Day-Length Control of Inflorescence Initiation in the Grass Rottboellia Exaltata L.F.

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Abstract
R. exaltata is a strict short-day plant with a critical photoperiod of about 13 hours. The number of short days required for inflorescence initiation varies with age, being 6 with plants 5 weeks old. Exposure to additional short days increases the rate of inflorescence development. The expanding leaf is the 1 most sensitive to short-day induction and removal of the leaves below it accelerates inflorescence development. Short-day exposures given to different leaves can, in some cases, be as effective for induction as when the short days are all given to the same leaves. Long days interpolated between the 1st 2 short days of an inductive sequence, or given to the lower leaves early in the inductive sequence while the uppermost leaf blade is exposed to short days, accelerate inflorescence development, while those interpolated or given simultaneously later in the sequence are inhibitory. It is concluded that short-day leaves produce a stimulus to inflorescence initiation which is translocated from them rapidly after each long night, while long-day leaves produce a transmissible substance which may either accelerate or inhibit inflorescence development depending on the progress toward induction.