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Article

Smoke Compounds Compensate for Light Irrespective of Its Spectrum in Positively Photoblastic German Chamomile Seeds, Although Red Light Is Crucial

by
Renata Bączek-Kwinta
1,* and
Sławomir Michałek
2
1
Department of Plant Physiology, Breeding and Seed Science, University of Agriculture in Kraków, ul. Podłużna 3, 30-239 Kraków, Poland
2
Department of Botany and Plant Physiology, University of Life Sciences in Lublin, 13 Akademicka Street, 20-950 Lublin, Poland
*
Author to whom correspondence should be addressed.
Agronomy 2025, 15(3), 700; https://doi.org/10.3390/agronomy15030700
Submission received: 27 January 2025 / Revised: 7 March 2025 / Accepted: 10 March 2025 / Published: 13 March 2025
(This article belongs to the Special Issue Advanced Lighting Strategies for Controlling Crop Development and Quality)
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Abstract

:
German chamomile (Matricaria chamomilla L.) is not only considered a weed but also an important crop cultivated for the pharmaceutical industry. Chamomile seeds are positively photoblastic and must be sown on the soil surface. However, heavy rainfall can bury the seeds, resulting in uneven germination and partial yield loss. To address both agricultural and scientific aspects, we applied various light sources with different spectra ranging from 400 to 720 nm versus darkness, as well as smoke compounds formulated in smoke water (SW), to chamomile seeds. Our results indicate that a high proportion of red light within the spectrum is crucial for seed germination and seedling establishment. Fluorescent lamps were the least effective due to their high blue light content, highlighting the need to use white or red LEDs in experiments with chamomile seeds. The smoke compounds present in SW compensated for the absence of light, increasing seed germination by 20% in the dark, and their mode of action was additive to light, suggesting that they share the same signaling pathway. The effect of SW on seeds was stimulatory regardless of the light regime, suggesting that smoke formulations may act as a priming factor for chamomile seeds.

1. Introduction

Chamomile is one of the oldest and most important medicinal plants used throughout the world [1]. Its raw material (anthodia and sometimes the whole herb) and essential oil, rich in chamazulene, α-bisabolol, and other biologically active compounds are also used in the pharmaceutical, perfumery, cosmetics, and food industries. Because of its industrial importance, it has been the subject of various agronomic and physiological studies [2,3,4]. Due to their positive photoblastism, chamomile seeds must be sown on the soil surface, but heavy rainfall can cause them to be buried in the soil, leading to uneven germination and partial yield loss [5]. Recently, the risk of unpredictable heavy rainfall has increased with climate change [6].
The physiological mechanism of the seed photoblastism is based on the perception of light by specific photoreceptors located in the embryo, namely phytochromes (phy) and cryptochromes (cry). Phy consist of a bilin chromophore bound to specific proteins. They exist in different photoconvertible forms, among which phyB is responsible for the positive red light response in the seeds of some species, while phyA is responsible for far-red sensitivity and the so-called very low-fluence response (VLFR) in the others [7]. This regulates species composition according to the light spectrum within the plant canopy or in the soil after tillage [8]. Some species, such as the dicot Cleome gynandra of African origin, produce seeds sensitive to blue light due to cry photosensitivity [9,10]. A photoperiod-sensitive Arabidopsis thaliana ecotype, Columbia, is also sensitive to continuous blue light, and in this case, not only cry but also some phy are required for blue light-dependent germination promotion [9,11]. Within plant cells, the photoreceptor response involves gene transcription and/or expression and the activation of specific epigenetic factors, such as chromatin remodeling and induction of specific miRNAs. This results in changes in the phytohormonal balance, where the level of abscisic acid (ABA), which prevents germination, decreases, while that of gibberellin (GA) increases [8].
Interestingly, positively photoblastic seeds of some species of different origins and taxa that respond to light can also germinate in the dark when treated with smoke or smoke-derived compounds. Such phenomenon was observed in Lactuca sativa, Heteropogon contortus, Hibbertia sp., Arctostaphylos pungens, and Solidago sp. [5,10,12,13,14,15]. For chamomile, comparisons have only been made for darkness and daylight [5]. The use of smoke volatiles, formulations, and pure smoke compounds with physiological activity to improve germination, seedling vigor, and various plant life processes is becoming increasingly popular [16,17,18,19,20,21]. The advantage of using smoke formulations is their low cost and the lack of negative environmental side effects.
In the agricultural field, after sowing seeds, the natural light spectrum is broad and uniform at any given moment. LED (light-emitting diode) seed lighting is a technique widely implemented in biology, agriculture, horticulture, forestry studies, and plant cultivation [10,22,23,24,25]. In artificial seed illumination for research purposes, other light sources such as fluorescent lamps, daylight, or high-pressure sodium lamps (HPS) are also used. However, these can introduce bias in the research, as seed responses differ under different light regimes [21]. However, their use in one specific experiment allows the physiological mechanism of action of specific spectral bands to be estimated. For this reason, we contrasted different light spectra with darkness. Knowing that smoke can substitute for light in some species, we decided to study its interaction with different light regimes. To the best of our knowledge, the combination of smoke formulations and different light sources has never been proposed to study photoblastism in chamomile. Therefore, our research is aimed both at the practical application of smoke formulations in chamomile cultivation and determining which bands of the visible light spectrum are responsible for seed germination and seedling growth in this species. We also hope to increase our knowledge of light and smoke signaling.
Our first hypothesis was that red light (620–700 nm) would stimulate chamomile seed germination and seedling growth more than the other light bands. The second was that smoke compounds formulated in a water extract (smoke water, SW) could compensate for the light, resulting in better germination and seedling performance.

