THE DETERMINATION AND VERIFICATION OF A BASELINE TEMPERATURE FOR THE GROWTH OF WESTAR SUMMER RAPE

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Abstract
Controlled environment growth cabinets set at mean temperatures of 10, 13.5, 15, 17, 20, 22 and 25 °C were used to determine a baseline temperature of 5 °C for the growth of Westar summer rape (Brassica napus L.). Temperatures in excess of 25 °C caused whole plant sterility. Phenological data obtained from ten field sites, collected over three years, was used to verify the 5 °C baseline temperature. Field growing degree days (GDD) and cabinet GDD were not significantly different. The percent development to physiological maturity (% DPM) of field grown Westar summer rape, as influenced by temperature, was not significantly different from that predicted by the cabinet determined equation. The agreement between field and cabinet GDD and observed and predicted % DPM verified the use of a 5 °C baseline temperature in field GDD equations. % DPM and GDD were found to be better estimators of phenological development in the field than calendar days. A simple linear model, relating % DPM to GDD was developed. It was concluded that temperature is the most important environmental factor regulating the phenological development of Westar summer rape in western Canada.Key words: Westar summer rape, Brassica napus, baseline temperature, phenological development, growing degree days