Localización del experimento

El experimento se realizó en el invernadero de la finca experimental "La María", de la Universidad Técnica Estatal de Quevedo, ubicada en el km 7,5 de la vía Quevedo-Mocache, cantón Mocache, provincia de Los Ríos, Ecuador (1°04'48,6" longitud oeste; 01°03'18" latitud sur; 75 m s. n. m.). La temperatura promedio anual del sitio fue de 24,4 °C, la precipitación de 3029,30 mm año^-1 y la humedad relativa del 88 %.

Tratamientos y diseño experimental

Se evaluaron tres concentraciones de quitosano que se obtuvo comercialmente como polímero de quitina desacetilado, D-glucosamine (Aldrich), el T1 consistió en (1000 mg L^-1), T2 (1500 mg L^-1 ) y T3 (2500 mg L^-1) y un tratamiento control con agua destilada, distribuidos en un diseño de bloques completos al azar con cinco repeticiones. Cada unidad experimental (UE) comprendió 12 plantas con distancias de siembra de 33 cm entre plantas y 43 cm entre hileras (1,70 m² cada UE), para un total de 240 plantas en el experimento.

Las plántulas se produjeron en bandejas de polietileno con sustrato compuesto por suelo y arena de río en proporción 3:2 (v:v). A los 20 días después de la siembra, las raíces de las plántulas fueron sometidas a inmersión durante una hora en las soluciones de quitosano correspondientes a cada tratamiento, o en agua destilada en el caso del control. Concluida la inmersión, se trasplantó una plántula por maceta con 2 kg del mismo sustrato utilizado en la fase de almácigo.

Manejo agronómico

El control de malezas se realizó de forma manual. A partir de los 15 DDT se aplicó azoxistrobina semanalmente para el manejo preventivo y curativo de enfermedades fúngicas, y metomilo para la prevención de plagas insectiles, no se aplicó fertilizantes de ningún tipo.

Variables evaluadas

Las variables morfoagronómicas se evaluaron en seis plantas por unidad experimental. Las variables de crecimiento vegetativo se registraron a los 8, 15, 22 y 30 DDT; las productivas, al momento de la cosecha.

La altura de planta (cm) se midió con cinta métrica desde la base del tallo hasta el ápice vegetativo. La longitud de hoja (cm) se determinó desde la base del limbo hasta el ápice foliar, y el ancho de hoja (cm) en la región de mayor expansión laminar. El número de hojas se obtuvo por conteo directo de hojas completamente desarrolladas.

El diámetro polar y el diámetro ecuatorial de la raíz se midieron con calibrador de pie de rey (mm); el primero correspondió a la distancia longitudinal máxima de la raíz y el segundo a la zona de mayor expansión transversal. El peso fresco de la raíz (g) se determinó en balanza analítica inmediatamente después de la cosecha. El rendimiento agrícola (kg ha^-1) se estimó a partir del peso fresco total de las raíces por parcela experimental (1,70 m²), extrapolado proporcionalmente a hectárea (10000 m²).

Análisis estadístico

Los datos fueron sometidos a pruebas de normalidad de residuales (Shapiro-Wilk) y de homogeneidad de varianzas (Bartlett), cuyos resultados confirmaron el cumplimiento de los supuestos paramétricos. Se aplicó análisis de varianza (ANOVA) de bloques completos al azar y, para las variables con diferencias significativas entre tratamientos, se realizó la comparación de medias mediante la prueba de Tukey (p < 0,05). Los análisis se ejecutaron con el software R versión 4.4.1 (R Core Team, 2024).

Crecimiento vegetativo: longitud de planta

La longitud de planta no mostró diferencias estadísticas entre tratamientos a los 8, 22 y 30 DDT; sin embargo, a los 15 DDT se registró un efecto significativo, con la mayor elongación en el tratamiento de 1000 mg L^-1 y los menores promedios en la dosis de 2500 mg L^-1 en todas las fechas de evaluación (Figura 1). Este patrón temporal indica que el efecto del quitosano sobre la elongación del tallo se concentra en las etapas de establecimiento temprano y se atenúa conforme avanza el ciclo del cultivo.

