Genetic Diversity of Milk Thistle Revealed by Advanced DNA Analysis Technology

Greg Howard
8th August, 2024

Genetic Diversity of Milk Thistle Revealed by Advanced DNA Analysis Technology

The milk thistle (Silybum marianum) germplasm collection exhibits considerable morphological diversity in stem, leaf, and inflorescence traits (a–f), reflecting the phenotypic variation among accessions used to investigate genetic structure and its relationship to agronomically important characteristics.

Image adapted from: Puglisi et al. / CC BY (Source)

Key Findings

  • The study analyzed the genetic diversity of 31 milk thistle accessions from different regions using 5,178 SNP markers
  • Three distinct genetic groups were identified, reflecting their geographical origins: Central Europe/UK, Italy, and various other areas
  • Italian genotypes showed unique traits in fruit oleic and linoleic acid content, suggesting potential for targeted breeding programs
Silybum marianum (L.) Gaertn., commonly known as milk thistle, is a multipurpose crop native to the Mediterranean and Middle East regions, renowned for its hepatoprotective properties due to fruit-derived silymarin. Despite the increasing interest in milk thistle for its medicinal value, its potential in the agroindustry has been hindered by incomplete domestication and limited genomic knowledge. This has impeded the development of competitive breeding programs. A recent study conducted by the Council for Agricultural Research and Economics (CREA), Italy, aimed to evaluate the genetic diversity in a panel of S. marianum accessions using 5,178 polymorphic DArTseq SNP markers[1]. The study focused on 31 accessions of S. marianum, previously characterized for their morphological and phytochemical traits. The genetic structure was investigated using both parametric and non-parametric approaches, such as Principal Component Analysis (PCA), AWclust, and Admixture. These analyses revealed three distinctive groups reflecting geographical origins. Pop1 grouped accessions from Central Europe and the UK, Pop3 consisted mainly of accessions of Italian origin, and Pop2 included accessions from various geographical areas. Interestingly, the Italian genotypes (Pop3) showed a divergent phenotypic distribution, particularly in fruit oleic and linoleic acid content, compared to the other two groups. Genetic differentiation among the three groups was confirmed by computing the pairwise fixation index (FST), which indicated a greater differentiation of Pop3 compared to other subpopulations. This was also supported by other diversity indices such as private alleles and heterozygosity. The study identified 22 markers as putatively under natural selection, with seven significantly affecting important phenotypic traits like oleic, arachidonic, behenic, and linoleic acid content. These findings suggest that these markers, particularly the seven SNP markers identified within Pop3, could be exploited in specific breeding programs aimed at diversifying the use of milk thistle. Incorporating genetic material from Pop3 haplotypes carrying the selected loci into milk thistle breeding populations might be the basis for developing lines with higher levels of oleic, arachidonic, and behenic acids, and lower levels of linoleic acid. This could enhance the nutritional and agronomic characteristics of milk thistle. Previous studies have laid the groundwork for understanding the genetic and chemical composition of S. marianum. For instance, crossing experiments between S. marianum and S. eburneum revealed that leaf color is monofactorially inherited, indicating that these two species are variants[2]. This study also showed that S. marianum is predominantly a self-pollinator, which has implications for breeding programs. Another study investigated the distribution and quantification of silymarin and other phenolic compounds within different fruit regions, confirming that silymarin and its precursor taxifolin are accumulated in the seed integuments[3]. This knowledge is crucial for optimizing silymarin extraction processes. Milk thistle has been used for over 2,000 years for its therapeutic properties, particularly in treating liver diseases. Despite encouraging preclinical data, further well-designed randomized clinical trials are needed to fully substantiate the real value of milk thistle preparations in liver diseases[4]. The availability of public genomic resources can greatly assist biodiversity assessment, conservation, and restoration efforts by providing evidence for scientifically informed management decisions[5]. The current study by CREA contributes to this by providing valuable genomic data that can be used to enhance milk thistle breeding programs. In summary, this study advances our understanding of the genetic diversity in S. marianum and identifies key genetic markers that can be utilized in breeding programs to improve the nutritional and agronomic traits of milk thistle. The incorporation of these findings into breeding strategies could pave the way for the development of superior milk thistle lines, thereby enhancing its potential in the agroindustry.

GeneticsBiochemPlant Science

References

Main Study

1) Genetic diversity of a Silybum marianum (L.) Gaertn. germplasm collection revealed by DNA Diversity Array Technology (DArTseq).

Published 7th August, 2024

https://doi.org/10.1371/journal.pone.0308368

Related Studies

2) Genetic investigations on Silybum marianum and S. eburneum with respect to leaf colour, outcrossing ratio, and flavonolignan composition.

Journal: Planta medica, Issue: Vol 61, Issue 1, Feb 1995

3) Localization of phenolic compounds in the fruits of Silybum marianum characterized by different silymarin chemotype and altered colour.

https://doi.org/10.1016/j.fitote.2018.09.002

4) Milk thistle (Silybum marianum): A concise overview on its chemistry, pharmacological, and nutraceutical uses in liver diseases.

https://doi.org/10.1002/ptr.6171

5) How genomics can help biodiversity conservation.

https://doi.org/10.1016/j.tig.2023.01.005


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