2. Materials and Methods

2.1. Plant Material, Illumination Regimes, and SW Treatment

The experiment was conducted in July–August 2020 on seeds of Matricaria chamomilla L. (tetraploid cultivar ‘Złoty Łan’, supplier: Zakład Hodowlano-Nasienny Polan, Kraków, Poland, expiry date: 2021). The weight per thousand seeds was 0.0893 g. Seeds of similar size were selected (small seeds were discarded) and sown on 9 cm diameter Petri dishes lined with filter paper (medium type). The seeds were soaked in distilled water or smoke-saturated water (two treatments, details below) and either incubated in the dark under aluminum foil or illuminated by different light sources (i.e., nine light regimes). The experiment consisted of 18 experimental units (objects). Each object contained three (3) replicates (Petri dishes of 20 seeds each), for a total 1080 seeds. Daylight or specific lamps were used: white fluorescent lamps (58 W, 840, Philips, Eindhoven, The Netherlands), high-pressure sodium lamps (HPS, 600 W Bloom, Secret Jardin, Manage, Belgium), warm white LEDs (12 diodes), narrow-band red LEDs (12 diodes), and narrow-band red LEDs accompanied by narrow-band blue LEDs (resulting in different shades of purple; 92% red = 11 red and 1 blue LEDs, 83% red = 10 red and 2 blue LEDs, and 75% red = 9 red and 3 blue LEDs). We chose different red/blue ratios to optimize conditions for further experiments, as this has not yet been elucidated for chamomile seeds. The selection of light sources was based on our previous research, including LED lighting studies on lettuce [26]. All LEDs had a 1 W radiant flux (Epiled, Wrocław, Poland). Daylight PPFD was 50–200 μmol (quantum) · m−2 · s−1, fluorescent lamps provided 200 μmol (quantum) · m−2 · s−1, and in the other light regimes provided 400 μmol (quantum) · m−2 · s−1. PPFD was regulated by adjusting the height (position) of the lamps to achieve approximately 200–400 μmol (quantum) · m−2 · s−1 of artificial light in each case and to standardize the temperature at the seed level, as fluorescent lamps give off more heat than LEDs and chamomile is a thermophilic species. Measurements were taken at the Petri dish level, with the light meter directed perpendicularly to the light source. The spectral composition of the light sources was determined using a diode spectrometer (USB 4000, Ocean Optics, Dunedin, FL, USA), as shown in Figure 1. Light intensity measurements were performed using the Quantum Meter TES-1339P (TES Electrical Electronic Corp., Taipei, Taiwan).
Distilled water (control) and smoke-saturated water (smoke-water; SW) were used. SW was prepared prior to the experiment by bubbling smoke from the burning of 100 g of dry meadow grass in 300 mL of distilled water for 2 h and diluting the filtered extract with distilled water at 1:1000 (v/v) [19]. The method was similar to that described, for example, by Kulkarni [17]. All SW solutions were protected from light at all times, and their stimulatory effect on seeds and seedlings of different species was previously tested [19]. Seeds were treated with SW once, while control seeds were moistened with distilled water (5 mL per Petri dish in all cases). Starting on day two, seeds were treated with distilled water to maintain stable humidity. The temperature and humidity in the incubation rooms were standardized, ranging from 20 °C at night to 25 °C during the day, with a photoperiod of 16 h/8 h day/night, according to ISTA [27].

