Biocontrol Efficacy of Bacillus subtilis and Pseudomonas fluorescens Isolates against Bacterial Wilt Disease of Tomato under Protected Conditions
DOI:
https://doi.org/10.63359/g6ewcb68Abstract
Bacterial wilt, caused by Ralstonia solanacearum, remains one of the most destructive soil-borne diseases of tomato in protected cultivation systems. This study assessed the greenhouse performance of two rhizobacterial isolates, Bacillus subtilis (B-12) and Pseudomonas fluorescens (P-05), as potential biocontrol agents against the pathogen. Both isolates inhibited pathogen growth in vitro, producing identical inhibition zones of 18.4 ± 1.2 mm. Functional screening showed that B-12 expressed stronger siderophore production (+++; halo ratio 2.8) and higher protease activity (++) than P-05 (++ and +, respectively), whereas neither isolate showed detectable cellulase activity. Under greenhouse conditions, preventive soil application of either isolate significantly reduced disease incidence from 95.0 ± 4.2% in the pathogen-inoculated control to 35.0 ± 5.1%, corresponding to a biocontrol efficiency of 63.2%. Despite the similar effect on incidence, the two isolates differed in their capacity to limit symptom progression. Bacillus sp. B-12 lowered disease severity to 1.2 ± 0.3, compared with 2.1 ± 0.4 for P-05 and 3.6 ± 0.2 for the infected control. B-12 also restored plant height and chlorophyll status to levels approaching those of healthy plants, while P-05 showed a comparatively stronger effect on root dry weight. The data indicate that the two isolates express distinct but potentially complementary modes of action. B. subtilis B-12 appears particularly promising for limiting vascular symptom development, whereas P. fluorescens P-05 may contribute more strongly to rhizosphere fitness and root growth. These findings support further characterization of both isolates and provide a sound basis for testing single-strain and consortium-based biocontrol strategies for tomato bacterial wilt management under protected conditions.
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