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Article

Chitosan Soaking Improves Seed Germination of Platycodon Grandiflorus and Enhances Its Growth, Photosynthesis, Resistance, Yield, and Quality

by
Hai Liu
1,
Zhihong Zheng
1,
Xue Han
1,
Cheng Zhang
2,
Haitao Li
3,* and
Mingkai Wu
1,*
1
Institute of Modern Chinese Herbal Medicines, Institute of Crop Germplasm Resources, Guizhou Academy of Agricultural Sciences, Guiyang 550025, China
2
School of Public Health, Guizhou Medical University, Guiyang 550025, China
3
Department of Food and Medicine, Guizhou Vocational College of Agriculture, Qingzhen 551400, China
*
Authors to whom correspondence should be addressed.
Horticulturae 2022, 8(10), 943; https://doi.org/10.3390/horticulturae8100943
Submission received: 22 September 2022 / Revised: 11 October 2022 / Accepted: 11 October 2022 / Published: 14 October 2022
(This article belongs to the Special Issue Seed Germination and Micropropagation of Ornamental Plants)
Browse Figures
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Abstract

:
Platycodon grandiflorus is a medical, ornamental, and edible traditional Chinese medicine whose seed germination and plant growth are frequently restricted by dormancy and stresses. In this study, we investigated how chitosan soaking affected seed germination, growth, photosynthesis, resistance, yield, and quality of P. grandiflorus. The results indicated that chitosan soaking had a preferable enhancing effect on seed germination of P. grandiflorus, which significantly (p < 0.05) promoted its germination rate, energy, and index, as well as cotyl and radicle length. Furthermore, 0.15–0.20% chitosan soaking effectively enhanced the leaf growth, height, stem diameter, and overground part dry weight of P. grandiflorus and reliably improved their leaves’ chlorophyll, photosynthetic rate, transpiration rate, and water use efficiency. Moreover, 0.15–0.20% chitosan soaking effectively enhanced the stress resistance and adaptability of P. grandiflorus via increasing its resistance substances and triggering its defense enzyme activity. Meanwhile, 0.15–0.20% chitosan soaking effectively improved the underground part growth and medical quality of P. grandiflorus. This study highlights that chitosan can be used as a favorable, efficient, and economical candidate or promoter for enhancing seed germination of P. grandiflorus and improving its growth, photosynthesis, resistance, yield, and quality; it also highlights that 0.15–0.20% chitosan is a suitable concentration.

1. Introduction

Platycodon grandiflorus (Jacq) A.DC., a medical, ornamental, and edible perennial plant, has been widely planted in China, North Korea, South Korea, Japan, and Russia [1,2]. It is rich in saponins, polysaccharides, vitamins, amino acids, flavonoids, phenolics, anthocyanins, and various minerals, etc. [1,2,3]. As an oriental traditional herb, it is widely used for treating sore throats, excessive phlegm, coughing, amnesia, dementia, and inflammatory diseases due to its notably anti-asthmatic, anti-tumor, anti-oxidant, anti-inflammatory, anti-obesity, hepatoprotective and immunoregulative, and other characteristics [1,2,4,5,6]. Meanwhile, its flower buds are found in different colors, including blue, purple, red, violet, white, or pink, which have an extremely high ornamental value [2,7]. Moreover, as a functional food ingredient or wild vegetable, its tender seedlings and roots are usually processed as soup, salads, sauces, pickles, noodles, preserved fruits, and health drinks, etc. [8,9]. Recently, the P. grandiflorus industry in China has made a major contribution to alleviating poverty and revitalizing rural aspects, and its annual output reaches 1 million kg, of which exports account for half [7]. Due to the major development values and prospects of P. grandiflorus, artificial cultivation technology to enhance its yield and medicinal quality has been paid growing attention.
Unfortunately, the seed size of P. grandiflorus is small, its germination and emergence rates are also weak, and it easily dies from drought under the traditional artificial cultivation conditions. Furthermore, P. grandiflorus seeds frequently show dormancy as they contain endogenous germination inhibitory substances with high activity [10,11]. Additionally, its germination is also significantly influenced by several factors, such as various abiotic and biotic stresses [12,13]. Currently, stratification, chemical, physical, and hormone treatments are often used to relieve dormancy and promote germination of P. grandiflorus seeds [14]. For example, Wang et al. [15] reported that 0.005 g mL−1 KNO3 and 0.003 g mL−1 KMnO4 had the best enhanced influence on seed germination and seedling growth of P. grandiflorus. Zhang et al. [16] reported that 0.10–0.40 g L−1 of 15% alginate water-soluble fertilizer could effectively promote seed germination and plant growth of P. grandiflorus. Subsequently, the authors also found that 25,000–20,000 folds liquid of 0.136% gibbenic acid·indoleacetic acid·brassicin wettable powder could also significantly promote its seed germination and plant growth [17]. Considering the extremely limiting factors for seed germination of P. grandiflorus and the potentially low efficiency or restricting use of the reported techniques or chemicals, more novel candidate strategies or promoters need to be developed or found to enable meeting the sustainable development of the P. grandiflorus industry.
Chitosan, a linear copolymer of β-(1-4)-2-amido-2-deoxy-D-glucan (glucosamine) and β-(1-4)-2-acetamido-2-deoxy-D-glucan (acetylglucosamine), is not toxic to humans or other organisms [18,19]. As an ideal natural polymer, it has been widely utilized in agriculture, medical care, food, cosmetics, and other fields due to its favorable bioactivity, film-forming ability, biodegradability, non-toxicity, and renewability [20,21]. In agriculture, it has emerged as a promising resource used as a plant growth enhancer, resistance inductor, and bio-fungicide [21,22,23]. It can effectively stimulate and enhance plant growth by affecting plant physiological processes, such as seed germination, nutrient uptake, cell division and elongation, stress resistance, and so on, eventually leading to increased yield and improved quality [21,24,25,26,27,28]. Pan et al. [29] reported that 50 mg L−1 chitosan effectively enhanced the seed germination, radicle and germ length, plant height, fresh and dry weight, and root–shoot ratio of Trifolium repens under salt stress. Additionally, Li et al. [30] found that 0.15% chitosan significantly improved seed germination of Sctellaria baicalensis and its seedlings’ drought resistance. To date, there has been no documentation of whether chitosan enhances seed germination and growth of P. grandiflorus. In this case, whether chitosan can be used as an enhancer or candidate for enhancing seed germination and plant growth of P. grandiflorus is very worthy of intensive study.
In this study, the influences of chitosan soaking on seed germination of P. grandiflorus were primarily investigated. Moreover, the influences of chitosan soaking on growth, photosynthesis, resistance, yield, and quality of P. grandiflorus were also evaluated. This work provides a safe, effective, and economical candidate or enhancer for promoting seed germination of P. grandiflorus and improving its growth, underground part weight, and quality.

