Huanglongbing disease (HLB), caused by Candidatus Liberibacter asiaticus (CLas), affects all commercial citrus species. Persian lime (Citrus latifolia Tanaka), a crop of global economic importance, has shown tolerance to this disease. Efforts are focused on extending the productive life of diseased trees through effective agronomic management. This study aimed to evaluate how different fertilization strategies influence the physiological and hormonal responses of Citrus latifolia on both healthy and HLB-affected plants. It compared the effects of low (Ma-1), medium (Ma-2), and high (Ma-3) doses of macronutrients, with and without the addition of micronutrients (Mi-1), using either soil (Mi-2) or foliar (Mi-3) applications. Treatments were applied every 18 days for one year. C. latifolia showed tolerance; however, HLB infection negatively affected growth parameters, photosynthetic activity, vascular bundle anatomy, reflectance at 550 and 790 nm, carbohydrate metabolism, and the concentration of salicylic acid and its biosynthetic precursors. The hormonal response showed higher levels of benzoic acid and lower levels of salicylic acid than those reported in susceptible citrus. Plants treated with low doses of macronutrients along with soil-applied micronutrients (Ma-1 + Mi-2) showed a 17.9% increase in growth, a 31.3% larger canopy volume, and an 83.3% reduction in starch accumulation compared to the treatment with high doses of macronutrients and both soil and foliar applied micronutrients (Ma-3 + Mi-3). These findings indicate that split soil fertilization with low-dose macronutrients and micronutrients might influence plant physiological responses, potentially improving disease management and decreasing fertilizer inputs.

Una de las estrategias para el manejo del Huanglongbing en México es disminuir las poblaciones del insecto vector Diaphorina citri Kuwayama mediante su manejo en áreas regionales de control (ARCOs) y reducir el riesgo de dispersión de Candidatus Liberibacter asiaticus. La resistencia a insecticidas y las prácticas inadecuadas al realizar su aplicación son factores que disminuyen su efectividad. Se estimó la presión de selección ejercida en las ARCOs de Martínez de la Torre, Veracruz, por insecticidas de diferentes grupos toxicológicos (GT) utilizados para el control de D. citri en aplicaciones regionales supervisadas (ARS) en 2013, 2014, y 2015, y en aplicaciones locales no supervisadas (ALNS) en 2015. Además, se determinaron los factores operacionales y ambientales con impacto en la efectividad del aceite parafínico de petróleo. En agosto 2015 se evaluó la efectividad biológica de clorpirifos + aceite parafínico en cuatro parcelas, y en marzo 2016 la aplicación sola de aceite parafínico en 20 parcelas. Los insecticidas pertenecientes a los GT aceites minerales, organofosforados heterocíclicos S-etil y espinosinas ejercieron la mayor presión de selección absoluta y relativa en las ARCOs evaluadas. La mortalidad promedio de ninfas de D. citri por la aplicación de clorpirifos + aceite parafínico (71%), fue mayor a la obtenida con la aplicación sola del aceite (39%). La dosis y velocidad aplicación fueron los factores que influyeron en la efectividad del aceite parafínico de petróleo. Among the strategies for Huanglongbing management in Mexico is the reduction of Diaphorina citri Kuwayama populations, the insect vector, through its management in regional control areas (RCA), and reducing the dispersion risk of Candidatus Liberibacter asiaticus. Resistance to insecticide and inadequate application practices are factors that may reduce their efficacy. Selection pressure exerted by several insecticides of different toxicological groups (TG) in the RCA of Martínez de la Torre, Mexico, used for the control of D. citri in supervised regional applications (SRA), were estimated in 2013, 2014, and 2015, and in 2015 in nonsupervised local applications. Also, the operational and environmental factors with impact on the effectiveness of paraffinic petroleum oil were determined. In August 2015, the effectiveness of chlorpyrifos + paraffinic oil in four orchards, and in March 2016, paraffinic oil sprayed alone in 20 orchards, were evaluated. Insecticides classified in the TG as mineral oils, heterocyclic S-ethyl organophosphates, and spinosines, exerted the greatest absolute and relative selection pressure in the evaluated RCA. Mean D. citri nymph mortality by the application of chlorpyrifos + paraffinic oil (71%) was higher than that of paraffinic oil (39%) alone. Dose and application speed were the factors influencing paraffinic oil effectiveness.

