A Study on Adaptive Strategies of Wild and Cultivated Linum Populations Across Western Europe and Their Implications for Linum Trait Development and Ecology.

Abstract

Local adaptation plays a major part in plant survival and reproduction. Linum represents a genus of potential study models which provide insights for both applied and evolutionary biology. As a flowering plant, they may have evolved adaptations to achieve optimal flowering time. Most flowering plants have developed their own strategies to flower in specific habitats. There are interests from both evolutionary, and agricultural points of view regarding flowering development. In evolutionary terms, flowering time may affect offspring and population fitness. In agriculture, faster flowering time is a desirable trait for production. For this reason, Linum is a versatile model to study. Linum usitatissimum (cultivated flax) is useful in several industries. Their wild predecessors, the wild flax (Linum bienne) is relatively less studied in comparison to their cultivated relative. As their predecessor, we suggest that implications of local adaptation in the wild flax, may aid the development of their cultivar relatives. We examined both wild and cultivar type to determine local adaptation strategies, particularly in terms of flowering.

In chapter 2 of this thesis, we examined three flowering time genes and two duplicate genes. Linum is a temperate plant and as such requires vernalization. Vernalization is the process in which plants require colder temperatures to induce the flowering process. Plants that require vernalization often flower earlier when in colder temperatures than those that have not experienced cold induction. We studied expression of five flowering time genes for implication of local adaptation after treatment to vernalization. L. bienne appeared to express genes differently in comparison to the cultivars. The expression of Linum FLOWERING LOCUS T (LuFT) revealed a positive correlation with number of days to flower. This potentially identifies FLOWERING LOCUS T as one of the important genes regulating vernalization in Linum. Our result revealed variation in relative flowering time gene expressions. Wild and cultivated Linum demonstrate different relationships between flowering time and environmental variables.

In chapter 3, we quantified the viability of pollen, an important part in the transfer of the male gamete in flowering plants, under different temperature treatments. Linum is an established temperate plant. Sensitivity to temperature changes maybe more predominant in temperate plants as seasonal changes would reflect a challenge to flower in temperate environments. In this chapter, Linum pollen was treated under different temperatures to observe their ability to germinate. This is important to determine whether temperature plays a major part in affecting the viability of pollen, which in turn plays a major role in the formation of seeds. This chapter revealed a reduction in the number of pollen tubes formed under different treatments and across the two Linum species. In addition to this, correlations to local climates were also observed, with variation in trends across the temperature treatments.

In chapter 4 of this thesis, we examined population genetics of wild L. bienne samples originating from different latitudes across western Europe. We examined Wild flax (L. bienne) populations across western Europe to provide insights into their genetic structure and diversity. This population analysis will develop our understanding of adaptation in wild Linum in response to their environment. A double-digest RAD sequencing (DDRadSeq) protocol was utilized to look at variation in SNPs across different populations. Both L. bienne and L. usitatissimum samples were sequenced and aligned to an L. usitatissimum whole genome. Genetic structuring of our Linum samples were revealed across Western Europe. Cultivars in our collection revealed to be more genetically related to the Northern accessions of our wild samples.

In chapter 5 we summarized plant architectures. In this chapter traits and their relationship to the latitude were summarized in relation to the requirement for vernalization. Four traits were measured: overall height of the plants after first flowering, the number of stems of the plants after first flowering, and the number of flower buds on the plants at first flowering. In addition to this, seed size was examined in terms of its area. We also examined correlation between traits and environmental variables. We found that there was a relationship between traits when no-vernalization occurred. With vernalization, these relationships became less significant and, in some cases, not significant. This illustrates that vernalization influences the relationship of traits beyond flowering initiation. There were also suggestions that the traits measured correlate with latitude under no-vernalization treatments. For vernalized individuals, the correlation for the traits measured and latitude was not significant. Seed sizes were strongly correlated with both latitude and climatic variables in all cases of the treatments. The findings suggest there are effect of environmental variables in these measured traits, which suggests differentiation within wild Linum species.