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The Rest Period of Apricot Flower Buds as Described By a Regression of Time of Bloom on Temperature.

1957; Oxford University Press; Volume: 32; Issue: 2 Linguagem: Inglês

10.1104/pp.32.2.75

1532-2548

Dillon S. Brown,

Postharvest Quality and Shelf Life Management

The buds of deciduous fruit trees which remain dormant when temperatures are favorable for growth are said to be in a state of rest or in the rest period. The rest influence varies in intensity, however, such that dormancy from this cause also varies and is most intense only when the rest is the deepest. Buds with lesser intensities of rest respond to favorable growing temperatures with rates of growth which vary inversely with the depth of the rest influence. It is possible, therefore, to describe the rest period by evaluating periodically the responsiveness of buds to temperatures favorable for growth. Such an evaluation is herein described for the flower buds of the Royal apricot. The time of bloom is an end-point for measuring the rate of development of flower buds. For a given temperature favorability, the opening of the buds in the spring will depend on the amount of rest remaining after the buds have experienced the rest-breaking influence of chilling temperatures in the preceding winter. The deeper the rest remaining in the spring, other things being equal, the later will be the bloom. Bloom records of the Royal apricot, together with appropriate temperature data, were available for 24 seasons from Winters and for 20 seasons from Brentwood, California. The records were considered as 44 observations in the statistical treatment of the data, even though the same years were involved at both locations in 20 of the seasons. The dates of bloom were coded as the number of days from February 2 to full bloom inclusive. The temperature data were obtained from weekly thermograph records. Tabulations were made of the number of hours of temperatures experienced in a series of temperature classes listed below. These data were converted to a growth unit index which expresses the favorability of temperatures for growth. Growth units were calculated by summing the products of the number of hours in the temperature classes and appropriate coefficients of temperature efficiency. This procedure weights the effectiveness of different temperatures. The coefficients of temperature efficiency which were used are based on the apparent efficiencies of temperatures in promoting the development of apricot fruits (2). Although they were derived from fruit data, they were applied here as the best approximation for weighting the effectiveness of temperatures for bud development, since no such coefficients have been derived specifically for buds. The coefficients used are as follows: