W. Conejero

Maximum daily trunk shrinkage and stem water potential reference equations for irrigation scheduling of lemon trees

Measurements of midday stem water potential (ψstem) and maximum daily trunk shrinkage (MDS) were done over a 3-year period in adult Fino lemon trees (Citruslimon (L.) Burm. fil.) grafted on sour orange (C. aurantium L.) rootstocks. Plants were irrigated daily above their water requirements in order to obtain non-limiting soil water conditions. The results indicated that reference equations can be obtained for MDS and ψstem by pooling data across several seasons using crop reference evapotranspiration (ETo), daily mean vapor pressure deficit (VPDm) and mean daily air temperature (Tm) in the case of MDS, and ETo in the case of ψstem. The best predictor of MDS under non-limiting soil water conditions was Tm, suggesting that MDS reference values can be obtained by means of easy and cheap measurements. MDS and ψstem values were not influenced significantly by yield or crop load variations between years. A negative linear relationship between MDS and ψstem was found, pointing to an unchanging radial hydraulic conductivity in the bark tissues and suggesting that the MDS is controlled by water potential.

Establishing maximum daily trunk shrinkage and midday stem water potential reference equations for irrigation scheduling of early maturing peach trees

Measurements of midday stem water potential (Ψstem) and maximum daily trunk shrinkage (MDS) were taken over a 4-year period in early maturing peach trees (Prunus persica (L.) Batsch cv. Flordastar) grafted on GF-677 rootstock. Plants were irrigated daily above their water requirements in order to obtain non-limiting soil water conditions. The results indicated that seasonal reference equations can be obtained for MDS and Ψstem using crop reference evapotranspiration (ETo), daily mean vapour pressure deficit (VPDm) and mean daily air temperature (Tm) in the case of MDS, and ETo and VPDm in the case of Ψstem. In this way, VPDm was seen to be the best predictor of MDS and Ψstem, without both were influenced significantly by yield or crop load variations between years. When the postharvest regression between MDS or Ψstem and the meteorological parameters mentioned were broken down into early and late postharvest periods, the correlation coefficients improved and were closely related to the presence or absence of sugar-demanding sinks, such as active root growth. A negative linear relationship between MDS and Ψstem was found, pointing to unchanging radial hydraulic conductivity in the bark tissues and suggesting that MDS depends to a great extent of the water potential.

Using continuously recorded trunk diameter fluctuations for estimating water requirements of lemon trees.

Adult Fino lemon trees (Citrus limon L. Burm. fil.) grafted on sour orange (Citrus aurantium L.) and irrigated above their crop water requirements (T0 treatment) were compared with plants where water was applied according to maximum daily trunk shrinkage (MDS) (T1 treatment), in order to maintain MDS signal intensity [actual (T1) MDS/control (T0) MDS] threshold values close to unity. When MDS signal intensity on at least 2 of 3 consecutive days did not exceed the signal intensity threshold value, irrigation was reduced by 10%. In contrast, when the MDS signal intensity on at least 2 of 3 consecutive days exceeded the threshold value, the irrigation rate was increased by 10%. The results indicated that lemon tree irrigation scheduling can be based on MDS measurements, avoiding the appearance of any plant water stress situation without affecting yield or fruit quality. Also, the cumulative amounts of applied water in T1 plants can be considered as an estimate of lemon tree water requirements, because they were only 9% above the estimated crop evapotranspiration (ETc) and drainage did not occur. Nevertheless, to improve the precision of irrigation management, some changes in the irrigation protocol for periods of variable evaporative demand were proposed: for instance, increasing the irrigation scheduling frequency and/or using changes in the daily irrigation rate higher than those proposed in the protocol.

