January 18, 2005
Source: American Phytopathological Society, Plant Disease Notes [edited]

First report of leaf necrosis caused by Pseudomonas viridiflava on melon seedlings in Italy
C. Moretti, S. Sequino, and R. Buonaurio, Dipartimento di Arboricoltura e Protezione delle Piante, Borgo XX Giugno, 74, 06121 Perugia, Italy. Plant Dis. 89:109, 2005; published on-line as DOI: 10.1094/PD-89-0109A, 2005. Accepted for publication 20 Oct 2004.

In April 2001, necrotic lesions surrounded by thin, water-soaked halos were observed on cotyledons of 12-day-old melon seedlings (_Cucumis melo_ var. _reticulatus_, cv. Baggio, Calipso, and Proteo) grown in plant beds in an
unheated greenhouse located in the Province of Perugia (central Italy). The incidence of the disease was approximately 10 percent, and the economic impact was limited, as seedlings recovered from the disease.

Cream-colored, mucoid, bacterial colonies were consistently isolated on nutrient agar from the diseased leaf tissues. 2 representative strains selected for identification were gram-negative, fluorescent on King's medium B, and had oxidative but not fermentative metabolism. They were levan-negative, oxidase-negative, potato rot-positive, arginine dihydrolase-negative, and tobacco hypersensitive response-positive in LOPAT tests.

These isolates showed pectolytic activity at pH 8 but not at pH 4 and utilized L-arabinose, D(-)-tartrate and L-lactate. They did not utilize sucrose, L(+)-tartrate, or trigonelline, and did not produce acid from sucrose after 21 days of incubation. These results were similar to those obtained with the type strain LMG 2352(^T) of _Pseudomonas viridiflava_ (Burkholder) Dowson.

Although it was suitable for strain characterization, we found that repetitive sequence-based polymerase chain reaction (rep-PCR) conducted with primer BOXA1R was not appropriate for identifying _P. viridiflava_. In fact, each _P. viridiflava_ strain tested, (LMG 2352(^T), LMG 2353, LMG 5397, and NCPPB 1382) generated unique fingerprints, which differed from the 2 melon strains.

Pathogenicity tests were carried out with 3-week-old melon (cv. Baggio), cucumber (cv. Lungo verde degli ortolani), and zucchini (cv. Consul) plants (3 plants for each species and isolate). To prepare the inoculum, the 2 bacterial strains were grown on nutrient agar for 24 h at 27 deg C, suspended in sterile deionized water, and adjusted to 1 million CFU/ml. Young leaves of melon, cucumber, and zucchini plants infiltrated with bacterial suspensions by a glass atomizer at high pressure developed small, chlorotic spots with necrotic centers surrounded by water-soaked halos 5 to 7 days after inoculation. The most severe symptoms were observed on melon plants.

The 2 strains also induced severe symptoms (chlorosis and water soaking) on _Arabidopsis thaliana_ (ecotype Columbia-0) 3 to 4 days after inoculation. No symptoms were observed in control plants. The bacterium was readily recovered from inoculated plants, and their rep-PCR fingerprints were identical to the strains used for inoculation.

On the basis of biochemical, physiological, nutritional, and pathogenicity tests, it was concluded that the bacteria isolated from symptomatic melon seedlings were _P. viridiflava_.

To our knowledge, this is the 1st report of _P. viridiflava_ attacks on melon plants in Italy. The disease was previously recorded in Turkey (1) and Greece (2).

References:
(1) A. Aysan et al. Plant Pathol. 52:800, 2003.
(2) D. E. Goumans and A. K. Chatzaki. Eur. J. Plant Pathol. 104:181, 1998.

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[_Pseudomonas viridiflava_ [Pv] causes bacterial leaf blight of melon, tomato and eggplant and other food crops. It is rarely found in the region of Asturias in northern Spain and has been traditionally considered an epiphyte or opportunistic pathogen. _Pseudomonas_ strains with an atypical LOPAT profile (where LOPAT is a series of determinative tests: L, levan production; O, oxidase production; P, pectinolitic activity; A, arginine dihydrolase production; and T, tobacco hypersensibility) have been differentiated. Since 1999, a new _Pseudomonas_ type with an atypical LOPAT profile (convex colonies with uncharacteristic yellowish mucoid material in hypersucrose medium [L test]; O negative; P variable; A negative; and T positive) was frequently isolated from and associated with disease in plants in common bean (_Phaseolus vulgaris_). It has also appeared in material from other plants with disease symptoms, including kiwifruits (from spring of 2000) and lettuce (from 2001).

A novel family of peptide antimycotics, termed ecomycins, is described from Pv. Ecomycins B and C have molecular masses of 1153 and 1181, and they contain equimolar amounts of hydroxyaspartic acid, homoserine, threonine, serine, alanine, glycine and an unknown amino acid. Fatty acids were detectable after hydrolysis, methylation and gas chromatography and mass spectroscopy. The ecomycins have significant bioactivities against a wide range of human and plant pathogenic fungi, including _Cryptococcus neoformans_ and _Candida albicans_. Pv also produces what appears to be syringotoxin, an antifungal lipopeptide previously described from _Pseudomonas syringae_.

Links:
<http://mmbr.asm.org/cgi/content/full/67/4/491>
<http://aem.asm.org/cgi/content/full/69/5/2936>
<http://www.ingentaconnect.com/content/klu/ejpp/1998/00000104/00000002/00157429>
<http://www.ingentaconnect.com/content/bsc/jam/1998/00000084/00000006/art00003>
<http://www.actahort.org/books/462/462_103.htm>
- Mod.DH]