Bacterial Stem Rot in Greenhouse Pepper (Capsicum annuum L.) in Sardinia (Italy): Occurrence of Erwinia carotovora subsp. carotovora

An unusual bacterial disease was observed in pepper plants during research carried out in greenhouses in central-north Sardinia. The characteristics were: the presence of lesions and exudates on stems, soft rot of the pith, and a brownish-black colour in the petioles and leaf-veins. Only two isolates of 21 were pathogens. One was obtained from exudate present on the stem and the other from pith. Experimental infections revealed that the bacterial isolates were particularly aggressive in the stems and fruit of pepper and tomato. Biochemical, physiological and serological tests in conjunction with fatty acid profile analysis confirmed that they were Erwinia carotovora subsp. carotovora (Jones) Bergey et al. The product of 434 bp polymerase chain reaction (PCR) enabled a preliminary identification of isolates to be made. Restriction fragment length polymorphism (RFLP) analysis of amplification products showed that the isolates DPP 23ef and DPP 24m, strain type CFBP 2046 and DPP 281, isolated from pepper fruit, belonged to the RFLP group 12, whereas DPP 29, also isolated from pepper fruit, was included in RFLP group 1. Measures to prevent and control this recently introduced disease are suggested in the conclusion of this paper. Introduction As a result of surveys carried out periodically since 2000 in the greenhouses of central-north Sardinia, an unusual bacterial disease in pepper plants (Capsicum annuum L.) was observed. It was particularly harmful in two greenhouses in North Sardinia where approximately 15% of the plants were affected. In central Sardinia it was present in three greenhouses but a lower percentage of plants were affected. It was observed only sporadically during the next 2 years. The first signs of the disease were observed some weeks after the first fruit set. Symptoms (Fig. 1) typically occurred during the ripening of the first fruit. Signs of the disease were black spots and longitudinal lesions in the stem and branches, and a dirty-white exudate at the base of the stems. The petioles and veins of young leaves became brownish-black. When the stem was dissected at the lesions, the appearance of the pith was soft and water-soaked, dark green, verging on brown in colour. The same variation in colour as was seen in the tap root also affected the vascular tissue. Later young leaves rotted, the pith become hollow and necrotic and the whole plant wilted and collapsed. This unusual combination of symptoms led us to investigate the aetiology of this malady. We identified a new disease of pepper in Europe caused by Erwinia carotovora subsp. carotovora (Jones) Bergey et al