La respuesta diferencial entre dosis es coherente con el comportamiento dosis-dependiente del quitosano, en el que concentraciones moderadas activan rutas anabólicas vinculadas al crecimiento como síntesis de auxinas y expansión celular regulada por la pared celular, mientras que, concentraciones elevadas pueden ejercer un efecto osmótico adverso, saturando sitios de unión a receptores de membrana, reduciendo la eficiencia de la señal bioestimulante (1111. Román-Doval R, Torres-Arellanes SP, Tenorio-Barajas AY, Gómez-Sánchez A, Valencia-Lazcano AA. Chitosan: properties and its application in agriculture in context of molecular weight. Polymers [Internet]. 2023 [cited 2025 Feb 20];15(13):2867. Available from: https://doi.org/10.3390/polym15132867 , 1212. Malerba M, Cerana R. Chitosan effects on plant systems. Int J Mol Sci [Internet]. 2016 [cited 2025 Feb 20];17(7):996. Available from: https://doi.org/10.3390/ijms17070996 ). Algunos autores documentaron efectos positivos del quitosano sobre la biomasa de Raphanus sativus con respuestas claramente dependientes de la concentración (1414. Farouk S, Mosa AA, Taha AA, Ibrahim HM, EL-Gahmery A. Protective effect of humic acid and chitosan on radish (Raphanus sativus L. var. sativus) plants subjected to cadmium stress. J Stress Physiol Biochem [Internet]. 2011 [cited 2025 Feb 20];7(2):99-116. Available from: https://www.jspb.ru/issues/2011/N2/JSPB_2011_7_2_99-116.pdf ), y otros observaron que concentraciones altas como enmienda del suelo redujeron algunos parámetros de crecimiento en lechuga, resultados consistentes con los del presente estudio (1313. Xu C, Mou B. Chitosan as soil amendment affects lettuce growth, photochemical efficiency, and gas exchange. HortTechnology [Internet]. 2018 [cited 2025 Feb 20];28(4):476-80. Available from: https://doi.org/10.21273/HORTTECH04032-18 ).

Proliferación foliar: número, largo y ancho de hojas

Las variables de morfometría foliar presentaron diferencias estadísticas únicamente a los 15 DDT (Figuras 2, 3 y 4). La dosis de 1000 mg L^-1 produjo los mayores valores de número de hojas, longitud foliar y ancho foliar en esa fecha de evaluación. A los 30 DDT, todos los tratamientos alcanzaron sus valores máximos sin diferencias significativas entre sí, lo que indica que el efecto del quitosano sobre la morfometría foliar es predominante durante el establecimiento y se atenúa con la madurez del cultivo.

El estímulo sobre el aparato foliar a dosis bajas e intermedias se explica por la capacidad del quitosano para inducir la división celular y la iniciación de nuevos primordios foliares, probablemente mediante la modulación de citoquininas endógenas (1212. Malerba M, Cerana R. Chitosan effects on plant systems. Int J Mol Sci [Internet]. 2016 [cited 2025 Feb 20];17(7):996. Available from: https://doi.org/10.3390/ijms17070996 ). Las hojas representan el principal órgano de captación lumínica y producción de fotoasimilados; por tanto, su mayor área durante las etapas tempranas del desarrollo favorece la acumulación de reservas que se translocan posteriormente al órgano de cosecha (33. Rouphael Y, Colla G. Editorial: Biostimulants in Agriculture. Front Plant Sci [Internet]. 2020 [cited 2025 Feb 20];11:40. Available from: https://doi.org/10.3389/fpls.2020.00040 ). El peso molecular y el grado de acetilación del quitosano condicionan estas respuestas, por lo que una misma concentración puede generar efectos distintos entre especies, órganos y etapas fenológicas (1111. Román-Doval R, Torres-Arellanes SP, Tenorio-Barajas AY, Gómez-Sánchez A, Valencia-Lazcano AA. Chitosan: properties and its application in agriculture in context of molecular weight. Polymers [Internet]. 2023 [cited 2025 Feb 20];15(13):2867. Available from: https://doi.org/10.3390/polym15132867 ).

