Studies in the Physiology of Flowering of Timothy (Phleum pratense L.)

The influence of shoot age on flowering in S.48 timothy was investigated in partially controlled conditions and outdoors. In artificial long days sensitivity to photo-induction increased with age of the shoot from soon after germination until about five leaves were produced; no further increases in response to photoperiod were evident in older plants. The minimum leaf number to ear emergence in plants exposed to continuous light from germination was nine; of these, five had been produced before spikelet initiation, while the remainder developed during spike differentiation. In natural conditions, only main shoots on plants sown in March or earlier were sufficiently advanced to respond to the increasing natural daylength and to produce ears in late June. In later sowings ear emergence became increasingly delayed until, in plants sown in June, some main shoots failed to develop inflorescences. Nitrogen deficiency further delayed or inhibited flowering in these later-formed shoots. The minimum period of 10 weeks for inflorescence production in main shoots was attained in plants sown some weeks before midsummer. The equivalent period in subsidiary tillers arising in midsummer on the same plants decreased to less than 5 weeks. The implications of the results are discussed in relation to previous investigations in this species.