Hani Antoun’s research while affiliated with University of Quebec and other places

Bacillus pumilus strain PTB180 and Bacillus subtilis strain PTB185 were recently reported for their strong in vitro antagonistic activity against several plant pathogens including Fusarium oxysporum, Rhizoctonia solani, Sclerotinia sclerotiorum, Phytophthora capsici, and Pythium ultimum. In this study, strains PTB180 and PTB185 were investigated for the production of lipopetides (LPs), antifungal activity, and biocontrol capabilities against Botrytis cinerea. Strain PTB185 was shown to secrete LPs of the surfactin, iturin, and fengycin families while strain PTB180 was shown to secrete exclusively surfactins. Dual-culture overlay assays indicated that both strains produced antifungal compound(s) that strongly inhibit(s) B. cinerea mycelial growth and conidial germination. The strains were shown to survive for at least 21 days with a survival rate varying from 43% to 61% in the tomato phyllosphere. Survival rate of both PTB180 and PTB185 was approximately 50% when they were applied as a mix (1:1) with almost no variation in the proportion of each strain over time. Preventive foliar applications of the strains alone or as a mix (1:1) reduced significantly (P ≤ 0.01) the incidence and severity of gray mold on tomato plants grown in greenhouse as compared to the control. Incidence and severity of gray mold of tomato plants treated with PTB180, PTB185, or mix of both strains (1:1) were not significantly different. Although PTB180 and PTB185 have a different LPs signature, they showed (1) comparable in vitro antagonistic activity against B. cinerea, (2) comparable survival on the phyllosphere of tomato plants, and (3) comparable biocontrol activity against B. cinerea on tomato plants.

Forty-eight bacteria isolates from the rhizosphere of three cultivars of corn and three different soils were examined for their phosphate solubiling ability. The tests were realized on NBRIP (National Botanical Research Institute of Phosphate Growth medium) containing the Tilemsi phosphate rock (TPR) as the only source of insoluble phosphorus. All the isolates solubilized the TPR in solid and liquid media. Twenty isolates were selected for their high solubilizing capacity in liquid medium (105 to 311 mg P/ ml/g of TPR). These isolates were submitted to different stress conditions (acid medium with pH 7 to 5, five successive growths and the temperature range of 30°C to 45°C). Only six isolates (I 1 , I 2 , I 3 , I 4 I 5 ad I 6) were able to maintain their ability of solubilizing the TPR and also they were not antagonistics. These selected isolates were also tested for their solubilization efficiency (SE) of TPR and phytate on NBRIP solid medium containing the TPR and phytate as the only insoluble source of phosphorus and phytate respectively. The maximum solubilization (300%) for TPR was obtained with the isolate I 5 and 167% for phytate with the isolate I 1. It has been observed that the bacteria isolates have an average solubilization capacity of 18.54 kg P 2 O 5 out off 30 kg contained in 100 kg of PNT. The same bacteria strains were tested for their plant growth promotion (PGPR) characteristics which indicated that all produced low molecular weight Organic Acids, Siderophores, Indole Acetic Acid (IAA or auxine), but none of them produced the Hydrocyanic Acid (HCN).

The foxglove aphid, Aulacorthum solani (Kaltenbach) (Hemiptera: Aphididae), and the melon aphid, Aphis gossypii Glover (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 pumilus Meyer 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 lycopersicum Linnaeus (Solanaceae), and cucumber, Cucumis sativus Linnaeus (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.

Co-applying biochar and paper mill biosolids (PB) improves the potential of these by-products as soil amendments. Assessing the response of soil microbial communities to the co-application of biochar and PB is of great importance to further understanding their effectiveness. This hypothesis was tested in a 112-day incubation study performed separately on two acidic soils (Kamouraska clay and St-Antoine sandy loam) using two PB types (PB1 with C/N = 24 and PB2 with C/N = 13), co-applied with one of three rates (0%, 2.5%, and 5% w/w) of pine (Pinus strobus L.) biochar. An unamended control and a mineral-fertilized treatment were used as a reference. In the Kamouraska clay soil, co-applying 5% biochar and any PB increased microbial activity compared to PB-only application, as indicated by the fluorescein diacetate (FDA) hydrolysis assay. In both soils, co-applying biochar and PB did not affect microbial diversity and community structure compared with PB only. The application of any PB, however, increased microbial activity in both soils, while only PB2 shifted microbial community structure. Within each amendment and in both soils, microbial activity was lower at day 112 than at days 28 and 56, while major temporal shifts were observed only for bacterial community structure. Indeed, the difference in bacterial community structure between amendments was more pronounced at day 112. This study suggests that co-applying biochar and PB can improve soil properties than application of PB alone by increasing soil microbial activity without side effects on microbial diversity and community structure, especially in acidic clay soils.