Prolonged drying cycles stimulate ABA accumulation in Citrus macrophylla seedlings exposed to partial rootzone drying

Partial rootzone drying (PRD) establishes discrete wet and dry parts of the rootzone (for example using parallel drip lines on either side of the crop row), and alternates them to stimulate root growth and root-to-shoot ABA signalling. To assess whether alternation frequency affects plant physiological responses, Citrus macrophylla Wester seedlings were grown with the root system split between two pots and 5 irrigation treatments applied: Control, PRD-Fixed (where wet and dry parts of the rootzone were not alternated) and three alternate PRD treatments where the wet and dry parts were swapped at 3 (PRD1), 6 (PRD2) and 12 (PRD3) days intervals, to dry the soil to different degrees before alternating the irrigation. Water was equally distributed between both pots in Control plants, whereas only one pot was watered and the other allowed to dry in PRD plants, with all plants receiving the same irrigation volume. After 24 days, soil water content (θv), leaf water potential (Ψleaf), root water potential (Ψroot), abscisic acid (ABA) concentration in roots ([ABA]root), leaves ([ABA]leaf) and shoot xylem sap ([X-ABA]shoot), biomass allocation and leaf area were measured. Higher soil water availability of the dry side (PRD1 and PRD2) had no significant effects on leaf water relations, ABA status and plant biomass allocation. However, increasing the duration of exposure of part of the root system to dry soil (PRD3 and PRD-Fixed) further decreased Ψroot and stimulated root ABA accumulation, while decreasing Ψleaf and increasing [ABA]leaf of PRD3 plants compared to the other treatments. Differences in physiological response between PRD3 and PRD-Fixed plants were attributed to differences in the proportion of root mass exposed to drying soil: PRD3 plants had a lower Ψleaf and a higher [ABA]leaf with a smaller proportion of their root mass in wet soil. Since long drying cycles were required to alter plant biomass allocation and physiological responses in PRD plants, these should be implemented in designing suitable PRD strategies for field application

Rootstock modify the productive response of ‘Verna’ lemon under regulated deficit irrigation

[SPA] El objetivo principal de este trabajo fue evaluar la respuesta agronómica del limonero ‘Verna’ injertado sobre dos patrones con diferente vigor en condiciones de riego deficitario controlado (RDC). El ensayo se llevó a cabo durante tres años en una parcela experimental del IMIDA en árboles de 8 años de la variedad de limonero ‘Verna’ injertados sobre Citrus macrophylla Wester (CM) y naranjo amargo (Citrus aurantium L.) (SO). Se aplicaron dos tratamientos de riego, un tratamiento control (100 % ETc) y un tratamiento de RDC, regado al 100% ETc durante todo el año menos durante dos fases de desarrollo del fruto, F-I (fase I) y F-III (fase III), en las que la dosis de riego se redujo al 25% ETc. En condiciones óptimas de riego, los árboles injertados sobre CM mostraron un mejor estado hídrico, un mayor crecimiento vegetativo y fueron más productivos. Sin embargo, el portainjerto menos vigoroso (SO) presentó un mejor comportamiento en condiciones de RDC, manteniendo la producción y el crecimiento vegetativo similares al tratamiento Control además de aumentar la productividad del agua, por lo que podría ser recomendado cuando la disponibilidad de agua no esté asegurada. [ENG] The aim of this study was to evaluate the agronomic response of ‘Verna’ lemon trees grafted on two different vigour rootstocks on regulated deficit irrigation (RDC) conditions. The experiment was carried out during 3 consecutive years in the IMIDA experimental orchard, using 8-years-old trees of the variety ‘Verna’ lemon, grafted on Citrus macrophylla Wester (CM) and on sour orange (Citrus aurantium L.) (SO). There were two irrigation treatments: Control (100% ETc) and a RDC treatment, where trees were full irrigated (100% ETc) along the season unless in two fruit growth periods, F-I (phase I) and F-III (phase III) that irrigation was 25% ETc. The ‘Verna’ lemon trees grafted on CM showed better plant water status, greater vegetative growth and were more productive on full irrigation conditions. However, the less vigorous rootstock SO showed a better performance under RDC conditions, increasing water productivity and maintaining production and vegetative growth similar to Control treatment, so that SO could be recommended when water availability is not assured.Los autores agradecen a M.I. García-Oller, J.M. Frutos, J.L. Lozano, E.M. Arques y V. Quinto por su ayuda tanto en el campo como en el laboratorio. Este trabajo fue financiado parcialmente por el proyecto POI07-12 y el contrato post-doctoral FIT a través de fondos FEDER-80%, con la colaboración del proyecto INIA RTA2012-00102-00-00

