Karim Kadri

This study reports the first documented occurrence of double-seeded fruits (DSF) in date palm (Phoenix dactylifera L.), a phenomenon distinct from previously described polyembryony. DSF were observed only in the cultivars ‘Kentichi’ and ‘Deglet nour’, where they occurred at very low frequencies (2.8 × 10⁻³% and 1.6 × 10⁻⁴%, respectively). Morphological observations indicate that DSF arise through partial or complete fusion of two carpels, resulting in syncarpic fruits that are significantly heavier and wider than single-seeded fruits, while fruit length remains unchanged. Germination rates were high and similar in both groups, but seeds from DSF germinated 8 days earlier than those from single-seeded fruits. In contrast, seedlings derived from DSF showed slower early growth. These findings identify DSF as a rare, genotype-dependent developmental variant in date palm and suggest that syncarpy influences fruit morphology, seed allocation, and germination behaviour.

A stable tetraploid date palm mutant with the potential for increased fruit size was recovered from a sectorial di-tetraploid chimera via the in vitro culture of flower explants. Callus was induced using 2,4-D, followed by shoot regeneration on a medium containing NAA and BAP and rooting with IBA. Regenerated plantlets, confirmed as tetraploid via flow cytometry, were acclimatized and grown for six years. The leaves of tetraploids exhibited significantly wider petiole bases, thicker rachis and spines, broader leaflets, and a more intense green leaf color compared to diploids. However, leaf length, spine count, and overall leaf number were reduced. This is the first report of successful tetraploid recovery from a chimeric date palm, demonstrating the potential of this technique to generate novel germplasm and highlighting the phenotypic differences associated with tetraploidy in this species.

Date palms are a vital part of oasis ecosystems and are an important source of income in arid and semi-arid areas. Crossbreeding is limited due to the long juvenile stage of date palms and their dioecious nature. The aim of this study was to create triploid date palms to obtain larger and seedless fruits and to increase resilience to abiotic stresses. A tetraploid date palm mutant was crossed with a diploid male palm, yielding hundreds of seeds suspected of containing triploid embryos. Six years after planting, four palms with confirmed triploidy reached maturity. They are phenotypically distinct from diploids, with a thicker rachis, thinner spines, wider and longer midleaf spines, and a longer apical spine. They were classified as sterile bisexual, sterile male and fertile female. One of the latter produced very tasty dates with a very small seed, which is promising for the marketability and profitability of date palm fruits. This first report on triploid date palms provides a way in which to make a significant leap forward in date palm breeding. Given the vigor and fruit quality of female triploid date palms, compared to their diploid counterparts, they will be the target of breeding programs and may spearhead new oases.

Given the dioecious nature of date palms, selecting an effective pollinizer bearing a substantial quantity of high-quality pollen is imperative. In this study, we investigated the effects of 11 male date palm cultivars from Tunisia on the production of female trees, fruit sets, and the characteristics of 'Deglet Nour' cultivar dates. The comparison of pollen germination rates showed that ABD1 and P169 pollens exhibited outstanding viability, with 98.7% and 98.3%, respectively. On the other hand, P169 pollen had the highest germination rate, at 86.3%. The most remarkable fruit set (90.7%) and retention rate (69.7%) were observed in response to P13 pollen. In response to the P165 pollinator, the fruit stood out among the resulting fruits for their notable weight, averaging 11.6 g. In addition, pollination with P90 increased total soluble solids (measured at 74.4°Brix in the Tamr stage), whereas P7-pollinated fruits recorded the highest levels of reducing sugars, reaching 41%. Notably, the highest acidity levels were found in P7-pollinated fruits (0.29%), and pollen sources significantly influenced the fruits' mineral content.Moreover, regarding pomological characteristics, fruits pollinated with P4 attained maximum size, measuring 4.10 cm. Conversely, P7-pollinated fruits had a notable width of 2.02 cm. These findings illustrate the possibility of the selective application of high-value pollinizers and emphasize the direct influence of pollen sources on fruit quantity and quality.

Background The date palm breeding programs need to discover useful genetic fingerprints to characterize cultivars and assess their genetic diversity. This study assessed the genetic diversity among thirty-nine date palm cultivars from Tunisia and India using six AFLP (Amplified Fragment Length Polymorphism) markers. Results A total of 360 loci were amplified, with 127 loci polymorphic (34.35%). The Jaccard's similarity coefficient ranged from 0.161 to 0.931, with the mean genetic distances of 0.568. AFLP's average marker index value was 7.28, with a resolving power of 10.91. The dendrogram showed a clear separation between Tunisian and Indian cultivars. Furthermore, the heat map analysis allowed the identification of 10 bands specific to the Indian accessions, which were not detected in Tunisian genotypes. Conclusions These loci could be linked to genes involved in the adaptation of the specie in Indian lands. The current finding can be used in the future breeding program by helping to select accessions adaptable to the specific environment.

Tunisian oases reveal an important genetic heritage of date palm cultivars, with various qualities of use. Since the beginning of the century, this heritage has evolved to a selective orientation based on the monoculture of "Deglet Nour," this orientation risks causing the loss of many cultivars. The male of the date palm is part of this heritage and so far remains marginalized. Although they are important for the date palm production cycle, it is in this context that lies our work to study the genetic diversity of a collection of male date palm pollinators from southern Tunisia. The morphological study of the 20 date palm pollinators using 45 IPGRI (International Plant Genetic Resources Institute) descriptors showed significant discrimination, with a similarity index ranging from 0.207 to 0.457, divided them into five similarity groups. The use of 7 ISSR (Inter Simple Sequences Repeat) primers resulted in 64 reproducible bands, of which 57 were 90% polymorphic, and statistical analysis showed a more or less significant genetic diversity with genetic distances 0.491 to 0.873. According to the Mentel test, a non-significant weak correlation (r = 0.015) was noted between the molecular and morphological data. However, the processing of molecular data by various methods generated very significant correlations. Indeed, the correlation between the SM (Simple matching) coefficient and the DICE coefficient showed an important correlation with r = 0.748, which confirms the discriminating power of the ISSR markers in studying the genetic diversity of date palm pollinators.

In Tunisian oases, pollination remains a traditional process and the male' spikelets are manually inserted into female inflorescences. The drawback of this ancestral practice forced us to look for a new alternative pollination technique for improving date palm productivity. The present investigation aimed to compare agronomic and biochemical characteristics of 'Deglet Nour' variety following three pollination techniques: the handmade traditional technique, the dusting (spraying pollen grains by powder) and the water suspension technique. The results affirmed that the dusting technique was the most efficient technique followed by the handmade pollination. Sprinkling showed the highest fruit set rate (82.21%), retention rate (68.34%) and yield per bunch (5.5 kg) with the lowest number of partenocarpic fruits (less than 2%). Besides, data revealed that pollination techniques were not involved in physicochemical and pomological characteristics during the different stages of date maturation. However, other studies can be carried out to explore these different pollination techniques on other varieties growing in different oasis systems.