2. Materials and Methods

2.1. Experimental Materials

Chitosan with deacetylation of 90.00% and molecular weight of 50 KDa was purchased by Mingrui Bioengineering Co. Ltd. (Zhengzhou, China). KMNO4 was produced from Kemiou Chemical Reagent Co. Ltd. (Tianjin, China). P. grandiflorus seeds were collected from the medicinal botanical garden at the Guizhou Academy of Agricultural Sciences and identified as seeds of P. grandiflorus (Jacq.) A.DC. by Prof. Mingkai Wu, who is a researcher of Guizhou Academy of Agricultural Sciences. The potted soils were also collected from the above-mentioned medicinal garden, and the soil fertility information is shown in Table 1.

2.2. Seed Germination Experiment of P. grandiflorus

Six soaking concentrations of chitosan were designed: 0.00%, 0.05%, 0.10%, 0.15%, 0.20%, and 0.25% chitosan solution. Distilled water was used to dissolve and dilute chitosan. The full seeds of P. grandiflorus were first sterilized with 0.5%KMNO4 for 30 min and then washed with distilled water and subsequently soaked in a 50 mL chitosan solution for 12 h. The soaked seeds were washed with distilled water and then arranged evenly on the germination bed, which was a 9 cm diameter Petri dish with a covering of two wet filter papers. Each germination bed had one hundred seeds and each treatment was repeated three times. The germinating bed was incubated in a dark incubator at 25 °C; an appropriate amount of distilled water was added every day to ensure that the filter paper was moist. Germination rate, energy, and index of P. grandiflorus seeds were investigated according to Equations (1)–(3), respectively. Meanwhile, cotyl length and radicle length of P. grandiflorus were determined after 18 d of incubation.
Germination rate (%) = 100 × (Number of normally germinated seeds within 22 days/Total seed number)
Germination energy (%) = 100 × (Number of normally germinated seeds in the first 10 days/Total seed number)
Germination index = (Number of germinated seeds at a given incubation time/Incubation time)

2.3. Growth Experiment of P. grandiflorus

The operation of soaking the P. grandiflorus seeds in different concentrations of the chitosan solution was the same as above. The soaked seeds were washed with distilled water and then evenly scattered in a flowerpot containing 4 kg of soil for growth. The outer diameter, inner diameter, and height of each flowerpot were 26 cm, 22 cm, and 17 cm, respectively. Each pot was sown with 50 soaked seeds, and each treatment consisted of three replicates. After emergence, 10 strong seedlings were kept in each pot for further growth. Irrigation was timely during growth of the P. grandiflorus to avoid drought. The growth, photosynthesis, and resistance parameters of the P. grandiflorus leaves were investigated 110 days after sowing. Moreover, the overground part growth, underground part growth, and quality parameters of P. grandiflorus were determined 300 days after sowing.

