Phenological calendar in some walnut genotypes grown in Romania and its correlations with air temperature.

Phenology is the study of periodic biological events in the plant world that are influenced by the environment. Temperature increase in spring season can advance the spring phases, but warming in autumn and winter may slow the fulfillment of chilling requirements and lead to later onset of spring events. This study examined different genotypes of walnut trees under environmental conditions, and measured the cold demand, heat requirements, and average time from budburst till flowering for 28 walnut genotypes. The information obtained provides a better understanding of the phenological temperature response of walnuts that will be useful for walnut production and will also contribute to the development of adaptation measures in the light of the expected climate change.