Citrus blast caused by bacterium Pseudomonas syringae is a very important disease of citrus occuring in many areas of the world, but with few data about genetic structure of the pathogen involved. Considering the above fact, this study reports genetic characterization of 43 P. syringae isolates obtained from plant tissue displaying citrus blast symptoms on mandarin (Citrus reticulata) in Montenegro, using multilocus sequence analysis of gyrB, rpoD, and gap1 gene sequences. Gene sequences from a collection of 54 reference pathotype strains of P. syringae from the Plant Associated and Environmental Microbes Database (PAMDB) was used to establish a genetic relationship with our isolates obtained from mandarin. Phylogenetic analyses of gyrB, rpoD, and gap1 gene sequences showed that P. syringae pv. syringae causes citrus blast in mandarin in Montenegro, and belongs to genomospecies 1. Genetic homogeneity of isolates suggested that the Montenegrian population might be clonal which indicates a possible common source of infection. These findings may assist in further epidemiological studies of this pathogen and for determining mandarin breeding strategies for P. syringae control.
Unusual blight-like symptoms appeared on highbush blueberry plants in Serbia during August 2015 and infected plants showed browning and reddening of leaves, drying of foliage, and brown discoloration of internal vascular stem tissues. The objective of this study was to isolate and confirm a causal agent of the disease. Five diseased blueberry plants (2-yr-old), with visible brown discoloration in the wood, were collected for isolation on potato dextrose agar (PDA). Morphological analysis of the selected fungal isolates showed the presence of abundant black, round to oblong, or irregularly-shaped microsclerotia immersed in the PDA. Dark, globose pycnidia formed on water agar with an initially hyaline, granular content and single-celled conidia, indicating the presence of plant pathogenic fungus Macrophomina phaseolina associated with symptomatic plant tissues. Pathogenicity was confirmed on potted blueberry plants based on the initial symptoms of leaves turning yellowish to brown at the leaf edges, followed by the defoliation of leaves of the inoculated stems. Discoloration of vascular tissues was also observed on transverse sections of inoculated stems. The pathogen M. phaseolina was confirmed using molecular analysis of the ITS1-5.8S-ITS2 region of rDNA and a part of the TEF-1α gene region. This is the first report of M. phaseolina causing a blight disease on highbush blueberry in Serbia. The study should help in elucidating disease symptomatology and provide the knowledge on the risk which this fungus could pose in blueberry production.
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