Introduction
Lettuce, with the scientific name Lactuca sativa L., is an annual, self-pollinating, cool-season vegetable belonging to the Asteraceae family. Its leaves are rich in antioxidant compounds, vitamins, and essential nutrients beneficial to human health. The genus Lactuca comprises over 100 species, of which 20 belong to lettuce (Lactuca sativa). Numerous researchers have reported extensive diversity in morphological, biochemical, and genetic traits among different lettuce genotypes (Kumar et al., 2016; Dahal et al., 2021; Volpe et al., 2021; Asadi et al., 2022). According to FAO statistics, the production of various lettuce cultivars and lines has experienced a 118% growth over the past two decades, placing lettuce as the fifth most widely cultivated crop globally after corn, rice, potatoes, and tomatoes in terms of cultivated area (FAO, 2023). In Iran, lettuce is one of the most common leafy vegetables cultivated across various regions of the country. Alongside increasing market demand and the economic viability of lettuce production, diverse genotypes of different types—including leaf, stem, romaine, and iceberg—have been developed. Although romaine-type lettuces account for the majority of cultivated areas in Iran, in recent years, several well-adapted genotypes suitable for different regions in the north and south of the country have been introduced or are under development, receiving widespread acceptance. Evaluating and introducing suitable and adapted lettuce genotypes with desirable quantitative and qualitative traits, alongside indigenous Iranian lettuces, is of great importance (Mousavi et al., 2024). Accordingly, in the present study, several commercial lettuce genotypes of stem and leaf types were investigated under field conditions to identify superior cultivars and lines based on qualitative characteristics.
Materials and methods
The present study was conducted in both field and laboratory settings at the Greenhouse and Controlled Environment Research Institute, using a randomized complete block design with three replications. Seeds of lettuce cultivars including Batavia, Mignonette, Prize Head, Bull Red, Tango, French Red, Ice Green, Lines 4, 7 and 20 Roman were sown in 6×12-cell seedling trays containing a cocopeat : perlite (4:1) growing medium for seedling production. Seedlings at the 3-4 leaf stage were transplanted to the main cultivation beds in the field. Each cultivar was planted in 25-meter-long rows with 50 cm bed width, maintaining 50 cm spacing between plants within rows. Uniform cultivation practices including temperature control, humidity management, irrigation, and weed removal were applied to all plants. The drip irrigation system operated for one hour every two days. Following harvest, qualitative traits including pH, titratable acidity, total soluble solids, chlorophylls, carotenoids, total phenolic compounds, anthocyanin and antioxidant capacity were measured in the collected cultivars and lines. Statistical analysis was performed using SPSS software (version 21), with mean comparisons conducted using Duncan's test at the 5% probability level. Graphs were generated using Microsoft Excel (2013 version).
Results and discussion
According to the results of analysis variance, the qualitative traits studied were significantly influenced by lettuce cultivar type. The highest titratable acidity (1.52%), pH (5.38), and soluble solids content (6.83 Brix) were measured in Bull Red, Ice Green, and Line 20 Roman, respectively. The maximum chlorophyll a (13.36 mg g-1 fresh weight) and b (7.57 mg g-1 fresh weight) content were recorded in Mignonette and French Red cultivars, respectively. Line 20 Roman showed the highest carotenoid content, while Line 7 Roman exhibited the lowest value. Significant differences were observed among lettuce genotypes regarding total phenol and anthocyanin content. The highest total phenol content was recorded in Bull Red (616.17 mg g-1 fresh weight), followed by French Red (553.95 mg g-1 fresh weight). Bull Red and Mignonette cultivars contained the highest anthocyanin levels (3.768 and 1.823 mmol g-1 fresh weight, respectively). Regarding antioxidant capacity, Bull Red (97.75%), Line 20 Roman (93.41%), and Mignonette (92.74%) demonstrated the highest antioxidant activity. Variations in qualitative characteristics among different lettuce cultivars and lines are primarily influenced by genetic traits that determine flavor and taste differences among genotypes. The diversity in qualitative leaf traits (e.g., color and flavor) among lettuce cultivars has been attributed to underlying genetic differences (Volpe et al., 2021). Biosynthetic pathways and enzymes involved in the metabolism of various compounds—such as carotenoids and phenolic—vary significantly. Furthermore, their synthesis mechanisms, transporters, and metabolic pathways are genetically regulated (Dahal et al., 2021; Asadi et al., 2022).
Conclusion
Based on the assayed quality traits, Bull Red, Mignonette, French Red, and Line 20 Roman cultivars with desirable qualitative characteristics are recommended for lettuce cultivation and production. |
