Pseudomonas pseudoalcaligenes subsp. citrulli subsp. nov.

Abstract

Ten nonfluorescent Pseudomonas strains isolated from water-soaked lesions on cotyledons of plants of five Citrullus lanatus (watermelon) plant introductions were characterized and compared phenotypically with 22 other pseudomonads. The strains were distinguished phenotypically from other known plant pathogenic pseudomonads. The watermelon bacterium was aerobic. Cells were rod-shaped, gram negative, and motile by means of a single polar flagellum. They were nonfluorescent and grew at 41°C but not at 4°C. Oxidase production and the 2-ketogluconate reaction were positive. The 10 strains utilized p-alanine, rA-leucine, D-serine, n-propanal, ethanol, ethanolamine, citrate, and fructose for growth. No growth occurred with sucrose or glucose. Their deoxyribonucleic acid base composition was 66 1 mol% guanine plus cytosine. The bacterium is phenotypically similar to P. pseudoalcaligenes but differs from it in being pathogenic to watermelon, Cucumis melo (cantaloupe), Cucumis sativus (cucumber), and Cucurbita pep0 (squash). The name P. pseudoalcaligenes subsp. citrulli is proposed for the new subspecies, of which strain C-42 (= ATCC 29625) is the type strain.For several years a bacterial disease of watermelons, characteAed by water-soaked lesions of cotyledons, has been observed on certain plant introductions at the Regional Plant Introduction Station, Experiment, Ga. A disease with similar symptoms on watermelon seedlings was reported to be caused by Pseudomonas lachrymans (9), but we could not isolate a pathogenic fluorescent pseudomonad. Our preliminary investigations showed that the causal bacterium was similar to the unidentified nonfluorescent pseudomonad isolated by Webb and Goth (22) from plants of watermelon plant introductions 174103 and 174104. The purpose of this investigation was to identify the causal bacterium isolated from diseased watermelon seedlings and to compare it with several other fluorescent and nonfluorescent pseudomonads, including the strain of P. lachrymans isolated from watermelon (9). Isolation and cultural properties. Seeds from different watermelon plant introductions were sown in trays (30 by 50 cm) of soil in a greenhouse with a day/night .ternpertwe of approximately 30/21 "C. Cotyledons and the first true leaves showing greasy, dark green lesions were collected, and the surfaces were disinfested in a freshly prepared 0.5% solution of sodium hypochlorite for 3 min. After rinsing for 2 min in sterile distilled water, the tissue from the lesions was removed and cut into smaller pieces in 0.1 ml of sterile distilled water, using a sterile scalpel. The suspension was streaked onto King medium B (KB; 11) and incubated for 5 days at 27°C (colonies of nonpathogenic pseudomonads were usually present after 2 days). Colonies of the watermelon bacterium were removed from the agar with a transfer loop and purified by streaking onto plates of KB. Stock cultures were maintained on KB slants. The media used for determining cultural characteristics were KB, yeast extract-dextrose-CaC03 (22), and Difco...

Reclassification of subspecies of Acidovorax avenae as A. Avenae (Manns 1905) emend., A. cattleyae (Pavarino, 1911) comb. nov., A. citrulli Schaad et al., 1978) comb. nov., and proposal of A. oryzae sp. nov.

“…Schaad et al [41] described a non-fluorescent pseudomonad as the causal agent of a seedling blight of watermelon. The bacterium differed phenotypically from other known plant pathogenic pseudomonads and was classified as P. pseudoalcaligenes subsp.…”

“…The bacterium differed phenotypically from other known plant pathogenic pseudomonads and was classified as P. pseudoalcaligenes subsp. citrulli [41]. Later, Wall and Santos determined that the same organism caused a disease referred to as watermelon fruit blotch of mature watermelon fruit [42].…”

Polyphasic analysis of Acidovorax citrulli strains from northeastern Brazil

“…This compound can be considered a virulence factor because some strains are pathogenic but do not form cavities. Amylase, protease, pectinase and cellulase activities were mentioned as A. citrulli virulence factors (Schaad et al, 1978;Walcott et al, 2004;Burdman et al, 2005), but the role of such enzymes in A. citrulli virulence on fruit tissues remains to be determined (Burdman et al, 2005). In contrast, the production of amylolytic, proteolytic, pectolytic and cellulolytic enzymes was not detected in 41 A. citrulli strains, even if lipolytic activity was detected (Oliveira et al, 2007).…”

“…At first, it was observed that the ATCC29625 type strain (obtained from watermelon) did not cause a hypersensitive response (HR) in tobacco and had little virulence on watermelon compared with other strains isolated from the same host (Schaad et al, 1978;Somodi et al, 1991). Furthermore, strains causing BFB epidemics in cantaloupe melon in Queensland, Australia were considerably more virulent on melon and less virulent on the invading plant Cucumis myriocarpus Naudin compared with strains obtained from watermelon in the same state (O´Brien and Martin, 1999).…”

Detection of Acidovorax avenae subsp. avenae in commercial corn seeds and its correlation with seedling transmission

“…The causal agent was reported as a serious seedborne pathogen of various plants such as rice (Shakya, 1987), watermelons, and cantaloupes (Schaad et al, 1978). It can be recovered from seeds using general agar medium (Song et al, 2000; but seedborne contamination of corn was not detected.…”