Molecular variability and population structure of a core collection of date palm (Phoenix dactylifera L.) cultivars from Australia and the Middle East

Abstract

Understanding genetic relatedness in date palm (Phoenix dactylifera L.) germplasm is important for effective plant improvement. Microsatellite (SSR) markers were used to assess the molecular variation and population structure of 60 Australian locally selected and exotic genotypes (24 female, 30 male and 6 related species), 12 Iraqi female cultivars and 10 female cultivars from Jordan. The main objectives were to survey genetic diversity and determine population structure in this core date palm collection which includes the most important and widely distributed cultivars in Australia. These Australian accessions were then compared to those originating from the date palm center of origin in the Middle East. PCR of 17 SSR primers (co-dominant markers) produced a total of 313 alleles ranging from 5 to 31 with an average of 18.4 alleles per locus. The PIC value for these 17 primers ranged from 0.4771 to 0.8199 with a mean of 0.670. The mean expected heterozygosity (0.841), mean observed heterozygosity (0.946) and Shannon's information index (2.067) indicated a high level of genetic diversity among the accessions. Multi-locus DNA fingerprints based on the 17 SSR loci unambiguously differentiated all accessions and revealed an absence of duplicated samples. Ordination and cluster analyses showed that the Australian accessions did not group together geographically; instead separate male and female groups differentiated among the six clusters. A Bayesian cluster analysis also partitioned the accessions into six groups and this result was largely compatible with the result of ordination analysis. The Australian date palm germplasm is highly diverse and thus provides an effective platform for plant improvement, enhancement of date production and the conservation of genetic resources.