Synergistic Effect of Organic Acids and Antagonistic Bacteria on Sustainable Management of Rhizoctonia solani Diseases in Chia (Salvia hispanica L)

Rhizoctonia solani Kühn is a destructive soil-borne fungal pathogen responsible for damping-off, root rot, and sore shin diseases in a wide range of plant species,leading to substantial economic losses. This study evaluates the efficacy of citric, formic, and oxalic acids in combination with Bacillus subtilis strain BPeK8 and Pseudomonas fluorescens strain K77 as sustainable management for Rhizoctonia-induced diseases in chia plants. The study reports the first confirmed occurrence of Rhizoctonia sore shin disease on chia in Egypt, based on morphological characteristics and molecular identification. R. solani was consistently isolated from infected chia tissues with isolation frequencies of 95.0 and 93.1% in Bani Suef and El-Fayoum Governorates, respectively. In vitro assays demonstrated that citric, formic, and oxalic acids significantly inhibited the mycelial growth of R. solani in a concentration-dependent manner, with oxalic acid showing the strongest effect. Furthermore, these organic acids did not impede the growth of the antagonistic bacteria B. subtilis or P. fluorescens, thereby enhancing their biocontrol potential against R. solani. Soil drenching with organic acids increased the endogenous exudation of organic acids from chia roots and stimulated bacterial chemotaxis, which in turn enhanced the biocontrol activity against the pathogen. Combined treatments of B. subtilis or P. fluorescens with oxalic or citric acid effectively reduced disease incidence and severity by bolstering plant defense responses. These results highlight the potential of integrating biocontrol agents with eco-friendly organic acids, which constitutes a viable and sustainable strategy for managing R. solani-induced diseases in chia, thereby enhancing crop protection and agricultural sustainability.