Kamel Gargouri

Efficacy of olive mill waste water and its derivatives in the suppression of crown gall disease of bitter almond

Olive mill waste water (OMW) and some of its indigenous bacterial strains were tested in vitro and in planta for their efficacy against crown gall disease caused by Agrobacterium tumefaciens. OMW and polyphenols displayed a high level of antibacterial activity, however the volatile fraction was less efficient as only a bacteriostatic effect was observed. In pot experiments, the percentage of bitter almond rootstock showing symptoms of crown gall was significantly reduced with the dosage rate of OMW 1% as compared to the control (highly natural infected soil treated with water). Five indigenous bacterial strains isolated from OMW exhibited an antagonistic effect against the bacterium. Based on the gene 16S rRNA sequence analysis, one isolate showed 99.2% similarity to known sequences of Bacillus subtilis, one isolate demonstrated high percentage similarities (99.3%) to the genera Bacillus pumilis, and two isolates were associated with Stenotrophomonas maltophilia and Pseudomonas putida 100% and 99.6% similarities respectively. Among these bacteria, the strain B1 proved efficient against the soil borne pathogen in vitro and pot experiments. Our study in controlled conditions suggested that the addition of OMW to soil exerts significant disease suppressiveness against A. tumefaciens.

Influence of Olive Mill Wastewater (OMW) Spread on Carbon and Nitrogen Dynamics and Biology of an Arid Sandy Soil

Olive mill wastewater (OMW) contains large amounts of organic substances, including phenols, that can have negative environmental consequences when applied to soil. Because of the high concentrations of organic matter and mineral nutrients, OMW holds promise as a fertilizer source for cropping systems. The effects of the addition of 0.5, 1, or 2% OMW to a soil on carbon (C) and nitrogen (N) dynamics and microbiological characteristics of the soil were investigated. Mineral N presented a significant negative correlation with the amount of OMW. The total number of soil bacteria and fungi increased. However, the nitrifying population was sensitive to 2% OMW during the first month. The increase in microbiological activity accelerated the loss of soil organic carbon (SOC). However, the treated soil recovered the SOC, and the total C gains were 2.1, 1.9, and 2.4 g kg−1 for the three doses, whereas the SOC loss was 1.1 g kg−1 for the control.

EFFECT OF FOLIAR BORON APPLICATION ON GROWTH, REPRODUCTION, AND OIL QUALITY OF OLIVE TREES CONDUCTED UNDER A HIGH DENSITY PLANTING SYSTEM

Boron (B) foliar treatments (300 mg L−1 as Solubor DF) were applied at two different dates in 2006 and 2007, prior to flowering and just after fruit set, on olive (Olea europaea L.) trees with no visual symptoms of B deficiency. Leaf B level increased after the first application as compared to control (−B). After July treatment, leaf B levels in −B and +B treated trees increased when compared to the first sampling date. Foliar B application did not significantly affect vegetative growth in either year. During the first year of study (considered as an “on year”), B application had no significant effect on several phenological characteristics including fruit set, yield oil contents and oil quality. In the second year (“off year”), B sprays improved blooming rate, which increased from 20% in −B to 30% in + B treated trees, and olive yield, which increased by 27% in response to B.

A novel method to assess drought stress of olive tree

Threats of desertification have been projected for the Mediterranean basin under relatively minor warming and drying scenarios. This situation raises the need for mitigation strategies and adaptation of crop production. Crop vulnerability assessment is therefore needed. In Tunisia, olive culture is a major activity. In some cases, olive is the only crop able to grow in local conditions. However, olive production may be among the more vulnerable systems to climate change since perennial crops adapt slowly. No studies have been dedicated to vulnerability evaluation of olive production. Here, the vulnerability of Tunisian olive trees to drought was assessed under extremely low precipitation levels, of 50% of normal precipitation, from 1999 to 2002. The impact of drought was quantified using a severity scale with three levels. A map of the impact of drought on olive trees was constructed for all Tunisian olive groves. We found that the number of wilting olive trees in 2002 was 7.8 millions of about 60 millions trees. A correlation was observed between olive tree affection by drought and olive orchard age. Thus, under the same drought conditions, senescent orchards were less resistant to drought than young ones. Locally, data showed that compact soils and soils containing more than 1% gypsum were not suitable for olive growth under drought.