Effect of bacterial biological factors on reducing incidence and severity of cucumber root rot disease

Abstract

This investigation is carried out.in the laboratories of the Plant Protection Directorate, Ministry of Agriculture, to evaluate the pathogenicity of eleven fungal isolates obtained from the roots of diseased cucumber plants, and to assess the efficacy of three bacterial strains—Bacillus cereus, Bacillus thuringiensis, and Bacillus rugosus— in minimizing the incidence and severity of cucumber root rot induced by Rhizoctonia solani under pot conditions. Biologically synthesized nanoparticles, particularly silver nanoparticles (AgNPs), have shown strong antimicrobial activity against a wide range of plant pathogenic fungi. The results showed that all fungal isolates significantly reduced seed germination and increasing intensity of the illness. Isolates of R. solani are particularly aggressive, with four isolates completely inhibiting seed germination and causing 100% disease severity. The remaining isolates resulted in germination rates ranging from 30% to 93.3%, and severity levels between 13.3% and 46.7%, compared to the healthy control (100% germination, 0% severity). Nucleotide sequence analysis confirmed the identity of the fungal isolates as R. solani, Fusarium oxysporum, and Macrophomina phaseolina, and the sequences are deposited in GenBank under accession numbers PP892963.1, PQ810062, and PV008703.1, respectively. All three bacterial strains significantly reduced disease incidence and severity, with B. rugosus showing the greatest effect, followed by B. cereus and B. thuringiensis, reducing disease incidence to 6.6%, 26.6%, and 63.3% and severity to 23.3%, 43.3%, and 73.3%, respectively.