Growth Regulation by Air Stream-Based Mechanical Stimulation in Tomato (Solanum Lycopersicum L.) Part I – Optimization of Application Frequency and Intensity

Stem elongation control is a fundamental requirement for the production of high-quality seedlings in terms of plant compactness and stability. It is known that with mechanical stimulation the stem elongation of seedlings can be inhibited. In this study a custom-built air stream applicator was used to apply intermittent stimuli to tomato ( Solanum lycopersicum cv. ‘Romello’). Tomato plants were cultivated under greenhouse conditions for 21 days and then exposed to intermittent air stimuli at different air stream application frequencies (8, 24, 40, 56, 72 and 80 d -1 ) and different air stream velocities (0.7 – 6.0 m s -1 ) for 14 days. Tomato plants responded with a inhibition of stem elongation of approximately 31% compared to the untreated control, without a systematic dose-response relationship related to application frequency. In contrast, stem elongation inhibition was significantly affected by air velocity, with a sigmoid dose-response relationship with negligible effects up to 2.0 m s -1 , followed by a steep increase in the reduction effect up to 4.7 m s -1 and a fading of the effect at 36 % reduction for air velocities beyond that. Dry mass of leaves, stems, and petioles was reduced by approximately 10%, 41%, and 19%, respectively, after 14 days of treatment at a gradually increasing air velocity from 3.5 m s -1 at day 0 to 6.1 m s -1 at day 14 and an application frequency of 8 d -1 . Root dry mass was less affected by the air stream application, but showed a slight tendency to decrease compared to control plants