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Boussadia O.,Institute of the Olive Tree station of Sousse | Steppe K.,Ghent University | Zgallai H.,Bayer BioScience N.V. | El Hadj S.B.,Agronomic National Institute of Tunisia | And 3 more authors.
Photosynthetica | Year: 2011

For Tunisian olive tree orchards, nitrogen deficiency is an important nutritional problem, in addition to the availability of water. Establishment of relationships between nutrients such as nitrogen and ecophysiological parameters is a promising method to manage fertilisation at orchard level. Therefore, a nitrogen stress experiment with one-year-old olive trees (Olea europaea L. 'Koroneiki' and 'Meski') was conducted with trees respectively subjected to four nitrogen supply regimes (23.96 meq l-1, 9.58 meq l-1, 4.79 meq l-1 and 0 meq l-1 NO3 -1). The current paper focuses on the use of the SPAD-502 portable chlorophyll (Chl) meter, a nondestructive method for fertilisation management under nitrogen stress conditions of olive trees. Maximum net photosynthetic assimilation rates, chlorophyll fluorescence parameters and the SPAD Chl index were therefore measured simultaneously and the Chl and nitrogen content of the leaves were analysed. Significant correlations were established in the olive tree leaves between SPAD-502 readings on the one hand and Chl content, nitrogen content, photosynthetic assimilation rate, and Chl fluorescence parameters (ΦPSII and ETR) on the other hand. © 2011 Springer Science+Business Media B.V.


Boussadia O.,Institute of the Olive Tree Station of Sousse | Steppe K.,Ghent University | Zgallai H.,Bayer BioScience N.V. Nazarethsesteenweg 77 | Ben El Hadj S.,Agronomic National Institute of Tunisia | And 3 more authors.
Scientia Horticulturae | Year: 2010

The effects of nitrogen deficiency on CO2 assimilation, carbohydrate content and biomass were studied in two olive (Olea europaea L.) cultivars ('Meski' and 'Koroneiki'). One-year-old plants were grown in pots and subjected to four nitrogen levels for 58 days. Nitrogen-deficient plants had significant lower leaf nitrogen and chlorophyll a contents. They also showed a significant reduction in their photosynthetic capacity. A tolerance difference between cultivars was observed: 'Meski' proved to be more efficient in maintaining CO2 assimilation rates than 'Koroneiki' under nitrogen deficiency, which was reflected by increased photosynthetic nitrogen use efficiency. Accumulation of carbohydrates, especially starch, mannitol, sucrose and glucose, was observed in nitrogen-deficient leaves. This indicates that both the high carbohydrate and the low nitrogen content inhibit photosynthesis in nitrogen-deprived olive plants. Total biomass was strongly reduced (mainly caused by a decrease in leaf dry weight) under nitrogen deficiency for both cultivars, but root:shoot ratio was hardly affected. Elongation of fine roots was enhanced in 'Koroneiki' under severe nitrogen-deprivation. © 2009 Elsevier B.V. All rights reserved.


Boussadia O.,Institute of the Olive Tree station of Sousse | Steppe K.,Ghent University | Van Labeke M.-C.,Ghent University | Lemeur R.,Ghent University | Braham M.,Institute of the Olive Tree station of Sousse
Journal of Plant Nutrition | Year: 2015