Diámetro polar y ecuatorial de la raíz

Los diámetros polar y ecuatorial de la raíz mostraron diferencias estadísticas entre tratamientos (Figura 5). La dosis de 1500 mg L^-1 produjo los mayores valores en ambas variables, mientras que el tratamiento testigo registró las medidas más reducidas. La dosis de 2500 mg L^-1 presentó valores intermedios, superiores al testigo, pero inferiores a las dosis de 1000 y 1500 mg L^-1, lo que confirma el patrón de inhibición a concentraciones elevadas observado en las variables vegetativas.

El incremento en los diámetros de la raíz con 1500 mg L^-1 puede atribuirse a una mayor eficiencia fisiológica durante la fase de llenado del órgano reservante. El quitosano a concentraciones intermedias estimula la actividad de enzimas relacionadas con la síntesis de carbohidratos de reserva y mejora la conductividad hidráulica radical, lo que favorece la translocación de asimilados hacia la raíz engrosante (77. Suwanchaikasem P, Idnurm A, Selby-Pham J, Walker R, Boughton BA. The impacts of chitosan on plant root systems and its potential to be used for controlling fungal diseases in agriculture. J Plant Growth Regul [Internet]. 2024 [cited 2025 Feb 20];43(10):3424-45. Available from: https://doi.org/10.1007/s00344-024-11356-1 ). En tomate, algunos investigadores reportaron incrementos significativos en diámetros polares y ecuatoriales del fruto con aplicaciones de quitosano, comportamiento que sugiere un mecanismo fisiológico común relacionado con la movilización de fotoasimilados hacia el órgano de cosecha, independientemente de la especie (88. Reyes-Pérez J, Enríquez-Acosta EA, Ramírez-Arrebato MÁ, Zúñiga Valenzuela E, Lara-Capistrán L, Hernández-Montiel LG. Efecto del quitosano sobre variables del crecimiento, rendimiento y contenido nutricional del tomate. Remexca [Internet]. 2020 [cited 2025 Feb 20];11(3):457-65. Available from: https://doi.org/10.29312/remexca.v11i3.2392 , 1515. Pincay-Manzaba D, Cedeño-Loor J, Espinosa Cunuhay K. Efecto del quitosano sobre el crecimiento y la productividad de Solanum lycopersicum. Centro Agricola [Internet]. 2021 [cited 2025 Feb 20];48(3):25-31. Available from: https://ediciones.inca.edu.cu/index.php/ediciones/article/view/1458 ).

Peso fresco y rendimiento agrícola

El peso fresco de la raíz y el rendimiento agrícola presentaron diferencias estadísticas entre tratamientos (Figuras 6 y 7). La dosis de 1500 mg L^-1 produjo el mayor peso fresco, seguida de 1000 mg L^-1 (27,17 g), 2500 mg L^-1 (23,00 g) y el testigo (13,50 g). En términos de rendimiento, la dosis de 1500 mg L^-1 alcanzó 3885,18 kg ha^-1, equivalente a un incremento del 159 % respecto al testigo (1500 kg ha^-1); la dosis de 1000 mg L^-1 obtuvo 2945,55 kg ha^-1 (96 % superior al testigo).

El marcado incremento productivo con 1500 mg L^-1 evidencia que esta concentración representa el umbral óptimo de bioestimulación en las condiciones evaluadas. A nivel fisiológico, el quitosano en dosis intermedias incrementa el peso fresco y seco de raíces, modifica la arquitectura radical y mejora la absorción de agua y nutrientes (77. Suwanchaikasem P, Idnurm A, Selby-Pham J, Walker R, Boughton BA. The impacts of chitosan on plant root systems and its potential to be used for controlling fungal diseases in agriculture. J Plant Growth Regul [Internet]. 2024 [cited 2025 Feb 20];43(10):3424-45. Available from: https://doi.org/10.1007/s00344-024-11356-1 ), potenciando la acumulación de biomasa en el órgano comercial. En algunos estudios se ha señalado que el quitosano activa microorganismos promotores del crecimiento en la rizósfera y regula rutas de señalización que se traducen en mayor productividad, mecanismo que podría explicar parte de los incrementos observados (66. Rojas-Pirela M, Carillo P, Lárez-Velásquez C, Romanazzi G. Effects of chitosan on plant growth under stress conditions: similarities with plant growth promoting bacteria. Front Plant Sci [Internet]. 2024 [cited 2025 Feb 20];15:1423949. Available from: https://doi.org/10.3389/fpls.2024.1423949 ).

