Faten Gorsane

Effect of salt stress on ion concentration, proline content, antioxidant enzyme activities and gene expression in tomato cultivars

Understanding plant response to salinity, one of the major abiotic stresses, provides insights into the improvement of tomato salt tolerance. This work focuses on the responses of tomato cultivars to salt stress. Genotypes, representative of content and enzyme activities. QPCR analysis of WRKY, ERF, LeNHX and HKT genes was also performed. A high K+, Ca2+ and proline accumulation as well as a decrease in Na+ concentration mediated salt tolerance. Concomitant with a pattern of high antioxidant enzyme activities, tolerant genotypes also displayed differential patterns of gene expression.

Molecular characterization of Bemisia tabaci populations in Tunisia: genetic structure and evidence for multiple acquisition of secondary symbionts.

ABSTRACT A survey was conducted during 2009–2010 seasons to identify the distribution of Bemisia tabaci (Gennadius) biotypes in Tunisia. The genetic affiliation of collected populations was determined by polymerase chain reaction (PCR)-restriction fragment-length polymorphism (TaqI) of the mitochondrial cytochrom oxidase I (mtCOI) gene. Results, validated by sequencing and phylogenetic analysis, allowed the clustering of sampled sweetpotato whiteflies into B and Q biotypes. As B. tabaci harbors the obligatory bacterium Portiera aleyrodidarum, and a diverse array of secondary symbionts including Rickettsia, Hamiltonella, Wolbachia, Cardinium, Arsenophonus, and Fritschea, we report here the infectious status of Tunisian populations by secondary symbionts to find out a correlation between bacterial composition to biotype. The genetic variability and structure of B. tabaci populations in Tunisia was driven by analysis of molecular variance (AMOVA) and the hypothesis of isolation by distance was explored. Selective neutrality and genetic haplotype network tests suggested that Tunisian sweetpotato whiteflies have been undergoing a potential expansion followed by gene flow restriction.

Some Biological and Molecular Properties of Pepper Veinal Mottle Virus Isolates Occurring in Tunisia

The potyviruses, PVY (potato virus Y) and PVMV (pepper veinal mottle virus) were identified by serological and symptom diagnosis in pepper (Capsicum annuum L.) in Tunisia during 1995–1997. Both were known to be major constraints to pepper production in North Africa. Pepper veinal mottle virus (PVMV) has not been reported previously in North Africa, but PVMV was found to be widely spread in peppers throughout Tunisia. By using reverse transcription followed by polymerase chain reaction (RT-PCR), we have now amplified the PVMV coat protein gene of two Tunisian isolates. DNA polymorphism, determined by restriction fragment length polymorphism (RFLP) of the coat protein gene, revealed two patterns distinguishing PVMV from PVY. Within PVMV isolates, molecular and biological properties showed no polymorphism suggesting that all isolates are representative of one PVMV strain occurring in Tunisia.

Insights into the genetic diversity and the phylogenetic analysis of Tunisian isolates of Tomato chlorosis virus

A one-step RT-PCR was used to identify Tomato chlorosis virus (ToCV) (Crinivirus members) infections on some Tunisian cultures. Results provided evidence that the ToCV is the most prevalent virus on Tunisian tomato crops. Findings were validated with specific primers. Genetic analysis of ToCV isolates was explored based on sequence data of viral segments within the coat protein (CP), the heat shock protein (HSP70h) and the polymerase protein (RdRp). Synonymous (dS) and non-synonymous (dN) substitution rates and their ratio were analyzed. The patterns of mutations were shaped depending on the considered fragment from the three viral regions. Selective neutrality test was significantly negative, suggesting a recent expansion of ToCV isolates. Pairwise mismatch distribution gave a bimodal pattern and pointed to the clustering of ToCV isolates into two distinct geographical clades. Genetic haplotype network provided evidence of the existence of two distinct clusters. The star-like shaped pattern confirmed recent expansion of ToCV isolates.

SSR marker-assisted screening of commercial tomato genotypes under salt stress

Salt stress was applied to tomato commercial genotypes to study adverse effects on their phenotypic traits. Three were saline tolerant (San Miguel, Romelia and Llanero), two were mildly tolerant (Perfect peel HF1 and Heinz 1350) whereas the remaining were sensitive. Genotyping cultivars using 19 polymorphic SSRs out of 25 tested produced a total of 70 alleles with an average of 3.68 alleles per locus and PIC values ranging from 0.22 (SSR 26, 92, 66 and TG35) to 0.82 (SSR 356). Principal component analysis (PCA) showed two contrasting panels discriminating tolerant and sensitive groups and one panel with scattered genotypes. STRUCTURE analysis clustered genotypes within three groups in accordance with their salt stress behavior. The success of tomato salt-tolerance breeding programs can be enhanced through molecular characterization of diversity within commercial cultivars that adapt differently to stress conditions. To this end, we combined phenotypes and SSR marker-genotypes to seek sources of salt tolerance that might be tomato species-specific. We integrated and represented genotype-phenotype associations from multiple loci into a multi-layer network representation. It is a systemic view linking discriminating genotypes to salt stress phenotypes, which may guide strategies for the introgression of valuable traits in target tomato varieties to overcome salinity.

A landscape genetic analysis of important agricultural pest species in Tunisia: The whitefly Bemisia tabaci

Combining landscape ecology and genetics provides an excellent framework to appreciate pest population dynamics and dispersal. The genetic architectures of many species are always shaped by environmental constraints. Because little is known about the ecological and genetic traits of Tunisian whitefly populations, the main objective of this work is to highlight patterns of biodiversity, genetic structure and migration routes of this pest. We used nuclear microsatellite loci to analyze B. tabaci populations collected from various agricultural areas across the country and we determine their biotype status. Molecular data were subsequently interpreted in an ecological context supplied from a species distribution model to infer habitat suitability and hereafter the potential connection paths between sampling localities. An analysis of landscape resistance to B. tabaci genetic flow was thus applied to take into account habitat suitability, genetic relatedness and functional connectivity of habitats within a varied landscape matrix. We shed light on the occurrence of three geographically delineated genetic groups with high levels of genetic differentiation within each of them. Potential migration corridors of this pest were then established providing significant advances toward the understanding of genetic features and the dynamic dispersal of this pest. This study supports the hypothesis of a long-distance dispersal of B. tabaci followed by infrequent long-term isolations. The Inference of population sources and colonization routes is critical for the design and implementation of accurate management strategies against this pest.