2.2. Germination Indicators and Morphometrical Analyses

Visible radicle protrusion was defined as germination initiation. The germinated seeds were counted daily between 2 and 7, and the germination percentage was calculated each day.
Based on the data from days 2 to day 7, the following germination indicators were obtained: Final Germination Percentage (FGP), Germination Rate Index (GRI, ref. [28]), and Germination Index (GI, ref. [29]). The latter two were calculated as follows:
GRI = g2/d2 + … + g7/d7 (Maguire’s index),
GI = (7 × n2) + (…) + (2 × n7).
where:
  • g2, … and g7 = the percentage of germinated seeds on day 2, …. and day 7
  • n2, … and n7 = the number of germinated seeds on day 2, …. and day 7,
  • d2, …d7 = the number of days,
  • 7, …, 2 in GI = weights assigned to the seeds germinated on the day 2, …, and 7, respectively.
Morphometrical analyses (post-germination indicators) were performed on days 7 and 14, measuring seedling length and seedling biomass according to ISTA [27]. Length was measured on the five longest seedlings from each Petri dish (a total of 270 measurements), and biomass was measured on the ten longest seedlings from each Petri dish (540 measurements in total). The largest seedlings were selected to minimize the error in the measurements.

2.3. Statistical Analysis

All data were processed using Excel 2016 (Microsoft Corporation, Redmond, WA, USA) and Statistica 14 (Tibco Software, Palo Alto, CA, USA). Percentage data were arcsin transformed before further analysis. The Kolmogorov-Smirnov test was used to test the normality of the data. ANOVA was performed for datasets with a normal distribution, and the nonparametric Kruskal-Wallis test and multiple comparisons of means within treatment were used otherwise. For comparisons between two means, the Student’s t-test was performed at p = 0.05.

3. Results

3.1. Light Spectrum Recordings

The spectral characteristics of the illumination regimes within the 400–720 nm range are shown in Figure 1. For daylight, the relative spectral response was high (50–100%) throughout the wavelength range. A broad and large peak of 100% was present within the blue-green spectrum (between 470–500 nm). Other wavelengths were represented by the relative spectral response of 50–80%.
Fluorescent lamps also exhibited a broad blue-green peak, though smaller than that of daylight, 50% of the relative spectral response, with a larger peak (69%) within the red spectrum at 600–620 nm.
The spectrum of HPS lamps lacked blue light and displayed a series of narrow peaks from green to yellow (500, 530, 560, 580 nm), followed by an orange light (610 nm). The peaks between 560 and 610 nm were high (80–100% of the relative spectral response).
Spectral recordings for white LEDs showed a small peak for the blue light at 470 nm and a broad large peak within the green to orange spectrum, with the maximum value of 100% at 580 nm (yellow light).
All red LEDs gave a maximum relative spectral response at 670 nm (100%). The higher the number of the blue diodes that accompanied the red ones within the whole set (resulting in more purple than red light), the higher the peak at 450 nm, although it was rather small (highest for 75% red LEDs, at 21% relative spectral response; see Figure 1).
In summary: (1) blue light was absent in the HPS and red LED illumination regimes. In the others, blue light was present but with different peaks, maximum wavelengths, and ratios to red light. The highest intensity of the blue light was in the daylight regime, lower under the fluorescent lamps and then for white warm diodes; (2) red light (>620 nm) was present in all illumination regimes but with different intensities and wavelength peaks, although in all cases it was more than 50% of the relative spectral response; (3) in all illumination regimes except the 100% red LEDs, the light spectrum within 500 and 600 nm (green to orange) was present.