Comparison of potential irrigation strategies to confront water restriction period of yield and fruit quality in lemon tree

[SPA] El presente estudio comparó la respuesta agronómica de dos estrategias de riego (riego salino controlado (RSC) y riego deficitario controlado (RDC)) durante dos campañas. Se utilizaron árboles de limonero ‘Fino 49’ (Citrus limon (L.) (Burm. fil.) de 15 años injertados sobre Citrus macrophylla Wester. Se aplicaron tres tratamientos de riego: Control (100% ETc, de agua no salina); RDC (25% ETc, de agua no salina) y el RSC (145% ETc, agua salina 40 mM NaCl). Los tratamientos RDC y RSC se mantuvieron durante todo el ciclo de cultivo, excepto durante el período de alta evapotranspiración (ETo) (fase II de crecimiento del fruto) aplicando el 100% ETc con agua no salina. El tratamiento RDC no tuvo impacto en la distribución de recursos, pero en el RSC, la acumulación de Cl- en hoja, afectó mucho más a la producción que al crecimiento vegetativo. La producción total se vio afectada de manera similar, pero la reducción fue mayor en el RSC en el segundo año. El RDC no mejoró la EUA y el RSC la redujo al aplicar una dosis de lavado. El RSC no afectó a la calidad del fruto, mientras que el RDC retrasó la maduración del fruto. [ENG] This study compared the agronomic response of two irrigation strategies (regulated saline irrigation (RSC) and regulated deficit irrigation (RDC)) for two seasons. Lemon trees 'Fino 49' (Citrus limon (L.) (Burm. fil.) of 15 years old grafted on Citrus macrophylla Wester were used. Three irrigation treatments were applied: Control (100% ETc, non-saline water); RDC (25% ETc, non-saline water) and RSC (145% ETc, saline - 40 mM NaCl). The RDC and RSC treatments were maintained throughout the growing season, except during the period of high evapotranspiration (ETo) (phase II of fruit growth) using 100% ETc with non-saline water. The RDC treatment had no impact on the resources distribution, but in RSC, the accumulation of Cl- in the leave, affected much more production than vegetative growth. The total production was affected similarly, but the reduction was greater in the RSC in the second year. The RDC did not improve the EUA and the RSC reduced it by applying a leaching fraction. The RSC does not affect the quality of the fruit, while the RDC delayed fruit ripening.Este trabajo fue parcialmente financiado por el proyecto POI07-12 y el contrato FIT a través del programa FEDER-80% y por el proyecto INIA (RTA2012-00102-00-00

Respuesta del limonero ‘Fino 49’ al riego deficitario. Efectos sobre el crecimiento, la producción y la calidad del fruto

El limonero es uno de los cultivos más representativos en la Región de Murcia. Sin embargo, la escasez de recursos hídricos provoca que sea necesario utilizar otras técnicas de cultivo, como la aplicación de estrategias de riego deficitario para intentar optimizar los recursos hídricos disponibles. El ensayo se llevó a cabo durante dos años en una parcela experimental del IMIDA en Torre Pacheco (Murcia) en árboles de 13 años de la variedad de limonero Fino 49 injertados sobre Citrus macrophylla Wester. Se aplicaron dos tratamientos de riego, un tratamiento control (100 % ETc) y un tratamiento de riego deficitario (RD) al que se le suprimió el riego en dos periodos de desarrollo del fruto, P‐I (fase I de división celular e inicio de fase II de desarrollo del fruto) y P‐II (final desarrollo del fruto hasta la cosecha) y resto del año se mantuvo como el control. Durante los dos años de ensayo, la estrategia de riego provocó, en los periodos en los que se suprimió el riego, un déficit hídrico en el cultivo, causando una reducción de la tasa de crecimiento del tronco media de un 51 %. La cosecha disminuyó un 22 % debido a un menor peso medio del fruto (22 % menos). Respecto a la calidad del fruto, el tratamiento RD presentó frutos de menor calibre pero mayor acidez total y sólidos solubles totales en el zumo. En general, la estrategia de RD provoca un retraso del momento de recolección y una reducción de la cosecha.Este trabajo ha sido financiado por CICYT (AGL2006‐11319‐C04‐04 y AGL2007‐6537‐C04‐ 04) y por la beca predoctoral FPI concedida por el Instituto Murciano de Investigación y Desarrollo Agrario y Alimentario (IMIDA) a J.M. Robles

Suitability of using trunk diameter fluctuations for irrigation management in sub-surface drip irrigation in lemon trees

