The influence of environment and nutrition on the development of rye-grasses

The study was concerned with the influence of environmental factors such as light, temperature and nutrition on the production of tillers and inflorescences and induction of cold hardiness in ryegrasses. Field trials were carried out to determine if nitrogen fertiliser altered the degree of flowering in perennial ryegrass varieties. Although tiller numbers increased due to nitrogen in one experiment, the percentage of flowering tillers was not markedly altered. This applied to both an early (Pax tofte) and late (S23) perennial ryegrass. A study of nitrate effects on the production of leaf primordia, tillers and inflorescences under glasshouse conditions was carried out* Nitrate increased leaf appearance in main axes and tillers as well as increasing total primordia production and tiller bud expansion. An observation from field and glasshouse experiments that tiller production in ryegrasses at the flowering stage decreased both in annual and perennial ryegrasses This suggested that apical dominance existed in ryegrasses. Using surgical techniques, removal of the apical region and expanding leaves in annual and perennial ryegrasses increased the expansion of tiller buds. Employing tiller number and tiller bud expansion as criteria apical dominance was also found to exist in annual ryegrasses (Westerwolds and Lolium temulentum) when the main axis was flowerings but was most marked under conditions of low nitrate. Results are discussed in terms of current theories of apical dominance, particularly- with relevance to grasses. As well as apical dominance lack of cold tolerance was also a factor which limited the perennation of ryegrasses. Cold tolerance was measured by survival or regrowth after subjection to low temperatures or by the degree of damage brought about by low temperatures, measured by the amount of electrolytes released from the plants. Hardening of perennial ryegrasses was found to be dependant on low temperatures. Long photoperiods at low, but above zero, temperatures induced hardiness at a faster rate than short photoperiods in some experiments. However at higher temperatures, the effect of daylength varied according to species and variety. Nitrogen fertiliser decreased hardiness in ryegrass in the field but the reverse was found under controlled environmental conditions. Roots were generally less responsive to hardening conditions than shoots. Conclusions are drawn and are considered in terms of future research and, in particular, the role of perenniality in determining persistence in ryegrass