3.2. Germination Pattern

The seeds germinated quickly, and even in the dark control treatment, the germination percentage on day 2 was 10, while in the illuminated controls, it was over 40% (Figure 2). From the ANOVA results (Table 1), it can be seen that both the illumination regime and the SW treatment were significant factors that stimulated germination at the early stage of the experiment (day 2). The interaction of the factors was not significant, indicating that the SW-treated seeds germinated better than the control objects regardless of the illumination regime (Table 1, Figure 2).
Considering the pattern of illumination regime objects, the germination percentage was the lowest in darkness (10% for control and 27% for SW, Figure 2). Each type of illumination applied increased the parameter, with the highest values (65% for control and SW) obtained under white LEDs within a wide range of the spectrum. Red LEDs and 75% red LEDs (purple) illumination resulted in germination percentages of 57–58%, regardless of the treatment. Germination under other light sources was at 35–47% for control and 50–57% for SW.
SW stimulated germination in darkness. Direct comparison of the dark control and SW-treated seeds revealed a threefold increase in germination percentage following SW application (Figure 2, Student’s t-test). When any light source was applied, individual differences within the illumination regimes were smaller and insignificant but became significant after data aggregation in ANOVA (Table 1).
The lack of interaction between factors (Table 1) and the similar pattern of control–SW relationships across light regimes (Figure 2) indicate that early-stage germination was influenced by smoke water (SW) irrespective of the light quality, quantity, or lack thereof (darkness).
Further germination recordings (from the day 3 to day 7) showed the impact of light in general, but neither its spectrum nor the SW treatment affected the final germination percentage (FGP, Table 2 and Table 3). The FGP values for all illuminated objects ranged from 80–88%, while those in darkness were 74 (73% for control and 75% for SW). When analyzing differences between light regimes, the Kruskal-Wallis test revealed a difference between darkness and white LED-illuminated objects (H = 26.27, p = 0.0009, Table 3).
On the other hand, germination parameters GRI and GI showed the influence of the light spectrum, smoke compounds, or both (Table 1 and Table 2). The illumination regime had a stronger effect on GRI than the treatment (higher F and lower p values for the illumination regime factor, Table 1). GRI was highest for seeds under white light and 75% red LEDs (values: 126–128, Table 2) and lowest for dark-germinated seeds (GRI 92–98). SW increased GRI values irrespective of light composition (interaction of factors not significant, Table 1). A similar response was obtained for GI (Table 1 and Table 2).

3.3. Seedling Morphometry

As with the germination parameters, the morphometric parameters of seedlings obtained on days 7 and day 14 also revealed the influence of both factors and the lack of their interaction. The strength of the effect of the treatment or illumination differed depending on biomass and length (Figure 3, Table 1 and Table 3).

3.3.1. Seedling Biomass

The impact of SW treatment was stronger than that of the illumination regime (Table 1), as the F and p values were higher for the treatment factor. It was also additive (synergistic) with light (interaction of factors insignificant, Table 1; see the pattern of column heights in Figure 3).
On day 7, in the direct comparison of the effect of SW on the seeds within the illumination regime, 7 out of 9 individual control/SW differences were significant according to the Student’s t-test (Figure 3A).
Regarding light regime-related patterns, it was similar for both control and SW treatments (Figure 3A and Table 1). The lowest biomass was found in seedlings grown in darkness (153 mg and 183 mg for control and SW, respectively). The highest biomass was observed in seedlings grown under red LEDs (control: 280 mg, SW: 320 mg). For red light accompanied by blue light, the more red in the combined purple LED setup, the greater seedling biomass. Daylight, fluorescent, HPS, and white LEDs resulted in lower and similar values (Figure 3A).
On day 14, the pattern of changes was identical to that of day 7. As before, treatment with SW stimulated seedling biomass, although in this case some differences within each illumination regimes were less pronounced than before, according to the results of the Student’s t-test (Figure 3B).

3.3.2. Seedling Length

Seedling length varied with the light regime and was stimulated by SW during the experiment (Table 3, Figure 3C,D).
On day 7, control seedlings emerging from dark-germinated seeds were the largest (14.9 mm, group a according to the Kruskal-Wallis test and multiple comparison of means, Figure 3C), while those from the fluorescent light were the shortest (6.1 mm, group b). The lengths of other seedlings ranged from 7.1 mm to 13.6 mm (ab group). A similar effect was obtained for SW, as the longest seedlings were those in darkness (31.1 mm, group A), the shortest under fluorescent light (8.7 mm, group B), and the others belonged in the both groups.
SW treatment resulted in seedling enlargement 2 to 3 times larger than those in the control (Figure 3C). Similar to germination percentage and seedling biomass, the effects of light and SW were synergistic.
By day 14, the seedling length pattern was almost identical to that of day 7 (Figure 3D, Table 3).

