Genomics of Self-Incompatibility and Male-Fertility Restoration in Rye

Allogamous grasses like rye (Secale cereale L.) developed a two-locus gametophytic self-incompatibility (SI) system that forces outcrossing and allows for maintaining a high level of diversity. The strong built-in SI mechanism renders rye the only outbreeding small grain cereal species and an excellent crop to breed hybrids. Hybrid breeding requires self-pollination and hybridization systems in order to perform targeted crosses for a systematic exploitation of heterosis. A managed SI could be applied as a genetic fertilisation control system supplementing systems based on cytoplasmic male sterility and restorer-of-fertility genes. The ability to develop inbred lines to capture and manage the genetic diversity is a crucial precondition for efficient hybrid breeding. Indeed, spontaneous self-fertility detected in some rye mutants overcomes this limitation. Other mechanisms of reproductive isolation affect the production of interspecific wheat (Triticum aestivum L.) and rye hybrids and face problems of low crossability, embryo lethality and overall hybrid weakness. This limits the transfer of agronomically important traits from rye to wheat and impairs the development of triticale (X Triticosecale Wittmack) lines, which combine the yield potential and grain quality of wheat with the disease and environmental tolerance of rye. This chapter will discuss the most current knowledge of the molecular basis of SI in rye as compared to better understood SI in other plant systems, wheat-rye crossability as well as male sterility in rye and their possible applications to advance rye breeding.