Paclobutrazol soaked marigold, geranium, and tomato seeds produce short seedlings

Bedding plants and many vegetable crop seeds are often sown in plug trays. Some crops, like marigold (Tagetes sp. L.), tend to stretch early after ger mination, especially if grown in low light environments. By the time grower s apply plant growth regulators (PGRs), stretching of the hypocotyl has alr eady occurred and seedling applications are ineffective. Seedling height ma y be controlled by applying the plant growth regulator directly to the seed . Seeds of 'Bonanza Gold' marigold (Tagetes patula L.), 'Cherry Orbit' gera nium (Pelargonium xhortorum L.H. Bailey), and 'Sun 6108' tomato (Lycopersic on esculentum Mill.) were soaked for 6, 16, or 24 hours in paclobutrazol so lutions of 0, 500, or 1000 mg.L-1. After the soak treatment, seeds were dri ed for 24 hours prior to laboratory germination testing or sowing in plug t rays. Percentage of emergence and seedling height were measured 16, 26, and 36 days after sowing. Laboratory germination of treated seeds was less tha n that of the control, which was attributed to the PGR being concentrated a round the seed on the blotters. In contrast, seedling survival was unaffect ed in plugs. The higher concentration of PGR and longer times of soaking in creased growth regulation, but also inhibited emergence of geraniums (71% v s. 99%). When seeds were imbibed 6,16, or 24 hours, growth restriction was 31%, 31 %, and 40%, respectively, for tomato, 61%, 37%, and 76%, respective ly, for geranium and 30%, 38%, and 41%, respectively, for marigold. These r esults indicate that PGR application to geranium, marigold, and tomato seed s may be feasible using a 6- or 16-hour soak in 500 mg.L-1 paclobutrazol. C hemical name used: (+/-)-(R*,R*)-beta-[(4-chlorophenyl)methyl]-alpha-(1,1-d imethyl)-1H-1,2,4-triazole-1-ethanol (paclobutrazol).