Effects of nitrogen (N) deficiency on photosynthetic carbon dioxide (CO2) assimilation, photosystem II (PSII) photochemistry and photoinhibition were investigated in young trees of two olive cultivars ‘Meski’ and ‘Koroneiki’ grown in a greenhouse under controlled conditions. The trees were subjected to four different levels of N supply. N deficient trees had a significantly smaller CO2 assimilatory capacity, but showed little changes in maximum quantum efficiency of PSII photochemistry. However, modifications in PSII photochemistry induced by N deficiency were observed. This was reflected in decreases in quantum yield of PSII electron transport (ΦPSII) and efficiency of excitation energy capture by open PSII reaction centres (Fv’/Fm’) and in an increase in non-photochemical quenching (NPQ). These results suggest that modifications in PSII photochemistry might be a mechanism to down-regulate photosynthetic electron transport so that production of adenosine triphosphate (ATP) and nicotinamide adenine dinucleotide phosphate (NADPH). would be in equilibrium with the decreased demand in the Calvin cycle in the N deficient trees. Therefore, both CO2 assimilation rate and total electron flow (Jt) with its compound electron flows devoted to either carboxylation (Jc) or oxygenation (Jo) can be considered as useful tools to assess the N nutrition status of the trees. Clear relationships were found between Amax and the nitrogen nutrition index (NNI) on the one hand, and between Jt and NNI on the other hand. The results demonstrate that ‘Meski’ is more efficient than ‘Koroneiki’ when subjected to N deficiency. © 2015, Copyright © Taylor & Francis Group, LLC.


Zeiri A.,University of Carthage | Ahmed M.Z.,University of Florida | Ahmed M.Z.,South China Agricultural University | Braham M.,University of Sousse | And 2 more authors.
Bulletin of Entomological Research | Year: 2015

Scolytus amygdali is a polyphagous insect pest that feeds on fruit trees and forest trees. Our study assessed the host preference and reproductive potential of S. amygdali on four tree species: almond (Prunus dulcis), apricot (Prunus armeniaca), peach (Prunus persica), and plum (Prunus domestica). Females of S. amygdali produced maternal galleries that were longer on peach than the other three trees, and female fecundity was highest on peach. Females with longer maternal galleries produced more eggs, indicating a positive correlation between maternal gallery length and female fertility. The under-bark development time of S. amygdali is significantly shorter on plum (45 days) and almond (56 days) than on apricot (65 days) and peach (64 days). Despite this longer development time on peach, our results still suggest that, of the four types of tree tested, peach is the most preferred host for S. amygdali. © Cambridge University Press 2015.


Vandegehuchte M.W.,Ghent University | Braham M.,Institute of the Olive Tree Station of Sousse | Lemeur R.,Ghent University | Steppe K.,Ghent University
Irrigation and Drainage | Year: 2012

Improvement in irrigation techniques has led to an expansion of the irrigated olive area in Tunisia and consequently a rise in agricultural water consumption. Here, the actual water use of Olea europaea L. 'Meski' as estimated by thermal dissipation probe measurements was compared for different irrigation regimes: three plots with irrigation doses based on Penman-Monteith crop evapotranspiration (ETc), 0.33×ETc and the local grower's experience (about 0.6×ETc), respectively. The scaling up of sap flux densities proved to be difficult given the azimuthal and radial sap flux density variability and the conductive surface area asymmetry. Moreover, natural thermal gradients may lead to inaccurate use of standard sap flow formulas. Depending on the manner of upscaling, differences in water use of more than 50 l day-1 per tree were obtained (up to 0.7×ETc irrigation dose). Despite these difficulties, sap flow calculations seem crucial to accurately determine the water needs of the orchard under investigation, as they corresponded closely to the lowest irrigation dose which was considered sufficiently high as no significant differences in drought stress variables were detected between the plots. Therefore, irrigation based solely on ETc leads to wasting of water; hence, careful application of both meteorological and sap flow methods is desirable in irrigation scheduling. © 2012 John Wiley & Sons, Ltd.


Zeiri A.,University of Carthage | Ayberk H.,Istanbul University | Braham M.,University of Sousse | Braham M.,Institute of the Olive Tree station of Sousse
Egyptian Journal of Biological Pest Control | Year: 2015

The almond bark beetle Scolytus amygdali Geurin-Meneville (Coleoptera: Scolytinae) is a main pest of almond orchards in Tunisia. Among many chalcidoids species collected in rearing cages of this pest, three specimens were identified by morphological and molecular tools as belonging to the genus Necremnus Thomson. A comprehensive survey of published literature concluded that Necremnus species have been previously recorded as parasitoids associated with the almond bark beetles. Further information about their use as biocontrol agents is still required. © 2016, Egyptian Society for Biological Control of Pests. All rights reserved.

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