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The purposes of this study were to provide palynological information about apricots and to reveal the relationships among six ecological groups of apricots by describing the morphological characteristics of their pollen. The pollen grains of 175 accessions belonging to three species (Prunus armeniaca L., Prunus sibirica L., and Prunus mume Sieb. et Zucc.) of Prunus were examined using light microscopy and scanning electron microscopy. The pollen grains were isopolar monads, radially symmetric, medium to large in size, prolate or subprolate, and 3-colporate. Most pollen grains exhibited striate exine ornamentation, and a few exhibited striato-reticulate or cerebroid exine ornamentation. Cluster analysis divided the six ecological groups into two groups: one including the Central Asian, North China, and Dzhungar-Ili ecological group accessions and another including the Northeast Asian, European, and East China ecological group accessions. Principal component analysis revealed that equatorial diameter, colpus length, colpus width, and ridge width were the most important metrical pollen traits, and can be used as powerful diagnostic characters in apricot identification. We speculated that the cultivated apricots in Xinjiang were domesticated from wild apricots from the Ili Valley. This study describes the morphological characteristics of apricot pollen grains and provides some morphological information for future studies on the phylogenetic relationships of apricots. [ABSTRACT FROM AUTHOR]

Single-nucleotide polymorphisms (SNPs) are the most abundant form of genomic polymorphisms and are widely used in population genetics research. Here, high-throughput sequencing was used to examine the genome-level diversity, population structure, and relationships of apricot, which are important for germplasm conservation and molecular breeding. Restriction site-associated DNA sequencing (RAD-seq) was adopted to sequence 168 Prunus spp. accessions distributed in five ecological groups, including 74 accessions of cultivated Prunus armeniaca L. and 94 accessions of wild apricots (P. armeniaca L. and Prunus sibirica L.), which generated 417,961 high-quality SNPs. We used cluster, genetic structure, and principal component analyses to examine the genetic diversities and genetic relationships of the 168 accessions. The Dzhungar-Ili ecological group accessions showed the highest genetic diversity in terms of private allele number, observed heterozygosity, and nucleotide diversity. We speculate that the Central Asian ecological group accessions were domesticated from the Dzhungar-Ili ecological group accessions. The population structure and gene flow of the North China and European ecological group accessions suggested a genetic background of P. sibirica. We argue that the two groups should be considered hybrid swarms connected to P. sibirica by continuous and extensive gene flow. P. armeniaca originated in Northwest China (Ili Valley), subsequently spread throughout Central Asia, and eventually spread to Europe. In addition, selective sweep signatures in P. armeniaca during domestication from wild to cultivated apricots, combined with differentially expressed genes, underlie distinct fruit traits, including sugars, aromas, organic acids, and carotenoids. This study provides substantive and valuable genomic resources that will significantly advance apricot improvement and effective utilization. [ABSTRACT FROM AUTHOR]

• Chromosome ploidy of selected taxa from Prunus armeniaca by flow cytometry were diploids. • Genome size of P. armeniaca varied from 0.590 to 0.708 pg. • Genome size of P.armeniaca has no significant correlation with longitude, latitude and altitude. • Genome size of P. armeniaca was highly stable. The assessment of plant genome size is important in many research fields, including crop improvement and molecular genetics. However, studies on the genome size of Prunus armeniaca is limited. The purpose of this study was to evaluate the differences in the genome size of P. armeniaca in different geographic ecological groups and estimate the ranges in genome size. Nuclear suspension of P. armeniaca was prepared by Marie's isolation buffer and propidium iodide fluorescent dye. The genome size of 51, 60, 11 and 2 accessions from the Central Asian Ecological Group , Dzhungar-ili Ecological Group, North China Ecological Group and European Ecological Group , respectively, were assessed by flow cytometry, and the levels of ploidy were evaluated. There were no polyploids from different ecological groups of P. armeniaca ; all accessions were diploids. The genome size of P. armeniaca varied from 0.590 to 0.708 pg, and the average genome size was 0.637 pg. The European Ecological Group had the largest genome size (0.661 pg/2C), which was the only group significantly different in size from the Central Asian , North China and Dzhungar-ili Ecological Group (P = 0.05), while the difference in genome size among these three ecological groups was small. There was no significant difference in genome size between different populations of wild accessions, and there was no significant correlation with longitude, latitude and altitude. The variation in the genome size of P. armeniaca was only 2.33%, and there was low intraspecies variation among the studied groups; the genome size of P. armeniaca is highly stable. [ABSTRACT FROM AUTHOR]