ABSTRACT During production of plug transplants, the high plant density results in rapid stem elongation as the plants try to outgrow one another. The resulting tall, weak-stemmed plants are difficult to transplant and are easily damaged. One techniques that can prevent excessive elongation is mechanical stimulation by brushing. Wide adoption of brushing is limited by a lack of information on how plants respond to variations in application of the technique. This investigation examined how tomato (Lycopersicon esculentum cv ňOh8245╝) seedling growth responded to varying doses of mechanical stimulation, varying intervals between brush strokes during stimulation, the time of day that stimulation was applied and the growth stage at which application was started. Seedlings were grown in 288-cell flats at 2100 plants per m2. Different daily doses from 0 to 40 brush strokes were applied from canopy closure until the untreated plants reached a canopy height of 15 cm. The final height was reduced by about 20% for all brushed treatments, with little further effect with more than 10 strokes per day. Intervals between strokes as long as 10 minutes resulted in the same reduction in the rate of stem elongation as did the same daily dose applied in one continuous treatment. The treatments were similarly effective whether applied in the morning or in the late afternoon. Treatments begun at a canopy height of 6 cm (canopy closure), at 8 cm or at 10 cm gave similar reductions in the rate of stem elongation. The plants grew 6 mm per day when they were not treated and 3 mm per day during treatment. Therefore, the final height was directly related to the number of treatment days. Stimulation appears to be sensed and integrated over at least half an hour and the reduction in the rate of stem elongation expressed over the subsequent daily cycle of growth. All of the results indicate that there is substantial flexibility in applying brushing for controlling elongation in tomato transplants.
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