Flowering propensity of two New Zealand perennial ryegrass cultivars originating from different ecotypes

Tiller turnover at flowering is an integral component of the perennation strategy in many temperate grasses. While vernalisation and daylength requirements for flowering, and cultivar flowering date characteristics are well known, there is little information on the effects of other factors, such as N fertiliser and grazing intensity, on flowering behaviour. We compared tiller dynamics of early flowering, endophyte-free, perennial ryegrass cultivars ('Ellett' and 'Grasslands Ruanui') under two N fertiliser and irrigation levels, and dairy cow grazing. In the first flowering period after sowing (October 1996-January 1997), 'Ellett' ryegrass averaged 19.5% reproductive tillers in the total tiller population, while 'Grasslands Ruanui' ryegrass averaged 13.0%. In the second season (September 1997-January 1998), 17.1% of 'Ellett' tillers were reproductive, compared with only 7.8% for 'Grasslands Ruanui'. There was a cultivar x N interaction in summer 1997/98, with N increasing the percentage of reproductive tillers in 'Ellett', but decreasing them in 'Grasslands Ruanui'. The irrigation treatment did not affect flowering behaviour. In another study, lax grazing of endophyte-infected 'Ellett' ryegrass resulted in 7% of total tillers flowering compared with 34% under hard grazing. The importance of considering the effects of latitude on flowering behaviour is discussed.