Unlocking the Genetic Diversity and Population Structure of a Wild Gene Source of Wheat, Aegilops biuncialis Vis., and Its Relationship With the Heading Time

Abstract

Understanding the genetic diversity of Aegilops biuncialis, a valuable source of agronomical useful genes, may significantly facilitate the introgression breeding of wheat. The genetic diversity and population structure of 86 Ae. biuncialis genotypes were investigated by 32700 DArT markers with the simultaneous application of three statistical methods- neighbor-joining clustering, Principal Coordinate Analysis, and the Bayesian approach to classification. The collection of Ae. biuncialis accessions was divided into five groups that correlated well with their eco-geographic habitat: A (North Africa), B (mainly from Balkans), C (Kosovo and Near East), D (Turkey, Crimea, and Peloponnese), and E (Azerbaijan and the Levant region). The diversity between the Ae. biuncialis accessions for a phenological trait (heading time), which is of decisive importance in the adaptation of plants to different eco-geographical environments, was studied over 3 years. A comparison of the intraspecific variation in the heading time trait by means of analysis of variance and principal component analysis revealed four phenotypic categories showing association with the genetic structure and geographic distribution, except for minor differences. The detailed exploration of genetic and phenologic divergence provides an insight into the adaptation capacity of Ae. biuncialis, identifying promising genotypes that could be utilized for wheat improvement.

Keywords: Aegilops biuncialis; DArTseq markers; genetic diversity; heading time; hierarchical clustering; population structure.

Figure 1

Estimation of the genetically most probable number of Ae. biuncialis subpopulations based on Evanno’s Delta K method (Evanno et al., 2005). The maximum value of delta K occurred at K = 5 indicates that the investigated Ae. biuncialis collection can be devided into five hypothetical subpopulations.

Figure 2

Comparison of grouping patterns based on STRUCTURE analysis at K = 5 and the neighbor-joining dendrogram in a collection of 86 Ae. biuncialis accessions. The order of the genotypes on the STRUCTURE plot matches that represented on the phylogenetic tree. The wheat genotype Mv9kr1 is represented as an outgroup accession in the dendrogram. Genotypes belonging to the same clade represent similar membership probability in the relevant subpopulation and are from a common area within the larger geographic regions. BIH: Bosnia and Herzegovina.

Figure 3

Geographic origin of the Ae. biuncialis collection. Circles represent accessions with known geographic location. Where only the country of origin is known, it is indicated by a square representing the capital. There is no information about the origin of six accessions in the collection. The different colors of the symbols (circle, square) in the figure represent the clusters (or subpopulations) corresponding to the population structure obtained by STRUCTURE analysis.

Figure 4

Principal coordinate analysis on the Ae. biuncialis accessions based on 32,700 DArT markers. Different colors indicate different subpopulations (A–E) in the population.

Figure 5

Boxplot chart of the heading times of the Ae. biuncialis subpopulations (A–E) showing the mean, median and range of the phenotypic data in 3 years. The heading time trait was expressed in number of days elapsed from January 1 to the DEV59 developmental stage. Different letters indicate significant differences between the subpopulations within the same year at P < 0.05, using one-way analysis of variance. *Indicates the heading time in 2018 differs significantly from the others within relevant subpopulation at the P < 0.05 level.

Figure 6

Correlation of the heading times of Ae. biuncialis accessions among three different seasons. Heading time was defined as the number of days required to reach the DEV59 developmental stage from January 1. Color codes indicate different subpopulations (A–E) identified from STRUCTURE analysis. Number of accessions (n), clustered into one subpopulation, are represented in the figure. The R² values of pair-wise correlation for each subpopulation among different seasons are included in the figure.

Figure 7

Scatter plot of principal components 1 and 2, explaining 97.29% of the phenotypic variance in the heading time (2016, 2017, and 2018) of the Ae. biuncialis collection. Different colored dots indicate the Ae. biuncialis accessions in the subpopulations (A–E) obtained from STRUCTURE analysis. Groups I–IV indicate the phenotypic categories for heading time.