New insights into the resistance of four citrus genotypes to Xanthomonas citri subsp. citri
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SHORT COMMUNICATION
New insights into the resistance of four citrus genotypes to Xanthomonas citri subsp. citri Peng Ying Mei 1 & Yan Zhou 1
&
Zhong An Li 1 & Chang Yong Zhou 1
Received: 2 April 2019 / Accepted: 17 January 2020 # Società Italiana di Patologia Vegetale (S.I.Pa.V.) 2020
Abstract The resistance of different citrus genotypes to citrus canker, caused by Xanthomonas citri subsp. citri (Xcc), is quite different. In this study, four citrus genotypes with different resistance, including resistant kumquat ‘Luofu’ (Fortunella margarita), moderately resistant Ponkan ‘18–1-10’ (Citrus reticulata), moderately susceptible sweet orange ‘Newhall’ (C. sinensis) and susceptible grapefruit ‘Duncan’ (C. paradisi) were used to elucidate the resistance mechanism. The antibacterial analysis in vitro showed low concentration of H2O2 promoted growth of Xcc, whereas high concentration inhibited growth. In addition, NADPH oxidases, also known as respiratory burst oxidase homologues (rbohs), are required for H2O2 burst during infection. Subsequently, Xcc accumulation, H2O2 production and expression of CsrbohD was measured to elucidate their roles in citrus-Xcc interaction. Through the Spearman correlation and multiple linear regression analysis, we found all three factors were significantly correlated with variety resistance, which was significantly affected by H2O2 content and expression of CsrbohD. Taken together, these data indicate a feedback regulation of CsrbohD and H2O2 in citrus. When the H2O2 content was lower than the threshold, it was not sufficient to suppress Xcc growth, and more Xcc populations suppressed H2O2 production, thus forming a vicious circle. By contrast, it can suppress Xcc growth, then CsrbohD was suppressed to reduce the oxidative damage. Keywords Respiratory burst oxidase homologues (rbohs) . Hydrogen peroxide . Xanthomonas citri subsp. citri . Resistance
Citrus canker, caused by Xanthomonas citri subsp. citri (Xcc), is a devastating bacterial disease of citrus worldwide. Following artificial inoculation, all commercial citrus cultivars are susceptible to Xcc (Schubert and Sun 1996; Schubert et al. 2001; Brunings and Gabriel 2003), but their field resistance to Xcc is quite different, according to which, citrus genotypes can be classified into susceptible, moderately susceptible, moderately resistant and resistant genotypes. Previous research showed that Xcc inoculation significantly induced H2O2 content in kumquat (Kumar et al. 2011c; Mei et al. 2019), which shows significant field resistance to Xcc (Gottwald et al. 1993; Schubert and Sun 1996; Gottwald et al. 2002; Brunings and Gabriel 2003; Das 2003). H2O2 is mainly induced by NADPH oxidases, also known as respiratory burst oxidase homologues (rbohs), in plant-pathogen interactions (Bolwell and Wojtaszek 1997;
* Chang Yong Zhou [email protected] 1
National Citrus Engineering Research Center, Citrus Research Institute, Southwest University, Chongqing 400712, China
Lamb and Dixon 1997; Torres et al. 2002; Sagi and Fluhr 2006; Suzuki et al. 20
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