Tunis, Tunisia
Tunis, Tunisia

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Khefifi H.,French National Institute for Agricultural Research | Tadeo F.R.,IVIA | Selmane R.,INAT | Ben Mimoun M.,INAT | And 2 more authors.
Acta Horticulturae | Year: 2016

Fruit shedding is an important cause of citrus fruit loss in different citrusproducing areas in the world. This physiological process can occur in certain citrus cultivars during the final stage of fruit maturation. The fruit maturation process interacts with the environment and more precisely with climatic factors such as temperature. The maturity parameters that induce fruit drop and the interaction between citrus fruit abscission and climate are not known. To evaluate the effect of environment on fruit maturation and abscission, a multi-site study was carried out in Spain, Tunisia and Corsica on six orange cultivars. The examined parameters were fruit detachment force (FDF), weight, diameter, colour, total soluble sugar (TSS) and titratable acidity (TA). We observed that FDF did not evolve in the same way in the three sites. While in Tunisia and in Spain it decreased, in Corsica, it remained constant throughout the fruit maturation process whatever the orange cultivar. Variation of temperature and radiation measured between the three sites cannot be the direct factors controlling this fruit process. Moreover, FDF seems not to be dependent on the evolution of any fruit quality parameters. Considering these results, fruit abscission and fruit maturation could be two independent phenomena at least under the environmental conditions in Corsica.

Kalai-Grami L.,Laboratoire des Substances Bioactives | Kalai-Grami L.,Laboratoire Of Biotechnologie Appliquee A Lagriculture | Ben Slimane I.,Laboratoire des Substances Bioactives | Mnari-Hattab M.,Laboratoire Of Biotechnologie Appliquee A Lagriculture | And 4 more authors.
World Journal of Microbiology and Biotechnology | Year: 2014

Isolate TEB1 an antagonistic endophytic bacterium, obtained from citrus leaves and identified as Bacillus amyloliquefaciens by 16S rDNA sequencing, was used for the biological control of mal secco disease of Citrus aurantium seedlings caused by the mitosporic fungus Phoma tracheiphila. The isolate TEB1 exhibited a good in vitro activity against P. tracheiphila in dual cultures as well as with the well diffusion method. C. aurantium seedlings watered with a suspension of TEB1 cells showed a reduction of 53.61 and 48.63 % in disease severity and incidence, respectively. A PCR test with specific primers was performed 365 days after inoculation and P. tracheiphila was detected along the whole stem in inoculated control plant while no amplification product was obtained in TEB1 treated seedlings. Molecular analysis of TEB1 revealed a positive amplification of fenD and ituC genes responsible of the biosynthesis of fengycin and iturin lipopeptides, respectively. Moreover, observations by optical microscope showed that TEB1 reduced by 55 % the germination of P. tracheiphila conidia and exhibited a marked effect on mycelia structure. Data suggest that lipopeptides produced by the bacterium interact with the cytoplasmic membrane of the fungus causing pore formation. TEB1 appears a potential candidate for the biological control of citrus mal secco disease. © 2013 Springer Science+Business Media Dordrecht.

Zribi M.,CNRS Center for the Study of the Biosphere from Space | Paris Anguela T.,LATMOS | Duchemin B.,CNRS Center for the Study of the Biosphere from Space | Lili Z.,INAT | And 3 more authors.
Water Resources Research | Year: 2010

The present paper proposes an empirical approach for the modeling of vegetation development, using moisture measurements only. The study is based simply on the use of two databases: one containing soil moisture products derived from ERS scatterometer data over the period 1991-2006 and the other containing normalized difference vegetation indices (NDVI) derived from advanced very high resolution radiometer over the period 1991-2000. The study is applied over the Kairouan plain, the central semiarid region of Tunisia (North Africa). Soil moisture products were first validated on the basis of comparisons with Global Soil Wetness Project, Phase 2 Data, outputs and rainfall events. The soil moisture distribution during the rainy period between October and May is described and is found to be correlated with the vegetation dynamics estimated using the NDVI products. Finally, a semiempirical model is proposed, based on satellite moisture and NDVI products, which allows the NDVI value to be estimated for a period of 1 month during the rainy season as a function of the moisture profile estimations obtained during the previous months. This approach could prove very useful and provide a simple tool for the modeling of vegetation dynamics during rainy seasons in semiarid regions. Copyright © 2010 by the American Geophysical Union.

