Molecular characterisation of Xanthomonas strains isolated from aroids in Mauritius.

Mauritius is one of the largest world producers of Anthurium cut flowers but outbreaks of bacterial blight have never been reported on the island. This work was about the characterisation and identification of bacterial strains isolated from Anthurium andreanum, Dieffenbachia maculata and Aglaonema simplex in Mauritius. Fifteen strains, that showed the morphological properties of Xanthomonas on conventional media, were tested on two semi-selective media (Esculin-trehalose and cellobiose-starch). ELISA tests using a panel of monoclonal antibodies were carried out and three out of 15 strains reacted with a Xanthomonas-specific monoclonal antibody (MAb XII). Analysis using four sets of ribosomal primers revealed that the same three Mauritius strains shared conserved PCR products with reference xanthomonads including virulent strains of Xanthomonas axonopodis pv. dieffenbachiae (Xad). BIOLOG tests and the Sherlock Microbial Identification system (MIDI) identified these three new strains at the species level as X. axonopodis. The complementary tests that were carried out clearly confirmed that the three strains are xanthomonads and, moreover, a DNA probe which showed specificity to Xad strains suggested that the three Mauritius strains are non-virulent forms of the pathogen causing Anthurium blight.

First Report of Bacterial Blight of Mulberries Caused by Pseudomonas syringae pv. mori in the Eastern Anatolia Region of Turkey.

During spring 1999, a severe bacterial blight disease was observed on white mulberry (Morus alba L.) trees grown in the Erzincan, Erzurum, and Artvin provinces in the eastern Anatolia region of Turkey. Initial symptoms appeared as small, water-soaked spots on leaves and shoots. The spots eventually expanded and resulted in dark brown to black, elongated, stripe-like lesions on shoots. Diseased leaves wilted at the twig tips and later died. Disease incidence was close to 100% in the regions surveyed. Fluorescent bacteria were isolated consistently from lesions on diseased leaves and shoots on King's medium B. Morphological and biochemical characteristics of 16 presumptive strains tested were rod-shaped, aerobic, gram negative, oxidase negative, and catalase and levan positive. None of the strains reduced nitrate or hydrolyzed gelatin. All strains were confirmed as Pseudomonas syringae by gas-chromatography fatty acid methyl ester (GC-FAME) analysis, with a similarity index ranging from 0.82 to 0.94. The pathogen was identified as P. syringae pv. mori based on pathogenicity tests performed by spray-inoculating healthy leaves (M. alba cv. Beyaz Dut) on 1-year-old host twigs with suspensions of 108 CFU/ml each strain (2). Inoculated plants and sterile water-sprayed controls were maintained in a greenhouse at 18 to 28°C. Plants were covered with polyethylene bags for 48 h after inoculation. Within 7 to 10 days, necrotic spots typical of those found in the nursery were observed on inoculated leaves. No symptoms were seen on control plants. The pathogen was reisolated from lesions on inoculated leaves. Recovered strains were identical to initial strains, based on morphological and biochemical tests and GC-FAME analysis. To our knowledge, the occurrence and incidence of this disease in different geographic regions of Turkey, except the central Anatolia and Aegean regions, have not been studied (1). This is the first report of bacterial blight of mulberries at high incidence in the eastern Anatolia region of Turkey. References: (1) K. Türkolu and Y. E. Öktem. Plant Prot. Bull 13:19, 1973. (2) J. M. Young et al. N. Z.J. Agric. Res. 21:159, 1978.