Paclobutrazol soaked ornamental kale seeds produce short seedlings

Ornamental kale (Brassica oleracea) 'Nagoya Red' seeds were soaked in water or four paclobutrazol solutions for 5, 45 and 180 minutes. Treated and non-treated seeds were sown one seed per cell in 288 plug trays filled with a soilless plug mix. Percentage usable plugs and seedling heights were measured 13 and 20 days after sowing. To study the long term effect of paclobutrazol on kale plants, four seedlings per replication per treatment were transplanted 28 days after sowing in 15.3 cm diameter plastic containers using a commercial soilless medium. As long as growth regulator concentrations were not greater than 200 mg L-1 and times of soaking were not longer than 45 minutes, the percentage of usable transplants was not significantly reduced. Significant trends in plug height reduction were measured with increasing concentrations of paclobutrazol. This significant trend was not noticeable on mature plants 116 days after planting. It was also noted that plants from seeds soaked with paclobutrazol at concentration 500 mg L-1 or higher had thicker, straighter stems. It was speculated that after sowing, the active ingredient diffuses from the seed coats into the growing medium and is then absorbed by the seedling root after germination and emergence.