Relationship between reproductive initiation and ear emergence development in Lolium perenne L.

During spring, perennial ryegrass tillers change from vegetative to reproductive growth in response to photoperiod and undergo irreversible morphological changes. The effect of latitude and meteorological factors on the timing of reproductive initiation and ear emergence (EE) were measured in the field on 40 vernalized spaced plants for each of eight cultivars. The measurements were made at two latitudes in Ireland (Moorepark 52°N, Crossnacreevy 54°N). There was a significant effect of site and cultivar on all the variables measured. Cultivar initiation responded to a specific photoperiod but detection through apical development incurred a small variation due to growing conditions affecting the time taken for a visible change in apical morphology to occur. When converted from photoperiod to initiation date this variance was minimal (±6 min). Timing of EE was dependent on growing conditions not photoperiod and so was specific to the studied conditions. As cultivar rank order for EE date was largely retained, there was a very strong correlation with published UK Plant Breeders Rights (PBR) heading dates for these cultivars, which in turn had a strong relationship with the ear initiation (EI) dates (R²=0.95). The latter relationship was sufficiently robust to allow estimation of photoperiod for any cultivar on the EU Common Catalogue based on its published heading date from Crossnacreevy, where the UK PBR trials are conducted. As photoperiod can be converted to calendar date by reference to latitude, this relationship can also be used to estimate the EI date for sites at latitudes other than those in the current study.