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...

Two species of lepidopteran herbivores, Manduca sexta (Sphingidae) and Trichoplusia ni (Noctuidae), were reared on synthetic diet containing either the alkaloid nicotine or the flavonoid rutin. Survival and pupal weight of the specialist M. sexta did not differ when larvae were reared on diet containing nicotine or rutin. In contrast, the generalist T. ni did not survive on diet containing 0.125% nicotine or greater, whereas larvae survived on all concentrations of rutin. These data demonstrate that the alkaloid nicotine is inhibitory toward generalist, but not specialist herbivores, whereas the flavonoid rutin has no effect on specialist herbivores and limited effects on generalist herbivores. Five species of Pseudomonas bacterial pathogens: P. syringae, P. syringae pv. angulata, P. syringae pv. tabaci, P. fluorescens, and P. solanacearum were grown on nutrient agar containing nicotine or rutin at concentrations ranging from 0.0 to 1.0% wet weight in 0.1% intervals. No species of Pseudomonas grew at concentrations greater than 0.5% nicotine when 10 colony forming units (cfu) were used, but growth occurred at all concentrations of rutin when 10 cfu were used. These data indicate that nicotine was inhibitory to growth of both herbivores and pathogens, suggesting that certain plant secondary chemicals with high toxicity are of a generalized nature and affect multiple species. Differences in the sensitivity of organisms to allelochemicals such as generalist or specialist can make it appear that specific allelochemicals affect specific organisms, when in fact it is the tolerance of the organism to the plant chemical that is responsible. In four separate studies, the growth of M. sexta, T. ni and Helicoverpa zea was significantly lower on plants inoculated with P. solanacearum. Alteration in leaf quality by P. solanacearum was due to either reductions in leaf nutrients or increases in allelochemicals. We speculate that localized or systemic induction by both herbivores and pathogens can cause changes in leaf quality, effecting each other's subsequent colonization. The generalized nature of plant secondary compounds and potential reciprocal effects on induction by both species suggests that herbivores and pathogens may affect plant quality through induction and diffuse interactions of disparate species can alter the community of organisms colonizing a plant.

Common scab of potato (Solanum tuberosum L.), caused by the soil‐borne bacterium Streptomyces scabies (Thaxter) Lambert & Loria, is an economically important potato disease. Tubers from susceptible plants may have superficial, raised, or pitted lesions. Quantitative methods to evaluate tubers for the amount of surface area covered (AI) and the type of lesion (LI) have previously been developed. The purposes of this study were to (i) estimate broad‐sense heritability on a mean basis for scab resistance in a tetraploid population of Solanum tuberosum for AI and LI, (ii) determine the importance genotype × environment interactions on AI nd LI, and (iii) determine the stability of potato genotypes for scab resistance. In 1992 and 1993, 23 potato clones were grown in replicated scab‐infested field plots in Presque Isle, ME, and Cranesville, WV, and rated for AI and LI. There were significant environment, genotype, and genotype × environment efftects for AI and LI. Broad‐sense heritabilities on a mean basis and their exact 95% confidence intervals for AI and LI wer estimated as 0.89 (0.78, 0.95) and 0.93 (0.86, 0.97), respectively. Shukla's stability‐variance statistics indicated that the most scab resistant genotypes were the most unstable, whereas, the most susceptible genotypes were the most stable. Thus, disease pressure was intense. Moderate levels of scab resistance were found. However, to obtain genotypes with high levels of scab resistance that are stable across environments will probably require development of populations incorporating new sources of scab resistant germplasm.