Contents lists available at ScienceDirect Physiological and Molecular Plant Pathology journal homepage: www.elsevier.com/locate/pmpp Physiological and antioxidant insights into common bean resistance to common bacterial blight L.C. Silva a , D. Debona a , C.E. Aucique-Pérez a , J.R. Oliveira a , J.I. Ribeiro Júnior b , V.V. Brás a , F.A. Rodrigues a,* a Universidade Federal de Viçosa (UFV), Departamento de Fitopatologia, Laboratório da Interação Planta-Patógeno, Viçosa, Minas Gerais State, Zip Code 36570-900, Brazil b UFV, Departamento de Estatística, Viçosa, Minas Gerais State, Zip Code 36570-900, Brazil ARTICLE INFO Keywords: Photosynthesis Phaseolus vulgaris Xanthomonas axonopodis pv. phaseoli var. fuscans ABSTRACT Common bacterial blight (CBB), caused by Xanthomonas axonopodis pv. phaseoli (Xap) (known also as X. cam- pestris pv. phaseoli and its variant Xap var. fuscans (Xapf)), is the most important bacterial disease of common bean worldwide. Information regarding Xap-common bean interaction and the mechanisms of host resistance involved needs to be elucidated. In the present study, we investigated physiological and biochemical responses in a susceptible (Ouro Negro) and a resistant (Diamante Negro) cultivar of common bean to CBB. To this end, analyses of gas exchange and chlorophyll (Chl) a fluorescence, activities of antioxidant enzymes (superoxide dismutase (SOD), peroxidase (POX), and ascorbate peroxidase (APX)) as well as concentrations of photosynthetic pigments, hydrogen peroxide (H 2 O 2 ), and malondialdehyde (MDA) were performed in cotyledonary leaves that were either infiltrated with a saline solution (control) or with a Xapf suspension. The CBB severity and lesion area were lower in plants from the resistant cultivar than in plants from the susceptible cultivar. The Xapf infection reduced gas exchange parameters and concentration of photosynthetic pigments but such decreases were significantly higher for the susceptible cultivar than for the resistant cultivar. Higher SOD, POX, and APX activities were recorded in the Xapf-infiltrated cotyledonary leaves than in control but greater activities occurred for the resistant cultivar than for the susceptible cultivar. The Xapf-infiltrated cotyledonary leaves, particularly those of the susceptible cultivar, displayed higher concentrations of H 2 O 2 and MDA than plants from the control treatment. Images of Chl a fluorescence showed that changes stemmed from Xapf infection were evident as early as 6 h after inoculation and became more expressive as CBB progressed, mainly for the susceptible cultivar. Area under the curve of Chl a fluorescence parameters was lower for inoculated plants than for plants from the control treatment but it was higher for the susceptible cultivar than for the resistant cultivar. Results of the present study suggest that the antioxidant system played a major role in common bean resistance to CBB limiting Xapf-trig- gered generation of reactive oxygen species, cellular damage as well as photosynthetic and photochemical dysfunctions. 1. Introduction Common bacterial blight (CBB), caused by Xanthomonas axonopodis pv. phaseoli (Xap) (known also as X. campestris pv. phaseoli and its variant Xap var. fuscans (Xapf)), is the most important bacterial disease of common bean (Phaseolus vulgaris L.) and can cause yield losses of up to 45% mainly when beans are cultivated under frequent rainfall or irrigation [1,2]. In Brazil, CBB occurs in almost all producing regions, mainly in the states of Minas Gerais, Paraná, Rio de Janeiro, and São Paulo [2]. Ref. [1], differentiated Xap from Xapf and nonpathogenic Xanthomonas species associated with common bean by using restriction fragment length polymorphism analysis of polymerase chain reaction amplified 16S ribosomal gene, including the 16S–23S intergenic spacer region and repetitive element PCR (rep-PCR), from a culture collection maintained at the Centro Internacional de Agricultura Tropical. Indeed, cluster analysis of rep-PCR profiles revealed a high level of genetic differentiation between Xap from Xapf, showing that they are geneti- cally distinct and no clonal being Xap with more genetic diversity than Xapf [1]. First symptoms of CBB appear as dark green and water-soaked lesions that are oily in appearance. As CBB progresses, lesions expand and become brown with chlorotic borders, thus conferring a necrotic (blight) aspect to the colonized leaf tissue [1]. CBB has been controlled https://doi.org/10.1016/j.pmpp.2020.101505 Received 28 November 2019; Received in revised form 8 March 2020; Accepted 27 April 2020 * Corresponding author. E-mail address: fabricio@ufv.br (F.A. Rodrigues). Physiological and Molecular Plant Pathology 111 (2020) 101505 Available online 03 May 2020 0885-5765/ © 2020 Elsevier Ltd. All rights reserved. T