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Surface Barriers of Mandarin ‘Okitsu’ Leaves Make a Major Contribution to Canker Disease Resistance

First, third, fourth, and eleventh authors: Instituto de Biología Molecular y Celular de Rosario (IBR)–Consejo Nacional de Investigaciones Científicas y Tecnológicas (CONICET), Área Virología, Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario (UNR), Ocampo y Esmeralda, S2000FHN Rosario, Argentina; first, second, ninth, and tenth authors: Facultad de Ciencias Agrarias, Universidad Nacional del Litoral (FCA-UNL), Depto. de Producción Vegetal, Kreder 2805, S3080HOF Esperanza, Argentina; fifth author: Instituto de Tecnología Agroindustrial del Noroeste Argentino (ITA-NOA), Estación Experimental Agroindustrial Obispo Colombres (EEAOC)-CONICET, Av. William Cross 3150, Las Talitas, T4101XAC Tucumán, Argentina; sixth author: Instituto de Ciencia y Tecnología Dr. Cesar Milstein, Fundación Pablo Cassará-CONICET, Saladillo 2468, C1440FFX Ciudad de Buenos Aires, Argentina; seventh author: Citrus Research and Education Center (CREC), University of Florida, 700 Experiment Station Rd., Lake Alfred 33850; and eighth author: Instituto de Biología Molecular y Celular de Plantas (IBMCP), Universidad Politécnica de Valencia-C.S.I.C, Ingeniero Fausto Elio, s/n, 46022 Valencia, España.

Field evaluations have shown that Satsuma mandarin (Citrus unshiu) ‘Okitsu’ is one of the mandarin cultivars that shows substantial resistance to Xanthomonas citri subsp. citri (X. citri), the causal agent of citrus bacterial canker disease. However, the mechanisms underlying this resistance are not well understood. In this study, we have shown that ‘Okitsu’ leaves are nevertheless susceptible to X. citri infection during a period of their development; however, this period is shorter than that seen in the susceptible mandarin ‘Clemenules’ (C. clementina). Under controlled growth conditions, the resistance of ‘Okitsu’ to X. citri was associated with the age of the leaf and was evident in spray-inoculated plants but not in those inoculated by infiltration. Furthermore, X. citri showed reduced attachment and biofilm formation in ‘Okitsu’ leaves compared with ‘Clemenules’. Taken together, our data suggest that structural features of the ‘Okitsu’ leaf surface, such as the physical properties of the cuticle, are involved in the resistance to X. citri.

Additional keywords: canker resistance, leaf surface properties, phenological stages.