Effects of Harvest Date on Growth Traits, Root Yield, and Inulin Accumulation in Three Root Chicory (Cichorium intybus L.) Cultivars

 
Introduction
Root chicory (Cichorium intybus L.), a perennial herbaceous species belonging to the family Asteraceae, is recognized as one of the major natural sources of inulin. Its roots contain storage carbohydrates, including sucrose, glucose, fructose, fructooligosaccharides, and inulin, with an average inulin content of approximately 21% of fresh root weight. Since inulin is the principal economic product of root chicory, extraction conditions, particularly extraction method, temperature, and pH, are critical for maximizing its yield and quality. Root yield and inulin accumulation are influenced by the interaction of genetic, environmental, and management factors, particularly genotype and harvest date. Therefore, this study aimed to compare the growth and yield performance of three root chicory cultivars (Chromite, Orchies, and Selenit) and to evaluate the effects of harvest date and sample preparation methods on growth, physiological traits, root yield, and inulin yield under the climatic conditions of Mashhad, Iran.
 
Materials and Methods
The experiment was conducted during the 2025 growing season at the Agricultural and Natural Resources Research Center of Khorasan Razavi Province, Mashhad, Iran. A split-plot experiment based on a randomized complete block design with three replications was employed. Three root chicory cultivars (Chromite, Orchies, and Selenit) were assigned to the main plots, while five harvest dates (23 September, 7 October, 23 October, 6 November, 22 November) were allocated to the subplots.
Seeds were sown on May 14 in plots measuring 8 m× 1.5 m with 50 cm row spacing and 15 cm plant spacing within rows. Irrigation was supplied weekly through a drip irrigation system. At each harvest date, plants were sampled from a 0.75 m² area in each experimental plot. Root yield, root length, root diameter, fresh biomass, harvest index, root dry matter percentage, and leaf electrolyte leakage were determined using standard agronomic and physiological procedures. Leaf electrolyte leakage was measured as an indicator of membrane stability during late-season growth.
To evaluate inulin yield, three sample preparation methods were compared, including fresh roots, air-dried roots, and oven-dried roots. Inulin was extracted from all samples using a hot-water extraction procedure (80–85°C), followed by centrifugation and filtration. Inulin concentration was determined using the anthrone–sulfuric acid colorimetric method, and inulin yield was subsequently calculated from root yield.
The experimental data were subjected to analysis of variance (ANOVA) using Minitab software. Treatment means were compared using the least significant difference (LSD) test at the 5% probability level. Pearson correlation analysis and Hierarchical clustering analysis with heatmap visualization were performed in R Studio to investigate the relationships among measured traits and classify variables according to their similarity patterns.
Results and discussion
Harvest date was the major factor influencing root growth, p hysiological characteristics, and inulin production in root chicory. Root yield increased progressively throughout the growing season, reaching its maximum value (approximately 62–63 t ha⁻¹) at the fourth and fifth harvests (6 November, 22 November). Likewise, root dry matter percentage, harvest index, root diameter, and inulin yield increased toward the end of the growing season, indicating continuous assimilate partitioning and carbohydrate accumulation in the storage roots. In contrast, shoot biomass gradually declined during the late harvests, suggesting the translocation of assimilates from shoots to the storage roots accompanied by leaf senescence. These findings are consistent with previous studies reporting that delayed harvesting promotes dry matter accumulation, root development, and inulin production in root chicory.
The sample preparation method considerably affected the measured inulin yield. Fresh root samples produced the highest inulin yield, followed by air-dried samples, whereas oven-dried samples consistently resulted in lower values. These findings suggest that drying conditions influence fructan stability during sample preparation and consequently affect the measured inulin yield. Similar observations were reported that oven drying reduced inulin recovery because of partial fructan degradation.
Cultivar effects were not significant for most of the measured traits. However, the interaction between cultivar and harvest date was significant for leaf electrolyte leakage and root length. Electrolyte leakage increased during the late harvests, particularly in the Chromite cultivar, indicating reduced membrane stability under end-of-season environmental conditions. Although delayed harvesting enhanced root yield and inulin accumulation, further delaying harvest may increase physiological stress, particularly in the Chromite cultiv .Similar genotype-dependent responses to harvest date have previously been reported in root chicory.
Pearson correlation analysis revealed strong positive relationships among root yield, harvest index, and inulin yield, confirming that greater assimilate allocation to the storage roots was directly associated with increased inulin production.
Conclusion
The present study demonstrated that harvest date is the principal management factor affecting root yield, root dry matter, harvest index, and inulin production in root chicory under the climatic conditions of Mashhad, Iran. Harvesting from early to late November maximized root yield and inulin accumulation, with no significant differences between the final two harvest dates. Cultivar effects were not significant for most agronomic traits. However, the interaction between cultivar and harvest date was significant for leaf electrolyte leakage, indicating that cultivars responded differently across harvest dates. Furthermore, the sample preparation method significantly influenced the measured inulin yield, with fresh and air-dried samples producing higher values than oven-dried samples. Therefore, optimizing both harvest  date and sample preparation method is essential for maximizing inulin production and obtaining reliable estimates of root and inulin yield.  Moreover, because cultivars differed in their physiological responses to harvest date, genotype-specific characteristics should be considered in crop management strategies and future research. Further multi-year and multi-location studies are recommended to validate these findings under different environmental conditions.