Abstract
BackgroundSelf-incompatibility (SI) is a physiological mechanism that many flowering plants employ to prevent self-fertilization and maintain heterozygosity. In the grass family this is known to be controlled by a two locus (S-Z) system; however, the SI system is intrinsically leaky. Modifier genes of both the S and Z loci and a further locus, T, are known to override SI leading to self-fertilization and self-seed production. This has implications for the ecological and evolutionary success as well as the commercial breeding of grasses. Here we report a study where the genetic control of self-compatibility (SC) was determined from the results of self-pollinating an F2 population of perennial ryegrass from two independently derived inbred lines produced by single-seed descent.Methods In vitro self-pollinations of 73 fertile plants were analysed. A genetic association analysis was made with a panel of 1863 single-nucleotide polymorphism (SNP) markers, generated through genotype-by-sequencing methodology. Markers were placed on a recombination map of seven linkage groups (LGs) created using Joinmap v.5. The seed set on self- and open-pollinated inflorescences was determined on 143 plants, including the 73 plants analysed for self-pollination response.Key ResultsSelf-pollinations revealed a bimodal distribution of percentage SC with peaks at 50 and 100 %. A single quantitative trait locus (QTL) was identified with peak association for marker 6S14665z17875_11873 that mapped to LG 6. Peak position was associated with maximum marker segregation distortion. The self-compatible plants were equally fecund after self- and open pollination.ConclusionsThis is the first report in the Poaceae family of an SC locus located on LG 6. This new SC QTL discovery, as well as indicating the complex nature of the pollen–stigma recognition process and its evolutionary significance, provides an additional source of SC for breeding perennial ryegrass.
Highlights
Self-incompatibility (SI) in perennial ryegrass (Lolium perenne), in common with all grasses studied, is controlled gametophytically at the stigmatic surface by two loci, S and Z (Cornish et al, 1979) located on linkage groups (LGs) 1 and 2, respectively (Thorogood et al, 2002)
We report a study where the genetic control of self-compatibility (SC) was determined from the results of self-pollinating an F2 population of perennial ryegrass from two independently derived inbred lines produced by single-seed descent
The F2 population was obtained by selfing a single F1 plant derived from the cross between two unrelated perennial ryegrass inbred lines that had been produced by single-seed descent over nine and ten generations for the maternal and paternal lines, respectively
Summary
Self-incompatibility (SI) in perennial ryegrass (Lolium perenne), in common with all grasses studied, is controlled gametophytically at the stigmatic surface by two loci, S and Z (Cornish et al, 1979) located on linkage groups (LGs) 1 and 2, respectively (Thorogood et al, 2002). A non-functional Z locus was shown to be responsible for self-compatibility (SC) in the annual species Lolium temulentum (Thorogood and Hayward, 1992) and a frameshift mutation of the L. temulentum orthologue of the candidate S gene, LpSDUF247, of L. perenne alters the last 24 amino acids of the C-terminus and might explain the failure of the SI system in this species (Manzanares et al, 2016). The existence of an effective SI system in forage grass crop species is problematic. It means that crop improvement methods are restricted to population improvement strategies. Following the foundation of the base population, rounds of recurrent selection to fix beneficial by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited
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