Effects of chitosan application on the yield and quality of lettuce

Ovalı, G., and Özdamar Ünlü, H. O. (2024). “Effects of chitosan application on the yield and quality of lettuce,” BioResources 19(1), 985-997.

Abstract

Modern agricultural production has adopted the principle of maximizing yields in an environmental-friendly, inexpensive, and non-hazardous way. With these characteristics, chitosan has become an increasingly preferred biostimulant in sustainable agriculture. The aim of this study was to determine the effects of chitosan application on yield and quality in lettuce cultivation. For this purpose, Yedikule 5107 lettuce variety was used, and foliar chitosan applications were applied 3 times at 4 different doses of 0, 75, 150, and 300 ppm levels. The total yield, leaf number, leaf width, chlorophyll, total phenolic, and antiradical activity values ranged from 2970 to 3290 kg da^-1, from 35.8 to 37.7, from 11.27 to 12.33 cm, from 38.05 to 41.82, from 21.50 to 38.71 mg/100 g, and 46.0% to 54.9%, respectively, and the highest values were obtained in the 300 ppm chitosan application. The highest root collar and plant diameter values were determined at 75 ppm and 150 ppm chitosan doses, respectively. All chitosan applications increased leaf length. Furthermore, chitosan applications were effective in preventing nitrate accumulation. In conclusion, it was determined that the effect of pre-harvest chitosan application was positive, and especially 300 ppm chitosan dose was more effective than other doses.

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Effects of Chitosan Application on the Yield and Quality of Lettuce

Gökhan Ovalı, and Halime Özdamar Ünlü *

DOI: 10.15376/biores.19.1.985-997

Keywords: Bioactive compounds; Chitosan; Lettuce; Nitrate accumulation; Quality; Yield

Contact information: Department of Horticulture, Faculty of Agriculture, Isparta University of Applied Sciences, 32260, Isparta, Türkiye; *Corresponding author: halimeunlu@isparta.edu.tr

INTRODUCTION

Vegetables, which are among the basic nutritional elements, are plants that have an important place in our nutrition in terms of vitamins, minerals, anthocyanins, phenolic, and antioxidant compounds they contain. Raw vegetables are one of the most preferred plant groups for a balanced and healthy diet. They are becoming increasingly popular and consumed because of their health benefits, as well as their accessibility and ease of consumption (Balki 2021; Kaçar 2022). In addition to nutritional health, colour and flavour (taste and aroma) are important quality criteria for consumers (Bhuiyan et al. 2015). Total soluble solids contribute to flavour formation and are responsible for the sweet taste (Vargas-Arcila et al. 2017).

Lettuce is one of the easiest crops to cultivate together with other agricultural products. In addition, due to its high yield and nutrient content, there is an increase in the amount of production in parallel with the awareness of healthy nutrition. For these reasons, considering consumption habits and production values, the importance of practices that will benefit sustainable agriculture in lettuce cultivation is increasing daily (Kaçar 2022). Moreover, the majority of governments and other organizations recognize that the nutritional quality of food is strategically important. Therefore, it is extremely important to identify and develop sustainable, innovative, and inexpensive approaches to increase vegetable production and reduce nitrate concentration at the same time. Excessive nitrate accumulation in vegetables is a widespread problem that poses a potential threat to human health (Bian et al. 2020). This problem is more common in vegetable species, such as lettuce, which has a short vegetation period of 2 to 3 months and whose vegetative parts are consumed. Nitrite, which is formed by the reduction of nitrates because of digestion, causes poisoning, cancer, vitamin A deficiency, “methemoglobinemia”, and other diseases (Karademir 2019).

Regarding the growing global population and the necessity to increase crop production in a sustainable way, the agricultural sector needs innovative ways to improve productivity and resource efficiency. Accordingly, biostimulants have appeared as new, hopeful, and eco-friendly products to enhance the general sustainability of production systems. Among biostimulants, chitosan, which has proven potential to improve plant growth and increase crop quality and yield, has recently attracted considerable attention (Afonso et al. 2022).

