Seed factors involved in early seedling establishment of Festuca arundinacea (tall fescue) : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Plant Biology and Biotechnology at Massey University, New Zealand

Abstract

New Zealand pastures are commonly based on vigorously growing Lolium (ryegrass) species. In many situations, however, it is often advantageous to combine the vigorous qualities of Lolium species with the versatility of other species such as Festuca arundinacea (tall fescue) to result in a pasture which is high in quality all year. F. arundinacea, however, has poor seedling vigour which places it at a competitive disadvantage when sown with Lolium. During seedling establishment, the seedling is dependent upon the food reserves present in the seed. The nature and amount of these reserves and the ability of the seed to mobilise them are therefore likely to have an affect on seedling perfonnance. While much knowledge exists about the processes involved in seed reserve mobilisation in some cereals, little information is available for pasture grasses. An in depth investigation of the behaviour of one seed lot of F. arundinacea was undertaken in order to gain a more detailed understanding of germination, reserve mobilisation and establishment processes in pasture grasses and how they relate to the processes of seedling growth. Comparisons between this species and Lolium multiflorum (Italian ryegrass) were undertaken throughout the study. Germination and seedling growth of the F. arundinacea seed lot was found to be heterogenous and slower than in L. multiflorum due to later radicle emergence. Mobilisation of reserves and the onset of α-amylase activity correlated well with the utilisation of reserves in L. multiflorum. In both prechilled and non prechilled F. arundinacea seeds, however, anomalies were identified in the process which indicated that reserve mobilisation was less tightly coupled to seedling growth in F. arundinacea. Reciprocal plot analyses indicated that the beneficial effects of prechilling in most seeds of the F. arundinacea seed lot were not related to residual dormancy but were a thermal time benefit. It appears prechilling was allowing rate limiting steps in embryo growth to be advanced before visible germination. Apart from this, no real differences were detected in the way the two species mobilised reserves. Differences in the appearance of α-amylase isoenzymes of F. arundinacea at different times during germination indicated that gene expression may be under some complex differential control mechanisms during germination and reserve mobilisation. Prechilling was not found to change the spectrum of isoenzymes, but merely to advance the time-course in which different isoenzymes appeared. There were also distinct differences in α-amylase isoenzyme patterns between F. arundinacea and L. multiflorum, and also wheat. Preliminary studies indicated that exogenous gibberellic acid was more effective in promoting α-amylase production in L. multiflorum than in F. arundinacea. However, α-amylase production in F. arundinacea was more susceptible to promotion by prechilling. This study has identified a wide range of variables impacting on germination and seedling establishment in F. arundinacea. This, together with the lack of previous detailed studies on grass seed germination and seedling growth and the lack of literature on F. arundinacea germination in particular, highlights the enormity of the task ahead of extending key areas of this study to different seed lots and species