A genetic association between leaf elongation rate and flowering time in perennial ryegrass.

Leaf elongation rate (LER) is a key component of forage grass dry matter yield. Leaf lamina initiate rapid expansion during the winter at a time that coincides with lengthening days but this extension is not associated with any large environmental shifts such as an increase in light intensity or temperature. The rate increase precedes any anatomical indication of floral initiation in apical meristems (double ridge formation) by around 2-3 weeks. We measured LER in a perennial ryegrass (Lolium perenne L.) pair-cross mapping family that has been extensively mapped with more than 1,200 SNP markers generated by Illumina’s Infinium platform. These have been anchored to the seven Lolium linkage groups as defined by Triticeae nomenclature with seven micro-satellite markers originally developed by ViaLactia Biosciences. Measurements were made in the winter/spring during extending day length, after full natural vernalisation. The plants’ leaves were beginning to expand rapidly with leaf extension rates varying between approximately 0.4 mm and 1.1 mm h ₋₁. We obtained a significant correlation between LER and both apical meristem elongation and ear emergence (the date at which inflorescences emerge above the flag-leaf ligule) measured in two separate seasons. A QTL for LER was revealed with a peak some distance away from the major floral initiation and ear emergence date QTL on linkage group 7. This is the first evidence of genetic linkage that determines the often observed association between LER in herbage grasses in the spring with floral initiation determined in large part by the action of Arabidopsis flowering initiation gene homologues, Flowering Time Locus (FT) and Constans (CO).