Chitosan is a natural, inexpensive, and safe biopolymer that can be obtained in abundant quantities from natural sources. It is of great interest due to its non-toxic, biocompatible, and easily biodegradable properties. Chitosan is used in many industries such as agriculture, food, pharmacy, medicine, cosmetics, wastewater treatment, and textiles (Malerba and Cerena 2016). Along with having antibacterial, antiviral, and antifungal effects, it additionally acts by enhancing the plant’s defensive mechanism to prevent and slow the spread of infections. Additionally, its use in agriculture has become important because of its many positive effects such as chelating metal ions in the environment (soil, water, etc.) and preventing the uptake of toxic metals in plants (Vasconcelos 2014). Chitosan’s effect on plants varies depending on the plant species, application conditions and time, chemical structure, concentration, and molecular weight (Kurtuluş and Vardar 2020). This is supported by a number of studies. For example, Monirul et al. (2018) reported that after applying different doses of chitosan (0, 25, 50, 75, and 100 ppm), the best results were obtained from the dose of 75 ppm in pepper and 50 ppm in tomato. In a study on strawberries, chitosan applications with different molecular weights (5, 12, 21, 50, 125, and 500 kDa) were compared. As a result, the highest yield values were obtained from chitosan with molecular weights of 12, 21 and 50 kDa (Ochmian et al. 2022). In another study, Sultana et al. (2015) reported that as a result of different doses of chitosan (0, 50, 75, 100 ppm) applied to spinach, the 100 ppm chitosan dose significantly increased yield by promoting growth. Elsharkawy and Ghoneim (2019) reported that as a result of applying chitosan to artichoke in different seasons (2014 and 2015) and doses (0, 150, and 300 ppm), the highest yield values were obtained from the 300 ppm chitosan dose in both seasons, but the yield values were lower in the second season than in the first season. This study aimed to determine the effects of different doses of chitosan applications on yield, quality, and nitrate accumulation in lettuce.

EXPERIMENTAL

Experimental Site

This study was conducted in Pamukkale district, Denizli province, Türkiye from October 2019 to February 2020 (37º55′ N, 29º6′ W). The soil texture of the study area was loamy, slightly alkaline (pH: 7.8), salt-free (0.0172%), high in lime (24.05%), low in organic matter (1.19%), high in potassium (K₂O – 48.17 kg/da), and very low in phosphorus (P₂O₅ – 2.75 kg/da). Table 1 presents some climatic parameters of the experimental site.

Table 1. Some Meteorological Data of the Experimental Site between 2019-2020

Materials

Yedikule 5701 lettuce variety was used as plant material in the study. Seedlings were obtained from Ufuk Greenhouse Seedlings and Seeds Company (Denizli, Türkiye).

Low molecular weight chitosan (Sigma–Aldrich, St. Louis, MO, USA) was used for the applications. Chitosan solutions were prepared in 0.15% acetic acid solution at 75 ppm, 150 ppm, and 300 ppm doses, and polyethylene glycol sorbitan monolaurate (Tween 20) (0.5%) was added as a spreader-adhesive. The doses in this study were determined by considering the doses of chitosan that gave the best results in studies conducted on some vegetable species. For example, 75 ppm in pepper and Malabar spinach (Mondal et al. 2011; Monirul et al. 2018), 100 and 125 ppm in okra (Mondal et al. 2012), 100 ppm in spinach (Sultana et al. 2015), and 300 ppm in artichoke (Elsharkawy and Ghoneim 2019).

Experimental Design and Cultural Practices

The experiment was configured in randomized plots, with three replicates, with 15 plants per replicate. Seedlings were planted in the field on 09.10.2019 at a distance of 40 × 25 cm² between rows and above rows. Four different doses (0, 75 ppm, 150 ppm, and 300 ppm) of chitosan as foliar spraying started 4 weeks after transplanting and were applied 3 times with 10-day intervals (November 9, November 19, and November 29). The fertilisation programme for lettuce was calculated and applied according to Güçdemir (2006), based on the data obtained from the soil analysis and taking into account the nutrients contained in the fertilisers to be applied. Therefore, a total of 20 kg mono ammonium phosphate, 10 kg ammonium sulfate, 5 kg potassium sulfate, and 2 kg zinc sulfate were applied twice during the vegetation period (on the 20^th and 40^th days after planting). Yield and quality analyses of lettuce harvested on February 6, 2020, were performed at Isparta University of Applied Sciences, Faculty of Agriculture, Horticulture Laboratory.

Variables Analyzed

Total yield (kg da^-1), plant height (cm), plant diameter (cm), root collar diameter (mm) number of leaves, leaf length and width (cm) were analysed in the study.

Chlorophyll and color values

Measurements were made from 3 different points on the outer 2^nd and 3^rd leaves. Chlorophyll and color values were determined by using the Minolta SPAD-502 chlorophyll meter and the Minolta CR-400 model color device, respectively. Color results were given in terms of CIE L^*, a^*, and b^*. Chroma (C^*) and hue angle (h°) values were calculated according to a^* and b^*values (McGuire 1992).