2.4. Determination Methods

The length and width of the fourth leaves of the P. grandiflorus plants were measured by a ruler, and the leaf area was approximately equal to the product of its length and width. The chlorophyll, photosynthetic rate (Pn), transpiration rate (Tr), and water use efficiency (WUE) in the third and fourth leaves of P. grandiflorus were determined following Zhang et al. [31]. The chlorophyll was determined using an SPDA-502 Plus chlorophyll analyzer (Konica-Minolta, Tokyo, Japan), and the Pn, Tr, and WUE were monitored by portable LI-6400XT photosynthesis determination equipment (LI-COR Inc., Lincoln, NE, USA) between 8:00 and 10:00 a.m. The resistance parameters of the P. grandiflorus leaves, including the soluble sugar and protein, proline (Pro), malonaldehyde (MDA), superoxide dismutase activity (SOD), and peroxidase (POD) activity, were analyzed following Wang et al. [32] and Zhang et al. [33]. The plants’ dry height, stem diameter at the second segment, and root diameter were measured using a ruler or digital caliper, and their overground part weight and the fresh and dry weight of the root were determined by an analytical balance. Meanwhile, the platycodin D, total platycodin, extractum, and polysaccharides of the P. grandiflorus roots were analyzed following Liu et al. [34] and Zhang et al. [35].

2.5. Statistical Analyses

The data were displayed as the mean value ± standard deviation (SD) of three replicates, and their significant differences were determined by a one-way analysis of variance (ANOVA) with Duncan’s test in SPSS 18.0 software (SPSS Inc., Chicago, IL, USA). The figures were edited using Origin 10.0 software (OriginLab, Northampton, MA, USA).

3. Results

3.1. Effects of Chitosan Soaking on Seed Germination of P. grandiflorus

The influences of chitosan soaking on seed germination, cotyl length, and radicle length of P. grandiflorus are shown in Table 2. Indeed, 0.05–0.25% chitosan soaking significantly (p < 0.05) enhanced the germination rate, germination energy, germination index, cotyl length, and radicle length of P. grandiflorus, which effectively increased by 1.18–1.46, 1.41–2.10, 1.18–1.46, 1.04–1.23, and 1.09–1.54 times compared to the control (0.00% chitosan), respectively. The germination rate, energy, and index, as well as the cotyl length of P. grandiflorus seeds treated by 0.15% chitosan soaking, were, respectively, 92.33%, 61.67%, 4.20, and 7.48 mm, which were significantly (p < 0.05) superior to those of other chitosan concentrations. Meanwhile, the radicle length of P. grandiflorus seeds treated by 0.15% chitosan soaking was also significantly (p < 0.05) superior to that of 0.05%, 0.10%, and 0.25% chitosan treatments. Moreover, the seed germination, cotyl length, and radicle length were not significantly different between 0.20% chitosan and 0.25% chitosan treatments, but they were significantly (p < 0.05) higher than those of 0.05% chitosan and 0.10% chitosan treatments. The present results show that 0.05–0.25% chitosan had a preferable enhancing effect on seed germination of P. grandiflorus.

3.2. Effects of Chitosan on Overground Part Growth of P. grandiflorus Plants

The influences of chitosan soaking on leaf growth of P. grandiflorus plants are depicted in Table 3. Indeed, 0.15–0.25% chitosan soaking significantly (p < 0.05) enhanced the leaf length, leaf width, and leaf area of P. grandiflorus plants compared to those of 0.05–0.10% chitosan soaking or control (0.00% chitosan). However, the leaf length, leaf width, and leaf area of P. grandiflorus plants were not significant different among 0.15%, 0.20%, and 0.25% chitosan treatments, and there were also not significant differences among 0.00% (control), 0.05%, and 0.10% chitosan treatments. Further, 0.15% chitosan soaking exhibited a relatively good promoting effect on leaf growth of P. grandiflorus plants, which effectively increased the leaf length by 11.21%, the leaf width by 11.17%, and the leaf area by 23.64% compared to non-soaked chitosan, respectively. These results showed that 0.15–0.25% chitosan soaking could effectively enhance leaf growth of P. grandiflorus plants.
The influences of chitosan soaking on height, stem diameter, and overground part dry weight of P. grandiflorus plants are depicted in Table 4. Compared with non-soaked chitosan, 0.05–0.25% chitosan soaking significantly (p < 0.05) enhanced the plant height of P. grandiflorus, and 0.15–0.25% chitosan soaking significantly (p < 0.05) promoted its stem diameter, as well as 0.10–0.25% chitosan soaking significantly (p < 0.05) increased its overground part dry weight. The height and overground part weight of P. grandiflorus plants treated by 0.15% chitosan soaking were respectively 35.13 cm and 2.86 g plant−1, which were significantly (p < 0.05) superior to those of other chitosan concentrations. The plants’ dry height of P. grandiflorus was not significant differences among 0.05%, 0.10%, 0.20%, and 0.25% chitosan treatments, its stem diameter was not significant differences among 0.15%, 0.20%, and 0.25% chitosan treatments. These results further indicate that 0.15–0.20% chitosan soaking could effectively enhance the growth and biomass formation of P. grandiflorus plants.

