The influence of growing season on fruit yield and quality of greenhouse melon (Cucumis melo L.) grown in nutrient film technique in a Mediterranean climate

The influence of growing season on some physiological and biochemical varia tes related to fruit yield and quality was investigated in melon (Cucumis m elo L.) plants cultivated in nutrient film technique in a greenhouse locate d at Pisa, Central Italy, from mid-March to mid-June, or from mid-July to m id-September. Compared with spring, the plants grown in summer exhibited fa ster growth and development, but produced fewer fruits of larger size and p oorer quality due to reduced sucrose content. Growing season did not affect total leaf area, but dry-matter production and partitioning to the fruits was significantly lower in summer than in spring. Summer fruit ripened with in 30-35 d after anthesis, about 14 d fewer than in spring. Higher average temperature was presumably responsible for earlier fruit maturation in summ er, as in both seasons all melons were harvested after 450-500 degree-days (base temperature of 12 degrees C) from anthesis. Fruit swelling did not ac count for the reduction of sucrose content in summer-grown fruits, which in stead was due to shortage of photoassimilate supply and inadequate sucrose synthesis, as suggested by the rate of leaf gas exchange and the activity o f sucrose phosphate synthase in the fruit flesh, as determined during the f inal stages of fruit development. Lower solar radiation was presumably resp onsible for the reduced leaf carbon assimilation in summer, as growing seas on did not affect leaf turgor, stomatal conductance, mineral status and chl orophyll content.