The effect of controlled environmental conditions on the photothermal requirement for growth and development, and on the yield of Selkirk wheat

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Boyd, William James Rodger
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The duration of the phases in the life cycle of a particular plant genotype is considered to be under environmental control and attempts have been made to mathematically express these intervals in terms of the data representing the prevailing environment. One such expression, involving the temperature level and length of photoperiod, is known as the "Photothermal Index" which represents the photothermal requirement for a certain interval. In the course of this study the concept of photothermal constants has been thoroughly tested for the common wheat variety Selkirk (Triticum aestivum L.) under artificial growing conditions. Controlled variations in temperature, photoperiod, moisture and fertility levels were possible and as an adjunct the effect of these variations on yield characteristics (tillering, seed number, seed size and protein percentage) were obtained. It was found that the photothermal requirement is relatively constant for the periods emergence to heading and heading to maturity. However, certain exceptions were noted. The requirement increases with increasing fertility and when the temperature of the dark period is lower than that prevailing during the photoperiod. There is also an indication that for the period heading to maturity, low temperatures and low moisture levels reduce the requirement slightly. Tiller number was found to be greatest at temperatures of 54*F. and 60*F. but a higher proportion of spikes produced at 54*F. failed to set seed. Seed number was found to be favoured by a temperature of 60*F. while seed weight was highest at 54*F. Both characters are influenced by moisture levels. Protein percentage was unaffected by temperature but appeared to depend on the availability of soil nitrogen.