First Report of Bacterial Soft Rot on Vanda Orchids Caused by Dickeya chrysanthemi (Erwinia chrysanthemi) in the United States

Abstract

Vanda orchids are epiphytes grown for their attractive flowers by commercial producers and hobbyists throughout Florida. In August 2007, five Vanda hybrids, with an economic value of $150 each, were found at a nursery in central Florida with leaves that were macerated, brown, and water soaked. According to the growers, the plants were normal the previous day but symptoms developed rapidly. The plants were immediately removed from the greenhouse to prevent potential disease spread. Bacteria were isolated according to the method of Schaad et al. (1). Isolated bacteria grew at 37°C, were gram negative, degraded pectate, and produced phosphatase. MIDI (Sherlock version TSBA 4.10; Microbial Identification 16 System, Newark, DE) (SIM 0.906) identified the bacteria as Erwinia chrysanthemi (Dickeya chrysanthemi Burkholder et al. 1953) Samson et al. 2005. PCR was performed on the 16S rRNA gene (GenBank Accession No. EU526397) with primers 27f (5′-GAGAGTTTGATCCTG GCTCAG-3′) and 1495r (5′-TACGGCTACCTTGTTACGA-3′) (2). Subsequent DNA sequencing and GenBank search showed the isolated strain is 99% identical to that of Dickeya chrysanthemi. Four leaves each of six Vanda hybrids were inoculated by injecting approximately 150 μl of a bacteria suspension at 1 × 108 CFU/ml into each leaf. One plant was inoculated with water in each of four leaves. Plants were enclosed in plastic bags and returned to the greenhouse under 50% shade at 29°C day and 17°C night temperatures. Within 24 h, soft rot symptoms appeared on inoculated leaves. The water control appeared normal. D. chrysanthemi was reisolated and identified with the above method, thus Koch's postulates were fulfilled. To our knowledge, this is the first report of a soft rot caused by D. chrysanthemi on Vanda hybrids. Because of the popularity and high value of Vanda orchids, proper identification of this rapidly progressing bacterial disease is of great importance for the commercial producer and homeowner alike. References: (1) N. W. Schaad et al. Erwinia soft rot group. Page 56 in: Laboratory Guide for Identification of Plant Pathogenic Bacteria. 3rd ed. N. W. Schaad et al., eds. American Phytopathological Society. St. Paul, MN, 2001. (2) W. G. Weisburg. J. Bacteriol. 173:697, 1991.

Pectobacterium and Dickeya: Environment to Disease Development

“…in South Korea (Lee et al 1999). Soft rot disease of orchids is a major disease problem of Phalaenopsis in Florida (McMillan et al 2007), with symptoms including macerated, brown and water-soaked leaves (Cating et al 2008). It has also been found worldwide on other orchid species including Vanda, Oncidium and Tolumnia, with Dickeya spp.…”

Management of Diseases Caused by Pectobacterium and Dickeya Species

“…This industry is particularly sensitive to bacterial diseases as production costs are relatively high and growth conditions are extremely conducive to bacterial spread. Several reports on soft rot infections in orchids are found in the literature (Cating et al 2008;Cating and Palmateer 2011;Cating et al 2009). Most losses in orchids are caused by Dickeya spp., although infections with Pectobacterium spp.…”

Destructive Phytophthora on orchids: current knowledge and future perspectives

“…The two most important bacterial species infecting orchids are Acidovorax avenae subsp. cattleyae (Syn: Pseudomonas cattleyae ), inciting bacterial brown spot disease ( Miller, 1990 ), and Pectobacterium chrysanthemi (Syn: Erwinia chrysanthemi ), inciting bacterial soft rot ( Chan et al, 2005 ; Cating et al, 2008 ). Among the fungal diseases, black rot caused by species of Phytophthora and Pythium, anthracnose caused by species of Colletotrichum , Fusarium rots ( Foster, 1955 ; Srivastava et al, 2018 ), flower spot ( Botrytis sp.…”