Effectiveness of over tree irrigation to control temperature stress in SRA63 Clementines

With the worldwide expansion of Citrus industry, new cultivation areas increase. This expansion may include areas with less favourable climatic condition to Citrus growing. Particularly, high temperatures occurring during fruit set, could determine a decrease in the quality and quantity of productions. The problem was observed in Clementine, which is very sensitive to high summer temperatures. The effect of over-tree irrigation on photosynthesis related characteristics was studied on 'SRA 63' Clementines grown in the South Sardinia (Italy). Results showed that over tree irrigation influenced the microclimate inside the canopy affecting air temperature and relative humidity. Moreover, evaporative cooling reduced leaf temperature down to 6 degrees C. Photosynthetic activity showed a significant increase as a consequence of the reduction of leaf temperature. Net photosynthesis in control plants was always very low (between 1-2 mu mol CO2 m(-2) s(-1)), while it was significantly higher in evaporatively cooled plants. Over tree irrigation was effective in keeping chlorophyll levels significantly higher in evaporative cooled plants. Chlorophyll content was between 1.5 and 3.5 mg/g of fresh weight.