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Background: The environmental control of flowering in apple (Malus × domestica Borkh.) has remained an enigma for generations. Methods: We studied growth and flowering effects of temperature under daylight phytotron conditions in 3-year old 'Summerred' and 'Discovery' apple trees. Flowering was assessed by dissection of buds on spurs and extension shoots at termination of treatments and flowering performance in the subsequent spring. Results: Exposure to constant temperatures ranging from 12 to 27 °C for 12 weeks yielded a hyperbolic response curve with optimum at 18-21 °C and little or no flowering at 12 and 27 °C. A drop from high to low temperature after 6 weeks caused growth cessation and initiation of flowering, whereas the reverse shift had the opposite effect. Shoot growth and leaf accumulation increased with increasing temperature, but under flower-inducing conditions, both levelled off and ceased towards the end of the treatment period. Conclusions: The results are discussed in relation to the extensive physiological and genetic literature on the subject. We interpret the results as two separate effects of temperature on flowering in apple. At 12 °C flowering seems to be limited by low temperature depression of growth and leaf production, while at 27 °C, flowering is blocked by inhibition of the floral initiation itself. Intermediate temperatures of 18-21 °C, on the other hand, seem to satisfy the requirements for both processes. These opposite effects of temperature have apparently confounded the understanding of the environmental control of flowering in apple.

The flowering phenology of six genetically distant strawberry cultivars (‘Candonga®’ (ES), ‘Clery’ (IT), ‘Florence’ (UK), ‘Frida’ (NO), ‘Gariguette’ (FR), and ‘Sonata’ (NL)) was studied for 3 years in relation to climatic parameters in open-field cultivation at three locations (Norway, Poland, Germany) and in soil-less cultivation at two locations (Italy, and France), covering a distance of 16 degrees of latitude. This proved to be a useful approach for unravelling the climatic adaptation and plasticity of strawberry genotypes and their suitability both for profitable cultivation and as a breeding pedigree. Despite the intercorrelated character of the climatic variables, the observed results highlight the importance of global radiation as a powerful modifying phenological factor in strawberry. Generally, early flower initiation was associated with elevated temperature and global radiation. ‘Frida’ revealed the highest dependency on global radiation for flower initiation, while ‘Sonata’ was least affected by temperature and radiation. In general, temperature and global radiation in periods both preceding and following flower initiation had a stronger positive effect on the number of flowers than on crowns, especially under open-field conditions. The influence of these factors was highly variable across the cultivars: ‘Clery’, ‘Florence’, and ‘Gariguette’ were most affected, while ‘Frida’ was least influenced.