A grower broiler experiment (from 14 to 35 days of age) was conducted to study the effect of using two commercial mixtures of organic acids (Galliacid ® and Biacid ® ) to substitute antibiotic growth promoter (Eneramycin ® ) on performance, carcass characteristics and intestinal microflora. 400 (Ross 308) broiler chicks were used. A basal corn-soybean meal diet were formulated and served as a control treatment. The control diet was supplemented with either 0.06% Galliacid, 0.1% Biacid or 0.02% Eneramycin. Birds fed the Galliacid-supplemented diet had 16% (p<0.001) more gain than the control, while those fed the Biacid-or Enramycinsupplemented diets recorded 3 and 5.5% more gain, respectively. Organic acids mixtures and Enramycin supplementation significantly (p<0.001) improved feed conversion ratio. These results indicated that birds fed either organic acid mixtures or Enramycinsupplemented diets utilized feed more efficiently than those fed the control diet. Galliacid significantly (p<0.01) increased dressing percentage and bursa weight (% body weight). No significant differences were detected on liver, spleen and thymus (% body weight) among treatments. Galliacid or Biacid significantly (p<0.001) decreased intestinal Escherichia coli and Salmonella compared to the control and Enramycin-supplemented diets. Dietary Enramycin significantly (p<0.001) decreased Escherichia coli, but had no effect on Salmonella counts. In conclusion, organic acid mixtures are more efficient than antibiotic growth promoter (Enramycin) in improving broiler performance and decreasing intestinal Escherichia coli and Salmonella spp., and could be successfully used to substitute antibiotic growth promoters in broiler diets. However, not all of the organic acid mixtures gave the same effect either on performance or intestinal bacterial counts.

Fourteen microsatellite loci of Phoenix dactylifera were targeted to examine the genetic diversity in Tunisian date-palms germplasm. They showed a high level of polymorphism in 49 accessions from three main oases with little geographic structure within Tunisia. The microsatellite data agrees with previous analyses of Tunisian germplasm using other molecular markers. 100% of local date-palms accessions were successfully fingerprinted and easily distinguished by the help of only three loci. The possibility of using microsatellites for large scale molecular labelling of offshoots and in vitro plantlets and their implication in the plant material certification is discussed.

Plant regeneration through somatic embryogenesis from young leaf explants (5-10 mm long) adjacent to the apex of 5-6 year old offshoots of Tunisian date palm (Phoenix dactylifera L.), cultivar Boufeggous was successfully achieved. Factors affecting embryogenic callus initiation, including plant growth regulators and explant size, were investigated. The highest induction frequencies of embryogenic calli occurred after 6-7 months on MS medium supplemented with 10 mg l -1 2,4-D and 0.3 mg l -1 activated charcoal. The subculture of these calli onto maintenance medium resulted in the formation of proembryos. Fine chopping and partial desiccation (6 and 12 h) of embryogenic calli with proembryos prior to transfer to MS medium supplemented with 1 mg l -1 ABA stimulated the rapid maturation of somatic embryos. Maturated somatic embryo yield per 0.5 g FW of embryogenic callus was 51 embryos with an average maturation time of 55 days. This was increased to 422 with finely chopped callus, and 124 and 306 embryos following 6 and 12 h desiccation treatments, respectively. The average time to maturation for these 3 treatments was 35, 43 and 38 days, respectively. Subsequent substitution of ABA in MS medium with 1 mg l -1 NAA resulted in the germination and conversion of 81% of the somatic embryos into plantlets with normal roots and shoots. The growth of regenerated somatic plants was also monitored in the field.

The study of intraspecific variation with respect to host plant utilization in polyphagous insects is crucial for understanding evolutionary patterns of insect-plant interactions. Aphis gossypii (Glover) is a cosmopolitan and extremely polyphagous aphid species. If host plant species or families constitute selective regimes to these aphids, genetic differentiation and host associated adaptation may occur. In this study, we describe the genetic structure of A. gossypii collected in six localities in Tunisia on different vegetable crops, on citrus trees and on Hibiscus. The aim was to determine if the aphid populations are structured in relation to the host plants and if such differentiation is consistent among localities. The genetic variability of A. gossypii samples was examined at eight microsatellite loci. We identified only 11 multilocus genotypes among 559 individuals. Significant deviations from Hardy-Weinberg equilibrium, linkage disequilibria and absence of recombinant genotypes, confirmed that A. gossypii reproduces by continuous apomictic parthenogenesis. Genetic differentiation between localities was not significant, whereas a strong differentiation was observed between host plant families (0.175

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