Total soluble solid (TSS %)

After the outer 2^nd and 3^rd leaves of lettuce plants were homogeneously shredded, the juices were obtained and the TSS was determined using a digital refractometer (Hanna HI96801, Hanna Instruments, Cluj-Napoca, Romania).

Dry matter (%)

Samples taken from the harvested lettuce plants were dried in an oven at 65 °C after determining their wet weights. After reaching constant weight, the samples were weighed on a precision balance, and dry weight values were recorded. The results were calculated according to Kul (2014) and expressed as a percentage.

Ascorbic acid (mg/100 g)

The ascorbic acid content in lettuce samples was determined according to the oxalic acid method described by Cemeroğlu (2013). A homogeneous mixture was obtained with the help of a blender with 2% oxalic acid solution as much as the amount of sample taken from lettuce leaves. The known amount of sample taken from this mixture was made up to 100 mL with oxalic acid and filtered. About 10 mL of the filtrate was titrated with the 2,6-dichlorophenol-indophenol solution. Results are given in mg/100 g.

Total phenolic (mg/100 g)

For the extraction process, 5 g of lettuce sample was homogenized in 20 mL of 95% ethyl alcohol for 2 min. After boiling for 10 min, the homogeneous mixture was centrifuged at 8000 rpm and filtered through a filter paper. Then, 20 mL of 80% ethyl alcohol was added to the samples and boiled for 10 min. The mixture was made up to 100 mL with 80% ethyl alcohol. After extraction, total phenolic matter analysis was completed using the Folin-Ciocalteu reagent according to the method described by Coseteng and Lee (1987), and the results were given in mg/100 g.

Antiradical activity (%)

The 2,2-diphenyl-1-picrylhydrazyl (DPPH) method (Dorman et al. 2003) was used to determine antiradical activity in lettuce leaves. Pureed samples were passed through a filter and centrifuged. About 50 μL of this filtrate was taken, and 450 μL of Tris-HCl buffer (50 mM, pH 7.4) and 1.0 mL of DPPH solution (0.10 mM, in methanol) were added. After the samples were kept in the dark for 30 min, absorbance readings were taken at a wavelength of 517 nm in a spectrophotometer (Boeco-S200 VIS; Bremen Optical Engineering Company, Hamburg, Germany model).

Nitrate accumulation (mg/kg)

Nitrate accumulation in leaves was determined by the salicylic acid method (Cataldo et al. 1975). After adding 10 mL of distilled water to 1.0 g of the sample, the mixture was kept in an incubator at 45 °C for 1 h and centrifuged at 5000 rpm for 15 min. About 0.8 mL of 5% salicylic acid dissolved in sulfuric acid was added to 0.2 mL of the sample. After incubation at room temperature for 20 min, 19 mL of 2 N NaOH solution was added to the samples. Absorbance readings were taken at 410 nm wavelength.

Statistical Analysis

The data were processed by analysis of variance using Minitab (17) Inc. (MINITAB LTD., Coventry, UK) package program. Significant differences between means were revealed using Tukey Test (P < 0.05).

RESULTS AND DISCUSSION

Total Yield

The results showed that chitosan applications significantly affected the total yield of lettuce (P < 0.05). Compared to the control, 300 ppm chitosan application increased the total yield value 8.52% (Table 2). Various studies have reported that chitosan applications significantly increased yield values in pepper (Chookhongkha et al. 2012), okra (Mondal et al. 2012), tomato (Rahman 2015), and in rocket (Özkan 2021). Costales-Menéndez and Falcón-Rodríguez (2020) reported that the yield increase was due to the stimulatory effect of chitosan on plant growth by increasing nutrient availability and absorption as well as photosynthesis through the accumulation of metabolites and increased leaf pigmentation.

Table 2. Effects of Chitosan Applications on Total Yield and Growth Characteristics in Lettuce

Plant Height

When Table 2 is examined, although the effects of the chitosan applications on the plant height of the lettuce were found to be insignificant (P < 0.05), it was determined that at 300 ppm chitosan dose increased the plant height 2.24% compared to the control. This increase can be explained by the fact that chitosan promotes plant growth by influencing plant physiological processes such as protein synthesis, enzyme activation, nutrient uptake, cell division, and cell elongation (Chakraborty et al. 2020). In different studies, chitosan applications increased plant height values in tomato (Rahman 2015), and spinach (Dewi et al. 2020), whereas Jan Mohammadi et al. (2014) found that the effect of chitosan applications on plant length values in lentil was not significant.