En contraste, la dosis de 2500 mg L^-1 produjo el menor rendimiento entre los tratamientos con quitosano. Esta inhibición puede atribuirse a la saturación de los receptores de quitosano en la membrana plasmática, al incremento en la producción de especies reactivas de oxígeno por encima de la capacidad antioxidante celular, o a un efecto osmótico adverso inducido por la alta concentración de la solución durante la inmersión radicular (77. Suwanchaikasem P, Idnurm A, Selby-Pham J, Walker R, Boughton BA. The impacts of chitosan on plant root systems and its potential to be used for controlling fungal diseases in agriculture. J Plant Growth Regul [Internet]. 2024 [cited 2025 Feb 20];43(10):3424-45. Available from: https://doi.org/10.1007/s00344-024-11356-1 , 1111. Román-Doval R, Torres-Arellanes SP, Tenorio-Barajas AY, Gómez-Sánchez A, Valencia-Lazcano AA. Chitosan: properties and its application in agriculture in context of molecular weight. Polymers [Internet]. 2023 [cited 2025 Feb 20];15(13):2867. Available from: https://doi.org/10.3390/polym15132867 ). La respuesta dosis-dependiente no lineal del quitosano ha sido documentada en múltiples hortalizas (88. Reyes-Pérez J, Enríquez-Acosta EA, Ramírez-Arrebato MÁ, Zúñiga Valenzuela E, Lara-Capistrán L, Hernández-Montiel LG. Efecto del quitosano sobre variables del crecimiento, rendimiento y contenido nutricional del tomate. Remexca [Internet]. 2020 [cited 2025 Feb 20];11(3):457-65. Available from: https://doi.org/10.29312/remexca.v11i3.2392 , 1313. Xu C, Mou B. Chitosan as soil amendment affects lettuce growth, photochemical efficiency, and gas exchange. HortTechnology [Internet]. 2018 [cited 2025 Feb 20];28(4):476-80. Available from: https://doi.org/10.21273/HORTTECH04032-18 ), y los resultados del presente estudio confirman la existencia de un rango de concentración óptima fuera del cual los efectos bioestimulantes se revierten en inhibitorios.

Los incrementos en rendimiento obtenidos con quitosano a 1500 mg L^-1 son comparables con los reportados para otras fuentes de manejo en rábano. Otros estudios documentaron mejoras en productividad con fertilización orgánica (1616. Sousa LDCD, Santos ARMD, Nogueira JC, Matos YCDS, Silva LJV, Calaça JDSG, et al. A adubação orgânica melhora o crescimento, produtividade e características físico-químicas do rabanete (Raphanus sativus L.) cv. Saxa. Research, Society and Development [Internet]. 2022 [cited 2025 Feb 20];11(11):e57111133423. Available from: https://doi.org/10.33448/rsd-v11i11.33423 ); con integración de fertilizantes minerales y vermicompost (1717. Kumar S, Kumar P, Jatav V, Dukpa P, Suman S. Influence of organic manure and inorganic fertilizers on growth and yield of radish (Raphanus sativus L.) in Gird Region of Madhya Pradesh, India. IJPSS [Internet]. 2023 [cited 2025 Feb 20];35(20):244-52. Available from: https://doi.org/10.9734/ijpss/2023/v35i203804 ); y con la combinación de fertilización orgánica y reducción de fertilizantes químicos (1919. Jin D, Lu Z, Song X, Ahammed GJ, Yan Y, Chen S. Improvement of yield and quality properties of radish by the organic fertilizer application combined with the reduction of chemical fertilizer. Agronomy [Internet]. 2024 [cited 2025 Feb 20];14(8):1847. Available from: https://doi.org/10.3390/agronomy14081847 , 2020. Kumari S, Dhiman S, Saini A. Impact of bioinoculants and organic manures on growth and yield of radish. Biol Forum Int J [Internet]. 2024 [cited 2025 Feb 20];16(3):95-100. Available from: https://www.researchtrend.net/bfij/pdf/BFIJ-4773.pdf ). El quitosano a la dosis óptima se posiciona como una alternativa bioestimulante de perfil de inocuidad ambiental favorable y eficiencia productiva comparable a la de insumos orgánicos.