Huanglongbing disease (HLB), caused by Candidatus Liberibacter asiaticus (CLas), affects all commercial citrus species. Persian lime (Citrus latifolia Tanaka), a crop of global economic importance, has shown tolerance to such disease. Efforts are therefore focused on prolonging the productive life of diseased trees through agronomic management. The objective of this study was to compare between healthy and HLB-affected Persian lime plants the effects of low (Ma-1), medium (Ma-2), and high (Ma-3) doses of macronutrients, in combination with treatments without the addition of micronutrients (Mi-1), using soil (Mi-2) or foliar (Mi-3) application. Treatments were applied every 18 days for one year. Even C. latifolia showed tolerance, HLB reduced its growth, chlorophyll content, and photosynthetic efficiency. In addition, it increased stem diameter of vascular bundles, reflectance in the visible spectrum, and the concentration of glucose, sucrose, starch, trans-cinnamic acid, benzoic acid, and salicylic acid in diseased plants. The hormonal response showed higher levels of benzoic acid and lower levels of salicylic acid than those reported in susceptible citrus. Those plants treated with low doses of macronutrients in combination with applying micronutrients to the soil (Ma-1+Mi-2) showed less effect of HLB with higher growth, chlorophyll concentration, and less starch accumulation. These results sug-gest that fractioning fertilizer application throughout the year might improve the efficiency of the agronomic HLB management and allow the reduction of the annual dose of fertilizers.

Resumen. Captura de adultos de Aeneolamia albofasciata1 con trampas adhesivas de color con y sin brillo El salivazo Aeneolamia albofasciata (Lallemand) (Hemiptera: Cercopidae), es la principal plaga de la caña de azúcar en los estados productores de México. Las trampas cromáticas adhesivas son una herramienta de monitoreo que aprovecha la respuesta de los adultos a estímulos visuales. Se evaluó el efecto de los parámetros colorimétricos (luminosidad L*, ángulo de tono h° (0° para el rojo, 90° para amarillo y 180° para verde) y cromaticidad C*), así como del brillo, sobre la captura de adultos de A. albofasciata. Tres experimentos con 30 tratamientos de trampas verdes y amarillas de diferente coloración fueron caracterizados mediante espectrofotometría de reflectancia (sistema CIE L*a*b*) y dos experimentos adicionales evaluaron el efecto del brillo sobre la captura de adultos. No se encontraron diferencias significativas entre los tratamientos verdes y amarillos, lo que indica ausencia de preferencia por un color específico por parte de los adultos de A. albofasciata. Ningún parámetro colorimétrico individual mostró correlación significativa con las capturas de adultos. El brillo de las trampas resultó determinante para las capturas: su eliminación redujo la captura en promedio 63.2 % (p=0.0007) en tres tratamientos, independientemente del color base de la trampa. Las trampas con acabado brillante mejoraron significativamente la captura de adultos de A. albofasciata. Las capturas realizadas en un periodo de 24 h registraron significativamente más machos, lo que podría limitar la efectividad del trampeo sobre la capacidad reproductiva de la población. Los resultados indican que el brillo de las trampas es más determinante que el color o la luminosidad para la atracción de adultos. Estos resultados sientan las bases para optimizar las trampas cromáticas utilizadas actualmente en los programas regionales de manejo integrado del salivazo en caña de azúcar.

Objective: Evaluate the spectral reflectance method to determine whether Persian lime leaves, under fertilization treatments, present wavelengths associated with Huanglongbing (HLB) symptoms. Design/methodology/approach: A completely randomized experiment with different fertilization treatments was performed to observe their effect on reflectance changes, chlorophyll content, the severity of HLB symptoms, and the quantity of bacteria on Persian lime leaves. Previously inoculated plants by grafting buds from a diseased tree were maintained under greenhouse conditions for 12 months. Results: Leaves of diseased plants showed significantly higher reflectance in the visible spectrum (VIS) and lower chlorophyll content than healthy plant leaves. An inverse trend was observed in the near-infrared (NIR) spectrum, although it was less consistent. Fertilization treatments were not significant in reflectance, chlorophyll content, severity of symptoms, or bacteria quantity. Limitations on study/implications: It is suggested that the evaluation of spectral reflectance be expanded to susceptible varieties that develop visible symptoms more quickly. The spectrometer's use should be complemented with multispectral and machine learning techniques for early detection of asymptomatic diseased plants. Findings/conclusions: Reflectance in the visible spectrum may differentiate effectively between leaves from healthy plants and leaves with dim HLB symptoms, being associated with a greater reflectance and a lower chlorophyll content in diseased leaves, even with management practices such as fertilization that might masc the symptom expression in diseased plants.