TACTILE CONDITIONING INCREASES WATER-USE BY TOMATO

Mechanical conditioning can be used to control the height of vegetable and ornamental transplants. Previous research indicated that brushing plants increases cuticular water loss from detached leaves, which may be an indication of decreased drought resistance. This might decrease post-transplant survival of the plants. The objectives of this study were to determine the effect of brushing on growth and gas exchange by tomato (Lycopersicon esculentum Mill.) and quantify whole-plant water use during a slow dry-down period. Tomato plants were grown from seed in a greenhouse during Fall 1995. The brushing treatment started 11 d ays after seeding and consisted of 40 strokes, twice each day. After 3 9 days of treatment, brushing reduced height 32%, leaf area 34%,and sh oot dry mass 29% compared to control plants. Brushing did not affect l eaf gas exchange. Brushed plants had a higher stem water flux than con trol plants during the first 3 days of a 6-day dry-down period. Stem w ater flux was lower than that of control plants later in the cycle, pr esumably because brushed plants used more of the available water durin g the first 3 days. On the third day of the dry-down period, leaf cond uctance of brushed plants was 35% higher than that of control plants, resulting in a 10% higher transpiration rate per unit leaf area. Becau se brushed plants had less leaf area than controls, differences in who le-plant water use were small. Time to wilting was similar for the bru shed and unbrushed plants (6 days after withholding water). It seems u nlikely that brushing would have a major effect on drought tolerance o f plants.