Iron deficiency enhances bioactive phenolics in lemon juice

BACKGROUND This study was designed to describe the phenolic status of lemon juice obtained from fruits of lemon trees differing in iron (Fe) nutritional status. Three types of Fe(III) compound were used in the experiment, namely a synthetic chelate and two complexes derived from natural polymers of humic and lignine nature. RESULTS All three Fe(III) compounds were able to improve the Fe nutritional status of lemon trees, though to different degrees. This Fe(III) compound effect led to changes in the polyphenol content of lemon juice. Total phenolics were decreased (∼33% average decrease) and, in particular, flavanones, flavones and flavonols were affected similarly. CONCLUSION Iron-deficient trees showed higher phenolic contents than Fe(III) compound-treated trees, though Fe deficiency had negative effects on the yield and visual quality of fruits. However, from a human nutritional point of view and owing to the health-beneficial properties of their bioavailable phenolic compounds, the nutritional quality of fruits of Fe-deficient lemon trees in terms of phenolics was higher than that of fruits of Fe(III) compound-treated lemon trees. Moreover, diosmetin-6,8-di-C-glucoside in lemon juice can be used as a marker for correction of Fe deficiency in lemon trees.

Stem water potential estimation of drip-irrigated early-maturing peach trees under Mediterranean conditions

Seasonal Ψstem is a useful diagnostic tool for peach tree irrigation management.The autumn rainfall events point to the resilient behaviour of the peach cultivar studied.The soil water content was the main contributor to Ψstem estimation.Ψstem was estimated by regression equation of soil water content, GDH and VPDm data. In the last decade deficit irrigation strategies allowed growers to deal with water shortages, while monitoring stem water potential (Ψstem) is deemed essential for maximising fruit yield and quality. However, because of the intensive labour involved in measuring Ψstem, alternative methods are desirable. The experiment described was conducted in Murcia (Spain) with adult peach trees (Prunus persica (L.) Batsch cv. Flordastar) submitted to different drip irrigation treatments, measuring Ψstem with a pressure chamber and the soil water content with a neutron probe. Agro-meteorological variables were recorded. Seasonal patterns of stem water potential provide a useful diagnostic tool for irrigation management in peach trees. Rainfall events and the meteorological conditions prevailing in autumn pointed to the resilient nature of the peach cultivar studied. Fitting Ψstem by linear regression analysis as a function of soil and atmosphere yielded a significant correlation, with the soil water content being the main contributor to estimating Ψstem. Linear regression analysis highlighted the importance of considering plant water status as a function of the peach tree cultivar, the atmospheric conditions in which it develops and the soil water conditions resulting from irrigation. A multiple linear regression equation based on soil water content in the soil profile, mean daily air vapour pressure deficit (VPDm) and growing degree hours (GDH) data explained 72% of the variance in Ψstem, and is proposed as an alternative to the field measurement of Ψstem.

Model-assisted evaluation of crop load effects on stem diameter variations and fruit growth in peach

Key messageThe paper identifies and quantifies how crop load influences plant physiological variables that determine stem diameter variations to better understand the effect of crop load on drought stress indicators.AbstractStem diameter (Dstem) variations have extensively been applied in optimisation strategies for plant-based irrigation scheduling in fruit trees. Two Dstem derived water status indicators, maximum daily shrinkage (MDS) and daily growth rate (DGR), are however influenced by other factors such as crop load, making it difficult to unambiguously use these indicators in practical irrigation applications. Furthermore, crop load influences the growth of individual fruits, because of competition for assimilates. This paper aims to explain the effect of crop load on DGR, MDS and individual fruit growth in peach using a water and carbon transport model that includes simulation of stem diameter variations. This modelling approach enabled to relate differences in crop load to differences in xylem and phloem water potential components. As such, crop load effects on DGR were attributed to effects on the stem phloem turgor pressure. The effect of crop load on MDS could be explained by the plant water status, the phloem carbon concentration and the elasticity of the tissue. The influence on fruit growth could predominantly be explained by the effect on the early fruit growth stages.

