Rachis brittleness in F1 barley crosses with different combinations at the non-brittle rachis genes

Abstract

Two dominant, closely linked and complementary genes, Btr1 and Btr2 control rachis brittleness in barley. Recessive mutations in any of these genes turn the fragile rachis (brittle) into a tough rachis phenotype (non-brittle). The cross of parents with alternative mutations in the btr genes leads to a brittle F1 hybrid that presents grain retention problems. We evaluated rachis fragility at different times after ripening, through a mechanical test and under natural conditions, in F1 crosses with different compositions at the btr genes. Brittleness was significantly higher in Btr1btr1Btr2btr2 crosses compared to hybrids and inbred parents carrying one of the mutations (btr1btr1Btr2Btr2 / Btr1Btr1btr2btr2), measured by means of a mechanic test and spontaneously in the field. This fact could jeopardize the efficient harvest of hybrids bearing alternative mutations, reducing the choice of possible crosses for hybrid barley breeding, and hindering the exploitation of potential heterotic patterns. Furthermore, non-brittle hybrids showed higher brittleness than inbreds, suggesting the presence of other dominant factors affecting the trait. Finally, for the first time, an increase in rachis fragility over time post-maturation was identified, specific to the hybrid genotypes, both brittle and non-brittle types. This increase in rachis fragility with time was only observed by mechanical threshing, but could result in an agronomic problem if it led to head shattering. In conclusion, this work encourages a deeper study of the genetic control of the rachis brittleness trait and urges the consideration of rachis tenacity as a target for hybrid barley breeding.