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The response of wheat to high temperature during grain growth

I.F. Wardlaw

CSIRO Division of Plant Industry, Canberra, ACT 2601

Throughout a large part of the Australian wheat belt the crop reaches heading when mean temperatures are about 15C (1) and the temperature then progressively increases until maturity. However the optimum temperature for grain development is, for many cultivars, less than 15C (2) and above this temperature grain size, and therefore yield, is reduced. A survey of a wide range of wheat cultivars has demonstrated considerable genetic variation in the response of the grain to high temperature (3),which provides a valuable base for both future improvement and understanding the physiological basis of the response.

Methods

Plants were grown in 8 cm diameter tubular pots under glasshouse conditions at a day/night temperature of 18/13C and either retained at this temperature until maturity, or transferred to high temperature (30/25C) for set periods after anthesis. Grain dry weights, water content and grain dimensions, as well as grain number per ear were determined on selected plants throughout development and at maturity.

Results and discussion

With a higher temperature throughout grain development (increased from 18/13 to 30/25C) most of the Australian cultivars tested showed a drop in grain dry weight of 30 to 35% (a fall of approximately 3% in dry weight for each 1C rise in temperature) There is evidence that low light may enhance the reduction in dry matter of the grain caused by high temperature and there is a need to establish the interaction between temperature and other factors, such as light,plant density and drought, before attempting field evaluation of selected lines. It appears that processes within the grain itself are responsible for the sensitivity of the grain to high temperature. Also preliminary investigations indicate that cultivars which are least sensitive to high temperature can compensate for a reduction in the duration of the period of grain growth by increasing the rate of growth.

Transferring plants to high temperature at different times after anthesis showed that the response to temperature varied with the stage of grain development.

1. Nix H.A.(1975) In "Australian field crops l. Wheat and other temperate cereals." eds.A.Lazenby,E.M Matheson;Angus & Robertson.

2. Chowdhury, S.I.and Wardlaw,I.F.(1978)Aust.J.Agric.Res.29,205-23.

3. Wardlaw, I.F.,Dawson,I.A.and Munibi,P.(1989) Aust.J.Agric.Res. (in press).

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