Location of the experiment

The experiment was conducted in the greenhouse of the "La María" experimental farm, at the State Technical University of Quevedo, located at km 7.5 on the Quevedo‑Mocache road, Mocache canton, Los Ríos province, Ecuador (1°04'48.6" west longitude; 01°03'18" south latitude; 75 m a.s.l.). The site's annual average temperature was 24.4 °C, annual rainfall was 3029.30 mm, and relative humidity was 88 %.

Treatments and experimental design

Three chitosan concentrations were evaluated. Chitosan was commercially obtained as a deacetylated chitin polymer, D‑glucosamine (Aldrich). T1 consisted of 1000 mg L⁻¹, T2 of 1500 mg L⁻¹, and T3 of 2500 mg L⁻¹, along with a control treatment with distilled water. These were arranged in a randomized complete block design with five replications. Each experimental unit (EU) comprised 12 plants, with planting distances of 33 cm between plants and 43 cm between rows (1.70 m² per EU), for a total of 240 plants in the experiment.

Seedlings were produced in polyethylene trays with a substrate composed of soil and river sand in a 3:2 (v:v) ratio. At 20 days after sowing, the seedling roots were immersed for one hour in the chitosan solutions corresponding to each treatment, or in distilled water for the control. After immersion, one seedling was transplanted per pot containing 2 kg of the same substrate used in the nursery phase.

Agronomic management

Weed control was carried out manually. From 15 DAT (Days after transplanting) onwards, azoxystrobin was applied weekly for preventive and curative management of fungal diseases, and methomyl for insect pest prevention. No fertilizers of any kind were applied.

Variables evaluated

Morphoagronomic variables were evaluated on six plants per experimental unit. Vegetative growth variables were recorded at 8, 15, 22, and 30 DAT; productive variables were recorded at harvest time.

Plant height (cm) was measured with a tape measure from the base of the stem to the vegetative apex. Leaf length (cm) was determined from the base of the blade to the leaf tip, and leaf width (cm) at the region of greatest laminar expansion. Leaf number was obtained by direct counting of fully developed leaves.

Root polar diameter and equatorial diameter were measured with a Vernier caliper (mm); the former corresponded to the maximum longitudinal distance of the root and the latter to the zone of greatest transverse expansion. Root fresh weight (g) was determined on an analytical balance immediately after harvest. Agricultural yield (kg ha⁻¹) was estimated from the total fresh weight of roots per experimental plot (1.70 m²), proportionally extrapolated to one hectare (10,000 m²).

Statistical analysis

Data were subjected to residual normality tests (Shapiro‑Wilk) and homogeneity of variance tests (Bartlett), whose results confirmed compliance with parametric assumptions. Analysis of variance (ANOVA) for a randomized complete block design was applied, and for variables with significant differences among treatments, means were compared using Tukey's test (p < 0.05). Analyses were performed with R software version 4.4.1 (R Core Team, 2024).

Vegetative growth: plant length

Plant length showed no statistical differences among treatments at 8, 22, and 30 DAT; however, at 15 DAT a significant effect was recorded, with the greatest elongation observed in the 1000 mg L⁻¹ treatment and the lowest averages in the 2500 mg L⁻¹ dose across all evaluation dates (Figure 1). This temporal pattern indicates that the effect of chitosan on stem elongation is concentrated during the early establishment stages and attenuates as the crop cycle progresses.

