Field Crops Research 39(2-3): 111-117 (Dec 1994)
Does temperature affect final numbers of primordia in wheat?
Gustavo A. Slafera, and H. M. Rawsonb
a Centre for Crop Improvement, Department of Agriculture, The University of Melbourne, Parkville, Vict. 3052, Australia
b Division of Plant Industry, CSIRO, GPO Box 1600, Canberra, A.C.T. 2601, Australia

Abstract
Photoperiod and vernalisation both affect the number of leaf and spikelet primordia and, hence, the duration of the early phases of development in wheat. Temperature also affects duration of developmental phases but it is not clear whether temperature-related changes in duration are similarly associated with final numbers of primordia. The objective of this study was to examine these temperature-related associations. A phytotron study was conducted in naturally-lit cabinets with four cultivars (Sunset, Condor, Rosella and Cappelle Desprez) and six temperature regimes between 10 and 25°C. Seedlings were vernalised for 50 days and then grown under a photoperiod of 18 h to avoid confounding the responses to vernalisation and photoperiod with those to temperature.

The duration of the period of terminal spikelet initiation was reduced by increases in temperature from 10 to 19°C, but extended at temperatures above 19°C. Cultivars differed in the time taken to the terminal spikelet stage. However, final numbers of leaf and spikelet primordia were affected only marginally by temperature. Final leaf number increased slightly with temperature, but this trend was only significant in Cappelle Desprez, and in that case accounted for only 1 leaf over the 15°C range. There was a curvilinear association between final spikelet number and temperature, with an optimum at about 19°C. However, temperature changed spikelet number by a maximum of only 3 per ear.

Although significant correlation was only found for leaf number, there was a general trend for a reduction in number of primordia with longer duration to terminal spikelet initiation. However, these trends were all very small. This suggests that the effects of temperature on the rate of apex development towards terminal spikelet initiation and on the rate of primordia initiation are similar. Cultivar differences in duration of primordia initiation were translated directly to differences in number of primordia initiated. The relative impact of temperature and other factors on the rates of primordia initiation and apex development towards terminal spikelet initiation were assessed using a simple model.

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