 2006a, Nordbring-Hertz et al., 2011). These fungi play a significant role in suppression of plant-parasitic nematodes, animal-parasitic nematodes and free-living nematodes in soil by capturing them into various types of adhesive and non-adhesive traps. The carnivorous habit of these fungi has been considered as an important strategy of their survival under unfavorable soil conditions (Kumar et al., 2015). In addition to their carnivorous habit, some nematode trapping fungi such as Arthrobotrys oligospora, A. robusta, A. superba and Monacrosporium ellipsosporum have been reported to parasitize Matruchotia varians, Rhizoctonia solani, Geotrichum spp. and Sclerotonia sclerotiorum through hyphal coiling (Tzean and Estey, 1978, Gui-Zhen et al., 2004, Singh et al., 2012a).
Many nematode- trapping fungi have not been studied for their mycotrophic potential against R. solani. The ability of R. solani to persist in soil and on crop residues allows it to contact with mycoparasitic species of nematode -trapping fungi in soil, which can be used as biological control agent against this pathogen. Therefore, the aim of this study was to isolate the species of nematode-trapping fungi from soil and evaluate their mycotrophic efficacies against various isolates of R. solani under laboratory and pot condition.
Section snippets
Fungal isolates
Four isolates of R. solani were isolated from diseased rice plants collected from Gangavathi, Kumarganj, Navsari and Pantnagar localities of Karnataka, Uttar Pradesh, Gujarat and Uttarakhand states of India respectively. Plant parts showing the sheath blight symptoms were cut into small sections, surface sterilized by dipping into 0.1% HgCl2 for 30 s followed by washing with sterilized distilled water thrice and then these sections were transferred aseptically to Petri plates poured with
Isolates of Rhizoctonia solani
Four isolates of R. solani were isolated from Faizabad (isolate FA), Pantnagar (isolate PA), Gujarat (isolate GU) and Karnataka (isolate KA) states of India. Based on the interaction of fungi isolated from infected rice leaves with the tester isolate of R. solani AG-IIA (ITCC-4110) and their disease inducing ability on rice variety Pusa Basmati, all four isolates were confirmed as Rhizoctonia solani AG-1.
Isolation of nematode-trapping fungi
Four species of fungi capturing nematodes by adhesive three-dimensional networks, adhesive
Discussion
Environmental concerns related with the use of pesticides have lead to research into alternative strategies with a strong focus on harnessing the bio-control potential of natural enemies of plant pathogens. Nematode-trapping fungi are an important group of soil fungi that capture and kill the plant and animal -parasitic nematodes (Kumar and Singh, 2006a, Kumar and Singh, 2006b, Singh et al., 2007). Numerous surveys on nematode - trapping fungi have shown that they are present throughout the
Acknowledgements
The authors would like to thank Dr. Abul Hasan, Ex. Head of Department of Nematology for scientific review of the manuscript, Dr. Bhagwan Singh, Head of Plant Pathology and Prof. Akhtar Haseeb, Vice Chancellor of Narendra Deva University of Agriculture Technology, Faizabad, India for all support and technical advice during this work.
Conflict of interest
No conflict of interest is declared.
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