The influence of temperature on the phenology of apple trees grown in mild winter regions of Brazil, based on long-term records

Abstract

Phenological events, such as flowering, are highly responsive to temperature and are directly influenced by the establishment of a dormancy period in temperate fruit trees. Increased temperatures, due to climate change, can cause advancement, delay or no change to temperate fruit tree flowering, putting production at risk and raising uncertainty about the future of crops in traditional apple producing regions. The objective of this work was to evaluate the effect of temperatures on the endodormancy and ecodormancy periods, and how they directly influence the flowering dates of apple trees grown in contrasting areas in a subtropical climate region. Phenological and climate data were obtained from orchards located in the São Joaquim – SC (SJ), Caçador – SC (CA) and Palmas – PR (PA), in Southern Brazil. The climate of all three areas is considered Cfb using the Köppen classification. First flowering date data for the apple cultivars Fuji and Gala were collected for 43 and 45 years at São Joaquim – SC, respectively for Fuji and Gala, for 39 years at Caçador – SC for both cultivars and for 9 years at Palmas – PR for both cultivars. The flowering date data were correlate with the daily mean temperatures during the year, using PLS analysis. Chill and heat accumulations were also calculated during the periods of chill and heat sensitivity (endodormancy and ecodormancy) delineated by PLS analysis. The PLS proved to be efficient at identifying periods where there was chill and heat accumulation by the apple tree in a subtropical region (mild winter region). The start date of flowering is influenced by temperatures during both the chilling and forcing periods. At CA and PA, the mean temperatures increased over the years, and the plants, especially the gala cultivar at CA, responded to this temperature increase with a significant change in their flowering date. At SJ, the coldest locality, temperature and phenology changes were not significant. The chill and heat requirements are different according to region and cultivar. When cultivars are exposed to conditions of low chill accumulation, the tendency is for heat requirement to increase. For the next few years, the temperature during the period of endodormancy could be a more decisive factor for the flowering process