Plant Diameter

The highest plant diameter value among the applications was obtained in the 150 ppm chitosan dose, and it was determined that this dose increased the plant diameter value 3.8% compared to the control. Pincay-Manzaba et al. (2021) and Abd El-Aziz et al. (2019) both reported that chitosan treatments increased diameter values in tomato and onion, respectively. Mondal et al. (2012) reported that chitosan positively affected plant growth and development by increasing the activities of key enzymes in nitrogen metabolism and improving nitrogen transport in leaves (Table 2).

Root Collar Diameter

Table 2 shows that the effects of the chitosan applications on root collar diameter were significant (P < 0.05). According to Riseh et al. (2023), chitosan can enter the vascular system of plants and activate plant metabolic pathways by forming a complex with other compounds. As well as providing the plant with the nutrients it needs, it can form bonds with other natural polymers and combine with fertiliser and other nutrients to improve the texture of the soil. This report may explain the reason for the 2.5% (75 ppm chitosan application) increase in root collar diameter compared to the control. Supporting this study, Abd El-Aziz et al. (2019) reported that chitosan increased the neck diameter of onion.

Number of Leaves per Plant

Table 2 demonstrates that the effect of chitosan application on leaf number was positive. Abd El-Aziz et al. (2019) in onion, Abdelaal et al. (2021) in garlic, and Nurliana et al. (2022) in lettuce reported that chitosan applications increased the number of leaves in plants. Supported by these reports, in this study, it was determined that the leaf numbers increased 3.2% in the 300 ppm chitosan application compared to the control. According to Vasconsuelo et al. (2004) chitosan applications increased the lignification of cell walls and lignin biosynthesis in plants and thus triggered shoot formation in plants.

Leaf Length

The effects of chitosan applications on the leaf length of lettuce were significant (P < 0.05). It was observed that chitosan applications increased leaf length 5.5% (150 ppm), 6.2% (300 ppm), and 6.6% (75 ppm) compared to the control (Table 2). In agreement with the current findings, Sultana et al. (2015) and Dewi et al. (2020) reported that chitosan increased leaf length in strawberry, and spinach, respectively. Furthermore, Saharan and Pal (2016) reported that chitosan application can enhance plant growth by increasing auxin hormone synthesis. However, the mechanism by which this hormone synthesis is increased is not yet understood.

Leaf Width

In this study, it was observed that chitosan applications (especially 300 ppm chitosan dose) had a positive effect on leaf width compared to the control (Table 2). Similarly, Dewi et al. (2020) in spinach, and Nurliana et al. (2022) in lettuce reported that chitosan applications increased leaf width.

Chlorophyll

Table 3 shows that the effects of chitosan applications on chlorophyll values were significant (P < 0.05). The highest values were found in 300 ppm chitosan application and control. Different from the current findings, Mondal et al. (2012) reported that chitosan applications increased chlorophyll content in okra, Xu and Mou (2018) in lettuce, and Özkan (2021) in rocket.

Table 3. Effects of Chitosan Applications on Chlorophyll, TSS, and Dry Matter in Lettuce

TSS

The effect of chitosan on the TSS of lettuce was insignificant (P < 0.05) (Table 3). The lowest value was found in the control (3.89%), while the highest value was obtained from the 75 ppm chitosan application. Similarly, Ibraheim and Mohsen (2015) in zucchini, and Özkan (2021) in rocket reported that chitosan applications increased the amount of TSS, but this increase was statistically insignificant.

Dry Matter

When the results on dry matter values were analyzed, despite being insignificant, the 75 and 300 ppm chitosan doses gave better values (Table 3). According to various studies on chitosan, it increases the dry matter content of okra (Mondal et al. 2012) and rocket (Özkan 2021).

Leaf Color

In this study, L^* values ranging from 45.3 to 46.5, a^* values from -17.2 to -18.0, b^* values between 26.2 and 27.5, C^* values from 31.3 to 32.8, and h° values between 123.7 and 123.6 were obtained (Table 4). Although the effects of chitosan treatments on leaf color values were insignificant, it was determined that chitosan caused relatively better results compared to the control. Chookhongkha et al. (2012) reported positive effects of chitosan applications on leaf color values in pepper and Özkan (2021) in rocket.