3.3. Effects of Chitosan Soaking on the Chlorophyll and Photosynthesis of P. grandiflorus Leaves

The influences of chitosan soaking on the chlorophyll, Pn, Tr and WUE of P. grandiflorus leaves are displayed in Figure 1. Compared with non-soaked chitosan, 0.05–0.25% chitosan soaking notably (p < 0.05) enhanced the chlorophyll content of P. grandiflorus leaves, and 0.10–0.25% chitosan soaking could significantly (p < 0.05) improve its Pn and Tr, as well as 0.15–0.25% chitosan soaking could significantly (p < 0.05) promote its WUE. The Pn, and Tr of P. grandiflorus leaves treated by 0.15% chitosan soaking were 8.54 μmol CO2 m−2 s−1 and 2.31 mmol H2O m−2 s−1, which were significantly (p < 0.05) superior to those of other chitosan concentrations. Moreover, the chlorophyll of P. grandiflorus leaves treated by 0.15% chitosan soaking was slightly higher than that of 0.10%, 0.20%, and 0.25% chitosan treatments, whereas there were no significant differences. Simultaneously, the WUE of P. grandiflorus was not significant differences among all chitosan soaking treatments. These results demonstrate that 0.15–0.20% chitosan soaking could effectively improve the chlorophyll, Pn, Tr and WUE of P. grandiflorus leaves, thereby enhancing its favorable growth and development.

3.4. Effects of Chitosan Soaking on Resistance of P. grandiflorus Plants

The influences of chitosan soaking on sugar, protein, Pro, and MDA of P. grandiflorus leaves are shown in Figure 2. Soluble sugar, soluble protein, and Pro are indispensable regulating compounds to maintain permeability equilibrium in various organs, while MDA reflects the intensity of membrane lipid peroxidation. Indeed, 0.05–0.25% chitosan soaking notably (p < 0.05) increased soluble sugar, soluble protein, and Pro of P. grandiflorus leaves compared with non-soaked chitosan and decreased MDA content. The soluble sugar value of P. grandiflorus leaves treated by 0.15% chitosan soaking was slightly superior to that of 0.10%, 0.20%, and 0.25% chitosan treatments, but there were no significant differences. Moreover, the soluble protein and Pro of P. grandiflorus leaves treated by 0.15% chitosan soaking were significantly (p < 0.05) superior to those of other chitosan concentrations. Further, the Pro of P. grandiflorus leaves treated by 0.20% chitosan soaking was significantly (p < 0.05) superior to that of 0.05%, 0.10%, and 0.25% chitosan treatments. Meanwhile, the soluble protein of P. grandiflorus leaves treated by 0.15% chitosan soaking was slightly inferior to that of 0.20% chitosan soaking, and significantly (p < 0.05) lower than that of 0.05%, 0.10%, and 0.25% chitosan treatments. The soluble sugar of P. grandiflorus was not significantly different among 0.05%, 0.10%, 0.20%, and 0.25% chitosan treatments, and its Pro was not significantly different among 0.00%, 0.05%, 0.10%, and 0.25% chitosan treatments, as well as its MDA was not significantly different between 0.20% and 0.25% chitosan treatments. These findings emphasize that 0.15–0.20% chitosan soaking could effectively enhance soluble sugar, soluble protein, and Pro of P. grandiflorus leaves, as well as reduce their MDA, thereby effectively promoting their stress resistance, environmental adaptability, and healthy growth.
The influences of chitosan soaking on SOD and POD activities of P. grandiflorus leaves are shown in Figure 3. SOD and POD are important defense enzymes participating in plants’ stress resistance. Compared with non-soaked chitosan, 0.15–0.20% chitosan soaking significantly (p < 0.05) enhanced the SOD activity of P. grandiflorus leaves, and 0.10–0.25% chitosan soaking could significantly (p < 0.05) promote its POD activity. The SOD activity of P. grandiflorus leaves treated by 0.05%, 0.10%, and 0.25% chitosan soaking was slightly lower than that of non-soaked chitosan, but there were no significant differences. Meanwhile, 0.15% chitosan soaking displayed an optimal promotion effect on the SOD and POD activities of P. grandiflorus leaves. The present results further demonstrate that 0.15–0.20% chitosan soaking could effectively enhance defense enzyme activity, stress resistance, and adaptability of P. grandiflorus.

