Interaction between paclobutrazol and gibberellic acid, absisic acid, plant growth, yield and seedling quality of cucumber

Paclobutrazol (PBZ) is the most important plant growth reterdand for commercial cucumber seedling production. PBZ effectively control seedling height which is the most important quality factor in cucumber seedlings. However, there are no enough available data on how treating seedlings with PBZ affects seedling quality, fruit yield parameters and PBZ level in cucumber fruits. Determination of PBZ accumulations in cucumber fruits is an important safety issue when it is applied to seedlings. This study was conducted to determine the effects of PBZ on the quality of cucumber (Cucumis sativus L. cv. Maya Fı) seedlings. The study was conducted in the autumn season in 2018 and in the spring season in 2019. In the study, different concentrations (0, 20, 30, 40, 50 and 60 ppm for autumn season and 30, 40, 50 and 60 ppm for spring season), application quantities (0,5 and 1,0 ml) and application times of PBZ were used. PBZ applications were carried out as spray while the cotyledon leaves of the plants became parallel with the ground (7-10 days after sowing-first application) and the first true leaves appeared (10-12 days after sowing-second application). The control plants were treated with distilled water. Seedling height, hypocotyl length, stem diameter, leaf number, seedling fresh and dry weight, root fresh and dry weight, seedling dry matter (%), fruit yield , absisic acid level and the residue level of PBZ in seedlings and fruits were investigated. As a result, PBZ application controlled seedling height effectively. The increased paclobutrazol concentrations caused a decrease in seedling height. The best seedling quality was obtained by applying of PBZ two times at cotiledonary and first true leafy stage with 30 ppm + 0,5 ml. Absisic acid was determined between 0,117 – 0,165 µg.kg-1 in seedlings while it was 0,065 µg.kg-1 in control plants. PBC residue was detected between 0,94 – 5,68 µg.kg-1 in seedlings and 0,013 µg.kg-1 in cucumber fruits. Its residue could not be detected above quantifiable level (0.01 ppm) in cucumber fruits according to European Union Commission. While the fruit yield was 7134,03 g/plant in the control plants, the fruit yield of PBZ applied seedlings was 9414,40 g in per plant in the most appropriate PBZ application.