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AbstractThe foxglove aphid, Aulacorthum solani(Kaltenbach) (Hemiptera: Aphididae), and the melon aphid, Aphis gossypiiGlover (Hemiptera: Aphididae), are among the serious insect pests found in greenhouses. The efficacy of microbial control against these insects has been demonstrated and can be enhanced by the combination of different microbial agents. This study evaluated the efficacy of Bacillus pumilusMeyer and Gottheil PTB180 and Bacillus subtilis(Ehrenberg) Cohn PTB185, used alone and together, to control these two aphids both in the laboratory and in greenhouse on tomato, Solanum lycopersicumLinnaeus (Solanaceae), and cucumber, Cucumis sativusLinnaeus (Cucurbitaceae), plants. The results from the laboratory tests showed an increase in mortality induced by all biological treatments. In the greenhouse, all treatments induced mortality rates significantly higher than that of the control for A. solani. Similarly, all treatments performed better than the control against A. gossypii, significantly reducing its reproduction. Furthermore, we found no additive effects when mixing products nor negative interactions affecting survival for the bacteria investigated. These microorganisms therefore have potential for use in biological control.

Abstract: A total of 237 microorganisms were isolated from five different greenhouse tomato growing media. Of those, 40 microorganisms reduced the in vitro mycelial growth of both Pythium aphanidermatum and Pythium ultimum. The ability of these microorganisms to control damping-off was then tested in rockwool. As a result, Pseudomonas corrugata strains 1 and 3, Pseudomonas fluorescens subgroup F and G strains 1, 2, 3, 4 and 5, Pseudomonas marginalis, Pseudomonas putida subgroup B strain 1, Pseudomonas syringae strain 1 and Pseudomonas viridiflava significantly reduced damping-off caused by P. ultimum or P. aphanidermatum. Pseudomonas marginalis was the only microorganism that significantly reduced damping-off caused by both pathogens.

Soil samples were collected in plots from a field experiment in maize monoculture receiving 0, 60 and 120 m 3 ha -1 liquid pig manure (LPM) for 19 years. Soils were sampled from the 0- to 20-cm layer in August and October 1997 and in June, July and September 1998. Subsurface samples were also evaluated in September 1998. Laboratory soil radiorespirometry was used to evaluate atrazine mineralization using [U- ring- 14C]-atrazine mixed with commercially available product. The effect of atrazine dose (50, 100 and 500 mg atrazine kg -1soil) was evaluated on soils sampled in August 1997. For the other sampling dates, the soils were spiked with 50 mg atrazine kg -1 soil. No LPM dose effect on atrazine mineralization was obtained in the different experiments. Increasing atrazine dose to 500 mg kg -1 decreased significantly the mineralization rate (R i) and the maximum of atrazine mineralized (MAX), while the time needed to mineralize 50% of MAX (DT-50%) was not significantly affected. Sampling time had a significant effect on atrazine mineralization. Atrazine mineralization in the soils sampled in June 1998 showed lower R i and MAX than in the soils sampled at the other dates. Atrazine mineralization in subsurface soils (20–60 cm) was very variable and quite high in some samples. This may be due to atrazine pre-exposure in subsoils resulting from atrazine deep movement by preferential flow.

Here we report the construction of three different vectors for the identification of bacterial genes induced in vitro and/or in vivo. These plasmids contain kanamycin, gentamicin, or tetracycline resistance genes as selectable markers. A promoterless cat and an improved GFP (mut3-gfp) can be used to follow the induction of gene expression by measuring chloramphenicol resistance and fluorescence, respectively.

Strains of Rhizobium leguminosarumbv. viciae, isolated from the legume species Lathyrus japonicusand Lathyrus pratensisin northern Quebec (Canada), showed different capacities for growing at low temperature. In the present study, we investigated some mechanisms related to cold adaptation. Two cold-adapted strains (psychrotrophs) were compared to a poorly adapted strain and to a cold-sensitive strain (reference strain) for freezing survival, protein induction and fatty acid composition under low temperature. Following cold shocks (25°C to 10, 5 and 0°C), a common 6.1-kDa CSP (cold shock protein) was induced in all strains, but the total number of CSPs synthesized at 0°C was higher in cold-adapted strains than in the cold-sensitive strain. The synthesis of CAPs (cold acclimation proteins) was observed under continuous growth at 5°C in all three strains capable of growth at this temperature. Levels of survival after 24 h at −80°C where higher in cold- (79%) and poorly adapted (64%) strains than in the cold-sensitive strain (33%), but a 2-h acclimation period at 5°C before freezing doubled the survival of the cold-sensitive strain. Low temperature conditions affected similarly the fatty acid composition of all strains, regardless of their cold adaptation level. The proportion of unsaturated fatty acids increased significantly with the lowering of growth temperature from 25 to 5°C, but showed a tendency to decrease after a cold shock from 25 to 5°C. A specific unsaturated fatty acid, cis-12 octadecanoic acid, was produced during growth at 5°C. The unsaturated cis-vaccenic acid was the principal component under all conditions. The cold adaptation trait was weakly reflected in symbiosis with the agronomic legume, Lathyrus sativus, with which one cold-adapted strain showed a slightly higher nitrogenase activity and shoot dry matter yield than a commercial strain under a sub-optimal temperature regime.

