Phenotypic and nuclear DNA variation in Tunisian cultivars of date palm (Phoenix dactylifera L.)

Abstract

The aim of this study was to assess the morphological diversity of the five most important and widely consumed Tunisian date palm (Phoenix dactylifera L.) cultivars and the possible relationship between phenotypic variation and genome size and ploidy, since polyploidy can occur in this species. Five Tunisian palm date cultivars were evaluated, based on morphological traits and nuclear DNA content. The analysis of variance revealed statistically highly-significant differences among cultivars (Alig, Bsser, Deglet Nour, Kinticha and Hamra) for average palm length (LP) (m), perianth diameter (PD) (mm), pulp thickness (ThP) (cm), 30 fresh fruit weight (30 FrW) (g), 30 fresh seed weight (30 SW) (g), 30 SW/30 FrW ratio (%), fresh seed length (SL) (cm), fresh seed width (SWi) (cm) and water content (WaC) (%). The relationship among these characters was analyzed by principal component analysis (PCA), resulting in the separation of these cultivars into three groups. The first group included Alig and Deglet Nour, characterized by high values for perianth diameter, pulp thickness, 30 fresh fruit weight and water content. The cultivar Hamra (H) formed a separate group, characterized by high values for seed width, 30 seed weight, 30 seed weight /30fruit weight ratio and seed length. This study shows that certain Tunisian cultivars, apart from Deglet Nour (Alig and Hamra), are particularly recommended for future selection and breeding programs. The morphological variation was not due to differences in ploidy, since the tested cultivars had 2C nuclear DNA contents of 1.729 to 1.80 pg and were all diploids (2n = 2x = 36). The data suggested that the Tunisian cultivars have limited geographical distribution and that P. dactylifera is an ancestral species.

Key words: Date palm, fruit, genome size, morphological traits, seed.