3.5. Effects of Chitosan Soaking on Growth and Yield of P. grandiflorus Roots

The influences of chitosan on diameter, fresh weight, and dry weight of P. grandiflorus roots are shown in Table 5. Compared with non-soaked chitosan, 0.05–0.25% chitosan soaking significantly (p < 0.05) enhanced the plant height of P. grandiflorus, and 0.15–0.25% chitosan soaking could obviously (p < 0.05) improve the fresh and dry weight of roots. The diameter, fresh weight, and dry weight of P. grandiflorus roots treated by 0.15% chitosan soaking were, respectively, 7.13 mm, 1.43 g plant−1, and 0.38 g plant−1, which were obviously (p < 0.05) superior to those of other chitosan concentrations and effectively increased by 1.35-, 1.96-, and 1.90-fold compared to non-spray chitosan, respectively. Moreover, those treated by 0.20% chitosan soaking were also obviously (p < 0.05) superior to those of 0.05%, 0.10%, and 0.25% chitosan treatments. The diameter, fresh weight, and dry weight of P. grandiflorus roots were not significantly different between 0.10% and 0.25% chitosan treatments, and its fresh weight and dry weight were not significantly different between 0.05% and 0.10% chitosan treatments. These findings indicate that 0.15–0.20% chitosan soaking could effectively enhance growth and yield formation of P. grandiflorus roots.

3.6. Effects of Chitosan Soaking on Medical Quality of P. grandiflorus

The influences of chitosan soaking on the platycodin D, total platycodin, extractum, and polysaccharides of P. grandiflorus are depicted in Figure 4. Compared with non-soaked chitosan, 0.05–0.25% chitosan soaking significantly (p < 0.05) increased the platycodin D, extractum, and polysaccharides of P. grandiflorus, and 0.10–0.25% chitosan soaking could obviously (p < 0.05) improve its total platycodin. The platycodin D and polysaccharides of P. grandiflorus treated by 0.15% chitosan soaking were obviously (p < 0.05) superior to those of 0.05%, 0.10%, and 0.25% chitosan treatments; meanwhile, its total platycodin and extractum were obviously (p < 0.05) superior to those of other chitosan concentrations. The platycodin D, total platycodin, extractum, and polysaccharides of P. grandiflorus treated by 0.1–0.20% chitosan soaking effectively increased by 1.20–1.18-fold, 1.19–1.31-fold, 1.19–1.28-fold, and 1.29–1.31-fold compared to non-soaked chitosan, respectively. The results presented here reveal that soaking in a suitable concentration of chitosan could effectively improve the medical quality of P. grandiflorus.

