A study of seed production in 'Grasslands Ruanui' perennial ryegrass(Lolium Perenne L.) 'Grasslands Kahu' Timothy (Pheleum Pratense L.) prairie grass (Bromus Unioloides H.B.K.) : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy at Massey University, New Zealand

Abstract

The place of grasslands in the economy of New Zealand is paramount. Consequently grassland seeds must and do play a vital role in the agricultural industry. Increasing land values and soaring costs make it imperative that our farms are sown with seed of the highest quality. On many farms seed production is only considered as secondary to the production of meat and milk. It is only in seasons when stock feed is abundant that many areas are closed for the production of seed. It would be to the advantage of the seed industry if grass seed production was viewed more as a primary consideration with stock grazing being employed to assist in the management of the seed crop rather than the present 'catch' crop system employed on many farms. This system would also help to reduce the large annual fluctuation in national seed production. Herbage seed production in this country amounts to about 18,000 tons annually although fluctuations in this figure do occur (1967 20,370 tons, 1968 17,430 tons, 1969 18,770 tons, 1970 14,880 tons). In 1970 seed exports represented a total value of over $7 million, of which approximately $0.7 million was obtained from the export of perennial ryegrass seed. In recent years a number of grassland workers have carried out studies on various aspects of seed development and production. Despite this, however, much work still remains to be done before the physiological processes underlying seed production are fully understood. Some of these workers have found it necessary to study the position and contribution of individual tillers to seed production. In comparison, studies of the factors influencing anthesis, fertilisation and seed maturation have been somewhat neglected. The production of a large number of head-producing tillers, each bearing large numbers of florets is obviously not enough. A high percentage of these florets must undergo anthesis, be effectively fertilised and ultimately develop to maximum seed weight and germination capacity if the potential yield of the crop is to be fully realised. This suggests that seed yield might be considerably increased if the conditions required at each of these stages were more fully understood. During the late summer, autumn and winter tillers grow vegetatively and it is not until the spring that those tillers destined to produce heads actually begin reproductive development. It is at this time that the first contribution to total seed yield occurs, viz. the number of reproductive tillers per unit area. Ear development continues until shortly before ear emergence at which point the number of florets per head is fixed. Subsequently, anthesis, pollination and fertilisation follow to determine the seed-set component of total yield. Finally the seeds develop and mature to determine the final yield component-seed weight.