Aglaonema (Aglaonema spp.) is a popular ornamental potted plant in Taiwan. In 2003, leaves showing soft rot symptoms were found on a number of Sithiporn aglaonema (A. marantifoloum var. tricolor × A. rotundum) plants in a nursery in southern Taiwan. The disease usually started from leaf tips or wounded sites and the affected areas appeared water soaked. The diseased tissue subsequently turned dark brown and became fragile. More than 50% of Sithiporn aglaonema plants were destroyed in the affected nursery. Bacteria isolated from the symptomatic leaves grew at 39°C, degraded pectate, caused soft rot on slices of potato tuber and petioles of Chinese cabbage, produced phosphatase and lecithinase, and utilized malonate, but did not grow in 5% NaCl or produce acid from trehalose. These characteristics were similar to those of Erwinia chrysanthemi Burkholder et al. (1,2) and the reference strain OS2 from Phalaenopsis sp. provided by K. C. Tzeng of National Chung Hsing University, Taichung, Taiwan. Polymerase chain reaction (PCR) analysis using the primer pair 5A (5′ GCGGTTGTTCACCAGGTGTTTT 3′) and 5B (5′ ATGCACGCTACCTGGAAGTAT 3′) specific for E. chrysanthemi (4) confirmed the identity of all seven isolates tested as E. chrysanthemi. The primer pair 5A/5B was designed from the sequences of pT8-1, idg (a gene for blue-pigment synthesis), and pecS (a gene for regulation of pectinase, cellulose, and pigment production). PCR products amplified from E. chrysanthemi DNA with the 5A/5B primer were 500 bp (4). Pathogenicity of isolates was confirmed by rubbing the leaf surface of Sithiporn aglaonema plants with Carborundum and spraying the wounded surface with a bacterial suspension at 1 × 108 CFU/ml in the greenhouse. Plant leaves sprayed with distilled water were used as the control. Three leaves were inoculated for each isolate, and the experiment was conducted twice. Symptoms appeared within 24 h after inoculation. All seven isolates tested were pathogenic, causing an average of 86 to 95% of inoculated leaves to show water-soaked symptoms similar to these observed in nature. Symptoms did not occur on control leaves. E. chrysanthemi was reisolated from diseased tissues of inoculated leaves. To our knowledge, this is the first report of bacterial blight caused by E. chrysanthemi on aglaonema in Taiwan and the first report of the disease on the Sithiporn cultivar of aglaonema. This disease on aglaonema was previously reported in the United States (3).
References: (1) R. S. Dickey and A. Kelman. Page 44 in: Laboratory Guide for Identification of Plant Pathogenic Bacteria. N. W. Schaad, ed. The American Phytopathological Society, St. Paul, MN, 1988. (2) M. Goto and K. Matsumoto. Int. J. Syst. Bacteriol. 37:130, 1987. (3) L. A. McFadden. Plant Dis. Rep. 53:253. 1969. (4) M. G. Zhu. Ph.D. diss, National Chung Hsing University, Taichung, Taiwan, 1995.
