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This study aimed at determining how source-sink balance and phloem/xylem flows affect nectarine fruit growth during development. Different levels of water and assimilate availability to growing fruits were induced in vivo by varying leaf:fruit ratio (L:F) of fruiting shoots and by interrupting the phloem stream (girdling) at the base of entire fruiting shoots. Two fruiting shoots in each of six ‘Big Top’ adult nectarine trees were selected, labeled and their L:F was adjusted by thinning fruits or removing leaves to two levels: high L:F and low L:F. Stem water potential, stomatal conductance, continuous fruit diameter and leaf turgor pressure were measured before and after girdling at stage I and stage III of fruit development. At stage I, fruits from high L:F shoots grew more than those from low L:F shoots both before and after stem girdling. At this stage, xylem flow from the whole tree and phloem flow from leaves of the same stem seem to be the major factors contributing to fruit growth. At stage III, fruits from high and low L:F shoots exhibited similar growth before girdling, whereas girdling induced a generally sharp decline of fruit growth and a marked shrinking of low L:F fruits. At this stage, regular fruit growth mostly relied on both water and carbon phloem imports from neighboring branches. Regardless of girdling or stage, the diel leaf turgor pressure (pc) range (maximum pc – minimum pc over 24 h) was always smaller in leaves from low L:F shoots compared to those from high L:F shoots, indicating that the source-sink balance is a major factor driving water status changes in leaves. Overall, at stage I, nectarine fruit growth was mainly driven by water movements through the xylem, whereas at stage III, it mostly relied on phloem contribution (water + assimilates). Leaf pc variations were mostly influenced by L:F possibly via xylem backflow from fruits in both stages I and III.

Studying mango (Mangifera&nbsp, indica L.) fruit development represents one of the most important aspects for the precise orchard management under non-native environmental conditions. In this work, precision fruit gauges were used to investigate important eco-physiological aspects of fruit growth in two mango cultivars, Keitt (late ripening) and Tommy Atkins (early-mid ripening). Fruit absolute growth rate (AGR, mm day−1), daily diameter fluctuation (ΔD, mm), and a development index given by their ratio (AGR/ΔD) were monitored to identify the prevalent mechanism (cell division, cell expansion, ripening) involved in fruit development in three (‘Tommy Atkins’) or four (‘Keitt’) different periods during growth. In ‘Keitt’, cell division prevailed over cell expansion from 58 to 64 days after full bloom (DAFB), while the opposite occurred from 74 to 85 DAFB. Starting at 100 DAFB, internal changes prevailed over fruit growth, indicating the beginning of the ripening stage. In Tommy Atkins (an early ripening cultivar), no significant differences in AGR/ΔD was found among monitoring periods, indicating that both cell division and expansion coexisted at gradually decreasing rates until fruit harvest. To evaluate the effect of microclimate on fruit growth the relationship between vapor pressure deficit (VPD) and ΔD was also studied. In ‘Keitt’, VPD was the main driving force determining fruit diameter fluctuations. In ‘Tommy Atkins’, the lack of relationship between VPD and ΔD suggest a hydric isolation of the fruit due to the disruption of xylem and stomatal flows starting at 65 DAFB. Further studies are needed to confirm this hypothesis.

A comprehensive characterization of water stress is needed for the development of automated irrigation protocols aiming to increase olive orchard environmental and economical sustainability. The main aim of this study is to determine whether a combination of continuous leaf turgor, fruit growth, and sap flow responses improves the detection of mild water stress in two olive cultivars characterized by different responses to water stress. The sensitivity of the tested indicators to mild stress depended on the main mechanisms that each cultivar uses to cope with water deficit. One cultivar showed pronounced day to day changes in leaf turgor and fruit relative growth rate in response to water withholding. The other cultivar reduced daily sap flows and showed a pronounced tendency to reach very low values of leaf turgor. Based on these responses, the sensitivity of the selected indicators is discussed in relation to drought response mechanisms, such as stomatal closure, osmotic adjustment, and tissue elasticity. The analysis of the daily dynamics of the monitored parameters highlights the limitation of using non-continuous measurements in drought stress studies, suggesting that the time of the day when data is collected has a great influence on the results and consequent interpretations, particularly when different genotypes are compared. Overall, the results highlight the need to tailor plant-based water management protocols on genotype-specific physiological responses to water deficit and encourage the use of combinations of plant-based continuously monitoring sensors to establish a solid base for irrigation management.

Different irrigation levels corresponding to 30, 60 and 100% of estimated ETc were applied to a 'Gala' apple orchard from 50 days after full bloom (DAFB) until harvest. Treatments were applied both to trees in full light conditions and under a white 50% shading net. Fruit diameter variations were continuously monitored on 6 trees per treatment from 64 to 112 DAFB, using automatic fruit gauges connected to a wireless data-logger system. During this period, midday stem water potential (Ψstem) was determined weekly. Due to frequent rainfall the irrigation treatments affected tree water status only occasionally. Fruit growth-related parameters such as fruit shrinkage and fruit net daily growth were affected by irrigation and shading treatments mainly during the first period of measurements, when fruit had a higher surface conductance and xylem functionality. Shading and high water availability tended to increase fruit daily growth which was linearly related to midday Ψstem. Later in the season, fruit stopped shrinking during the day, while their daily growth showed a curvilinear relation with midday Ψstem. Due to the small range of Ψstem obtained within the trial, slight or no relationships were found between the other fruit-related parameters (fruit shrinkage; maximum and minimum hourly growth rates) and tree water status. These results suggest how monitoring fruit growth could potentially be used for the early detection of drought stress in decision support systems aimed at optimizing irrigation scheduling.

