James J. Sims

Reduced pathogen fitness of Pseudomonas syringae pv. tomato Tn5 mutants defective in coronatine production

Abstract Pseudomonas syringae pv. tomato strain PT23 produces necrotic lesions on tomato which are surrounded by a diffuse yellow chlorosis. Mitchell et al. (Physiological Plant Pathology 23 , 315–322) previously found that some strains of P. syringae pv. tomato produce the chlorosis-inducing phytotoxin, coronatine. In the present study, Tn 5 mutagenesis was used to isolate nontoxigenic mutants of PT23. One thousand Tn 5 mutants of PT23 were screened for loss of chlorosis induction on tomato leaves; 10 mutants were recovered which produced little or no chlorosis. Organic acids were extracted from two of the mutants and analysed by high performance liquid chromatography and a bean leaf bioassay; the two mutants were found to be defective in coronatine production. The necrotic lesions induced by the two mutants reached a maximum diameter (0·2 mm) 4 days after inoculation, but lesions induced by the wild-type strain continued to expand to a maximum diameter of 0·62 mm. An increase in bacterial populations was correlated with the increase in lesion size. Therefore, coronatine synthesis appears to play an important role in lesion expansion and multiplication of P. syringae pv. tomato in tomato leaves.

Inhibition of biofilm formation and swarming of Bacillus subtilis by (5Z)-4-bromo-5-(bromomethylene)-3-butyl-2(5H)-furanone

Aims: (5Z)‐4‐Bromo‐5‐(bromomethylene)‐3‐butyl‐2(5H)‐furanone(furanone) of the marine alga Delisea pulchra was synthesized, and its inhibition of swarming motility and biofilm formation of Bacillus subtilis was investigated.

Methyl iodide, an ozone-safe alternative to methyl bromide as a soil fumigant

Methyl iodide was tested as a possible replacement for methyl bromide as a soil fumigant due to the scheduled removal of methyl bromide from the market. Methyl iodide is a better methylating agent than methyl bromide; it is rapidly destroyed by UV light and therefore unlikely to be involved in stratospheric ozone depletion. In laboratory and field trials, we tested methyl iodide alone or in comparison with methyl bromide for effectiveness in controlling the fungi Phytophthora citricola, P. cinnamomi, P. parasitica, and Rhizoctonia solani; the nematode Heterodera schachtii; and the plants Abutilon theophrasti, Chenopodium album, C. murale, Convolvulus arvensis, Cyperus rotundus, Poa annua, Portulaca oleracea, and Sisymbrium irio. In addition, we compared methyl iodide for biocidal effectiveness with seven other alkyl iodides. In both laboratory and field trials, when compared at equivalent molar rates, methyl iodide was equal to or better than methyl bromide in controlling the tested soilborne plant pathogens and weeds. When compared with other alkyl iodides, methyl iodide was the most effective fumigant.

Syringolide 1 Triggers Ca2+ Influx, K+ Efflux, and Extracellular Alkalization in Soybean Cells Carrying the Disease-Resistance Gene Rpg4

Alleles of avirulence gene D (avrD) specify the production by bacteria of syringolides that elicit the hypersensitive response in soybean (Glycine max) plants carrying the disease-resistance gene Rpg4, but not rpg4 plants. Syringolide 1 caused extracellular alkalization, K+ efflux, and Ca2+ influx about 30 min after addition to suspension-cultured cells of two Rpg4 cultivars, Harosoy and Flambeau, but not in two rpg4 cultivars, Acme and Merit. All responses were sustained for at least 1.5 h and were inhibited by La3+, which blocks certain Ca2+ channels. These results suggest that syringolide 1 activates a Ca2+ influx-dependent signaling pathway only in Rpg4 soybean cells.