4. Discussion

Germination rate, energy, and index represent the vigor index of seeds, which are important metrics to evaluate seed quality. Pan et al. [29] found that 50 mg L−1 chitosan effectively enhanced the germination rate, energy, and index, as well as the vigor index, cotyl length, and radicle length of Trifolium repens under salt stress. Li et al. [30] found that 0.15% chitosan significantly improved the germination rate, energy, and index of Sctellaria baicalensis under drought stress. Moreover, 1000–3000 mg L−1 chitosan could also effectively increase the germination energy of Cucumis sativus [36]. The results here exhibited that 0.05–0.25% chitosan soaking obviously (p < 0.05) enhanced the germination rate, energy, and index, as well as the cotyl and radicle length of P. grandiflorus, and 0.15% chitosan soaking displayed an optimal enhancing effect. These results were similar to previous studies and extended application of chitosan in traditional Chinese medicine cultivation. We also found that, when the chitosan concentration was higher than 0.15%, the germination index of P. grandiflorus seeds decreased. This indicated that chitosan could significantly improve the respiration rate of seed germination, which increased with an increase in chitosan concentration, accelerating transformation of the substances in seeds and then promoting seed germination. However, with the increasing concentration of chitosan, the respiration rate of seeds was too fast, which might cause loss of a large amount of energy in the form of heat, decreasing the promotion effects of chitosan.
Chlorophyll is a very important pigment in photosynthesis, which is the physiological basis of plant growth. Chitosan can substantially enhance plants’ growth and yield via promoting the photosynthetic rate via improving chlorophyll [21]. Meanwhile, chitosan also acts as a growth promoter to enhance division and elongation of cells via activating signal transduction and gene expression of auxin and cytokinin, which promotes nutrient intake and plant growth [21,24,25,26,27,28]. Pan et al. [29] found that chitosan effectively increased the plant height, fresh and dry weight, and root–shoot ratio of Trifolium repens under salt stress, and Li et al. [30] also found that chitosan significantly improved the chlorophyll content of Sctellaria baicalensis under drought stress. The present results indicate that 0.15–0.20% chitosan soaking could effectively enhance the leaf growth, plant height, stem diameter, and overground part dry weight of P. grandiflorus and increase its leaf’s chlorophyll, Pn, Tr, and WUE, which was consistent with the previous reports on other plants. These findings imply that 0.15–0.20% chitosan soaking could reliably enhance growth, chlorophyll, Pn, Tr, and WUE of P. grandiflorus leaves, thereby improving growth and biomass formation of P. grandiflorus plants.
Soluble sugar and Pro are important osmoregulation substances in plant cells, and soluble protein is the metabolism basis of material and energy, which are closely related to plants’ stress resistance [37,38]. Pro can effectively maintain the osmotic balance between cytoplasmic matrix and environment, prevent water loss, and protect the structural integrity of protective film [38]. Soluble sugar can maintain plant growth under adversity by regulating osmotic potential of plant tissues [38]. Moreover, MDA reflects the degrees of membrane damage and stress resistance [38]. SOD plays a role in scavenging free radicals in plants, and POD is an important protective enzyme for catalyzing H2O2 decomposition in lignin biosynthesis, which is also connected to a plant’s slow death and stress resistance [37,38]. Many studies have also shown that chitosan can enhance the sugar, protein, and Pro contents in plants and reduce their MDA content, as well as boost their defense enzyme activity [39,40,41]. In this study, 0.15–0.20% chitosan soaking significantly (p < 0.05) enhanced soluble sugar, soluble protein, Pro, SOD activity, and POD activity of P. grandiflorus leaves as well as reduced their MDA, demonstrating that chitosan soaking could effectively improve the stress resistance, environmental adaptability, and healthy growth of P. grandiflorus plants.
Generally, P. grandiflorus is used as medication, especially its root and rhizome, and Platycodin D, total Platycodin, and polysaccharides are considered to be its main medical bioactive components [5,6,7,8,9]. Meanwhile, good growth determines the underground part yield and medical quality of P. grandiflorus. In this study, 0.15–0.20% chitosan soaking could effectively enhance the diameter, fresh weight, dry weight, platycodin D, total platycodin, extractum, and polysaccharides of P. grandiflorus roots. This favorable effect probably derived from the effects of chitosan on seed germination and plant growth of P. grandiflorus. Chitosan is a natural biopolymer with nontoxic, antibacterial, antioxidant, renewable, and biodegradable superiorities, and the safe interval time of more than 10 months for P. grandiflorus was very long; therefore, the quality and safety risks of the medicinal materials caused by chitosan were almost nonexistent [21,22,42,43]. This work emphasizes that chitosan can be applied as a favorable candidate or promoter for enhancing seed germination of P. grandiflorus and improving its growth, photosynthesis, resistance, yield, and quality, and 0.15–0.20% chitosan is a safe, cost-efficient, and suitable soaking concentration.

5. Conclusions

In conclusion, the present work indicates that chitosan soaking had a preferable enhancing effect on seed germination of P. grandiflorus, which could significantly (p < 0.05) enhance its germination rate, energy, and index, as well as cotyl and radicle length. Indeed, 0.15–0.20% chitosan soaking could effectively enhance the leaf growth, height, stem diameter, and overground part dry weight of P. grandiflorus plants, as well as reliably improve their leaves’ chlorophyll, Pn, Tr, and WUE. Moreover, 0.15–0.20% chitosan soaking notably enhanced the soluble sugar, soluble protein, and Pro contents, as well as the SOD and POD activities in leaves of P. grandiflorus, and reduced their MDA, thereby effectively promoting its stress resistance and adaptability. Meanwhile, 0.15–0.20% chitosan soaking effectively improved the underground part growth and medical quality of P. grandiflorus. This work highlights that chitosan can be used as a favorable promoter to enhance seed germination of P. grandiflorus and improve its growth, photosynthesis, resistance, yield, and quality.

Author Contributions

M.W. and H.L. (Haitao Li) constructed the project; M.W., H.L. (Haitao Li) and H.L. (Hai Liu) designed the experiments; H.L. (Hai Liu), Z.Z. and X.H. performed the experiments; C.Z. and H.L. (Hai Liu) analyzed the data; H.L. (Hai Liu) and C.Z. wrote the paper. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the National Key Research and Development Program of China (No. 2021YFD1601002) and the Modern Industrial Technology System of Chinese Medicinal Materials in Guizhou Province (No. GZCYTX2021-0202).

Data Availability Statement

The datasets used or analyzed during the current study available from the corresponding author upon reasonable request.

Conflicts of Interest

We declare that we do not have any commercial or associative interest that represents a conflict of interest in connection with the work submitted.

