S02 - Session O4 - I - Characterization of autumn senescence in the Swedish Central collection of heritage apple cultivars

Authors: Jonas Skytte af Sätra *, Inger Hjalmarsson, Pär Ingvarsson, Larisa Garkava-Gustavsson

Starting in the late 1970s, the use of modern apple cultivars prompted an inventory and collection of old apple cultivars grown in Sweden. This initially led to the establishment of a series of local clonal archives and, later, to the establishment of the Swedish Central collection between 2012 and 2016. Cultivars were selected for preservation in the Central collection based on cultural-historical criteria to preserve the cultural heritage represented by the cultivars, rather than their merits as genetic resources. Nevertheless, the collection contains considerable phenotypic variation for traits that could be relevant to future breeding goals of Sweden's national breeding program, such as climatic adaptation. Recommendations for cultivations of horticultural perennials are based on the classification of Sweden into nine climatic zones, including the alpine region. The Swedish Central Collection has apple cultivars recommended for cultivation up to zone 6, stretching up to latitude 65 along the coastal regions. Currently, most of the production of dessert apples in Sweden are produced around latitude 55 degrees north, though there are commercial orchards further north. Recently, commercial orchards aimed at cider production have been established as far north as 63 degrees north. Thus, Swedish commercial apple production is placed at the northern frontier, with special requirements for climatic adaptation. Currently, little is known about which key characters are underlying climatic adaptation but phenological properties are generally important for the adaptation of trees to northern climates. While certain phenological traits such as spring bud break and the onset of flowering have been relatively well studied in apple, autumn phenological traits such as senescence have received relatively little attention. Thus, we have assessed the Swedish Central collection of apple heritage cultivars for autumn senescence over three years (2019-2021). Factors such as year-to-year variation, the impact of temperature, and correlations with historical data on other traits were evaluated.