The purification of victorin and its phytoalexin elicitor activity in oat leaves

Victorin was isolated from high-producing isolates of Helminthosporium victoriae as three peaks by HPLC All of these purified toxins completely inhibited root growth of sensitive Pc-2 oats at approximately 50 pg ml −1 . The major toxin from high-producing isolates was not elaborated in significant quantity by two other H. victoriae isolates which yielded lower amounts of toxin as judged by the root growth bioassay. The major victorin HPLC peak was purified and tested for its ability to elicit production of the oat phytoalexins, avenalumins, in near-isogenic oat cultivars containing or lacking the Pc-2 allele for toxin sensitivity and crown rust resistance. Several known biotic and abiotic phytoalexin clicitors were relatively inefficient and elicited insignificant amounts of avenalumin in leaves of the two oat lines. Victorin, however, was an efficient elicitor of avenalu-min production only in the Pc-2 line, giving maximum phytoalexin production at 10 pg ml −1 on the other hand, vietorin did not elicit detectable avenalumin production in the pc-2 oat line at 10 ng ml −1 , Vietorin treatment resulted in loss of chlorophyll in the Pc-2 line at concentrations that elicited avenalumin production, but relatively little cellular necrosis occurred. At higher vietorin concentrations, considerable cellular necrosis was observed in Pc-2 leaves, but avenalumin accumulation was reduced, presumably because of the requirement for living cells to produce the phytoalexin. The protein synthesis inhibitors cycloheximide and blasticidin S blocked avenalumin production by Pc-2 oat leaves supplied with vietorin. Unlike the crown rust fungus, H. victoriae was relatively insensitive in vitro to the growth inhibitory properties of the avenalumins.

Evaluation of methyl iodide as a soil fumigant in container and small field plot studies

Methyl iodide was evaluated as a soil fumigant as a potential replacement for the widely used soil fumigant methyl bromide. In container trials, methyl iodide was significantly more effective than methyl bromide against the plant parasitic nematodes Meloidogyne incognita, Heterodera schachtii and Tylenchulus semipenetrans and the plant pathogenic fungus Rhizoctonia solani. In small field plots, soil populations of root-knot nematodes were no longer detected after methyl iodide fumigation at an application rate of 112 kg ha-1. However, after growing a susceptible lima bean host for two months, substantial root-knot galling occurred, while Rhizobium nodulation was absent. At 168 kg ha-1 of methyl iodide, root-knot galling was reduced to less than 1%, and no Pythium propagules were recovered on selective detection media. These efficacy data support the conclusion that methyl iodide is a likely candidate for replacing methyl bromide as a soil fumigant.

Marine natural products-XVI: Polyhalogenated acyclic monoterpenes from the red alga plocamium of antarctica

Abstract Examination of the red alga Plocamium sp. collected near the Antarctic penninsula yielded three new acyclic halogenated monoterpenes ( 1 – 3 ). A structure revision is proposed for a compound previously reported to have structure 1 . X-ray diffraction provided the structure of 1 including absolute stereochemistry. The structures of 2 and 3 followed from proton and 13 C NMR spectral interpretation.

The syringolides : bacterial C-glycosyl lipids that trigger plant disease resistance

Abstract The salient structural and bioorganic properties of this new class of signal molecules are reported.

Melleolide, a new antibiotic from

Abstract Melleolide, a new sesquiterpenoid orsellinate, has been isolated from cultures of Armillaria mellea . Its structures was elucidated by X-ray crystallography.

Efficacy of methyl iodide and synergy with chloropicrin for control of fungi

Efficacy of soil fumigation with methyl bromide and methyl iodide against Botrytis cinerea, Colletotrichum gloeosporioides, Fusarium oxysporum, Gliocladium virens, Phytophthora citricola, Phytophthora citrophthora, Pythium ultimum, Rhizoctonia solani and Verticillium dahliae was determined in laboratory experiments in closed fumigation chambers. Pythium ultimum was the most sensitive fungal species with EC 50 values for methyl bromide and methyl iodide of 15.5 and 8.6 μM, respectively. R solani was the least sensitive with EC 50 values of 253.4 and 161.4 μM for methyl bromide and methyl iodide, respectively. Relative potency ([methyl bromide]/[methyl iodide]) values ranged from 5.2 for P citricola to 1.5 for F oxysporum. Methyl iodide was 2.7 more efficacious than methyl bromide averaged over all fungal species. Methyl bromide/chloropicrin and methyl iodidelchloropicrin applied jointly were 2.2 and 2.8 times more efficacious, respectively, against F oxysporum than when the compounds were applied singly. Combining methyl bromide and methyl iodide with chloropicrin resulted in a significant synergistic increase in activity against F oxysporum.