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...

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SUMMARY A new virus, peanut stripe (PStV), isolated from groundnut (Arachis hypogaea) in the USA, induced characteristic striping, discontinuous vein banding along the lateral veins, and oakleaf mosaic in groundnut. The virus was also isolated from germplasm lines introduced from the People's Republic of China. PStV was transmitted by inoculation of sap to nine species of the Chenopodiaceae, Leguminosae, and Solanaceae; Chenopodium amaranticolor was a good local lesion host. PStV was also transmitted by Aphis craccivora in a non‐persistent manner and through seed of groundnut up to 37%. The virus remained infective in buffered plant extracts after diluting to 10‐3, storage for 3 days at 20°C, and heating for 10 min at 60°C but not 65°C. Purified virus preparations contained flexuous filamentous particles c. 752 nm long, which contained a major polypeptide of 33 500 daltons and one nucleic acid species of 3·1 × 106 daltons. In ELISA, PStV was serologically related to blackeye cowpea mosaic, soybean mosaic, clover yellow vein, and pepper veinal mottle viruses but not to peanut mottle, potato Y, tobacco etch, and peanut green mosaic viruses. On the basis of these properties PStV is identified as a new potyvirus in groundnut.

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