Biological control of common bacterial blight and reduction of transmission of Xanthomonas phaseoli pv. phaseoli to bean seeds

Abstract

Common bacterial blight (CBC), caused by Xanthomonas phaseoli pv. phaseoli (Xpp), is one of the most important diseases affecting common bean crops, with its incidence resulting in annual yield losses. The primary means of pathogen dissemination is through the association of the bacterium with bean seeds, which transmit the pathogen to emerging plants and subsequently lead to disease development. The limited availability of effective control methods highlights the need to develop alternative strategies integrated into crop management systems. Biological control of plant diseases is an efficient method and has shown positive results against several phytopathogens in bean cultivation. Therefore, the objective of this study was to evaluate the effects of spraying endophytic bacteria on bean plants for the control of common bacterial blight. Bacterial isolates obtained from bean seeds and one isolate from tomato (UFLA22) were selected for use as biological control agents, along with an Xpp isolate also obtained from bean seeds. Experiments were conducted under laboratory and greenhouse conditions in a randomized block design. The antibiosis effect of the selected bacteria against the Xpp isolate, disease severity, plant height and weight, phenolic compound contents, and phenylalanine ammonia-lyase (PAL) activity after treatment were evaluated. All evaluated isolates inhibited Xpp growth in vitro. Isolates G35, G37, G40, and UFLA22 showed greater effectiveness in controlling common bacterial blight, with isolate UFLA22 being the most efficient. Isolates G33, and UFLA22 contributed to the increase of plant weight in diseased plants, exceeding the values observed in the inoculated control and in the healthy control. Phenolic compound contents and PAL activity were higher in treatments with isolates G40 and UFLA22 compared with the inoculated control. Isolates G40 and UFLA22 reduced the transmission of Xpp to bean seeds, being recovered from seeds when applied on R6. These results demonstrate that bacteria isolated from bean seeds may be effective in controlling CBC.