Najla Mezghani

Plants of two potato (Solanum tuberosum L.) varieties ‘Spunta’ (mid-early maturity) and ‘Kensa’ (mid-late maturity) were subjected to three nitrogen (N), phosphorus (P), and potassium (K) fertilization regimes, with T1 optimal rates (as recommended by the Tunisian Potato Technical Centre), T2 high rates (+25% of T1), and T3 low rates (−25% of T1). Plant growth, yield components, chlorophyll fluorescence (Fo, Fm, Fv/Fm), photosynthetic active radiation (PAR), real evapotranspiration (RET), and biochemical parameters in mature leaves and tubers (total soluble sugars (TSSs) and starch in both leaves and tubers) were evaluated. Our results showed a significant effect of fertilizer rates on plant growth, physiological, yield, and quality traits, as well as on biochemical contents of leaves and tubers, as well as on the variety. The application of high rates (T2) resulted in increased chlorophyll fluorescence (Fo) and high ratios of Fv/Fm, and it reduced Fm and photosynthetic active radiation (PAR). The highest yield per plant (615.4 g of tubers) and average number of tubers/plant (6.44) were observed in cv. ‘Spunta’ subjected to optimal fertilizer rate (T1), while more than 50% of tubers of this variety were classified as size C1 (>50 mm). On the other hand, high rates (T2) increased the yield per plant (436.74 g; approximately 9.3% compared to T1) and the number of tubers per plant (5.70) in cv. ‘Kensa’, with approximately 56% of tubers being classified in the C1 category. High rates also increased sucrose and starch content in tubers, regardless of the variety, without being significantly different from the other fertilization regimes. In conclusion, our results provide important information regarding the effect of fertilization practice on potato growth and yield parameters and the biochemical composition of leaves and tubers. Therefore, it could be suggested that the application of reduced NPK rates (−25% of optimal rates) in mid-early varieties (namely cv. ‘Spunta’) could reduce the production cost without compromising yield and quality components.

Assessing and determining genetic diversity in rose species is a crucial step for conservation efforts, the establishment of a core collection, and the development of new varieties. This study represents the first investigation of genetic diversity among various rose species at different ploidy levels in Tunisia, with the aim of elucidating the genetic structure of the Rosa genus. It encompasses both spontaneous and cultivated accessions, featuring local and introduced species recognized for their adaptability, ornamental value, and fragrance. A total of 114 accessions representing eight rose species were collected. Significant genetic diversity was assessed using seven SSR markers, yielding an average of 21 alleles per locus and a PIC value ranging from 0.882 to 0.941. The results identified 343 phenotypic alleles across the seven primers, with 72 for the primer RhE2b (LG6), 55 for H10D03 (LG7), and 54 for RhB303 (LG2). One key finding was that most perfumed rose accessions (R. damascena Mill. and R. centifolia L.) are distinct from the other rose accessions, indicating a unique genetic pool for these roses. Another important finding was that the Tunisian accessions of ‘Rose of Ariana’ were closely related to R. centifolia accessions, commonly known as the ‘Rose of May’ from Grasse, France. To clarify the phylogeny of this species or subspecies, further molecular studies are warranted. Additionally, nomenclature confusion was identified between R. sempervirens L. and R. canina L. in the northwestern region of Tunisia, indicating that all wild accessions correspond to R. sempervirens.

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.

Salt stress is considered as one of the most common abiotic stresses reducing the productivity and fruit quality of crop plants. The present study was carried out to assess the salt tolerance among 15 local squash (Cucurbita maxima Duchesne) landraces. Different salt (NaCl) concentrations of 0, 100, 200 and 300 mM were selected in order to evaluate the response of the study germplasm to salt stress based on 12 agronomic parameters and 3 biochemical traits, proline, malondialdehyde (MDA) and chlorophylls. A varied effect of the salt stress level was observed among the studied landraces based on germination potential, as well as on growth and biochemical parameters at seedling stage. Results showed that all landraces were drastically affected at high stress level with a significant variation in their stress response, indicating the existence of considerable genetic variability. Landraces “746” and “747” were the best performing cultivars across stress levels, whereas “1007”, “1008” and “1009” were the most negatively affected. Based on the tested landrace performance, four landraceswere selected and further evaluated at biochemical level, focusing on the determination of compounds that play a key role in the ability to withstand salt stress. The mean MDA content across landraces was generally increased in stressed plants, as compared to the control treatment; the increase was attributed to a peak in MDA content at specific stress levels. In particular, “746” and “1007” showed the maximum content at 100 mM NaCl, while in landrace “751”, MDA content reached its peak at 300 mM NaCl. In addition, the response of most landraces to salt stress involved an increase in free proline content, with the exception of “746”, with the maximum content being observed either at 200 mM (“748” and “751” landraces) or at 300 mM NaCl, where only “747” expressed the highest content. These findings can be extrapolated into efforts to develop more salt-tolerant squash landraces and exhaust the possibilities of using saline water or soils under changing climate conditions.

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.