Effects of Osmotic Potential in Nutrient Solution on Diurnal Growth of Tomato Fruit

Tomato fruit on plants grown in circulating nutrient solution exhibited a diurnal cycle in growth rate, measured as a change in diameter, with a maximum during thc day. The diurnal growth cycle was less evident in those fruit grown at high electrical conductivity (17 mS), or on days of reduced irradiance. Girdled fruit of low conductivity plants grew at a much reduced rate with a diurnal cycle in reverse to that of ungirdled fruit, while girdled fruit of high conductivity plants showed no diurnal growth. The evidence suggests that phloem and xylem water transport into fruit operate on opposite diurnal cycles. Partitioning of available xylem water in detached fruit between the calyx and berry, as well as within the berry, was determined by berry size and relative humidity in the air. Although berry transpiration rate was unaffected by conductivity treatment during plant growth, water uptake capacity was greatly reduced in the berry from high conductivity plants, suggesting an increased resistance in the xylem transport system within the fruit.