Strains of Rhizobium leguminosarumbv. viciae, isolated from the legume species Lathyrus japonicusand Lathyrus pratensisin northern Quebec (Canada), showed different capacities for growing at low temperature. In the present study, we investigated some mechanisms related to cold adaptation. Two cold‐adapted strains (psychrotrophs) were compared to a poorly adapted strain and to a cold‐sensitive strain (reference strain) for freezing survival, protein induction and fatty acid composition under low temperature. Following cold shocks (25°C to 10, 5 and 0°C), a common 6.1‐kDa CSP (cold shock protein) was induced in all strains, but the total number of CSPs synthesized at 0°C was higher in cold‐adapted strains than in the cold‐sensitive strain. The synthesis of CAPs (cold acclimation proteins) was observed under continuous growth at 5°C in all three strains capable of growth at this temperature. Levels of survival after 24 h at −80°C where higher in cold‐ (79%) and poorly adapted (64%) strains than in the cold‐sensitive strain (33%), but a 2‐h acclimation period at 5°C before freezing doubled the survival of the cold‐sensitive strain. Low temperature conditions affected similarly the fatty acid composition of all strains, regardless of their cold adaptation level. The proportion of unsaturated fatty acids increased significantly with the lowering of growth temperature from 25 to 5°C, but showed a tendency to decrease after a cold shock from 25 to 5°C. A specific unsaturated fatty acid, cis‐12 octadecanoic acid, was produced during growth at 5°C. The unsaturated cis‐vaccenic acid was the principal component under all conditions. The cold adaptation trait was weakly reflected in symbiosis with the agronomic legume, Lathyrus sativus, with which one cold‐adapted strain showed a slightly higher nitrogenase activity and shoot dry matter yield than a commercial strain under a sub‐optimal temperature regime.

After screening several fungal isolates obtained from Venezuelan soils, the isolate IR‐94MF1 of Penicillium rugulosumwas selected for its high mineral phosphate solubilizing activity (Mps+) with hydroxyapatite. Mutants with altered (Mps−) or amplified activity (Mps++) were obtained by UV irradiation of conidia. When glucose was used as the sole C source by the fungus, gluconic acid was associated with the hydroxyapatite activity. In solid media, in comparison to glucose and maltose, sucrose appeared to be the best C source for the solubilization of hydroxy‐apatite and FePO4.

The mechanisms of action of mineral phosphate solubilization (MPS) were studied in the wild‐type Mps+Penicillium rugulosumstrain IR94‐MF1 and in negative (Mps−) and superpositive (Mps++) mutants derived from it. MPS activities were measured in liquid media using sucrose as C source, four N (arginine, nitrate, nitrate+ammonium and ammonium) and P sources (KH2PO4, hydroxyapatite, FePO4and AlPO4). Ammonium significantly (P<0.01) decreased phosphate solubilization, and this activity was 1–66 times higher in the Mps++mutant than in the wild‐type depending on the P and N sources used. The Mps+phenotype was strongly associated with the production of gluconic or citric acids. The results also suggest for the MPS−mutant the involvement of the H+pump mechanism in the solubilization of small amounts of phosphates.

After screening several fungal isolates obtained from Venezuelan soils, the isolate IR-94MF1 of Penicillium rugulosumwas selected for its high mineral phosphate solubilizing activity (Mps+) with hydroxyapatite. Mutants with altered (Mps−) or amplified activity (Mps++) were obtained by UV irradiation of conidia. When glucose was used as the sole C source by the fungus, gluconic acid was associated with the hydroxyapatite activity. In solid media, in comparison to glucose and maltose, sucrose appeared to be the best C source for the solubilization of hydroxy-apatite and FePO4.

The mechanisms of action of mineral phosphate solubilization (MPS) were studied in the wild-type Mps+Penicillium rugulosumstrain IR94-MF1 and in negative (Mps−) and superpositive (Mps++) mutants derived from it. MPS activities were measured in liquid media using sucrose as C source, four N (arginine, nitrate, nitrate+ammonium and ammonium) and P sources (KH2PO4, hydroxyapatite, FePO4and AlPO4). Ammonium significantly (P<0.01) decreased phosphate solubilization, and this activity was 1–66 times higher in the Mps++mutant than in the wild-type depending on the P and N sources used. The Mps+phenotype was strongly associated with the production of gluconic or citric acids. The results also suggest for the MPS−mutant the involvement of the H+pump mechanism in the solubilization of small amounts of phosphates.

Root nodules induced in Phaseolus vulgaris L. by the wild-type (WT) and a C4-dicarboxylic-acid mutant strain of Rhizobium leguminosarum biovar. phaseoli were compared on the basis of ultrastructure and cytochemistry of cellulose subunits. The mutant bacteroids failed to colonize infected host cells in a normal manner, and presented a premature degenerative appearance. Starch granules, rough endoplasmic reticulum and mitochondria were found to accumulate in the ineffective nodules. The most striking difference between effective and ineffective nodules was the presence of unusual spherical, laminated structures in plastids of mutant-infected host cells only. Cytochemical observations showed that these structures contain ß-1,4-glucans. The presence of ß-1,4-glucans within such structures may be caused by the activity of a cellulase which is produced by either the bacteroids or the host cell and is locally hydrolyzing the host cell-wall, thus releasing cellulose subunits into the cytoplasm. Another possibility is denovo synthesis of ß-1,4-glucans in the host cell.