4. Discussion

4.1. Photoblastism and Smoke-Induced Germination in Chamomile Seeds—Opportunities and Limitations

Our research indicates that chamomile seeds are a good model for studying photoblastism, as they respond to light, germinate quickly, and in large numbers. On day 2, the germination percentage ranges from 30 to 70%, and by day 7, the FGP reaches almost 90%, which is a high value. So far, the photoblastic response of chamomile has not been studied, so our work lays the foundation for further experiments on the mechanism of seed germination of this species.
The use of different light sources, compared to daylight and total darkness, allowed us to estimate which spectral characteristics are more stimulating for chamomile seeds than others, which may be useful in further laboratory experiments. In our experiment, the maximum PPFD of all illumination regimes at the seed level was approximately 200–400 μmol (quantum) · m−2 · s−1. These values are comparable to field light conditions and are sufficient to elicit a developmental response in seeds, which can perceive light two orders of magnitude lower than that we used in our experiment [22,25,29,30,31]. Based on our results, the ratio of blue to red light within the spectrum should not be less than 1:5 to improve germination. For this reason, we recommend using white LEDs for germination experiments.
The use of smoke formulation in the context of improving chamomile seed germination and seedling growth has not yet been established. Our research shows that smoke water (SW), in the form of an aqueous preparation, stimulates both processes. This means that smoke formulations can be used as priming factors for this species, either in the field to counteract the negative effects of accidental seed burial in the soil or prior to sowing to enhance seedling performance. However, the results of the laboratory experiments should be confirmed through field trials.
In addition, since non-standardized smoke formulations made from different materials may give different results [21], the use of smoke-isolated compounds, such as karrikins (KARs), nitriles, and phenolic acids derivatives with a phytohormone-like mode of action is also recommended. The chemical composition of smoke formulations can be determined chromatographically (using liquid chromatography/mass spectrometry systems) ([21], and references therein).
The additive (synergistic) effect of SW and light shows that during chamomile seed germination and the early growth of its seedlings, light can be replaced by smoke. This supports our hypothesis that smoke compounds can substitute for light in this species, a concept previously postulated by Bączek-Kwinta [5,21]. It also suggests that the signaling pathway leading to germination is shared by both light and smoke. This can be confirmed using SW and/or KARs in signal transduction mechanism experiments, but at the moment, it encourages the inclusion of chamomile in the list of model species for photoblastism studies.

4.2. Potential Mechanism of Light Signaling in Chamomile Seeds

It is well known that seed germination is inhibited by the phytohormones auxin (AUX) and abscisic acid (ABA), whereas germination is stimulated by gibberellin (GA) [8]. At the early stage of chamomile germination, the broad spectrum of light is effective, but it is distinctive that all light sources provide red light (>620 nm) at a level of at least 50% of the relative spectral response. Hence, chamomile belongs to the group of plants whose seed germination mechanism is based on the perception of red light by phytochromes, similar to lettuce or Arabidopsis seeds, for which the molecular mechanism has already been established [8,9]. Exposure of seeds to red light results in the conversion of phytochrome red (Pr) to phytochrome far-red (Pfr), and high levels of Pfr trigger signal transduction toward phytohormonal changes. In this case, the genes responsible for AUX and ABA biosynthesis (YUCCA and ABA2, respectively) are downregulated, while those for GA (GA3ox1 and GA3ox2) are upregulated, resulting in cell wall extension and elongation. Other effects are cell division, hydrolysis of storage materials, and biosynthesis of new proteins [7,32].

4.3. Seed Germination Parameters Under the Influence of Light and SW

For fast-germinating seeds, as in our experiment, only a limited number of germination parameters can be calculated. The GRI and GI obtained from the data collected over seven days of the experiment indicate seed vigor, which comprises not only germinability but also the ability of seeds to establish seedlings [25,29,33,34]. The highest GI and GRI values on the white and 75% red LED diodes indicate that both red and blue light are necessary for seedling establishment. The need for blue light results from the initiation of photosynthesis, as cotyledons turn green quickly, as observed in the experiment.
The ratio between the relative spectral response (peak height = intensity) of blue and red may be important, as can be deduced from the spectral curves for daylight and fluorescent lamp illumination regimes. Díaz-Rueda et al. [35] also showed that high red/blue ratios stimulated seedling elongation and biomass.
The lack of an effect of light on FGP is likely due to the seeds’ ability to take advantage of short light signals during counting, despite the long dark period between the subsequent recordings and our efforts to shorten the procedure as much as possible.
SW strongly stimulates chamomile germination in darkness, suggesting that its physiologically active compounds and light share the same or a very similar signaling pathway. The physiological mechanism of smoke and its formulations consists primarily in the presence of karrikins (KARs), butenolide-based compounds, as proven in many experiments [36,37,38,39]. KARs are not perceived by the phytochrome system, but they partially share the light-specific signaling pathway. After binding to their specific membrane receptors—α/β hydrolases called KARRIKIN-INSENSITIVE2 proteins (KAI2)—these compounds lead to the downregulation of genes responsible for AUX and ABA biosynthesis [38]. This, together with the increased expression of GA biosynthetic genes [39,40], alters the phytohormonal balance in seeds, triggering seed germination and seedling growth.