Table 4. Effects of Chitosan Applications on Leaf Color Values in Lettuce

Ascorbic Acid

The effects of the chitosan applications on ascorbic acid in lettuce were insignificant (P < 0.05) (Fig. 1). Ascorbic acid values ranged between 7.24 and 7.54 mg/100 g. However, when the data were examined, it was determined that chitosan applications decreased ascorbic acid values compared to the control. A similar situation, i.e., decrease in ascorbic acid values with increasing chitosan doses, was reported by Sultana et al. (2017) and Özkan (2021). Zoldners et al. (2005) described that as the presence of chitosan significantly accelerates ascorbic acid oxidation and this effect varies depending on the chitosan/ascorbic acid ratio.

Total Phenolic Content

The results showed that chitosan applications significantly affected the total phenolic content of lettuce (P < 0.05). A 300 ppm chitosan application showed the highest total phenolic value. This application was followed by the 150 ppm application. The lowest total phenolic values were found in 75 ppm chitosan and control applications (Fig. 1).

Plants need constitutive defense and induced defense to regulate their basal metabolism and thus accelerate secondary metabolic processes. It has been demonstrated that chitosan is an elicitor (stimulant) that causes a variety of biological reactions in some plants (Zheng et al. 2021). Kurtuluş and Vardar (2020) stated that chitosan is used as an abiotic elicitor in the production of secondary metabolites in plant cell and tissue cultures, increases defense responses against biotic and abiotic stresses in plants, and increases the amount of phenolic compounds and proteins by activating some genes in signaling pathways. Furthermore, in studies conducted by different researchers, it was found that chitosan applications increased phenolic matter content in Hypericum perforatum (Brasili et al. 2014), tea (Srisornkompon et al. 2014), and rocket (Özkan 2021). These reports further support the results from this study.

Fig. 1. Effects of chitosan applications on ascorbic acid, total phenolic, antiradical activity, and nitrate accumulation in lettuce

Antiradical Activity

When Fig 1 is examined, it is seen that the effects of the chitosan applications on antiradical activity are significant (P < 0.05). It was determined that chitosan applications increased the antiradical activity 10% (at 75 ppm chitosan dose), 15% (at 150 ppm chitosan dose), and 19% (at 300 ppm chitosan dose) compared to the control. In support of these results, different researchers reported that chitosan applications significantly increased antioxidant activity in lettuce sprouts (Viacava and Roura 2015), spinach (Singh 2016), tomato (Hernández-Hernández et al. 2018), and rocket (Özkan 2021).

Nitrate Accumulation

The effects of different doses of chitosan applications on nitrate content in lettuce were significant. The highest nitrate value was found in the control (1680 mg/kg), while the lowest nitrate content was obtained from the 300 ppm dose of chitosan application (1450 mg/kg) (Fig. 1).

According to the Turkish Food Codex 2008 data, the highest acceptable nitrate value for lettuce grown in open conditions harvested between October 1 and March 31 is 4000 mg/kg, while this value is 4500 mg/kg for lettuce grown under cover (Karademir 2019). The current study was below these limits, and it was determined that chitosan applications reduced nitrate content 4.4% (at 150 ppm chitosan dose), 13.05% (at 75 ppm chitosan dose), and 13.4% (at 300 ppm chitosan dose), respectively, compared to the control.

In support of the current findings, Chung et al. (2001) and Özkan (2021) found that chitosan applications reduced nitrate content in lettuce and rocket 14% to 18% and 4% to 9%, respectively, compared to the control group. Similarly, Mondal et al. (2012, 2016) reported that chitosan treatments increased nitrate reductase activity leading to reduced nitrate accumulation.

CONCLUSIONS

In this study, lettuce yield varied between 2970 and 3290 kg/da, and it was determined that 300 ppm chitosan application increased the yield 8.5% compared to the control. In addition, 300 ppm chitosan application had a positive effect on leaf number, leaf width, chlorophyll and total phenolic contents, and antiradical activity values. While 75 ppm chitosan application had the highest root collar diameter value, 150 ppm chitosan application had the highest plant diameter value.

It was determined that all chitosan doses increased leaf length and decreased nitrate accumulation compared to the control.

As a result, when all parameters were evaluated, it was observed that chitosan application, especially 300 ppm dose, made positive contributions not only to yield and yield parameters but also to bioactive compounds (total phenolic and antiradical activity) and nitrate, which are of great importance for human health.

In addition, the fact that the best results were generally determined at the highest dose among the applications in the study reveals the necessity of new studies at higher levels of this dose.

ACKNOWLEDGMENTS

This study is derived from Gökhan Ovalı’s master’s thesis.

