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UBC Theses and Dissertations

A study of certain phenological factors as they influence growth in the apple, malus pumila, (mill.) Beingessner, Henry Francis


The investigation is a study of the science of phenology in relation to the maturation of the fruit of the apple, Malus pumila. (Mill.) through the medium of the Heat Unit Theory, which is an expression of the climatological factor of temperature and more particularly average temperature. The study may be divided into three parts, the first of which introduces the problem of variability in total degree days (the basic unit employed in the Heat Unit Theory) between varieties of apple and between years. A maturity classification is established based on total degree days for several varieties grown at the Central Experimental Farm, Ottawa, Ontario. The second part examines the three basic difficulties encountered in the establishment of a phonological period, namely, when to begin the period, what base or unit temperature below which the apple is assumed not to grow and when to end the period. It was found that starting the phonological period ten days before full bloom gave better precision than when the period was started at full bloom. No one base temperature or combination of temperatures appeared to be entirely satisfactory although the base temperature of 42°F. occupied a medial position. The adoption of the ordinary date of harvest as obtained from field records proved to be as reliable as the index of maturity established by research. Temperature statistics other than the average, such as minimum and night temperatures, used in the calculation of heat units did not improve the precision of a prediction. An accumulation of temperature range appeared superior to accumulation of temperature statistics based on the Heat Unit Theory. No relationship was found to exist between accumulation of sunshine and solar radiation units and the length of the phonological period. In the third part of the investigation the value of total degree days as well as that of various base temperatures is determined for a relatively long period of time at two Experimental Stations, one at Summerland, British Columbia, and the other at Ottawa, Ontario. Actual measurements of the rate of enlargement of an apple are correlated with average temperature for the same period. No increases in precision were noted with the extension of the time interval under study, nor were the correlations obtained indicative of a good relationship between growth of an apple and average temperature. The number of days in the phonological period proved to be as good for prediction purposes as any of the methods used in the investigation, particularly for the climatological environment experienced at Summerland.

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