Endophytic Fungi as Potential Biocontrol Agents against Rhizoctonia solani J.G. Kühn, the Causal Agent of Rice Sheath Blight Disease

SIMPLE SUMMARY: Rice, together with wheat and corn, is among the most important food crops for mankind. Half of the world’s population consumes rice, mainly in Asia, southern Europe, tropical America, and parts of Africa. Rice sheath blight, caused by Rhizoctonia solani, is one of the main diseases in rice production. The control of this pathogen is difficult due to its ecological behavior, broad host range, and the high survival rate of sclerotia under various environmental conditions. In this research, after morphological and molecular identification of fungal isolates, five superior isolates, including Trichoderma virens, Trichoderma harzianum, Curvularia lunata, Aspergillus fumigatus, and Aspergillus awamori were studied in the in vitro and greenhouse trials, towards their potential to inhibit R. solani. The statistical analysis showed a significant difference between the effectiveness of fungi used in the volatile metabolites assay and in terms of height and fresh weight of plants in the greenhouse. It can be concluded that T. virens and A. fumigatus are the most effective antagonists in rice sheath blight disease control. ABSTRACT: The rice sheath blight disease, caused by Rhizoctonia solani J.G. Kühn fungus, is a major disease of Oryza sativa L. occurring all over the world. Therefore, efforts need to be undertaken to limit the spread of this pathogen, preferably by using environmentally friendly methods. In the present study, 57 fungal isolates were recovered by surface sterilization technique from 120 rice samples collected from paddy fields in Guilan province, Iran. Biological characterizations of the isolated taxa were performed in vitro, in the dual culture, volatile metabolites, and slide culture methods. Among the studied isolates, Trichoderma virens (J. H. Miller, Giddens and A. A. Foster) Arx was most effective in inhibiting the mycelial growth of R. solani in the dual culture (44.16% inhibition level), while Aspergillus fumigatus Fresen and T. virens had a 62.50–68.75% inhibition efficiency by volatile metabolites. In the slide culture, all of the isolates, except for T. harzianum Rifai, were effective in inhibiting the hyphae growth of R. solani. Under greenhouse conditions, rice plants inoculated with these potential antagonistic fungi showed a reduction in disease severity by even 41.4% as in the case of T. virens. Moreover, phenotypic properties of rice, such as plant height, fresh weight, and dry weight were increased in the plants inoculated with all antagonistic fungi tested, compared to the infected plants, except for the fresh weight of plants inoculated with Curnularia lunata (Wakker) Boedijn. The present in vivo and in vitro studies revealed that T. virens and A. fumigatus are the most effective antagonists in rice sheath blight disease control and could be applied in agricultural practice.