The differential response between doses is consistent with the dose‑dependent behavior of chitosan, in which moderate concentrations activate anabolic pathways linked to growth, such as auxin synthesis and cell expansion regulated by the cell wall, while high concentrations may exert an adverse osmotic effect, saturating membrane receptor binding sites and reducing the efficiency of the biostimulant signal (1111. Román-Doval R, Torres-Arellanes SP, Tenorio-Barajas AY, Gómez-Sánchez A, Valencia-Lazcano AA. Chitosan: properties and its application in agriculture in context of molecular weight. Polymers [Internet]. 2023 [cited 2025 Feb 20];15(13):2867. Available from: https://doi.org/10.3390/polym15132867 , 1212. Malerba M, Cerana R. Chitosan effects on plant systems. Int J Mol Sci [Internet]. 2016 [cited 2025 Feb 20];17(7):996. Available from: https://doi.org/10.3390/ijms17070996 ). Some authors documented positive effects of chitosan on Raphanus sativus biomass with clearly concentration‑dependent responses (1414. Farouk S, Mosa AA, Taha AA, Ibrahim HM, EL-Gahmery A. Protective effect of humic acid and chitosan on radish (Raphanus sativus L. var. sativus) plants subjected to cadmium stress. J Stress Physiol Biochem [Internet]. 2011 [cited 2025 Feb 20];7(2):99-116. Available from: https://www.jspb.ru/issues/2011/N2/JSPB_2011_7_2_99-116.pdf ), while others observed that high concentrations applied as a soil amendment reduced certain growth parameters in lettuce, results consistent with those of the present study (1313. Xu C, Mou B. Chitosan as soil amendment affects lettuce growth, photochemical efficiency, and gas exchange. HortTechnology [Internet]. 2018 [cited 2025 Feb 20];28(4):476-80. Available from: https://doi.org/10.21273/HORTTECH04032-18 ).

Vegetative growth: plant length

Plant length showed no statistical differences among treatments at 8, 22, and 30 DAT; however, at 15 DAT a significant effect was recorded, with the greatest elongation observed in the 1000 mg L⁻¹ treatment and the lowest averages in the 2500 mg L⁻¹ dose across all evaluation dates (Figure 1). This temporal pattern indicates that the effect of chitosan on stem elongation is concentrated during the early establishment stages and attenuates as the crop cycle progresses.

The differential response between doses is consistent with the dose‑dependent behavior of chitosan, in which moderate concentrations activate anabolic pathways linked to growth, such as auxin synthesis and cell expansion regulated by the cell wall, while high concentrations may exert an adverse osmotic effect, saturating membrane receptor binding sites and reducing the efficiency of the biostimulant signal (1111. Román-Doval R, Torres-Arellanes SP, Tenorio-Barajas AY, Gómez-Sánchez A, Valencia-Lazcano AA. Chitosan: properties and its application in agriculture in context of molecular weight. Polymers [Internet]. 2023 [cited 2025 Feb 20];15(13):2867. Available from: https://doi.org/10.3390/polym15132867 , 1212. Malerba M, Cerana R. Chitosan effects on plant systems. Int J Mol Sci [Internet]. 2016 [cited 2025 Feb 20];17(7):996. Available from: https://doi.org/10.3390/ijms17070996 ). Some authors documented positive effects of chitosan on Raphanus sativus biomass with clearly concentration‑dependent responses (1414. Farouk S, Mosa AA, Taha AA, Ibrahim HM, EL-Gahmery A. Protective effect of humic acid and chitosan on radish (Raphanus sativus L. var. sativus) plants subjected to cadmium stress. J Stress Physiol Biochem [Internet]. 2011 [cited 2025 Feb 20];7(2):99-116. Available from: https://www.jspb.ru/issues/2011/N2/JSPB_2011_7_2_99-116.pdf ), while others observed that high concentrations applied as a soil amendment reduced certain growth parameters in lettuce, results consistent with those of the present study (1313. Xu C, Mou B. Chitosan as soil amendment affects lettuce growth, photochemical efficiency, and gas exchange. HortTechnology [Internet]. 2018 [cited 2025 Feb 20];28(4):476-80. Available from: https://doi.org/10.21273/HORTTECH04032-18 ).