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Horticulturae 08 00943 g001 550
Figure 1. Influences of chitosan soaking on chlorophyll (A), Pn (B), Tr (C), and WUE (D) of P. grandiflorus leaves. The SD of three replicates was indicated by error bar. A one-way analysis of variance (ANOVA) followed by Duncan’s test was used, and the significant differences at a 5% level (p < 0.05) in the six treatments are represented by different letters.
Figure 1. Influences of chitosan soaking on chlorophyll (A), Pn (B), Tr (C), and WUE (D) of P. grandiflorus leaves. The SD of three replicates was indicated by error bar. A one-way analysis of variance (ANOVA) followed by Duncan’s test was used, and the significant differences at a 5% level (p < 0.05) in the six treatments are represented by different letters.
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Figure 2. Influences of chitosan soaking on soluble sugar (A), soluble protein (B), Pro (C), and MDA (D) of P. grandiflorus leaves. The SD of three replicates was indicated by error bar. A one-way analysis of variance (ANOVA) followed by Duncan’s test was used, and the significant differences at a 5% level (p < 0.05) in the six treatments are represented by different letters.
Figure 2. Influences of chitosan soaking on soluble sugar (A), soluble protein (B), Pro (C), and MDA (D) of P. grandiflorus leaves. The SD of three replicates was indicated by error bar. A one-way analysis of variance (ANOVA) followed by Duncan’s test was used, and the significant differences at a 5% level (p < 0.05) in the six treatments are represented by different letters.
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Figure 3. Influences of chitosan soaking on SOD (A) and POD (B) activities of P. grandiflorus leaves. The SD of three replicates was indicated by error bar. A one-way analysis of variance (ANOVA) followed by Duncan’s test was used, and the significant differences at a 5% level (p < 0.05) in the six treatments are represented by different letters.
Figure 3. Influences of chitosan soaking on SOD (A) and POD (B) activities of P. grandiflorus leaves. The SD of three replicates was indicated by error bar. A one-way analysis of variance (ANOVA) followed by Duncan’s test was used, and the significant differences at a 5% level (p < 0.05) in the six treatments are represented by different letters.
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Figure 4. Influences of chitosan soaking on platycodin D (A), total platycodin (B), extractum (C), and polysaccharides (D) of P. grandiflorus. The SD of three replicates was indicated by error bar. A one-way analysis of variance (ANOVA) followed by Duncan’s test was used, and the significant differences at a 5% level (p < 0.05) in the six treatments are represented by different letters.
Figure 4. Influences of chitosan soaking on platycodin D (A), total platycodin (B), extractum (C), and polysaccharides (D) of P. grandiflorus. The SD of three replicates was indicated by error bar. A one-way analysis of variance (ANOVA) followed by Duncan’s test was used, and the significant differences at a 5% level (p < 0.05) in the six treatments are represented by different letters.
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Table
Table 1. The fertility information of the potted soils.
Table 1. The fertility information of the potted soils.
IndicesContentIndicesContent
Organic matter15.36 g kg−1Available zinc0.83 mg kg−1
Total nitrogen1.45 g kg−1Available iron7.04 mg kg−1
Total phosphorus1.73 g kg−1Available boron0.16 mg kg−1
Total potassium1.18 g kg−1Available manganese16.31 mg kg−1
Available nitrogen57.33 mg kg−1Exchangeable magnesium315.78 mg kg−1
Available phosphorus4.92 mg kg−1Exchangeable calcium16.85 cmol kg−1
Available potassium28.27 mg kg−1pH value6.42
Table
Table 2. Influences of chitosan soaking on seed germination, cotyl length, and radicle length of P. grandiflorus.
Table 2. Influences of chitosan soaking on seed germination, cotyl length, and radicle length of P. grandiflorus.
Chitosan (%)Germination Rate (%)Germination Energy (%)Germination IndexCotyl Length (mm)Radicle Length (mm)
0.0063.33 ± 2.52 d29.33 ± 1.53 e2.88 ± 0.11 d6.08 ± 0.16 e7.18 ± 0.14 e
0.0574.67 ± 3.51 c41.33 ± 1.53 d3.39 ± 0.16 c6.32 ± 0.12 d7.84 ± 0.26 d
