Abstract
Self-incompatibility (SI) is a genetic mechanism preventing self-pollination in ~40% of plant species. Two multiallelic loci, called S and Z, control the gametophytic SI system of the grass family (Poaceae), which contains all major forage grasses. Loci independent from S and Z have been reported to disrupt SI and lead to self-compatibility (SC). A locus causing SC in perennial ryegrass (Lolium perenne L.) was previously mapped on linkage group (LG) 5 in an F2 population segregating for SC. Using a subset of the same population (n = 68), we first performed low-resolution quantitative trait locus (QTL) mapping to exclude the presence of additional, previously undetected contributors to SC. The previously reported QTL on LG 5 explained 38.4% of the phenotypic variation, and no significant contribution from other genomic regions was found. This was verified by the presence of significantly distorted markers in the region overlapping with the QTL. Second, we fine mapped the QTL to 0.26 centimorgan (cM) using additional 2,056 plants and 23 novel sequence-based markers. Using Italian ryegrass (Lolium multiflorum Lam.) genome assembly as a reference, the markers flanking SC were estimated to span a ~3 Mb region encoding for 57 predicted genes. Among these, seven genes were proposed as relevant candidate genes based on their annotation and function described in previous studies. Our study is a step forward to identify SC genes in forage grasses and provides diagnostic markers for marker-assisted introgression of SC into elite germplasm.
Highlights
Several species of the grass family (Poaceae) are economically valuable forage crops and represent a fundamental component of our grasslands
The SC locus mapped to a single quantitative trait locus (QTL) on linkage group (LG) 5 with a maximum logarithm of odds (LOD) value of 7.17 explaining 38.4% of the phenotypic variance (Figure 2C)
We found that the single QTL on LG 5 was not interacting with other genomic regions, confirming the single-locus inheritance
Summary
Several species of the grass family (Poaceae) are economically valuable forage crops and represent a fundamental component of our grasslands. The genetic gain achieved in self-incompatible grasses with population breeding strategies has lagged behind compared to inbred crops, such as maize (Zea mays L.), wheat (Triticum aestivum L.), and rice (Oryza sativa L.) (Laidig et al, 2014). This is partially caused by the inability to develop F1-hybrid cultivars and exploit the hybrid vigor that occurs when two genetically distant (and usually highly homozygous) parents are crossed. Inbred lines belonging to different heterotic groups can be crossed to systematically assemble desirable combinations of genes and maximize heterosis
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