4.4. Initial Growth of Seedlings

Once the chamomile seedlings are established (on day 7), they are the longest in darkness, which is expected, but their biomass is smaller compared to those of light. Since illumination stimulates germination, seedlings exposed to light had more time to accumulate biomass.
Among the illumination regimes, red is the most favorable for elongation, but in this case, a high ratio of red-to-blue is characteristic. This can be seen in the shortening of seedlings under fluorescent lamps and daylight regimes characterized by a high proportion of blue in their light spectrum. The superior effect of LEDs compared to fluorescent lamps is consistent with the work of Sanoubar et al. [41]. The blue-to-red ratio in the purple LED setups is also striking, because there is a decreasing trend in both biomass and length with increasing blue light. This can be explained by natural germination conditions, where the proportion of blue light in the soil light spectrum is very low [42,43]. Furthermore, after germination, blue light (B) does not act continuously on seedlings, but is accompanied by R and FR, and its proportion is dominant at the beginning and end of the day. Arabidopsis studies show that B, first through phototropin 1 (phot1) and then through cryptochrome 1 (cry1), suppresses hypocotyl elongation to establish seedling length [44]. B controls hypocotyl growth by regulating CRY1 and CRY2, which positively influence the catabolic GA2ox genes while inhibiting the biosynthetic GA20ox1 and GA3ox1 genes. At the molecular level, species-specific red/blue ratios will likely optimize the seedling photoreceptor responses to induce specific metabolic changes [45].
Regarding seedling morphometry, it is interesting that both length and biomass increase after SW treatment, with an additive effect to that of light. Fresh biomass is mainly dependent on water content, but the combination of seedling biomass and length provides valuable information on seedling size and growth potential. Based on the pattern of all changes, SW-stimulated germination, especially in combination with light, enhances the life processes of chamomile seedlings.
The combination of low-cost biostimulants such as SW [20] and optimized lighting under controlled conditions may allow for accelerated and uniform production of chamomile plants for various purposes. The advantages of LED lighting include lower energy costs and lower heat output compared to HPS and fluorescent lighting. Selecting the appropriate spectral composition for a plant species allows for obtaining plants with a specific shape, an appropriate ratio of the above-ground part to the roots, better root development, and more efficient photosynthesis [25,26,35,46]. Plants that produce specific metabolites, such as terpenoids in chamomile, also require additional UV lighting [47,48], which may be the subject of further research.

5. Conclusions

Red light is effective in initiating the germination of chamomile seeds, suggesting the involvement of phytochrome signaling. Both blue and red light are important for seedling establishment, but the red-to-blue ratio is crucial, as a high proportion of blue light negatively affects seedling length and biomass. Therefore, fluorescent lamps are the least beneficial, while white LEDs are the most effective for accelerating germination. Red LEDs, on the other hand, are best for producing stronger seedlings with greater length and biomass.
SW compensates for the absence of light at the beginning of germination in chamomile seeds. Moreover, the effects of SW and light on germination and seedling growth are additive, suggesting that smoke compounds and light share a similar signaling pathway. SW also increases seedling biomass and/or length, making it a potential seed priming agent. However, its use must be optimized individually for each laboratory and seed batch due to variations in the concentrations of physiologically active compounds in smoke formulations. Alternatively, pure KAR can be used for standardization. In addition, the results of laboratory experiments should be confirmed by field trials.

Author Contributions

Conceptualization, R.B.-K. and S.M.; methodology, R.B.-K. and S.M.; software, R.B.-K. and S.M.; validation, R.B.-K. and S.M.; formal analysis, R.B.-K. and S.M.; investigation, R.B.-K. and S.M.; resources, R.B.-K. and S.M.; data curation, R.B.-K. and S.M.; writing—original draft preparation, R.B.-K.; writing—review and editing, R.B.-K. and S.M.; visualization, R.B.-K.; supervision, R.B.-K. and S.M.; project administration, R.B.-K.; funding acquisition, R.B.-K. and S.M. All authors have read and agreed to the published version of the manuscript.