The effect of fruit transpiration on the mechanisms driving peach (Prunus persica (L.) Batsch) daily growth was investigated. In peach, fruit water losses increase during the season and might play a key role in determining fruit growth. Skin transpiration was reduced during the cell expansion stage by enclosing fruit in plastic bags fitted with holes. In the first year, diameter changes of bagged and control fruit were precisely monitored for 15 days, and percentage dry matter and soluble solids content were determined during the experiment and at harvest. In the second year, midday fruit water potential, daily patterns of fruit growth and of vascular and transpiration flows were monitored. Bagging reduced fruit daily growth on some days, and negatively affected both fruit dry matter percentage and soluble solids content. Fruit transpiration rate was reduced during the midday hours, thus increasing midday fruit water potential and lowering xylem inflows. In accordance with the Münch hypothesis on traslocation, these conditions likely decreased the necessary gradient needed for the transport of phloem sap to sink organs, as in the afternoon, bagged fruit showed lower phloem inflows. These data suggest that skin transpiration in peach has a positive effect on fruit growth, as it enhances fruit phloem import.

The relative contributions of xylem, phloem, and transpiration to fruit growth and the daily patterns of their flows have been determined in peach, during the two stages of rapid diameter increase, by precise and continuous monitoring of fruit diameter variations. Xylem, phloem, and transpiration contributions to growth were quantified by comparing the diurnal patterns of diameter change of fruits, which were then girdled and subsequently detached. Xylem supports peach growth by 70%, and phloem 30%, while transpiration accounts for approximately 60% of daily total inflows. These figures and their diurnal patterns were comparable among years, stages, and cultivars. Xylem was functional at both stage I and III, while fruit transpiration was high and strictly dependent on environmental conditions, causing periods of fruit shrinkage. Phloem imports were correlated to fruit shrinkage and appear to facilitate subsequent fruit enlargement. Peach displays a growth mechanism which can be explained on the basis of passive unloading of photoassimilates from the phloem. A pivotal role is played by the large amount of water flowing from the tree to the fruit and from the fruit to the atmosphere.

This work describes a fruit gauge based on a low-cost linear potentiometer interfaced to a data-logger, which allows continuous measurement of fruit diameter. The sensor is supported by a custom-built stainless steel frame designed to be easily applied to different size fruits. Highly significant linear relationships between tension (mV) and displacement (mm) have been found during sensor calibration. The average slope of this relationship, 5.4 · 10 -3 with a standard deviation of 5 · 10 -5 , was used as conversion coefficient. Temperature stability was tested by submitting both the sensor and the whole gauge to a temperature range of 5-60 8C. The maximum deflection found was ±1 mV. Measurements performed during the three developmental stages of peach (Prunus persica (L), Batsch.) fruit showed high sensitivity of the gauge which allowed clear detection of diurnal patterns of fruit diameter changes and precise monitoring of minute variations in fruit growth rates during 24 h. Fruit growth dynamics has received little attention over the years. Knowledge of the daily variations in fruit size in response to environmental and physiological conditions is highly desirable, but it is hampered by the technical difficulty of measuring fruit diam- eter changes accurately and at a sufficiently low cost to allow proper replication of the experiments. In recent decades, continuous and precise monitoring of stem and fruit diameter changes have been carried out by automatic gauges, most often custom-built by the authors for the specific studies they intended to carry out (Araki et al., 2000; Berger and Selles, 1993; Garnier and Berger, 1986; Jones and Higgs, 1982; Peramaki et al., 2001). However, either the high cost of the components or technical difficulties in con- struction could hinder their use both for research and practical purposes. The measurement of fruit diameter change is of great interest both for whole- tree and single-fruit physiology research and for commercial applications, as it may pro- vide useful information for orchard manage- ment. Several papers report fruit or stem diurnal shrinkages in response to environ- mental conditions and tree water status (Berger and Selles, 1993; Garnier and Berger, 1986; Jones and Higgs, 1982; Tromp, 1984). Studies on fruit growth mechanisms were made possible by precise monitoring of fruit diameter changes over time, such as the daily in/outflows of phloem, xylem, and transpiration to/from the single fruit in apple (Lang, 1990) and peach (Morandi, 2006). Likewise, models to manage orchard irriga- tion have been developed (Huguet, 1985) and patented, complete with field systems for automatic data collection and analysis (patent numbers: US2004088916; WO02084248; WO0235193; US20020170229). Many devices for accurate measurement of fruit growth have been developed in the past (Beedlaw et al., 1986; Higgs and Jones, 1984; Tukey, 1964). In most cases, a sensor, supported by a frame, is placed in contact with the epidermis of the growing fruit. Although supporting frames have been pro- gressively modified and improved in their shapes and structures, the most adopted sensors are either linear variable differential transducers (LVDTs) or strain gauges. LVDT technology, though precise, accurate, and stable under field conditions, is expensive; strain gauges are cheaper than LVDTs, but they require some very specific electronic sensor arrangements (Wheatstone bridge) and need to be mounted on flexible frames (Beedlaw et al., 1986; Link et al., 1998). Commercial units are also available, but their price seems to hinder their widespread adop- tion, as a large number of units would be needed for both research and orchard man- agement purposes. One aspect that bears considerably on the choice of sensor and of the materials used in constructing field probes is their ruggedness and accuracy under varying environmental conditions, including large temperature, precipitation, and air moisture changes. This is more so when the degree of accuracy required of the