Root polar and equatorial diameter

Root polar and equatorial diameters showed statistical differences among treatments (Figure 5). The 1500 mg L⁻¹ dose produced the highest values for both variables, while the control treatment recorded the smallest measurements. The 2500 mg L⁻¹ dose presented intermediate values, higher than the control but lower than the 1000 and 1500 mg L⁻¹ doses, confirming the inhibition pattern at high concentrations observed for vegetative variables.

The increase in root diameters with 1500 mg L⁻¹ can be attributed to greater physiological efficiency during the filling phase of the storage organ. Chitosan at intermediate concentrations stimulates the activity of enzymes related to reserve carbohydrate synthesis and improves root hydraulic conductivity, which favors the translocation of assimilates toward the thickening root (77. Suwanchaikasem P, Idnurm A, Selby-Pham J, Walker R, Boughton BA. The impacts of chitosan on plant root systems and its potential to be used for controlling fungal diseases in agriculture. J Plant Growth Regul [Internet]. 2024 [cited 2025 Feb 20];43(10):3424-45. Available from: https://doi.org/10.1007/s00344-024-11356-1 ). In tomato, some researchers reported significant increases in fruit polar and equatorial diameters with chitosan applications, a behavior that suggests a common physiological mechanism related to the mobilization of photoassimilates toward the harvest organ, regardless of the species (88. Reyes-Pérez J, Enríquez-Acosta EA, Ramírez-Arrebato MÁ, Zúñiga Valenzuela E, Lara-Capistrán L, Hernández-Montiel LG. Efecto del quitosano sobre variables del crecimiento, rendimiento y contenido nutricional del tomate. Remexca [Internet]. 2020 [cited 2025 Feb 20];11(3):457-65. Available from: https://doi.org/10.29312/remexca.v11i3.2392 , 1515. Pincay-Manzaba D, Cedeño-Loor J, Espinosa Cunuhay K. Efecto del quitosano sobre el crecimiento y la productividad de Solanum lycopersicum. Centro Agricola [Internet]. 2021 [cited 2025 Feb 20];48(3):25-31. Available from: https://ediciones.inca.edu.cu/index.php/ediciones/article/view/1458 ).

Fresh weight and agricultural yield

Root fresh weight and agricultural yield showed statistical differences among treatments (Figures 6 and 7). The 1500 mg L⁻¹ dose produced the highest fresh weight, followed by 1000 mg L⁻¹ (27.17 g), 2500 mg L⁻¹ (23.00 g), and the control (13.50 g). In terms of yield, the 1500 mg L⁻¹ dose reached 3885.18 kg ha⁻¹, equivalent to a 159 % increase over the control (1500 kg ha⁻¹); the 1000 mg L⁻¹ dose obtained 2945.55 kg ha⁻¹ (96 % higher than the control).

The marked productive increase with 1500 mg L⁻¹ shows that this concentration represents the optimal biostimulation threshold under the evaluated conditions. At the physiological level, chitosan at intermediate doses increases root fresh and dry weight, modifies root architecture, and improves water and nutrient uptake (77. Suwanchaikasem P, Idnurm A, Selby-Pham J, Walker R, Boughton BA. The impacts of chitosan on plant root systems and its potential to be used for controlling fungal diseases in agriculture. J Plant Growth Regul [Internet]. 2024 [cited 2025 Feb 20];43(10):3424-45. Available from: https://doi.org/10.1007/s00344-024-11356-1 ), enhancing biomass accumulation in the commercial organ. Some studies have pointed out that chitosan activates plant growth‑promoting microorganisms in the rhizosphere and regulates signaling pathways that translate into higher productivity, a mechanism that could explain part of the observed increases (66. Rojas-Pirela M, Carillo P, Lárez-Velásquez C, Romanazzi G. Effects of chitosan on plant growth under stress conditions: similarities with plant growth promoting bacteria. Front Plant Sci [Internet]. 2024 [cited 2025 Feb 20];15:1423949. Available from: https://doi.org/10.3389/fpls.2024.1423949 ).

