Influence of Different Temperature Levels on the Date of Full Bloom of Peach Varieties in Subtropical Climate

Abstract

-The dormancy dynamics of temperate fruit tree species is complex and highly variable according to genotype and environment. Due to this variability, many phenological models of cold units have not been suitable for subtropical climatic conditions in southern Brazil. The aim of this study was to evaluate the influence of air temperature on the peach dormancy in Urussanga-SC. For this purpose, the correlations between the date of full bloom of sixteen peach varieties and the total hours in which the temperatures remain in certain thermal levels were evaluated. Two groups of varieties with highly differentiated responses to temperature in various times were identified. In the first group, consisting of ten varieties, the beginning of significant influence (p<0.05) of temperatures on the date of full bloom occurred as earlier, in February. In this group, temperatures between 16 and 22 °C accumulated from March to June were those that most contributed to the flowering advance. In the second group, the beginning of the significant influence of temperatures occurred later in April. In this group, the accumulated high temperatures from early April to late May anticipated the full bloom, but from May 25, temperatures below 10 °C were responsible for this advance. This behavior differs from traditional phenological models that consider a sequential cold and heat requirement in the resting phase. The results obtained indicate the possibility of an alternating or parallel influence of different temperature levels on dormancy. Index terms: Prunus persica, dormancy, temperature, statistical method. The phenological data used came from a collection composed of peach tree selections resulting from genetic improvement located in Urussanga, state of Santa Catarina, Brazil (28º 31 'S, and 49º 19' W, 49 m asl). Sixteen selections considered to be adapted to the climate of the region were evaluated. This collection was formed by five plants in sequence of each variety, and for the average phenological records, three central plants were used. The selections, grafted on Okinawa rootstock, were cultivated with spacing of 6 m between rows and 5 m between plants in a Typic Hapludalf of granitic origin. The climate of the region is subtropical humid, with hot summer and no defined dry season (Cfa, according to the Köppen classification). The average annual temperature is 19.4°C, with maximum average temperature of 25.9 ° C and minimum of 14.2°C. The total annual rainfall is 1624.0 mm, and is normally well distributed throughout the year. The hours of cold below 7.2 ° C occur from May to September with an average annual total of 234 hours. INFLUÊNCIA DE DIFERENTES NÍVEIS TÉRMICOS SOBREThe average daily air temperature data (T a ) were collected at the conventional meteorological station of Urussanga-SC, where T a = (T max + T min + T 9 + 2T 2 ) /5, where T max is the maximum daily temperature, T min is the daily minimum temperature, and T 9 and T 2 are temperatures from 9:00 a.m. to 9:00 p.m. respectively. For the calculation of ...

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