Nagaz K.,Institute des Regions Arides | Masmoudi M.M.,INAT | Mechlia N.B.,INAT
Journal of Applied Horticulture | Year: 2012

A two-year study was carried out to assess the effect of different irrigation scheduling regimes with saline water on soil salinity, yield and water productivity of pepper under actual commercial-farming conditions in the arid region of Tunisia. Pepper was grown on a sandy soil and drip-irrigated with water having an ECi of 3.6 dS/m. Four irrigation treatments were based on the use of soil water balance (SWB) to estimate irrigation amounts and timing while the fifth consisted of using farmers practices. SWB methods consisted in replacement of cumulated ETc when readily available water is depleted with levels of 100% (FI), 80% (DI-80) and 60% (DI-60). FIwas considered as full irrigation while DI-80 and DI-60 were considered as deficit irrigation regimes. Regulated deficit irrigation regime where 40% reduction is applied only during ripening stage (FI-MDI60) was also used. Farmer method consisted of applying the producer method corresponding to irrigation practices implemented by the local farmers. Results on pepper yield and soil salinity are consistent between the two-year experiments and showed significant difference between irrigation regimes. Higher soil salinity was maintained over the two seasons, 2008 and 2009, with DI-60 and FM treatments than FI. FI-MDI60 and DI-80 treatments also resulted in low ECe values. Highest yields for both years were obtained under FI(22.3 and 24.4 t/ha) although we didn't find significant differences with the regulated deficit irrigation treatment (FI-DI60). However, DI-80 and DI-60 treatments caused significant reductions in pepper yields through a reduction in fruits number/m2 and average fruit weight in comparison with FItreatment. The FM increased soil salinity and caused significant reductions in yield with 14 to 43%, 12 to 39% more irrigation water use than FI, FI-MDI60 and DI-80 treatments in 2008 and 2009, respectively. Yields for all irrigation treatments were higher in the second year compared to the first year. Water productivity (WP) values reflected this difference and varied between 2.31 and 5.49 kg/m3. The WP was found to vary significantly among treatments, where the highest and the lowest values were observed for DI-60 treatment and FM, respectively. FItreatment provided significant advantage on yield and water productivity, compared to FM in pepper production under experimental conditions. For water-saving purposes, the FIirrigation scheduling is recommended for drip irrigated pepper grown under field conditions and can be used by farmers to optimize the use of saline water and to control soil salinity. In case of limited water supply, adopting deficit irrigation strategies (FI-DI60 and DI-80) could be an alternative for irrigation scheduling of pepper crop under the arid Mediterranean conditions of Tunisia.

PubMed | INAT, CIRAD - Agricultural Research for Development and IVIA
Type: | Journal: Journal of plant physiology | Year: 2016

For grafted plants, salt stress tolerance of the aerial plant part is poorly documented. Thus, we developed a simple, fast and inexpensive method to identify tolerant genotypes. Twigs of 14 mandarin accessions that we previously analyzed as seedlings were cut in solution to prevent embolism and were then evaluated in salt stress condition for a week. Physiological parameters such as gas exchanges, leaf Cl(-) and Na(+), as well as the presence of H2O2 and the activity of enzymes involved in ROS synthesis and detoxification processes were analyzed. One accession known to be tolerant as rootstock was shown to be sensitive with limited Cl(-) translocation from the solution to the shoot while sensitive accessions when grown as seedlings presented limited wilting symptoms and accumulated large leaf Cl(-) content. A model is proposed to explain the different strategies of the plant to cope with high toxic ion content. This method allows separation of the root compartment, where ion exclusion mechanisms may exist and have an impact on the salt stress tolerance of the whole plant.

Hanafi S.,Laboratoire Of Genie Rural | Frija A.,ICARDA | Jamin J.-Y.,CIRAD - Agricultural Research for Development | Zairi A.,Laboratoire Of Genie Rural | And 2 more authors.
Cahiers Agricultures | Year: 2015

Despite research efforts and the multiple interventions of States, the productivity of water, land, and capital resources is often low, particularly in Tunisia. This study provides a framework for analyzing the performance of irrigated farms and examines the level and the effective determinants of this performance. Technical and economic data were collected through detailed questionnaires and used to calculate technical efficiency (TE) and irrigation water use efficiency (IWUE) for each farm, with the data envelopment analysis (DEA) approach. These efficiencies were subjected to statistical analysis for a set of field variables. The results show that TE is satisfactory at 0.84 on average. However, IWUE is much lower, at 0.61 on average. There is therefore significant potential for improving it. The most important determinants of the efficiencies are access to water and access to credit, both of which are possible levers to improve TE and IWUE. Neither irrigation techniques nor the choice of crops nor the water distribution method influence the differences in the efficiencies. Livestock presence is significant for the differences in IWUE, showing that water is used more efficiently with forage crops for livestock. Current modernization projects in Tunisia to convert open canal systems to pressurized pipe systems should take these results into account. But converting the irrigation system alone is not enough to improve efficiency. Scenarios that do not require such large investment may thus be more worthwhile.

