GENETIC DIVERSITY ANALYSIS OF DATE PALM (Phoenix dactylifera L.) CULTIVARS OF PAKISTAN

Abstract

Date palm has a long history of cultivation and a valuable germplasm in Pakistan with little knowledge about genetic makeup and variation among the most important cultivars. Date palm is among the top three fruit crops of Pakistan which is grown throughout the country except the northern highlands. This study was conducted for evaluation of morphological, chemical and molecular diversity of date palm cultivars of Pakistan. Important morphological parameters of fruit, leaf and trunk of forty five locally adapted cultivars were evaluated for this purpose. Proximate analysis of the date fruit was also carried out. Morphological traits of trunk, leaves and spines had no significant correlation with fruit traits. Seven components explained 81% variability in the data set by principal component analysis. Length, weight, volume of fruit, pulp weight, total soluble solids, % reducing sugars, % total sugar, % ash content, length and width of leaf, midrib length with pinnae, spine number, leaf base width and perianth height largely contributed to variability among the cultivars. Forty six simple sequence repeat markers were used to find genetic diversity in date palm cultivars under study. Only two SSR markers showed polymorphism with five amplicons, 24 markers showed monomorphic bands while the remaining 20 primers did not amplify. Coefficient matrices were computed to form clusters to assess the relationship among the studied cultivars. Dendrogram based on morphological and proximate composition data divided the cultivars into four clusters while due to the less number of polymorphic SSR markers the studied cultivars were divided into two groups. Currently characterization of commercially important varieties is made primarily through morphological and yield parameters and to a lesser extent on genetic analysis using RAPD markers. There is a great need to develop some genetic x identification system that could be used at sucker stage without relying on phenotypic traits of adult plant such as fruit characteristics. For this purpose, a detailed genetic analysis of seven commercially important cultivars was performed. Initially more than 3.5 kb of DNA fragments belonging to rbcL, atpB, GGR, matKand 16S rRNA genes of date palm chloroplast genome from seven commercially important date palm cultivars of Pakistan were sequenced. All these genomic fragments were found near identical among the selected cultivars. Twelve DNA fragments already reported to harbor single nucleotide polymorphisms (SNPs) in date palm nuclear genome were also sequenced. Eight novel SNPs were also found in the sequenced fragments in addition to those already reported. The analysis of sequencing data indicated that three fragments have the highest marker index (MI) of 4.61, 3.61 and 2.26 and bear eight, seven and five SNPs respectively. A SNP typing system was developed for varietal identification of date palm cultivars which is able to distinguish not only all the seven studied cultivars from Pakistan but also other cultivars from the world. The study suggests, that SNPs are important markers to study closely related cultivars and in some instances might prove superior even to sequencing of genes. An authentic sequence based identification key for date palm germplasm in Pakistan can be developed by extending this study to all the indigenous cultivars.