Apple (Malus × domestica Borkh.) Ovule Senescence as Affected by Different Temperatures

In apple (Malus × domestica Borkh), temperature during flowering strongly influences ovule viability and reproductive success, particularly under changing climate conditions. Five apple cultivars—‘Red Aroma’, ‘Discovery’, ‘Elstar’, ‘Rubinstep’, and ‘Summerred’—were exposed to constant temperatures (8 °C, 12 °C, and 16 °C) in the days following anthesis to evaluate ovule degeneration. At six time points after anthesis, fluorescence-stained ovules were visually categorized to assess ovule vitality and degeneration stages. Ovule viability decreased in a highly temperature-dependent manner across all cultivars. High percentages of viable ovules were observed at 8 °C and 12 °C, whereas ovule senescence was significantly accelerated at 16 °C, leading to a rapid loss of viability. Based on fluorescence intensity, ovule degeneration is irreversible once initiated and involves both physiological and morphological changes at higher temperatures. The cultivar ‘Elstar’ exhibited the slowest loss of ovule viability, while the other cultivars showed more rapid degeneration. These findings demonstrate that both temperature and genetic background affect ovule viability, making this stage of the reproductive process crucial in the context of future climate change.