Sahli A.,INAT | Moyne C.,University of Lorraine | Stemmelen D.,University of Lorraine
Transport in Porous Media | Year: 2010

Boiling in a porous layer heated from below at constant heat flux and cooled at constant temperature from the upper permeable surface leads below the critical flux of appearance of a vapor zone at the bottom in the approximation of dominated reservoirs to two solutions: a liquid-dominated one and a vapor-dominated one. The stability of these two situations is analyzed. The approach allows to understand the respective roles played by the gravitational instability, natural convection in the liquid upper layer, and movement of the interface between the two regions. Taking into account the confinement allows the comparison of these theoretical results with experimental results obtained in the laboratory. © 2009 Springer Science+Business Media B.V.

Masmoudi M.M.,INAT | Mahjoub I.,INAT | Lhomme J.P.,Montpellier SupAgro | Ben Mechlia N.,INAT
Annals of Forest Science | Year: 2012

• Context Recent works have showed the possibility of measuring sap flow density (u) by a single heated probe using the transient regime just after the heating current is switched off. The method (SP-T) is based on a thermal index (I) which involves the temperature of the probe at three different times of the cooling kinetics (beginning, intermediate time, and end), the latter representing wood temperature at equilibrium. • Aims The present paper re-examines the method to better estimate wood temperature and to account for possible variations in probe-wood thermal properties. • Methods After a recalibration of the method on an olive branch with a hydraulic bench, the SP-T method is used to measure sap flow on two olive trees under field conditions. • Results Estimated flow densities are compared to those obtained with the transient thermal dissipation-dual probe method (TTD-DP) of Do and Rocheteau. • Conclusions Obtained results show that: (1) wood reference temperature is better estimated when using the probe temperatures just before heating and at the end of the cooling phase; (2) calibration relationships based on a "normalized" thermal index Kt=(I-Io)/I o, where Io represents the value of I under zero flow conditions, better account for differences in the wood-probe thermal properties; (3) Io, taken as the lowest I over a 24-h span, has shown consistent stability for a given probetree complex; (4) the SP-T method used in its normalized form appears to be in good agreement with the TTD-DP method. © INRA / Springer-Verlag France 2012.

Amri R.,CNRS Center for the Study of the Biosphere from Space | Zribi M.,CNRS Center for the Study of the Biosphere from Space | Lili-Chabaane Z.,INAT | Duchemin B.,CNRS Center for the Study of the Biosphere from Space | And 2 more authors.
Remote Sensing | Year: 2011

The analysis of vegetation dynamics is essential in semi-arid regions, in particular because of the frequent occurrence of long periods of drought. In this paper, multi-temporal series of the Normalized Difference of Vegetation Index (NDVI), derived from SPOT-VEGETATION satellite data between September 1998 and June 2010, were used to analyze the vegetation dynamics over the semi-arid central region of Tunisia. A study of the persistence of three types of vegetation (pastures, annual agriculture and olive trees) is proposed using fractal analysis, in order to gain insight into the stability/instability of vegetation dynamics. In order to estimate the state of vegetation cover stress, we propose evaluating the properties of an index referred to as the Vegetation Anomaly Index (VAI). A positive VAI indicates high vegetation dynamics, whereas a negative VAI indicates the presence of vegetation stress. The VAI is tested for the above three types of vegetation, during the study period from 1998 to 2010, and is compared with other drought indices. The VAI is found to be strongly correlated with precipitation. © 2011 by the authors.

Fontanelli G.,CNR Institute of Neuroscience | Paloscia S.,CNR Institute of Neuroscience | Zribi M.,CNRS Center for the Study of the Biosphere from Space | Chahbi A.,INAT
Remote Sensing Letters | Year: 2013

Remote sensing of vegetation by using active microwave sensors is important for the management of land and water resources. Microwave radiation at X-band penetrates only the upper part of the canopy; thus, radar backscattering comes mainly from the top vegetation layer, making the scattering from soil almost negligible. Fourteen in situ measurement campaigns were carried out during which sixteen SAR images of COSMO-SkyMed and TerraSAR-X were acquired on the test site of Merguellil Basin, in the centre of Tunisia, from March to May 2012. A clear sensitivity of the backscattering coefficient, measured by both sensors, to the leaf area index (LAI) of green plants of wheat and barley (at both HH and VV polarizations) was observed, and it did not seem to be greatly affected by the variations in soil moisture, even in HH polarization. As expected, the sensitivity to LAI of dry plants was, instead, almost negligible. The decreasing trend of backscattering as vegetation grows, which has already been observed in past investigations, also at lower frequencies, was confirmed. Due to the similar geometry and dimensions of the two crop types, none of the sensors succeeded in separating the two crop types. © 2013 Taylor and Francis.

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