Deficit irrigation strategies combined with controlled atmosphere preserve quality in early peaches

Due to the water scarcity in the Mediterranean countries, irrigation must be optimized while keeping fruit quality. The effect of deficit irrigation strategies on changes in quality parameters of the early “Flordastar” peaches was studied. The deficit irrigation was programmed according to signal intensity of the maximum daily trunk shrinkage; deficit irrigation plants were irrigated to maintain maximum daily trunk shrinkage signal intensity values close to 1.4 or 1.3 in the case of DI1 or DI2 plants, respectively. Results were compared to a control watered at 150% crop evapotranspiration. Fruits were stored up to 14 days at 0 ℃ and 95% Relative Humidity (RH) in air or in controlled atmosphere (controlled atmosphere; 3–4 kPa O2 and 12–14 kPa CO2), followed by a retail sale period of 4 days at 15 ℃ and 90–95% Relative Humidity in air. Weight losses were lower in controlled atmosphere stored peaches from deficit irrigation. Air-stored fruits developed a more intense red color due to a faster ripening, which was not affected by the type of watering. At harvest, deficit irrigation peaches showed higher soluble solids content, which provided a better sensory evaluation. The soluble phenolic content was initially higher (55.26 ± 0.18 mg gallic acid equivalents/100 g fresh weight) and more stable throughout postharvest life in DI1 fruits than in those from the other irrigation treatments. Concerning vitamin C, control fruits at harvest showed higher ascorbic acid than dehydroascorbic acid content (5.43 versus 2.43 mg/100 g fresh weight, respectively), while water stressed peaches showed the opposite results. The combination of DI2 and controlled atmosphere storage allowed saving a significant amount of water and provided peaches with good overall quality, maintaining the bioactive compounds analyzed.

Soft computing applied to stem water potential estimation

Soft computing was applied to agro-meteorological and soil moisture data.Soil moisture at 0.3m, day of year and air temperature were the most relevant inputs.Fuzzy rules-based model with only 5 rules estimated Ψ st with 86% variance explained.Supplied agro-linguistic terms improved the interpretability of the fuzzy rules.The model was almost as accurate as artificial neural networks, while being simpler. Measuring the stem water potential ( Ψ st ), which is an essential parameter for assessing plant water status, is a tedious and labor-consuming task. In this work, hybrid soft computing techniques were applied to design a model able to estimate Ψ st based on agro-meteorological and soil water content data. A Takagi-Sugeno-Kang fuzzy inference system (TSK-FIS) was obtained. This kind of model approximates non-linear systems by combining a set of functions local to fuzzy regions described by fuzzy rules. Such models have approximative power and are sufficiently descriptive. Starting from a set of input-output data, inputs relevant to Ψ st were automatically selected and fuzzy rules were identified based on the fuzzy clusters found in the data. The rule parameters were optimized by means of a neuro-fuzzy approach. The result was an accurate (86% variance explained) and simple model with five rules that considered soil water content at 0.3m depth, the day of the year and mean daily air temperature as input variables, confirming the suitability of such approach. In addition, a rule simplification method allowed a consistent agro-linguistic interpretation of the fuzzy sets of the rules: DRY, MOIST and WET for the soil water content, BLOOM, FRUIT GROWTH, EARLY POSTHARVEST and LATE POSTHARVEST for the day of the year, and COLD, MILD and WARM for mean daily air temperature.

Lime-Induced Iron Chlorosis in Citrus: Diagnosis Through Physiological and Metabolic Evidences

Iron is essential for plants nutrition, being required in small but in critical concentrations for plant growth and crop productivity. Despite total iron content in soils is much higher than that required by plants, soil iron bioavailability is low, particularly in calcareous soils. For this, many agricultural crops worldwide growing in semiarid climates and calcareous soils suffer from iron deficiency (iron chlorosis or lime-induced chlorosis). In this sense, chlorotic leaves may contain as much or more total iron than healthy leaves of the same age (chlorosis paradox). In this chapter, we discuss the strengths and weaknesses of the leaf visual rating of chlorosis, floral mineral analysis and leaf active iron for diagnosing citrus iron nutritional status. The effect of iron chlorosis on yield and physical and chemical characteristics of citrus fruits was also reviewed. We analyse the metabolic response of citrus to iron deficiency, paying special attention to the inducible mechanisms developed under low-iron stress and to the metabolic changes able to be used to evaluate the iron deficiency. Finally, we reviewed the bioactive compounds in the citrus fruits, paying special attention to the fact that iron deficiency enhances phenolics and, as a consequence, health-promoting effects of the fruits for the human body.