The population structure and diversity of eggplant from Asia and the Mediterranean Basin

Abstract

A collection of 238 eggplant breeding lines, heritage varieties and selections within local landraces provenanced from Asia and the Mediterranean Basin was phenotyped with respect to key plant and fruit traits, and genotyped using 24 microsatellite loci distributed uniformly throughout the genome. STRUCTURE analysis based on the genotypic data identified two major sub-groups, which to a large extent mirrored the provenance of the entries. With the goal to identify true-breeding types, 38 of the entries were discarded on the basis of microsatellite-based residual heterozygosity, along with a further nine which were not phenotypically uniform. The remaining 191 entries were scored for a set of 19 fruit and plant traits in a replicated experimental field trial. The phenotypic data were subjected to principal component and hierarchical principal component analyses, allowing three major morphological groups to be identified. All three morphological groups were represented in both the "Occidental" and the "Oriental" germplasm, so the correlation between the phenotypic and the genotypic data sets was quite weak. The relevance of these results for evolutionary studies and the further improvement of eggplant are discussed. The population structure of the core set of germplasm shows that it can be used as a basis for an association mapping approach.

Figure 1. STRUCTURE analysis.

(K) and ΔK plots derived from the genotypic data. The germplasm set forms two distinct sub-groups, with a small number of entries being intermediate.

Figure 2. STRUCTURE output at K = 2.

Each entry is represented by a horizontal line representing subgroup 1 (yellow) and subgroup 2 (blue). a) Entries ordered according to their subgroup membership. b) Entries ordered according to their geographical origin: WE: “Occidental”, EA: “Oriental”.

Figure 3. HCPC analysis, based on the leading six PC’s (eigenvalues >1).

a) Scree plot showing the proportion of variance explained by each PC. b) PCA based on the leading two PC’s. Entries belonging to each morphological group marked by a different color (red: group 1, blue: group 2, green: group 3).

Figure 4. Fruits of accessions belonging to the three main morphological groups.

Group 1∶1a = AM 269-Talindo; 1b = AM 026-Dr2; Group 2∶2a = AM 168-Angio 5; 2b = AM 031-FantE63D; 2c = AM 160-Dourga; Group 3∶3a = AM 037-Violetta di Toscana; 3b = AM 291∶17CAAS; 3c = AM 210-67/3.

Figure 5. PCA based on geographical origin (blue: “Occidental”; yellow: “Oriental”).

a) The full germplasm set, and entries within b) morphological group 1, c) morphological group 2, d) morphological group 3.

Figure 6. PCA based on geographical origin showing the clustering of the “Oriental” entries with their country of origin.

The accessions from Myanmar and Thailand were classified as Indochinese region.