[SPA] El objetivo de este trabajo fue evaluar la idoneidad del uso de las variaciones de diámetro de tronco para la programación del riego por goteo subterráneo en árboles adultos de limonero. Para ello, se compararon árboles adecuadamente regados en riego por goteo superficial (SUR) y subterráneo (SUB). Se mantuvo, en ambos sistemas, el contenido de agua del suelo en la zona radicular entorno al 80 % del agua útil disponible y el potencial hídrico de tallo a mediodía (Ψmd) > -1.3 MPa. Las ecuaciones de referencia generadas entre la máxima contracción diaria del tronco (MDS) y meteorológicas (evapotranspiración de referencia, déficit de presión de vapor y temperatura de aire) fueron diferentes para cada sistema de riego. En ambos casos, la variable que mejor se correlacionó con Ψmd y MDS fue la temperatura. La relación entre MDS y Ψmd estuvo influenciada por el sistema de riego, siendo la pendiente de SUB significativamente menor. Basándonos en estos resultados, la medida del MDS puede ser apropiada para el ajuste de la programación del riego en limonero, pero las diferencias encontradas entre los sistemas de riego en las líneas base de referencia del MDS pone de manifiesto la necesidad de determinar las líneas de base para cada sistema de riego. [ENG] The aim of this work was to assess the suitability of using trunk diameter fluctuations for irrigation scheduling in subsurface drip irrigation system in adult lemon trees. Trees were maintained well-watered for surface (SUR) and subsurface (SUB) drip irrigation systems by applying irrigation water independently, maintaining in both systems the soil water content of the rootzone ≈ 80% of the amount of water available and the midday stem water potential (Ψmd) > -1.3 MPa. The results indicated that the reference equations generated from maximum daily trunk shrinkage (MDS) and reference evapotranspiration (ET0), vapour pressure deficit (VPD) and mean air temperature (T) parameters were different for each irrigation system, although there were not significant differences in the slopes of the MDS reference equations indicating that the prediction powerful of MDS was similar in both systems. In both cases, the environmental variable that best correlated with Ψmd and MDS was T. The relationship between MDS and Ψmd was also influenced by the irrigation system, being the slope of SUB significantly lower. The results suggested that MDS measurements can be suitable for adjusting the irrigation scheduling of lemon trees, but differences found between irrigation systems in the MDS reference baselines underline the need to determine the baselines for each irrigation system.Este trabajo fue parcialmente financiado por el "Instituto Nacional de Investigaciones Agrarias", a través del proyecto RTA 2012-00102-00-00, con la colaboración del Fondo Social Europeo de la Unión Europea FEDER al 80%

Design and simulation of techniques for mitigation of harmonic distortion in a three-phase rectifier

Rectifiers are electrical devices that receive an alternating signal and deliver a direct current signal at their output, this process by which they transform one type of energy to another is known as rectification. This type of device incorporates a phenomenon called harmonic distortion into the electrical network, which consists of malformations presented in the waveform of the alternating signal from which it feeds, which generate unwanted effects on electrical systems. Because of this, this work presents the combination of two harmonic distortion mitigation strategies (12-pulse multilevel converter and harmonic frequency tuned filtering stage) in order to reduce total harmonic distortion levels generated by a three-phase rectifier. © Published under licence by IOP Publishing Ltd

Alternation of wet and dry sides during partial rootzone drying irrigation enhances leaf ethylene evolution

Soil drying increases endogenous ABA and ACC concentrations in planta, but how these compounds interact to regulate stomatal responses to soil drying and re-watering is still unclear. To determine the temporal dynamics and physiological significance of root, xylem and leaf ABA and ACC concentrations in response to deficit irrigation (DI) or partial rootzone drying (PRD-F) and re-watering, these variables were measured in plants exposed to similar whole pot soil water contents. Both DI and PRD-F plants received only a fraction of the irrigation supplied to well-watered (WW) plants, either to all (DI) or part (PRD-F) of the rootzone of plants grown in split-pots. Both DI and PRD-F induced partial stomatal closure, increased root ABA and ACC accumulation consistent with local soil water content, but did not affect xylem or leaf concentrations of these compounds compared to WW plants. Two hours after re-watering all (DI-RW) or part of the rootzone (PRD-A) to the same soil water content, stomatal conductance returned to WW values or further decreased respectively. Re-watering the whole rootzone had no effect on xylem and leaf ABA and ACC concentrations, while re-watering the dry side of the pot in PRD plants had no effect on xylem and leaf ABA concentrations but increased xylem and leaf ACC concentrations and leaf ethylene evolution. Leaf water potential was similar between all irrigation treatments, with stomatal conductance declining as xylem ABA concentrations and leaf ACC concentrations increased. Prior to re-watering PRD plants, accounting for the spatial differences in soil water uptake best explained variation in xylem ACC concentration suggesting root-to-shoot ACC signalling, but this model did not account for variation in xylem ACC concentration after re-watering the dry side of PRD plants. Thus local (foliar) and long-distance (root-to-shoot) variation in ACC status both seem important in regulating the temporal dynamics of foliar ethylene evolution in plants exposed to PRD. © 2020 Elsevier B.V