Funding

This research was financed from the institutional funding of the Ministry of Science and Higher Education of the Republic of Poland awarded to the University of Agriculture in Kraków and University of Life Sciences in Lublin.

Data Availability Statement

Dataset available on request from the authors.

Conflicts of Interest

The authors declare no conflicts of interest.

Abbreviations

The following abbreviations are used in this manuscript:
MDPIMultidisciplinary Digital Publishing Institute
DOAJDirectory of open access journals

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Agronomy 15 00700 g001
Figure 1. Spectral characteristics of light regimes used in the experiment on chamomile seeds, including daylight, fluorescent, high-pressure sodium (HPS), and LEDs (light-emitting diodes, white and with varying proportions of red to blue).
Figure 1. Spectral characteristics of light regimes used in the experiment on chamomile seeds, including daylight, fluorescent, high-pressure sodium (HPS), and LEDs (light-emitting diodes, white and with varying proportions of red to blue).
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Figure 2. Germination percentage of German chamomile seeds at the initial stage of germination (day 2) under different light regimes and smoke water (SW) treatment versus control (distilled water). HPS—high-pressure sodium lamps, LED—light-emitting diode; see Figure 1. SW was applied once at the beginning of the experiment. Each bar represents the mean of 60 seeds ± standard error (SE). The effects of the experimental factors and their interaction are shown in Table 1. * Indicates the significance of the difference between control and SW within the illumination regime according to the Student’s t-test at p = 0.05.
Figure 2. Germination percentage of German chamomile seeds at the initial stage of germination (day 2) under different light regimes and smoke water (SW) treatment versus control (distilled water). HPS—high-pressure sodium lamps, LED—light-emitting diode; see Figure 1. SW was applied once at the beginning of the experiment. Each bar represents the mean of 60 seeds ± standard error (SE). The effects of the experimental factors and their interaction are shown in Table 1. * Indicates the significance of the difference between control and SW within the illumination regime according to the Student’s t-test at p = 0.05.
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Figure 3. Biomass (A,B) and length (C,D) of German chamomile seedlings (days 7 and 14, respectively) under different light regimes and smoke water (SW) treatment versus control (distilled water). HPS—high-pressure sodium lamps, LED—light-emitting diode; see Figure 1. SW was applied once at the beginning of the experiment. Each bar represents the mean of 30 seedlings (biomass) or 15 seedlings (length) ± standard error (SE). The effects of the experimental factors and their interaction are shown in Table 1 and Table 3. Differences between control and SW are indicated according to the Student’s t-test at * p = 0.05, ** p = 0.01, *** p = 0.001. Differences within the control groups are marked a–c, and within the SW group A–C, according to the non-parametric multiple comparison of means following the Kruskal-Wallis test.
Figure 3. Biomass (A,B) and length (C,D) of German chamomile seedlings (days 7 and 14, respectively) under different light regimes and smoke water (SW) treatment versus control (distilled water). HPS—high-pressure sodium lamps, LED—light-emitting diode; see Figure 1. SW was applied once at the beginning of the experiment. Each bar represents the mean of 30 seedlings (biomass) or 15 seedlings (length) ± standard error (SE). The effects of the experimental factors and their interaction are shown in Table 1 and Table 3. Differences between control and SW are indicated according to the Student’s t-test at * p = 0.05, ** p = 0.01, *** p = 0.001. Differences within the control groups are marked a–c, and within the SW group A–C, according to the non-parametric multiple comparison of means following the Kruskal-Wallis test.
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Table 1. Analysis of variance (ANOVA) of seed germination percentage, seed germination parameters (GRI and GI) obtained from the day 2 to day 7, and seedling biomass. Illumination regime: darkness, daylight, fluorescent light, high-pressure sodium (HPS) lamps, and LEDs (light-emitting diodes, white and with varying proportions of red to blue; see Figure 1). Treatment: control—distilled water, and SW—smoke water, applied once at the beginning of the experiment. The significance of the effect of a given factor is marked: ** at p ≤ 0.01 and *** at p ≤ 0.001.
