Basil seedling production environment influences subsequent yield and flavor compound concentration during greenhouse production

Abstract

Radiation intensity and carbon dioxide (CO2) concentration can be precisely controlled to manipulate plant yield and quality. Due to increased plant densities during seedling production, fewer inputs per plant are required, creating the potential to increase production efficiency. Therefore, the objectives of this research were to: 1) quantify the extent radiation intensity and CO2 concentration under sole-source lighting influence morphology and yield of sweet basil (Ocimum basilicum) seedlings, and 2) determine if differences in morphology, yield, and volatile organic compound (VOC) concentration persist after transplant in a common environment. Sweet basil 'Nufar' seedlings were grown in growth chambers with target CO2 concentrations of 500 or 1,000 μmol·mol‒1 under light-emitting diodes (LEDs) providing target photosynthetic photon flux densities (PPFD) of 100, 200, 400, or 600 μmol·m‒2·s‒1 for 16 h per day. After two weeks, seedlings were transplanted into a common greenhouse environment and grown until harvest. At transplant and three weeks after transplant (harvest), growth and developmental differences were quantified along with key terpenoid and phenylpropanoid concentrations at harvest. Radiation intensity and CO2 interacted influencing many aspects of plant morphology, though CO2 concentration effects were less pronounced than those of radiation intensity. As radiation intensity during seedling production increased from 100 to 600 μmol·m‒2·s‒1, basil seedlings were 38% taller, had a 713% larger leaf area, and had 65% thicker stems; at harvest, plants were 24% taller, had 56% more branches, 28% more nodes, 22% thicker stems, and weighed 80% more when fresh and dry. Additionally, after growing in a common environment for three weeks, eugenol concentration was greater in plants grown under a PPFD of 600 μmol·m‒2·s‒1 as seedlings compared to lower intensities. Therefore, increasing radiation intensity during seedling production under sole-source lighting can carry over to increase subsequent yield and eugenol concentration during finished production.

Fig 1. Spectral quality of broad-spectrum light-emitting diode (LED) fixtures providing 20:40:40 blue:green:red radiation ratios (%), a red:far-red ratio of 13:1, and target radiation intensities of 100, 200, 400, or 600 μmol·m^–2·s^–1.

Fig 2

Radiation intensity (100, 200, 400, or 600 μmol·m^–2·s^–1) for a 16-h photoperiod to create daily light integrals of (6, 12, 23, or 35 mol·m^‒2·d^‒1) and CO₂ concentration (, 500 μmol·mol^–1; 1,000 μmol·mol^–1; pooled) effects on sweet basil ‘Nufar’ (Ocimum basilicum) seedling height (A), dry mass (B), leaf area (C), fresh mass (D), and stem width (E) two weeks after sowing. Lines represent linear or quadratic regressions. Symbols (means ± se) represent measured data (and, n = 30; n = 60). *, **, and *** indicate significant at P ≤ 0.05, 0.01, or 0.001, respectively.

Fig 3. Radiation intensity (100, 200, 400, or 600 μmol·m^–2·s^–1) for a 16-h photoperiod to create daily light integrals of (6, 12, 23, or 35 mol·m^‒2·d^‒1) and CO₂ concentration (, 500 μmol·mol^–1; 1,000 μmol·mol^–1; pooled) administered during seedling production, two weeks after sowing.

The figures depict seedling treatment effects on sweet basil ‘Nufar’ (Ocimum basilicum) height (A), branch number (B), stem width (C), node number (D), dry mass (E), and fresh mass (F) three weeks after transplant into a common enviornment. Lines represent linear or quadratic regressions. Symbols (means ±se) represent measured data (and, n = 30; n = 60). * and *** indicate significant at P ≤ 0.05 or 0.001, respectively.

Fig 4

Concentrations [ng·mg^‒1 dry mass (DM)] of 1,8 cineole (A), linalool (B), eugenol (C), and methyl chavicol (D) of sweet basil ‘Nufar’ (Ocimum basilicum) seedlings grown under radiation intensity (100, 200, 400, or 600 μmol·m^–2·s^–1) for a 16-h photoperiod to create daily light integrals of (6, 12, 23, or 35 mol·m^‒2·d^‒1) for two weeks and then transplanted in a common greenhouse environment and grown for three weeks. Each symbol represents the mean of 20 plants ± se. Lines represent linear or quadratic regression. ** indicates significant at P ≤ 0.01.