REFERENCES CITED

Abd El-Aziz, M. E., Morsi, S. M. M., Salama, D. M., Abdel-Aziz, M. S., Abd Elwahed, M. S., Shaaban, E. A., and Youssef, A. M. (2019). “Preparation and characterization of chitosan/polyacrylic acid/copper nanocomposites and their impact on onion production,” International Journal of Biological Macromolecules 123, 856-865. DOI: 10.1016/j.ijbiomac.2018.11.155

Abdelaal, K., AlKahtani, M., Attia, K., Hafez, Y., Király, L., and Künstler, A. (2021). “The role of plant growth-promoting bacteria in alleviating the adverse effects of drought on plants,” Biology 10(6), article 520. DOI: 10.3390/biology10060520

Afonso, S., Oliveira, I., Meyer, A. S., and Gonçalves, B. (2022). “Biostimulants to improved tree physiology and fruit quality: A review with special focus on sweet cherry,” Agronomy 12(3), article 659. DOI: 10.3390/agronomy12030659

Balki, V. M. (2021). Investigation of Expanded Spectrum Beta Lactamase and Carbapenemase Producing Enterobacteriales Strains in Green Vegetables, Master’s Thesis, School of Graduate Studies Department of Food Engineering, Çanakkale Onsekiz Mart University, Çanakkale, Turkey.

Bhuiyan, F., and Rahim, A. T. M. (2015). “Consumer’s sensory perception of food attributes: A survey on flavor,” Journal of Food and Nutrition Sciences 3(1), article 157. DOI: 10.11648/j.jfns.s.2015030102.40

Bian, Z., Wang, Y., Zhang, X., Li, T., Grundy, S., Yang, Q., and Cheng, R. A. (2020). “A review of environment effects on nitrate accumulation in leafy vegetables grown in controlled environments,” Foods 9(6), article 732. DOI: 10.3390/foods9060732

Brasili, E., Pratico, G., Marini, F., Valletta, A., Capuani, G., Sciubba, F., Miccheli, A., and Pasqua, G. (2014). “A non-targeted metabolomics approach to evaluate the effects of biomass growth and chitosan elicitation on primary and secondary metabolism of hypericum perforatum in vitro roots,” Metabolomics 10(6), 1186-1196.

Cataldo, D. A., Maroon, M., Schrader, L. E., and Youngs, V. L. (1975). “Rapid colorimetric determination of nitrate in plant tissue by nitration of salicylic acid,” Communications in Soil Science and Plant Analysis 6(1), 71-80. DOI: 10.1080/00103627509366547

Cemeroğlu, B. (2013). Basic Analysis Methods in the Fruit and Vegetable Processing Industry, Biltav Publications, Ankara, Turkey.

Chakraborty, M., Hasanuzzaman, M., Rahman, M., Khan, M. A. R., Bhowmik, P., Mahmud, N. U., et al. (2020). “Mechanism of plant growth promotion and disease suppression by chitosan biopolymer,” Agriculture 10(12), article 624. DOI: 10.3390/agriculture10120624

Chookhongkha, N., Miyagawa, S., Jirakiattikul, Y., and Photchanachai, S. (2012). “Chili growth and seed productivity as affected by chitosan,” International Conference on Agriculture Technology and Food Sciences (ICATFS’2012), Manila, Philippines, pp. 146-149.

Chung, J. B., Park, S. G., and Park, S. (2001). “Suppression of nitrate accumulation in lettuce by application of Mg and micronutrients,” Korean Journal of Environmental Agriculture 20(5), 340-345.

Coseteng, M. Y., and Lee, C. Y. (1987). “Changes in apple polyphenoloxidase and
polyphenol concentrations in relation to degree of browning,” Journal of Food
Science 52(4), 985-989. DOI: 10.1111/j.1365-2621.1987.tb14257.x

Costales-Menéndez, D., and Falcón-Rodríguez, A. B. (2020). “Effect of chitosan molecular mass on germination and in vitro growth of soy,” Cultivos Tropicales 41(1), article E05.

Dewi, A. K., Aulya, D. Z. Z., and Suryadi, E. (2020). “The effect of chitosan radiation of spinach plant based on agronomy characteristics on hydroponics floating system,” Journal of Physics: Conference Series 1436(1), 1-6. DOI: 10.1088/1742-6596/1436/1/012031

Dorman, H. J. D., Peltoketo, A., Hiltunen, R., and Tikkanen, M. J. (2003). “Characterisation of the antioxidant properties of de-odourised aqueous extracts from selected lamiaceae herbs,” Food Chemistry 83(2), 255-262. DOI: 10.1016/S0308-8146(03)00088-8

Güçdemir, İ. H. (2006). Türkiye Fertiliser and Fertilisation Guide (Updated and Expanded 5th Edition), Soil Fertiliser and Water Resources Central Research Institute Directorate, General Publication No: 231, Technical Publication No: T69, Ankara.