Table 1. Analysis of variance (ANOVA) of seed germination percentage, seed germination parameters (GRI and GI) obtained from the day 2 to day 7, and seedling biomass. Illumination regime: darkness, daylight, fluorescent light, high-pressure sodium (HPS) lamps, and LEDs (light-emitting diodes, white and with varying proportions of red to blue; see Figure 1). Treatment: control—distilled water, and SW—smoke water, applied once at the beginning of the experiment. The significance of the effect of a given factor is marked: ** at p ≤ 0.01 and *** at p ≤ 0.001.
FactorGermination Percentage, Day 2GRI (Germination Rate Index)GI (Germination Index)Seedling Biomass, Day 7Seedling Biomass, Day 14
FpFpFpFpFp
Illumination regime19.380.000 ***16.480.000 ***14.950.000 ***72.000.000 ***86.90.000 ***
Treatment17.320.000 ***9.770.003 **8.000.008 **124.300.000 ***148.50.000 ***
Illumination regime × Treatment1.570.1670.520.8310.420.9000.7000.7270.90.518
Table 2. Germination factors obtained from germination recordings from the day 2 to day 7. FGP—final germination percentage, GRI—germination rate index, GI—germination index. HPS—high-pressure sodium lamps, LED—light-emitting diode, see Figure 1. Control—distilled water, SW—smoke water, applied once at the beginning of the experiment. The significance of the effect of a given factor is given in Table 3.
Table 2. Germination factors obtained from germination recordings from the day 2 to day 7. FGP—final germination percentage, GRI—germination rate index, GI—germination index. HPS—high-pressure sodium lamps, LED—light-emitting diode, see Figure 1. Control—distilled water, SW—smoke water, applied once at the beginning of the experiment. The significance of the effect of a given factor is given in Table 3.
Illumination RegimeFGP
[%]		GRI
[%/day]		GI
[Number × Day]
ControlSWControlSWControlSW
Darkness73759892288326
Daylight8382115113383390
Fluorescent8387119118388409
HPS8082114115372397
LED white8888126128438441
LED Red8282110116389400
LED Red 92%8387120121385420
LED Red 83%8383116111371387
LED Red 75%8788124124422431
Table 3. Kruskal-Wallis non-parametric analysis of chamomile seed final germination percentage (FGP) and seedling length. Illumination regimes: darkness, daylight, fluorescent light, high-pressure sodium (HPS) lamps, and LEDs (light-emitting diodes, white and with varying proportions of red to blue; see Figure 1). Treatment: control—distilled water, and SW—smoke water, applied once at the beginning of the experiment. The significance of the effect of a given factor is marked *** at p ≤ 0.001.
Table 3. Kruskal-Wallis non-parametric analysis of chamomile seed final germination percentage (FGP) and seedling length. Illumination regimes: darkness, daylight, fluorescent light, high-pressure sodium (HPS) lamps, and LEDs (light-emitting diodes, white and with varying proportions of red to blue; see Figure 1). Treatment: control—distilled water, and SW—smoke water, applied once at the beginning of the experiment. The significance of the effect of a given factor is marked *** at p ≤ 0.001.
FactorFGP [%]Seedling Length, Day 7Seedling Length, Day 14
HpHpHp
Illumination regime26.270.0009 ***25.270.0014 ***37.720.0000 ***
Treatment0.740.388322.090.0000 ***10.410.0013 ***
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Bączek-Kwinta, R.; Michałek, S. Smoke Compounds Compensate for Light Irrespective of Its Spectrum in Positively Photoblastic German Chamomile Seeds, Although Red Light Is Crucial. Agronomy 2025, 15, 700. https://doi.org/10.3390/agronomy15030700

AMA Style

Bączek-Kwinta R, Michałek S. Smoke Compounds Compensate for Light Irrespective of Its Spectrum in Positively Photoblastic German Chamomile Seeds, Although Red Light Is Crucial. Agronomy. 2025; 15(3):700. https://doi.org/10.3390/agronomy15030700

Chicago/Turabian Style

Bączek-Kwinta, Renata, and Sławomir Michałek. 2025. "Smoke Compounds Compensate for Light Irrespective of Its Spectrum in Positively Photoblastic German Chamomile Seeds, Although Red Light Is Crucial" Agronomy 15, no. 3: 700. https://doi.org/10.3390/agronomy15030700

APA Style

Bączek-Kwinta, R., & Michałek, S. (2025). Smoke Compounds Compensate for Light Irrespective of Its Spectrum in Positively Photoblastic German Chamomile Seeds, Although Red Light Is Crucial. Agronomy, 15(3), 700. https://doi.org/10.3390/agronomy15030700

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