The effects of brushing, drought stress andpaclobutrazol applications on seedling growth andquality in tomato, cucumber and crisp lettuce

Tomato, cucumber and lettuce cultivation is mostly done using commercial seedlings. In commercial seedling production, paclobutrazol (PBZ) is used as a plant growth regulator to control the seedling height and improve quality. PBZ is a synthetic chemical and carries significant risks for human and environmental health. There is a need for environmentally friendly alternative practices in seedling cultivation. In this study, it was investigated whether drought stress and brushing can be used instead of PBZ in the cultivation of tomato, cucumber and lettuce seedlings. In the study, Atakan Fı indeterminate tomato variety, Olay Fı greenhouse cucumber variety and Maritima Fı lettuce variety were used. PBZ (Cultar 250 g/l PBZ, 23% w/w) was used as synthetic plant growth inhibitor, and peat+perlite mixture (70% peat and 30% perlite) was used as seedling growing medium. Tomato seedlings were grown in 216 celled plug-trays, cucumber seedlings with 150 celled plug-trays, and lettuce seedlings were grown in 384 celled plug-trays. 140 cm telescopic extendable microfiber soft head gray dusting brush was used for brushing. Brushing began when the first true leaves were fully formed. Brushing was applied between 08:00 in the morning and 18:00 in the evening, as 3 applications at intervals of 2, 5 and 10 hours, for 2 minutes and at a speed of 30 rpm. Drought stress was initiated when the first true leaves were formed. Irrigation was done 2 and 4 hours after wilting symptoms were seen in the plants. The wilting was determined visually. Brushing and drought stress treatments were continued for 15 days. No water restrictions were applied to control plants and PBZ-treated plants. After sowing, the plants were irrigated twice a day with a boom irrigation system without using fertilizers. Irrigation was done with nutrient solution 7 days after germination. The nutrient solution has been prepared 10:52:10:10:10 (N:P:K:Ca:Mg) for the first week, 20:10:20:10:10 (N:P:K:Ca:Mg) after 1 week. The irrigation water concentration was adjusted to be EC 1.4 mmhos/cm for the first 15 days, 1.8 mmhos/cm for the next 1 week, and 2.0 mmhos/cm thereafter. In the study, seedling height, hypocotyl height, number of leaves, stem diameter, root length, % dry weight, biomass, chlorophyll content and color measurements were made. As a result of the experiment, in the evaluations made by considering the seedling quality parameters, brushing application with 2 hours intervals in cucumber and tomato, and drought stress application for 2 hours in curly leaf head salad were determined as the most effective applications in terms of seedling quality and applicability of the method. As a result, drought stress and brushing have been effective methods to replace PBZ in seedling cultivation.