Phytophthora ramorum Occurrence in Ornamentals in Serbia

In a survey to determine the presence of Phytophthora ramorum in Serbia, ornamentals from garden centers, nurseries, and private and public gardens, as well as imported plant material, were inspected. In total, 577 plant, soil, and potting media samples were tested using various detection methods: lateral flow diagnostic test, enzyme-linked immunosorbent assay, conventional polymerase chain reaction, and isolation, followed by identification based on growth characteristics in culture and morphological features. P. ramorum was not detected in any of the 162 soil or potting media tested by the baiting method. P. ramorum was detected in 12 Rhododendron samples from one private garden in Zemun (City of Belgrade District) exhibiting symptoms of leaf necrosis and blight and petiole necrosis, and in three samples of Pieris spp. from one garden center exhibiting symptoms of leaf necrosis. Eight Phytophthora isolates were obtained from the positive Rhododendron plants and three isolates from Pieris plants, and all were identified as P. ramorum on the basis of their uniform morphological and growth characteristics. P. ramorum conformation was also made by sequencing of the internal transcribed spacer regions for a single isolate taken from one infected rhododendron and one pieris plant. Serbian isolates were determined as A1 mating type, due to formation of a few typical sexual structures when crossed with the A2 mating type of P. cinnamomi and P. cryptogea. Pathogenicity test on nonwounded detached leaves of 19 popular ornamentals, as well as the most frequently imported ones, revealed that 10 host species were susceptible, including Robinia pseudoacacia, which is widely distributed in Serbia. During this study, Cotoneaster horizontalis and C. dammeri were determined to be new experimental hosts of P. ramorum. This article provides evidence of P. ramorum introduction into Serbia. Although P. ramorum has not been detected in Serbian production nurseries, its presence outdoors might cause severe damages on susceptible common urban plants in public green and natural ecosystems.