Effects of water stress at different growth stages on greenhouse tomato yield and quality

Tomatoes (Lycopersicon esculentum Mill. cv. Sunstart) were grown in a greenhouse during Summer 1999 and again in Winter 2000. Two available soil water (ASW) deficit thresholds, 65% and 80%, at which plants were irrigated to field capacity were factorially combined with five irrigation timing patterns: 1) no water stress; 2) stress throughout the entire growing season; 3) stress during first cluster flowering and fruit set 4) stress dur- ing first cluster fruit growth; and 5) stress during first cluster fruit ripening. Crop yields, water use efficiency, as well as maximum and minimum equatorial fruit diameters and fruit height were measured. Quality parameters of soluble solids, pH, and fruit color were also measured. Water stress throughout the growing season significantly reduced yield and fruit size, but plants stressed only during flowering showed fewer but bigger fruit than completely non-stressed plants. Consequently, on a weight basis the stressed at flowering and nonstressed plants had similar yields. Nonstressed and flowering-stressed fruit showed lower soluble solids and a lighter color of red ripe fruit than the other stress treatments. No significant differences in yield or quality were found between the two stress levels (65% vs. 80% ASW depletion before irrigation). Water stress only during flowering resulted in better yields and quality than stress at other specific developmental stages or at all times, but equal or poorer yields and water use efficiency than nonstressed plants. quality of greenhouse tomatoes was studied during Summer 1999 and again in Winter 2000. In both years, identical experiments were set up in the Macdonald Campus greenhouse of McGill Univ. in Montreal, Quebec. Two available soil water (ASW) deficit levels, 65% and 80%, at which irrigation up to field capacity was implemented were factorially combined with five irrigation timing patterns: (1) no stress (NS); (2-4) stress during flow- ering and fruit set (F), fruit growth (G), or fruit ripening (R) of the first cluster; and (5) stress from flowering through ripening of the first cluster (FGR), in a randomized complete- block design with four replicates. This resulted in nine treatments, as the "NS" controls for both 65% and 80% ASW were identical and hence reduced to a single treatment. Plants were grown in 24-cm-high polyethyl- ene pots that had an upper diameter of 28 cm and a diameter of 22 cm at the base, and a mean inner diameter of 24.5 cm in the por- tion containing soil (soil volume of roughly 9.6 L/pot). Each pot was placed in a 55 × 28.5 × 7-cm white plastic seedling tray on the concrete floor of the greenhouse, in order to trap any irrigation overflow or soil mate- rial escaping from the drainage holes at the base of the pots. Plants were spaced 60 cm apart both within and between rows. Natural lighting was supplemented with overhead lighting to provide a daylength of 16 h. The overhead lighting consisted of 400-W (fixtures rated for 485W, 208V, 2.5 A) high-pressure sodium bulbs (P.L. Light Systems, Canada), resulting in a photosynthetic photon flux (PPF) at canopy level of s 60 µmol·m -2 ·s -1 . The daytime temperature was maintained at 25 ± 2 °C, and the nighttime temperature at 18 ± 2 °C. Relative humidity (RH) was main- tained at 65% ± 5% throughout the growing season.