High vapour pressure deficit influences growth, transpiration and quality of tomato fruits

Plants were grown in two glasshouse compartments under two vapour pressure deficit (vpd) levels: low vpd was obtained by increasing air humidity with a fogging system, and high vpd was obtained during sunny hours in a greenho use where air humidity was not controlled. The mean value, of the six dries t hours of the day concerning the growing period of the fruits considered, was 1.6 kPa under low vpd and 2.2 kPa under high vpd conditions. Over the w hole experimental period, the difference in mean hourly temperature never e xceeded 0.8 degrees C. The oldest leaves were removed to different extents in different plots to analyse whether a different leaf/fruit ratio could mo dify the effect of high vpd. Fruit growth and transpiration rates greatly varied during daylight hours; these variations were enhanced under high vpd condition. The increase in vp d produced a significant reduction in fruit fresh weight and in fruit water content, and an increase in soluble solids, while fruit dry weight was not affected. High vpd also enhanced the variability of fruit weight. When mor e leaves were removed the effect of vpd on soluble solids and water content was less important. The study shows that during summer, as vpd increases from 1.6 to 2.2 kPa, e ffects can be observed both on tomato growth and quality characteristics. T herefore, an improvement of the control of vpd for the optimisation of gree nhouse tomato production is discussed. (C) 2000 Elsevier Science B.V. All r ights reserved.