Hernández-Hernández, H., González-Morales, S., Benavides-Mendoza, A., Ortega-Ortiz, H., Cadenas-Pliego, G., and Juárez-Maldonado, A. (2018). “Effects of chitosan–PVA and Cu nanoparticles on the growth and antioxidant capacity of tomato under saline stress,” Molecules 23(1), article 178. DOI: 10.3390/molecules23010178

Ibraheim, S. K. A., and Mohsen, A. A. M. (2015). “Effect of chitosan and nitrogen rates on growth and productivity of summer squash plants,” Middle East Journal 4(4), 673-681.

Janmohammadi, M., Mostafavi, H., Kazemi, H., Mahdavinia, G. R., and Sabaghnia, N. (2014). “Effect of chitosan application on the performance of lentil genotypes under rainfed conditions,” Acta Technologica Agriculturae 17(4), 86-90. DOI: 10.2478/ata-2014-0020

Kaçar, Y. (2022). The Effects of Some Plant Activators on the Yield and Quality Properties of Bacchus Lettuce Cultivar, Master’s Thesis, Institute of Natural and Applied Sciences, Akdeniz University, Antalya, Turkey.

Karademir, S. (2019). Determination of the Effects of Vermicompost Applications at Different Rates on Plant Growth, Quality Properties and Nutrient Content in Lettuce (Lactuca sativa L.), Master’s Thesis, Graduate School of Natural and Applied Sciences, Bolu Abant Izzet Baysal University, Bolu, Turkey.

Kul, R. (2014). Effect of Fish Manure, Mineral Fertilizer and Combinations on Plant Growth and Nutrient Content of Lettuce (Lactuca sativa L.), Master’s Thesis, Graduate School of Natural and Applied Sciences, Atatürk University, Erzurum, Turkey.

Kurtuluş, G., and Vardar, F. (2020). “Kitosanın özellikleri, uygulama alanları, bitki sistemlerine etkileri [Properties of chitosan, application areas, effects on plant systems],” International Journal of Advances in Engineering and Pure Sciences 32(3), 258-269.

Malerba, M., and Cerena, R. (2016). “Chitosan effects on plant systems,” International Journal of Molecular Sciences 17(7), article 996. DOI: 10.3390/ijms17070996

McGuire, R. G. (1992). “Reporting of objective color measurements,” HortScience 27(12), 1254-1255.

Mondal, M. M. A., Malek, M. A., Puteh, A. B., Ismail, M. R., Ashrafuzzaman, M., and Naher, L. (2012). “Effect of foliar application of chitosan on growth and yield in okra,” Australian Journal of Crop Science 685, 918-921.

Mondal, M., Puteh, A. B., and Dafader, N. C. (2016). “Foliar application of chitosan improved morphophysiological attributes and yield in summer tomato (Solanum Lycopersicum),” Pakistan Journal of Agricultural Sciences 53(2), 339-344. DOI: 10.21162/PAKJAS/16.2011

Monirul, I., Humayun, K., Mamun, A. N. K., and Pronabananda, D. (2018). “Studies on
yield and yield attributes in tomato and chilli using foliar application of oligochitosan,” GSC Biological and Pharmaceutical Sciences 3(3), 20-28.
DOI: 10.30574/gscbps.2018.3.3.0038

Nurliana, S., Fachriza, S., Hemelda, N. M., and Yuniati, R. (2022). “Chitosan application for maintaining the growth of lettuce (Lactuca sativa) under drought condition,” Earth and Environmental Science 980(1), 12-13. DOI: 10.1088/1755-1315/980/1/012013

Ochmian, I., Lachowicz, S., and Krupa-Małkiewicz, M. (2022). “The effect of different molecular weights of chitosan on the yield, quality, and health-promoting properties of strawberries,” Progress on Chemistry and Application of Chitin and its Derivatives 27, 194-203. DOI: 10.15259/PCACD.27.015

Özkan, A. (2021). The Effects of Chitosan Applications on the Yield and Quality in Rocket (Eruca sativa), Master’s Thesis, The Institute of Graduate Education, Isparta University of Applied Sciences, Isparta, Turkey.

Pincay-Manzaba, D. F., Cedeño-Loor, J. C., and Espinosa Cunuhay, K. A. (2021). “Efecto del quitosano sobre el crecimiento y la productividad de Solanum lycopersicum,” [“Effect of chitosan on the growth and productivity of Solanum lycopersicum”], Centro Agrícola 48(3), 25-31.