Advances in screening methods and breeding for resistance to downy mildew and stem borers in maize

Maize is the most important cereal in sub-Saharan Africa. It is relatively inexpensive and provides many families with much-needed nutrients. For the farmers, it matures early and Is a source of ready income. Maize production Is being threatened by some diseases and pests, among which are downy mildew and stem borers. Serious yield losses often occur. This paper summarizes two studies that report the efforts of liT A scientists to screen and breed maize varieties for resistance to downy mildew and stem borers

Personalized monitoring of electrical remodelling during atrial fibrillation progression via remote transmissions from implantable devices

Atrial electrical remodelling (AER) is a transitional period associated with the progression and long-term maintenance of atrial fibrillation (AF). We aimed to study the progression of AER in individual patients with implantable devices and AF episodes. Observational multicentre study (51 centres) including 4618 patients with implantable cardioverter-defibrillator and results þ/resynchronization therapy (ICD/CRT-D) and 352 patients (2 centres) with pacemakers (median follow-up: 3.4 years). Atrial activation rate (AAR) was quantified as the frequency of the dominant peak in the signal spectrum of AF episodes with atrial bipolar electrograms. Patients with complete progression of AER, from paroxysmal AF episodes to electrically remodelled persistent AF, were used to depict patient-specific AER slopes. A total of 34 712 AF tracings from 830 patients (87 with pacemakers) were suitable for the study. Complete progression of AER was documented in 216 patients (16 with pacemakers). Patients with persistent AF after completion of AER showed ∼30% faster AAR than patients with paroxysmal AF. The slope of AAR changes during AF progression revealed patient-specific patterns that correlated with the time-to-completion of AER (R = 0.85). Pacemaker patients were older than patients with ICD/CRT-Ds (78.3 vs. 67.2 year olds, respectively, P < 0.001) and had a shorter median time-to-completion of AER (24.9 vs. 93.5 days, respectively, P = 0.016). Remote transmissions in patients with ICD/CRT-D devices enabled the estimation of the time-to-completion of AER using the predicted slope of AAR changes from initiation to completion of electrical remodelling (R = 0.45). The AF progression shows patient-specific patterns of AER, which can be estimated using available remote-monitoring technology

Personalized monitoring of electrical remodelling during atrial fibrillation progression via remote transmissions from implantable devices

Aims: Atrial electrical remodelling (AER) is a transitional period associated with the progression and long-term maintenance of atrial fibrillation (AF). We aimed to study the progression of AER in individual patients with implantable devices and AF episodes. Methods and results: Observational multicentre study (51 centres) including 4618 patients with implantable cardioverter-defibrillator +/-resynchronization therapy (ICD/CRT-D) and 352 patients (2 centres) with pacemakers (median follow-up: 3.4 years). Atrial activation rate (AAR) was quantified as the frequency of the dominant peak in the signal spectrum of AF episodes with atrial bipolar electrograms. Patients with complete progression of AER, from paroxysmal AF episodes to electrically remodelled persistent AF, were used to depict patient-specific AER slopes. A total of 34 712 AF tracings from 830 patients (87 with pacemakers) were suitable for the study. Complete progression of AER was documented in 216 patients (16 with pacemakers). Patients with persistent AF after completion of AER showed ∼30% faster AAR than patients with paroxysmal AF. The slope of AAR changes during AF progression revealed patient-specific patterns that correlated with the time-to-completion of AER (R2 = 0.85). Pacemaker patients were older than patients with ICD/CRT-Ds (78.3 vs. 67.2 year olds, respectively, P < 0.001) and had a shorter median time-to-completion of AER (24.9 vs. 93.5 days, respectively, P = 0.016). Remote transmissions in patients with ICD/CRT-D devices enabled the estimation of the time-to-completion of AER using the predicted slope of AAR changes from initiation to completion of electrical remodelling (R2 = 0.45). Conclusion: The AF progression shows patient-specific patterns of AER, which can be estimated using available remote-monitoring technology