Melon Fusarium wilt (MFW), caused byFusarium oxysporumf. sp.melonis(Fom), is one of the most destructive diseases of melon (Cucumis meloL.). The development and deployment of resistant cultivars is generally considered to be the best approach to control MFW. Based on the host resistance genes associated with variants of this pathogen,Fomisolates were classified into four physiological races designated 0, 1, 2, and 1,2. Two dominant resistance genes,Fom-1andFom-2, control resistance to races 0 and 2, and 0 and 1, respectively.Fomisolates classified as race 1,2 are able to induce disease in melon lines carrying the above resistance genes. Many sources of resistance toFomraces 0, 1, and 2 have been reported. Partial resistance to race 1,2 controlled by polygenic recessive genes was only detected in a few Far Eastern melon accessions, except for the breeding line BIZ where complete resistance was described. Identification of DNA markers tightly linked to genes conferring resistance toFomhas immediate application in MFW resistance breeding programs. TheFom-2gene has been cloned, and it encodes a protein with a nucleotide binding site (NBS) and leucine-rich repeats domain (LRR). Based on the sequence of this domain, some molecular markers linked to this gene were developed. Several DNA markers linked toFom-1have also been described. However, the usefulness of these markers was variety-dependent. Therefore, their combined use would be very useful in marker assisted selection for introducing resistance toFomraces 0 and 2 in melon. Recently, these markers were used for the positional cloning of this gene, which encoded a protein with a NBS–LRR domains that shows similarity to the toll and interleukin-1 receptores (TIR). RegardingFomrace 1,2, nine QTL were detected on five linkage groups by composite interval mapping. In this paper we review the current knowledge of MFW disease, and focus on genetic resistance toFomand marker-assisted selection for resistance.

The assessment of genetic diversity and structure of a gene pool is a prerequisite for efficient organization, conservation, and utilization for crop improvement. This study evaluated the genetic diversity and population structure of 24 Tunisian melon accessions, by using 24 phenotypic traits and eight microsatellite (SSR) markers. A considerable phenotypic diversity among accessions was observed for many characters including those related to agronomical performance. All the microsatellites were polymorphic and detected 30 distinct alleles with a moderate (0.43) polymorphic information content. Shannon’s diversity index (0.82) showed a high degree of polymorphism between melon genotypes. The observed heterozygosity (0.10) was less than the expected heterozygosity (0.12), displaying a deficit in heterozygosity because of selection pressure. Molecular clustering and structure analyses based on SSRs separated melon accessions into five groups and showed an intermixed genetic structure between landraces and breeding lines belonging to the different botanical groups. Phenotypic clustering separated the accessions into two main clusters belonging to sweet and non-sweet melon; however, a more precise clustering among inodorus, cantalupensis, and reticulatus subgroups was obtained using combined phenotypic–molecular data. The discordance between phenotypic and molecular data was confirmed by a negative correlation (r = −0.16, p = 0.06) as revealed by the Mantel test. Despite these differences, both markers provided important information about the diversity of the melon germplasm, allowing the correct use of these accessions in future breeding programs. Together they provide a powerful tool for future agricultural and conservation tasks.

The present study was carried out to evaluate and characterize, for the first time, the genetic potential of a collection of onion (Allium cepa L.) local accessions from the arid region of southern Tunisia. The genetic diversity among 135 onion individuals, belonging to 23 accessions, was evaluated using microsatellite (SSR) markers and phenotypic information. A total of 35 alleles were generated with 11 SSRs. The polymorphic information content (PIC) value ranged from 0.08 to 0.95, with an average PIC of 0.43. The expected heterozygosity averaged 0.37, and the observed heterozygosity averaged 0.42. The analysis of molecular variance (AMOVA) revealed that 79% of genetic variation existed within individuals. Structure and cluster analysis grouped the accessions into two major clusters: landraces and pre-breeding lines. For the phenotypic traits evaluated, field trials were conducted in two different environments. Significant differences among accessions were shown, and for most traits, there was also a significant environmental effect and a significant interaction between environment and accession. Great variability was found for all the traits that could be exploited to create new varieties of onion adapted to local conditions by selecting appropriate parents in hybridization breeding.

This study reports the nitrate level of 22 vegetables species collected from 40 farms in several locations of an intensive agricultural area in two regions of Tunisia (Sousse and Monastir). Nitrate levels ranged between 57 and 2970 mg kg^‒1. The highest and the lowest levels were found in turnip and tomato, respectively. Only five species (potato, field bean, cauliflower, pea and artichoke) had exceeded the norms established by the World Health Organization. Factors influencing nitrate accumulation in some vegetables were analyzed and discussed. It was observed that nitrate contents in vegetables varied depending on the type of vegetables, genetic factor, level of nitrogen fertilization and soil nitrogen content.

Local melon germplasm are sources of natural variation with great potential, unfortunately, they are being replaced by hybrids and modern high-yielding disease-resistant/tolerant varieties. To recognize, and encourage re-use, local melon genotypes previously selected for resistance to Fusarium wilt disease, were evaluated for morphological, nutritional and biochemical traits. The evaluated melons expressed a wide range of phenotypes for morphological fruit characteristics, taste, and composition. Differences occurred between botanical groups and within the same group. The “Galaoui” genotype of reticulatus botanical group presented the highest β-carotene value (6.6 mg∙kg⁻¹ FW) and the highest flavonoid content (45.45 mg CE∙kg⁻¹ FW). The “Dziri” genotype of inodorus botanical group had the highest phenolic content (896.67 mg GAE∙kg⁻¹ FW); genotype Rupa of cantalupensis group had the highest antioxidant activity value (14.61%). Genotype Asli of inodorus group had the highest vitamin C content (0.15 g/100mL fresh juice). These genotypes might be appropriate for breeding program to increase the functional properties of commercial varieties. Moreover, principal component analysis showed a great dispersion of melon genotypes. The hierarchical ascending classification indicated genotypes were sorted into four cluster groups based on fresh weight, fruit diameter, total soluble solids, total phenolic content, and β-carotene contents. The diversity identified in this study, especially from the four group types, showed that some Tunisian genotypes are featured with several morphological and biochemical characteristics, they had melon quality exceeding commercial hybrids, and could be further exploited as a promising material for the creation of new improved varieties.