Rahman, M. A. (2015). Performance of Modified Chitosan Treated Tomato (Lycopersicon esculentum) Seedlings on the Growth and Yield of Tomato, Ph.D. Thesis, Department of Soil Science, Sher-E-Bangla Agricultural University, Dhaka, Bangladesh.

Riseh, R. S., Vazvani, M. G., and Kennedy, J. F. (2023). “The application of chitosan as a carrier for fertilizer: A review,” International Journal of Biological Macromolecules 126483. DOI: 10.1016/j.ijbiomac.2023.126483

Saharan, V., and Pal, A. (2016). Chitosan-based Nanomaterials in Plant Growth and Protection, Springer, New Delhi, India.

Singh, S. (2016). “Enhancing phytochemical levels, enzymatic and antioxidant activity of spinach leaves by chitosan treatment and an insight into the metabolic pathway using DART-MS technique,” Food Chemistry 199, 176-184. DOI: 10.1016/j.foodchem.2015.11.127

Srisornkompon, P., Pichyangkura, R., and Chadchawan, S. (2014). “Chitosan increased phenolic compound contents in tea (Camellia sinensis) leaves by pre-and post-treatments,” Journal of Chitin and Chitosan Science 2(2), 93-98. DOI: 10.1166/jcc.2014.1056

Sultana, S., Dafader, N. C., Kabir, H., Khatun, F., Rahman, M., and Alam, J. (2015). “Application of oligo-chitosan in leaf vegetable (spinach) production,” Nuclear Science and Applications 24(1-2), 55-56.

Sultana, S., Islam, M., Khatun, M. A., Hassain, M. A., and Huque, R. (2017). “Effect of foliar application of oligo-chitosan on growth, yield and quality of tomato and eggplant,” Asian Journal of Agricultural Research 11(2), 36-42. DOI: 10.3923/ajar.2017.36.42

Turkish Food Codex (2008). “Notification No. 2008/26 on maximum levels for certain contaminants in foodstuffs,” https://faolex.fao.org/docs/pdf/tur106694.pdf

Vargas-Arcila, M., Cartagena-Valenzuela, J. R., Franco, G., Correa-Londoño, G. A., Quintero-Vásquez, L. M., and Gaviria-Montoya, C. A. (2017). “Changes in the physico-chemical properties of four lettuce (Lactuca sativa L.) varieties during storage,” Ciencia y Tecnología Agropecuaria 18(2), 257-273. DOI: 10.21930/rcta.vol18_num2_art:632

Vasconcelos, M. W. (2014). “Chitosan and chitooligosaccharide utilization in phytoremediation and biofortification programs: current knowledge and future perspectives,” Frontiers in Plant Science 5, article 616. DOI: 10.3389/fpls.2014.00616

Vasconsuelo, A., Giulietti, A. M., and Boland, R. (2004). “Signal transduction events mediating chitosan stimulation of anthraquinone synthesis in Rubia tinctorum,” Plant Science 166(2), 405-413. DOI: 10.1016/j.plantsci.2003.10.007

Viacava, G. E., and Roura, S. I. (2015). “Principal component and hierarchical cluster analysis to select natural elicitors for enhancing phytochemical content and antioxidant activity of lettuce sprouts,” Scientia Horticulturae 193, 13-21. DOI: 10.1016/j.scienta.2015.06.041

Xu, C., and Mou, B. (2018). “Chitosan as soil amendment affects lettuce growth, photochemical efficiency, and gas exchange,” HortTechnology 28(4), 476-480. DOI: 10.21273/HORTTECH04032-18

Zheng, K., Lu, J., Li, J., Yu, Y., Zhang, J., He, Z., Ismail, O. M., Wu, J., Xie, X., Li, X., et al. (2021). “Efficiency of chitosan application against Phytophthora infestans and the activation of defense mechanisms in potato,” International Journal of Biological Macromolecules 182, 1670-1680. DOI: 10.1016/j.ijbiomac.2021.05.097

Zoldners, J., Kiseleva, T., and Kaiminsh, I. (2005). “Influence of ascorbic acid on the stability of chitosan solutions,” Carbohydrate Polymers 60(2), 215-218. DOI: 10.1016/j.carbpol.2005.01.013

Article submitted: October 28, 2023; Peer review completed: December 2, 2023; Revised version received and accepted: December 7, 2023; Published: December 14, 2023.

DOI: 10.15376/biores.19.1.985-997