با همکاری انجمن علمی منظر ایران
نوع مقاله : مقالات پژوهشی
نویسندگان
1 گروه علوم باغبانی، دانشکده کشاورزی دانشگاه زنجان، زنجان، ایران
2 دانشگاه زنجان
3 علوم باغبانی، دانشکده کشاورزی دانشگاه زنجان، زنجان، ایران
کلیدواژه‌ها
عنوان مقاله English
نویسندگان English
Introduction
Strawberry (Fragaria × ananassa Duch.) is among the most economically important and widely consumed small fruits worldwide, owing to its high nutritional value, desirable flavor, and strong antioxidant properties. It is rich in vitamins (particularly vitamin C), minerals, and phenolic compounds such as anthocyanins, flavonoids, and ellagic acid, which contribute significantly to human health. As a non-climacteric fruit, strawberry does not undergo further ripening after harvest; therefore, its final quality is largely determined during the pre-harvest stage. This underscores the importance of pre-harvest management strategies to enhance fruit quality. In recent years, biostimulants have emerged as sustainable alternatives to conventional chemical inputs in agriculture., Even at low concentrations, these substances can enhance plant physiological processes, improve stress tolerance, and promote crop quality. Among them, amino acids and seaweed extracts have attracted considerable attention. Tryptophan serves as a precursor for auxin (IAA) and melatonin, playing a crucial role in cell division, enlargement, fruit set, and the biosynthesis of secondary metabolite. External application of tryptophan can increase endogenous auxin levels, improve nutrient uptake efficiency, and enhance plant growth and productivity. The brown seaweed extract Ascophyllum nodosum is widely used in agriculture due to its rich content of bioactive compounds such as polysaccharides, plant hormones (cytokinin, auxins, gibberellins), betaines, micronutrients, and antioxidants. Previous studies have shown that this extract can improve vegetative growth, nutrient absorption, and phenolic compound biosynthesis, ultimately enhancing fruit quality and yield. Hydroponic cultivation, which allows precise control of plant nutrition and eliminates soil-related limitations, provides an ideal system for producing high-quality strawberries. This study aimed to evaluate the effects of different concentrations of tryptophan and A. nodosum extract on morphological and biochemical traits of strawberry (cv. Albion) under hydroponic conditions.
Materials and Methods
The experiment was conducted in a greenhouse in Zanjan, Iran, on strawberry (cv.Albion) plants, using a randomized complete block design with seven treatments and three replications. Treatments included three concentrations of tryptophan (1, 2, and 3 mM), three concentrations of A.nodosum extract (1, 2, and 3 gL-1), and a control (distilled water). Foliar spraying was applied twice during the green fruit stage. Plants were grown in cocopeat and perlite substrate under controlled temperature and humidity conditions. Various traits were measured, including fruit weight, size, volume, firmness, total soluble solids (TSS), titratable acidity (TA), dry matter, leaf chlorophyll, ascorbic acid, total phenols, flavonoids, antioxidant capacity, and anthocyanin content. Statistical analysis was performed using SPSS software.
Results and Discussion
Treatments significantly affected fruit weight, length, diameter, volume, and firmness. The 1 mM tryptophan treatment produced the highest fruit weight, length, and volume, showing notable improvements compared to the control. Seaweed extract treatments (especially 2 and 3 gL-1) also increased fruit size and volume. These effects are mainly attributed to increased auxin synthesis, which stimulates cell division and enlargement. However, fruit firmness decreased in all treatments, especially with tryptophan. This reduction may be due to enhanced ripening processes influenced by melatonin and auxin, which regulate cell wall degradation. Although softer fruits may indicate better ripeness, this could negatively affect storage and transport.
The treatments significantly influenced dry matter, chlorophyll content, ascorbic acid, phenols, flavonoids, antioxidant capacity, and anthocyanin, but had no significant effect on TSS, TA, or taste index. The significantly enhancement of leaf chlorophyll content in all treatments, especially in 1 and 2 mM tryptophan, shows the role of this bio stimulate in improving the photosynthetic efficiency of plant. Amino acids involve in growing up chlorophyll content by increasing the absorbance of micronutrients like Iron and magnesium which attend in chlorophyll structure. The highest content of ascorbic acid was observed in 1 mM tryptophan and 1 gL-1 A. nodosum extract, this issue could be the result of enhancement of chlorophyll content and raising of photosynthesis level by amino acids efficiency. Amino acids improve the antioxidant system of plants by enhancing the activity of enzymes that involves in ascorbic acid synthesis. In addition, the results showed the highest content of total phenol in 2 and 3 gL-1 A. nodosum extract and the highest flavonoids content in 3 gL-1 concentrations of this treatment. The extract of A. nodosum is full of compositions which act as elicitors that stimulate the expression of genes which involve in biosynthesis of secondary metabolites. The highest antioxidant capacity belonged to 3 gL-1 A. nodosum extract and also the highest content of anthocyanin was determined in 3 mM tryptophan and 2 gL-1 A. nodosum extract. Sea weeds are the affluent sources of antioxidants like various phenolic compounds that play the role in prevention of oxidation. Moreover, A. nodosum extract possess high content of potassium which participate in anthocyanin synthesis as a co-factor. Enhancement of anthocyanin in fruits treated with tryptophan can be related to the activity of this substance as precursor of IAA and melatonin synthesis that impact the signaling path and lead to expression of key genes of anthocyanin synthesis.
Conclusion
This research indicates that the pre-harvest application of tryptophan and extract of A.nodosum, could be an effective and environmentally friendly technique to ameliorate the qualitative and quantitative characteristics and enhancement the nutritional values of strawberry fruit (cv. Albion) which cultivated in hydroponic system. Based on obtained results, 1 mM tryptophan is recommended due to its ability to enhance the fruit weight and dimensions. On the other, the extract of A.nodosum in 3 gL-1 concentration is suggested because of capability in increasing of dry matter, antioxidant capacity and total phenols content of strawberry fruit. Moreover, 3 mM tryptophan and 2 gL-1 A.nodosum extract were more effective in rising of anthocyanin content. According to non-climacteric nature of strawberry fruit and determination of fruit terminal quality in pre-harvest phase, usage of bio stimulates could be an influential way for producing high quality and healthy crops with lower dependence to chemical inputs.
کلیدواژه‌ها English
