Genetic differentiation within and between natural populations of perennial and annual ryegrass (Lolium perenne and L. rigidum)

Abstract

Genetic structure of 120 wild populations of Lolium perenne and 50 populations of L. rigidum was studied using starch gel electrophoresis. Allelic frequencies were obtained from 12 polymorphic isozyme loci. Gene diversity indices (number of alleles (A), observed (Ho) and expected (He) heterozygosity) were significantly higher in L. rigidum (A=3.13; Ho=0.369; He=0.405) than in L. perenne (A=2.72; Ho=0.308; He=0.322). For both species, most of the diversity appeared to be within populations (GST=0.110 and 0.170 for L. perenne and L. rigidum, respectively). Despite this weak genetic differentiation, significant patterns of geographical variation for diversity indices and allele frequencies were observed in L. perenne populations; the three genetic indices (A, Ho, He) showed the same trend of variation, with the lowest values in the north‐west part of the distribution area (United Kingdom, Ireland) and the highest ones in the south‐east (Turkey, Lebanon, Cyprus, Iraq, Iran). In the same way, as indicated by logistic regression analyses between allelic frequencies and geographical data of L. perenne populations, the latitudinal gradient of allelic frequencies appeared to be more pronounced, although significant relationships also existed with longitude. In contrast, no spatial organization of the diversity was detected in L. rigidum. Hypotheses concerning the taxonomic relationships and the genetic and geographical origins of the two species are discussed. Lolium perenne could be derived from a small bottleneck of L. rigidum populations in the Middle East, and its present distribution area in Europe could be explained either by the extension of primitive agriculture from the fertile crescent, or as a consequence of postglacial recolonization from southern refugia.

Pleistocene climate changes, and not agricultural spread, accounts for range expansion and admixture in the dominant grassland species Lolium perenne L.

“…The split and subsequent start of range expansion overlap with a glacial period (Würm glaciation 12-110 kya; Figure 2e2). During the Würm glaciation, the Alps might have acted as a barrier to gene flow in L. perenne as previously suggested by Balfourier et al (1998), Balfourier et al (2000) and Blackmore et al (2015). In continental Europe, the continuous cooling during that period might have affected the dominance of tree species in favour of herbs, possibly including grass species such as L. perenne.…”

“…Indeed, in the frame of controlled experiments, it has been demonstrated that L. multiflorum and L. rigidum are completely interfertile with L. perenne (Terrell, 1966). A close relationship between ancestral L. perenne populations from the Near East and L. rigidum was previously inferred by Balfourier et al (1998). In addition, it is known that both L. perenne and L. multiflorum have been present in the northern plains of Italy since the late Middle Ages (Casler, 2006).…”

Genetic diversity and structure of Lolium perenne ssp. multiflorum in California vineyards and orchards indicate potential for spread of herbicide resistance via gene flow

“…rigidum have repeatedly evolved resistance to several herbicides from different classes (Heap, 2016;Owen, Martinez, & Powles, 2014;Preston et al, 2009). The ability of L. perenne to rapidly evolve resistance to herbicides has been attributed to high genetic diversity within populations resulting from large population sizes and a self-incompatible outcrossing mating system (Balfourier, Charmet, & Ravel, 1998;Busi & Powles, 2009). However, while the genetic diversity of cultivated and wild accessions of L. perenne have been reasonably well characterized (e.g., Brazauskas, Lenk, Pedersen, Stender, & Lübberstedt, 2011;Kubik, Sawkins, Meyer, & Gaut, 2001;McGrath, Hodkinson, & Barth, 2007;Wang, Dobrowolski, Cogan, Forster, & Smith, 2009), the genetic variation and structure of weedy populations in agricultural settings (crop fields, orchards, vineyards) have not been examined, to our knowledge, despite the unique demographic processes and selective pressures in agricultural systems that are likely to shape genetic diversity in weeds.…”

Global Genetic Diversity of the Perennial Ryegrass Fungal Endophyte Neotyphodium lolii

“…The annual ryegrass endophyte N. occultans appeared to be present in a small number of accessions. The endophytes in these accessions showed high levels of genetic similarity to endophyte detected in annual and Italian ryegrass and often occurred in the Mediterranean region, in which these grass species are common (Balfourier et al, 1998). Consistent with the heteroploid genetic structure of N. occultans (Moon et al, 2000), as many as two diff erent products were detected for each SSR locus.…”