In contrast, the 2500 mg L⁻¹ dose produced the lowest yield among the chitosan treatments. This inhibition can be attributed to the saturation of chitosan receptors on the plasma membrane, an increase in reactive oxygen species production above the cellular antioxidant capacity, or an adverse osmotic effect induced by the high concentration of the solution during root immersion (77. Suwanchaikasem P, Idnurm A, Selby-Pham J, Walker R, Boughton BA. The impacts of chitosan on plant root systems and its potential to be used for controlling fungal diseases in agriculture. J Plant Growth Regul [Internet]. 2024 [cited 2025 Feb 20];43(10):3424-45. Available from: https://doi.org/10.1007/s00344-024-11356-1 , 1111. Román-Doval R, Torres-Arellanes SP, Tenorio-Barajas AY, Gómez-Sánchez A, Valencia-Lazcano AA. Chitosan: properties and its application in agriculture in context of molecular weight. Polymers [Internet]. 2023 [cited 2025 Feb 20];15(13):2867. Available from: https://doi.org/10.3390/polym15132867 ). The non‑linear dose‑dependent response of chitosan has been documented in multiple horticultural crops (88. Reyes-Pérez J, Enríquez-Acosta EA, Ramírez-Arrebato MÁ, Zúñiga Valenzuela E, Lara-Capistrán L, Hernández-Montiel LG. Efecto del quitosano sobre variables del crecimiento, rendimiento y contenido nutricional del tomate. Remexca [Internet]. 2020 [cited 2025 Feb 20];11(3):457-65. Available from: https://doi.org/10.29312/remexca.v11i3.2392 , 1313. Xu C, Mou B. Chitosan as soil amendment affects lettuce growth, photochemical efficiency, and gas exchange. HortTechnology [Internet]. 2018 [cited 2025 Feb 20];28(4):476-80. Available from: https://doi.org/10.21273/HORTTECH04032-18 ), and the results of the present study confirm the existence of an optimal concentration range outside which biostimulant effects revert to inhibitory ones.

The yield increases obtained with chitosan at 1500 mg L⁻¹ are comparable with those reported for other management sources in radish. Other studies documented improvements in productivity with organic fertilization (1616. Sousa LDCD, Santos ARMD, Nogueira JC, Matos YCDS, Silva LJV, Calaça JDSG, et al. A adubação orgânica melhora o crescimento, produtividade e características físico-químicas do rabanete (Raphanus sativus L.) cv. Saxa. Research, Society and Development [Internet]. 2022 [cited 2025 Feb 20];11(11):e57111133423. Available from: https://doi.org/10.33448/rsd-v11i11.33423 ); with integration of mineral fertilizers and vermicompost (1717. Kumar S, Kumar P, Jatav V, Dukpa P, Suman S. Influence of organic manure and inorganic fertilizers on growth and yield of radish (Raphanus sativus L.) in Gird Region of Madhya Pradesh, India. IJPSS [Internet]. 2023 [cited 2025 Feb 20];35(20):244-52. Available from: https://doi.org/10.9734/ijpss/2023/v35i203804 ); and with the combination of organic fertilization and chemical fertilizer reduction (1919. Jin D, Lu Z, Song X, Ahammed GJ, Yan Y, Chen S. Improvement of yield and quality properties of radish by the organic fertilizer application combined with the reduction of chemical fertilizer. Agronomy [Internet]. 2024 [cited 2025 Feb 20];14(8):1847. Available from: https://doi.org/10.3390/agronomy14081847 , 2020. Kumari S, Dhiman S, Saini A. Impact of bioinoculants and organic manures on growth and yield of radish. Biol Forum Int J [Internet]. 2024 [cited 2025 Feb 20];16(3):95-100. Available from: https://www.researchtrend.net/bfij/pdf/BFIJ-4773.pdf ). Chitosan at the optimal dose positions itself as a biostimulant alternative with a favorable environmental safety profile and productive efficiency comparable to that of organic inputs.