0.1082.67 ± 3.21 b49.00 ± 2.00 c3.76 ± 0.15 b6.75 ± 0.13 c9.46 ± 0.27 c
0.1592.33 ± 3.51 a61.67 ± 3.51 a4.20 ± 0.16 a7.48 ± 0.14 a11.04 ± 0.24 a
0.2085.67 ± 2.52 b55.00 ± 3.00 b3.89 ± 0.11 b7.05 ± 0.06 b10.65 ± 0.28 ab
0.2584.00 ± 2.65 b53.67 ± 2.08 b3.82 ± 0.12 b6.83 ± 0.16 bc10.37 ± 0.27 b
The mean ± SD of three replicates represents value. A one-way analysis of variance (ANOVA) followed by Duncan’s test was used, and the significant differences at a 5% level (p < 0.05) in the six treatments are represented by different letters.
Table
Table 3. Influences of chitosan soaking on leaf growth of P. grandiflorus plants.
Table 3. Influences of chitosan soaking on leaf growth of P. grandiflorus plants.
Chitosan (%)Leaf Length (mm)Leaf Width (mm)Leaf Area (mm2)
0.0036.38 ± 0.46 b23.90 ± 0.33 b869.46 ± 22.92 b
0.0536.34 ± 0.69 b23.86 ± 0.44 b867.27 ± 32.48 b
0.1036.95 ± 1.06 b24.26 ± 0.68 b897.01 ± 50.45 b
0.1540.46 ± 0.58 a26.57 ± 0.36 a1075.02 ± 29.90 a
0.2040.15 ± 0.56 a26.34 ± 0.37 a1057.82 ± 29.72 a
0.2540.13 ± 0.83 a26.33 ± 0.54 a1057.06 ± 43.30 a
The mean ± SD of three replicates represents value. A one-way analysis of variance (ANOVA) followed by Duncan’s test was used, and the significant differences at a 5% level (p < 0.05) in the six treatments are represented by different letters.
Table
Table 4. Influences of chitosan soaking on height, stem diameter, and overground part dry weight of P. grandiflorus plants.
Table 4. Influences of chitosan soaking on height, stem diameter, and overground part dry weight of P. grandiflorus plants.
Chitosan (%)Plant Height (cm)Stem Diameter (mm)Overground Part Dry Weight (g Plant−1)
0.0027.13 ± 1.32 c1.80 ± 0.15 c1.48 ± 0.14 e
0.0530.32 ± 0.07 b1.79 ± 0.13 c1.53 ± 0.08 e
0.1029.68 ± 1.09 b1.86 ± 0.18 bc1.69 ± 0.07 d
0.1535.13 ± 1.01 a2.16 ± 0.12 a2.86 ± 0.08 a
0.2031.68 ± 1.30 b2.10 ± 0.14 ab2.24 ± 0.10 b
0.2531.32 ± 1.19 b2.05 ± 0.03 ab2.07 ± 0.04 c
The mean ± SD of three replicates represents value. A one-way analysis of variance (ANOVA) followed by Duncan’s test was used, and the significant differences at a 5% level (p < 0.05) in the six treatments are represented by different letters.
Table
Table 5. Influences of chitosan on diameter, fresh weight, and dry weight of P. grandiflorus roots.
Table 5. Influences of chitosan on diameter, fresh weight, and dry weight of P. grandiflorus roots.
Chitosan (%)Root Diameter (mm)Fresh Weight of Root (g Plant−1)Dry Weight of Root (g Plant−1)
0.005.28 ± 0.20 d0.73 ± 0.03 d0.20 ± 0.01 d
0.055.35 ± 0.10 d0.79 ± 0.10 d0.22 ± 0.01 cd
0.105.88 ± 0.23 c0.87 ± 0.03 cd0.23 ± 0.03 cd
0.157.13 ± 0.12 a1.43 ± 0.07 a0.38 ± 0.03 a
0.206.71 ± 0.17 b1.25 ± 0.09 b0.32 ± 0.03 b
0.255.84 ± 0.08 c0.98 ± 0.13 c0.26 ± 0.02 c
The mean ± SD of three replicates represents value. A one-way analysis of variance (ANOVA) followed by Duncan’s test was used, and the significant differences at a 5% level (p < 0.05) in the six treatments are represented by different letters.
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Liu, H.; Zheng, Z.; Han, X.; Zhang, C.; Li, H.; Wu, M. Chitosan Soaking Improves Seed Germination of Platycodon Grandiflorus and Enhances Its Growth, Photosynthesis, Resistance, Yield, and Quality. Horticulturae 2022, 8, 943. https://doi.org/10.3390/horticulturae8100943

AMA Style

Liu H, Zheng Z, Han X, Zhang C, Li H, Wu M. Chitosan Soaking Improves Seed Germination of Platycodon Grandiflorus and Enhances Its Growth, Photosynthesis, Resistance, Yield, and Quality. Horticulturae. 2022; 8(10):943. https://doi.org/10.3390/horticulturae8100943

Chicago/Turabian Style

Liu, Hai, Zhihong Zheng, Xue Han, Cheng Zhang, Haitao Li, and Mingkai Wu. 2022. "Chitosan Soaking Improves Seed Germination of Platycodon Grandiflorus and Enhances Its Growth, Photosynthesis, Resistance, Yield, and Quality" Horticulturae 8, no. 10: 943. https://doi.org/10.3390/horticulturae8100943

APA Style

Liu, H., Zheng, Z., Han, X., Zhang, C., Li, H., & Wu, M. (2022). Chitosan Soaking Improves Seed Germination of Platycodon Grandiflorus and Enhances Its Growth, Photosynthesis, Resistance, Yield, and Quality. Horticulturae, 8(10), 943. https://doi.org/10.3390/horticulturae8100943

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