Physiological and histological aspects of innate and shiitake-induced resistance against bacterial spot on tomatoes Tarsis de Aguiar & Eder Carlos Schimidt & Argus Cezar da Rocha Neto & Robson Marcelo Di Piero Accepted: 15 April 2020 # Koninklijke Nederlandse Planteziektenkundige Vereniging 2020 Abstract This study aimed to evaluate the protec- tive effects conferred by polysaccharides obtained from basidiocarps discarded from the commercial production of Lentinula edodes (shiitake mushroom) in tomato cultivars against bacterial spot disease and to study their mode of action. Among 13 cultivars analyzed for resistance to Xanthomonas gardneri cvs. Kada, Natália and Sena were selected and sprayed with polysaccharides from shiitake (PSHII – 1.5 mg/mL) or distilled water 4 days before inoc- ulation with the bacteria. PSHII promoted a 37.7% reduction in disease severity and its mode of action on plants was evaluated according to changes in photosynthetic parameters, and histopathological as- pects. Leaves of plants treated with PSHII showed lower stomatal conductance and transpiration rate compared to the control, at the time of inoculation. In addition, in plants of the most susceptible cvs. (Kada and Natalia) treated with PSHII, phenols accumulated in cells close to the epidermis. We observed that the plants of the most resistant culti- var, Sena, presented higher stomatal density, meso- phyll thickness and size of palisade cells. In Sena, we also observed intense cell proliferation near the X. gardneri infection site and deposition of phenolic compounds inside the mesophyll. Control of bacte- rial spot in different tomato cultivars through in- duced resistance and the mechanisms presented by the plants to resist the bacteriosis are discussed. Keywords Lentinula edodes . Polysaccharides . Resistance . Tomato . Xanthomonas gardneri Introduction Bacterial spot of tomato reduces crop productivity, as it compromises the photosynthesizing leaf area, damaging and depreciating the fruits. In Brazil, the symptoms of this disease are related to the species of X. euvesicatoria, X. vesicatoria, X. gardneri and X. perforans, frequently found in fields of fresh market and processing tomatoes. This disease is difficult to control mainly because the bacterial spread occurs through seeds, the efficiency of chemical control is low, and only a few cultivars are resistant (Quezado-Duval et al. 2004). Therefore, alter- native approaches to the management of the bacterial spot are needed, such as the induction of resistance (Burketova et al. 2015). In plants, induced resistance occurs after the application of different biotic or abiotic elicitors. Eur J Plant Pathol https://doi.org/10.1007/s10658-020-01979-x T. de Aguiar : A. C. da Rocha Neto : R. M. Di Piero (*) Laboratory of Plant Pathology, Crop Science Department, Federal University of Santa Catarina, 1346 Rod. Admar Gonzaga, Florianópolis, SC 88040-900, Brazil e-mail: robson.piero@ufsc.br E. C. Schimidt Laboratory of Plant Biology, Federal University of Santa Catarina, Florianópolis, SC 88040-900, Brazil A. C. da Rocha Neto School of Agricultural Engineering, Adventist University Center of São Paulo, Engenheiro Coelho, São Paulo 13165-000, Brazil