Abstract
The bacterial biocontrol agents (BCAs) treatments were used for seed microbiolization; the bacterial biocontrol agents (BCAs) used selected from previous study on the control of Xanthomonas-axonopodis pv. phaseoli Xap) includes: Bacillus (DFs093, DFs348 and DFs769), Pseudomonas (DFs513, DFs831 and DFs842), Rhodococcus (DFs843 and DFs912), and the combinations C01 (DFs093+DFs769+DFs831), C02 (DFs093+DFs769+DFs842) and C03 (DFs093+DFs769+DFs348). Sixteen (16) Xap strains were collected from several Brazilian regions, and were inoculated in cotyledonary leaves. The symptom development was followed for 10 days. The treatments were compared by the area under the disease progress curve for disease incidence, severity, and index. In general, majority of the BCAs reduced, to some degree, the disease caused by different Xap strains. The combination C01, and the isolate DFs831 resulted in highest mean disease control. The data from this study suggest a relationship between the region of origin of Xap strain and the efficacy of BCA to control the disease caused by it. The use of combinations of these organisms increased the efficacy of the biocontrol of several strains of the same pathogen. A strain-BCA interaction was shown by data collected from this study, which evidence the importance of selecting a BCA or a combination of BCAs with a wider spectrum of action. Key words: Biological control, co-inoculation, Bacillus, Pseudomonas, Rhodococcus, bean common blight.
Highlights
The bacterial blight (Xanthomonas axonopodis pv. phaseoli (Smith) Dye (Xap) of common beans (Phaseolus vulgaris L.) occurs worldwide and is especially serious in regions of high temperatures and relative humidity
The data from this study suggest a relationship between the region of origin of Xap strain and the efficacy of biocontrol agents (BCA) to control the disease caused by it
The aggressiveness was quite different among the strains, in general, the majority of the BCAs reduced, to some degree, the disease caused by different Xap strains (Figures 3 to 5); the degree of control as indicated by reduction of disease incidence (DI), disease severity (DS) and the disease index differed significantly among the BCA isolates
Summary
The bacterial blight (Xanthomonas axonopodis pv. phaseoli (Smith) Dye (Xap) of common beans (Phaseolus vulgaris L.) occurs worldwide and is especially serious in regions of high temperatures and relative humidity. Phaseoli (Smith) Dye (Xap) of common beans (Phaseolus vulgaris L.) occurs worldwide and is especially serious in regions of high temperatures and relative humidity. The disease is very damaging in rainy season crop (Almeida et al, 2015; Fourie, 2002) and losses of up to 50% have been reported (Vieira and Souza, 2000). Being widely distributed in Brazil, difference in the virulence Xap strains occurring in different regions are expected, which can affect the control strategies, especially development of resistant cultivars (Vieira and Souza, 2000). Frequent failure of disease control through the use of resistant cultivars and chemicals has been attributed to the differences in the virulence of the pathogen (Mutlu, 2008), which warrants developing alternate methods, including biological control
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