Serratia marcescens, a Phloem-Colonizing, Squash Bug -Transmitted Bacterium: Causal Agent of Cucurbit Yellow Vine Disease

Abstract

Cucurbit yellow vine disease (CYVD), which can inflict heavy losses to watermelon, pumpkin, cantaloupe, and squash in U.S. production areas from the midwest to northeastern states, causes phloem discoloration, foliar yellowing, wilting, and plant decline. Bacteria were cultured from the phloem of crown sections of symptomatic plants of Citrullus lanatas and Cucurbita pepo. Those bacteria testing positive in CYVD-specific polymerase chain reaction (PCR) were all gram negative and appeared morphologically identical, producing creamy white, smooth, entire, convex colonies on Luria-Bertani or nutrient agar. Characterized cucurbit-derived strains of Serratia marcescens were introduced into greenhouse-grown squash plants by puncture inoculation and into field-grown squash plants by enclosure with S. marcescens-fed squash bugs, Anasa tristis. Up to 60% of the bacteria-inoculated plants in the greenhouse and up to 17% of field plants caged with inoculative squash bugs developed phloem discoloration and tested positive for S. marcescens by CYVD-specific PCR. None of the controls developed phloem discoloration or tested positive by PCR. Of the diseased field plants, 12% (2 of 35) also yellowed, wilted, and collapsed, exhibiting full symptom development of CYVD. However, neither plant collapse nor decline was observed in the greenhouse-grown, puncture-inoculated plants. The morphology, growth habit, and PCR reaction of bacteria cultured from crown tissue of a subset of plants in each experimental group were indistinguishable from those of the inoculum bacteria. Evidence presented from our studies confirms that the squash bug can transmit S. marcescens, the CYVD causal bacterium. The S. marcescens-A. tristis relationship described here is the first instance in which the squash bug has been identified as a vector of a plant pathogen. Our experiments represent a completion of the steps of Koch's postulates, demonstrating that S. marcescens is the causal agent of CYVD and that the squash bug, A. tristis, is a vector of the pathogen.

Genomic Comparison of Plant Pathogenic and Nonpathogenic Serratia marcescens Strains by Suppressive Subtractive Hybridization

“…O antigen is the outermost component of lipopolysaccharide, the major structural and immunodominant molecule of the outer membrane. In plants the CYVD pathogen investigated in this study lives predominantly in the phloem sieve tubes, a tissue that is rich in nutrients and high in osmotic pressure, and is transmitted by an insect vector, the squash bug (Anasa trisits) (8). Although it is not known whether CYVD strains of S. marcescens can colonize other ecological niches, it certainly is possible.…”

Identificación molecular de bacterias asociadas a plantas ornamentales producidas in vitro

“…Anteriormente, se consideraba solo como un patógeno oportunista que causa enfermedades en los seres humanos, como cistitis (Liu et al, 2004), conjuntivitis (Hume y Willox, 2004), queratinitis (Schaefer et al, 2001), meningitis (Zaidi et al, 1989) y neumonía (Carlon et al, 1977;Khan et al, 1997), entre otras. Sin embargo, recientemente algunos informes muestran que esta bacteria puede provocar la enfermedad de la vid amarilla en cucurbitáceas, donde coloniza el floema de las plantas y les produce un aspecto amarillento y marchitamiento del follaje Bruton et al, 2003;Sikora et al, 2012).…”

“…It used to be considered an opportunist pathogen that causes diseases in humans, such as cystitis (Liu et al, 2004), conjunctivitis (Hume and Willox, 2004), keratitis (Schaefer et al, 2001), meningitis (Zaidi et al, 1989), pneumonia (Carlon et al, 1977;Khan et al, 1997), and others. However, some reports show that this bacterium can cause yellow vine disease in cucurbits, in which it colonizes the phloem of plants, producing a yellow color and wilting of leaves Bruton et al, 2003;Sikora et al, 2012).…”

Leaf-Footed Bugs (Coreidae)

“…Leptoglossus zonatus (Dallas) can transmit a trypanosomatid to corn kernels (Jankevicius et al 1993 ). In the United States, transmission by Anasa tristis De Geer of the fastidious phloem-colonizing bacterium causing cucurbit yellow vine disease has recently been documented and extensively studied (Bruton et al 2003 ). Although a few coreid species have been investigated as potential biocontrol agents (Mitchell 2000 ), none have been successfully adopted, either due to failure to disperse or insuffi cient host specifi city.…”

“…Mitchell ( 2000 ) reviewed this primarily North American literature, including life cycle, behavior, feeding and oviposition preferences, histological studies of feeding damage, insecticidal control methods, cultural controls, natural enemies, and tritrophic interactions. More recent studies have revealed that, in addition to direct damage to vascular tissues, the squash bug transmits a phloem-colonizing bacterium, Serratia marcescens Bizio, the causative agent of cucurbit yellow vine disease (Bruton et al 2003 ). This disease was fi rst described in 1988 in Texas and Oklahoma and subsequently spread eastward in the United States.…”