New Zealand Journal of Botany abstracts

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FLOWERING IN LOTUS PEDVNCULATVS CAV. 2. MINIMAL PHOTOPERIODIC REQUIREMENT FOR INFLORESCENCE INITIATION AND DEVELOPMENT

R. G. Thomas* B. J. Forde

Plant Physiology Division, Department of Scientific and Industrial Research, Palmerston North

Abstract The effect of light intensity and light-break treatments on inflorescence initiation and flower development were investigated in a north German variety of Lotus pedunculatus Cav. in controlled environment cabinets. A 1-10 scale of inflorescence and flower development is described and used as a basis for recording results. To determine the effects of light intensity, plants were grown in 16-hour photo-periods made up of an 8-hour main light period (MLP) and an 8-hour supplementary light period (SLP). Treatments given consisted of all combinations of 1,800, 900, and 450 foot-candle MLPs, and 900, 450, 180, and 60 foot-candle SLPs. Initiation was more rapid at the higher intensities, none occurring at MLP/SLPs of 900/60 and 450/60 foot-candles. However, rates of inflorescence growth after initiation differed little between treatment groups. In some conditions inflorescence growth ceased and primordia aborted after a certain stage of development. Abortion was most frequent when plants were transferred from long days to short days and at the lowest light intensities: with MLP of 1,800 foot-candles all inflorescences aborted with SLP of 60 foot-candles, but SLP of 180 foot-candles was sufficient to allow development to maturity. Thus, a stimulus which induces inflorescence initiation does not necessarily lead to full flower development. The influence of light breaks was determined by growing plants in 10-hour photoperiods and illuminating them for 2 hours during the dark period by a single 2-hour break, two 1-hour breaks, or four half-hour breaks. Flower initiation and full development were promoted by 2-hour breaks but not by the four half-hour breaks. Although the latter treatment did not induce inflorescence initiation, there were strong indications that it induced a condition within the plants which enabled them to flower more vigorously when subsequently placed in long days, i.e., it probably led to production of a subcritical level of inductive stimulus.

N.Z. Jl Bot. 5: 241-54.
(Received for publication 11 December 1966)

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