Molecular Characterization and Genetic Structure Evaluation of Breeding Populations of Fennel (Foeniculum vulgare Mill.)

Francesco Scariolo,Gianni Barcaccia,Fabio Palumbo

doi:10.3390/agronomy12030542

Abstract

Fennel, or Foeniculum vulgare Mill., is an important horticultural crop belonging to the Apiaceae family that is cultivated worldwide and used in the agri-food sector and for pharmaceutical preparations. Breeding strategies in this species usually involve three parental lines, including two maternal lines (one cytoplasmic male-sterile line and an ideotype representative maintainer line) that are crossed to obtain an ideotype representative of the cytoplasmic male-sterile line and one paternal line, used as a pollinator in crosses with the progeny of the derived maternal lines. From this cross, F1 hybrid progenies are obtained, which are characterized by high levels of heterozygosity and hybrid vigor. In this study, over 450 plants, representing 8 breeding populations and their respective 3 parental and 1 progeny line, were genotyped by means of codominant molecular markers. The 12 highly polymorphic microsatellites enabled the analyses of the genetic variability, distinctiveness and stability of each breeding line. Moreover, the genetic structure of the core collection was investigated, which, together with the homozygosity, gene flow and genetic similarity results, allowed the identification of unsuitable lines to be used in breeding plans due to their low homozygosity (10.4% in the pollinator line of population 7). Moreover, the Bayesian reconstruction of the core collection’s genetic structure, based on the codominant markers used, allowed us to confirm the distinctiveness results obtained from the genetic similarity investigation and the computed gene flow estimates. Among these, a trend in hybrid heterozygosity was also observed, that increased when the genetic similarity between the respective parental lines decreased. Thus, this research proposes a suitable method for genotyping fennel populations in pre- and post-breeding approaches, such as marker-assisted breeding or breeding line distinctiveness and stability verifications.

Highlights

Fennel (Foeniculum vulgare Mill., 2n = 2x = 22) is a diploid horticultural crop characterized by a biennial or perennial developmental cycle
The descriptive statistics for the simple sequence repeats (SSRs) markers used, which were selected from the study by Palumbo et al [11] for being highly polymorphic, demonstrated their informativeness in relation to the high number of alleles observed among the core collection, and the polymorphism information content (PIC) values were consistently greater than 0.63
The genotyping analysis of the core collection of fennel breeding stocks described in this work, along with its genetic descriptive statistics calculation and its genetic structure reconstruction, determined the reliability of the method proposed based on microsatellite markers and provided a suitable molecular approach for plant variety traceability and post-breeding controls

Summary

Introduction

Fennel (Foeniculum vulgare Mill., 2n = 2x = 22) is a diploid horticultural crop characterized by a biennial or perennial developmental cycle. This species belongs to the Apiaceae family and originates in the southern Mediterranean regions [1]. In this regard, hybrid seeds in fennel are commonly obtained by exploiting a three-line-based system characterized by a cytoplasmic male-sterile seed line (strain CMS), a male fertile sister line ( known as maintainer line, strain M) and a pollinator line (strain P) with a general combining ability (GCA) with the CMS line. The new variety must be distinguishable from those already registered, phenotypically uniform and stable during subsequent propagation cycles

Methods

Results

Conclusion