Fruit and Leaf Sensing for Continuous Detection of Nectarine Water Status

Continuous assessment of plant water status indicators might provide the most precise information for irrigation management and automation, as plants represent an interface between soil and atmosphere. This study investigates the relationship of plant water status to continuous fruit diameter (FD) and inverse leaf turgor pressure rates (pp) in nectarine trees [Prunus persica (L.) Batsch] throughout fruit development. The influence of deficit irrigation treatments on stem (Ψstem) and leaf water potential, leaf relative water content, leaf hydraulic conductance and fruit growth was studied across the stages of double-sigmoidal fruit development in 'September Bright' nectarines. Fruit relative growth rate (RGR) and leaf pressure change rate (RPCR) were derived from FD and pp to represent rates of water in- and outflows in the organs, respectively. Continuous RGR and RPCR dynamics were independently and combinedly related to plant water status and environmental variables. The independent use of RGR and RPCR yielded significant associations with midday Ψstem, the most representative index of tree water status in anisohydric species. However, the combined use of nocturnal fruit and leaf parameters unveiled an even more significant relationship with Ψstem, suggesting a different fruit-to-leaf water balance in response to pronounced water deficit. In conclusion, we highlight the suitability of a multi-organ sensing approach for improved prediction of tree water status

Recurrent deficit irrigation and fruit harvest affect tree water relations and fruitlet growth in ‘Valencia’ orange

Background. Partial rootzone drying is an irrigation strategy known for increasing water use efficiency without significantly affecting tree water status. ‘Valencia’ oranges have a very long development period and nearly mature fruit and new fruitlets may be present at the same time on the tree, competing for water and assimilates. Objectives. The present study investigates the effect of recurrent deficit irrigation and fruit harvest on tree water status and fruitlet growth of ‘Valencia’ orange. Methods. Forty-eight adult trees were exposed to three irrigation treatments for seven years (2007-2013): irrigation with 100% of ETc (CI), continuous deficit irrigation (DI, 50% of CI) and partial root-zone drying (PRD, 50% of CI on alternated sides of the root-zone). In spring 2014, stem water potential (Ψstem) and continuous measurements of sap flow and fruitlet growth were recorded before (May) and after (June) the harvest of mature fruit. Results. No differences in Ψstem were found among irrigation treatments, while Ψstem was lower in June than in May at midday. In both May and June, sap flow density (not sap flow per tree) was higher in DI than in CI and PRD trees suggesting more efficient water uptake/transport in the former. In May, DI and PRD fruit showed lower daily relative growth rate (RGR) than CI fruit due to a possible shortage of carbon and nutrients. After removing mature fruits, differences among irrigation treatments were canceled. Sap flow was directly related to fruit RGR at low sap flow rates, but inversely related to RGR at high sap flow rates. Conclusions. Our data show that the presence of maturing fruit does not impact the water status of ‘Valencia’ trees, while it may transiently limit fruitlet growth (by source limitation) in deficit irrigated trees

Reliability of a Handheld Bluetooth Colourimeter and Its Application to Measuring the Effects of Time from Harvest, Row Orientation and Training System on Nectarine Skin Colour

This work aimed to (i) determine the reliability of a portable Bluetooth colourimeter for fruit colour measurements; (ii) characterise the changes in quantitative skin colour attributes in a nectarine cultivar in response to time from harvest; and (iii) determine the influence of row orientation and training system on nectarine skin colour. The skin colour attributes measured with the colourimeter, namely L*, a* and b*, were calibrated and validated against a reference spectrophotometer. C* and h° were obtained from a* and b*. Skin colour was measured in situ from 42 days before to 6 days after harvest on ‘Majestic Pearl’ nectarines subjected to different row orientations and training systems. Validation models showed high reliability of colour estimations. The trends of colour attributes over time were characterised by cubic regression models, with h° proving to be the best parameter to describe changes of colour over time, with a clear link to the maturation process. No significant effects of row orientation and training system on skin colour were observed at harvest. Overall, the device proved reliable for fruit colour detection. Results of this study highlight the potential of h° as a quantitative index to monitor ripening prior to harvest in ‘Majestic Pearl’ nectarines

A Fruit Colour Development Index (CDI) to Support Harvest Time Decisions in Peach and Nectarine Orchards

Fruit skin colour is one of the most important visual fruit quality parameters driving consumer preferences. Proximal sensors such as machine vision cameras can be used to detect skin colour in fruit visible in collected images, but their accuracy in variable orchard light conditions remains a practical challenge. This work aimed to derive a new fruit skin colour attribute—namely a Colour Development Index (CDI), ranging from 0 to 1, that intuitively increases as fruit becomes redder—to assess colour development in peach and nectarine fruit skin. CDI measurements were generated from high-resolution images collected on both east and west sides of the canopies of three peach and one nectarine cultivars using the commercial mobile platform Cartographer (Green Atlas). Fruit colour (RGB values) was extracted from the central pixels of detected fruit and converted into a CDI. The repeatability of CDI measurements under different light environments was tested by scanning orchards at different times of the day. The effects of cultivar and canopy side on CDI were also determined. CDI data was related to the index of absorbance difference (IAD)—an index of chlorophyll degradation that was correlated with ethylene emission—and its response to time from harvest was modelled. The CDI was only significantly altered when measurements were taken in the middle of the morning or in the middle of the afternoon, when the presence of the sun in the image caused significant alteration of the image brightness. The CDI was tightly related to IAD, and CDI values plateaued (0.833 ± 0.009) at IAD ≤ 1.20 (climacteric onset) in ‘Majestic Pearl’ nectarine, suggesting that CDI thresholds show potential to be used for harvest time decisions and to support logistics. In order to obtain comparable CDI datasets to study colour development or forecast harvest time, it is recommended to scan peach and nectarine orchards at night, in the early morning, solar noon, or late afternoon. This study found that the CDI can serve as a standardised and objective skin colour index for peaches and nectarines

I Green Bond quale leva per la ripresa dell'economia nel contesto del NextGenerationEU plan

La necessità di tutelare il contesto socio-ambientale, negli ultimi anni, sta diventando una valutazione imprescindibile prima di effettuare qualsiasi investimento. Tutto questo è causato dai cambiamenti climatici, da problematiche sociali, da fenomeni ambientali ed in ultimo dalla crisi pandemica, ancora attuale, che condizionano sempre di più le scelte degli investitori. All’interno di questo contesto, nella finanza sostenibile si sono affermati con un ruolo sempre più importante i green bond, un normale titolo di debito la cui emissione, però, è legata a progetti in grado di generare un impatto positivo in termini di sostenibilità ambientale. Questo elaborato analizza i Green bond, con una particolare attenzione alle regolamentazioni che disciplinano questo strumento: Green Bond Principles, Climate Bond Standard e l’European Green Bond Standard. Infine, viene analizzata l’applicazione dei Green bond nel contesto del NextGenerationEU, piano temporaneo promosso dalla Commissione Europea per la ripresa dell’economia post crisi Covid-19, all’interno del quale il 30% dei fondi del programma viene raccolto attraverso i Green Bond

Water relations and carbohydrate partitioning of four greenhouse-grown olive genotypes under long-term drought

Olive plants of broad-leaved 'Minuta' (MN) and 'Nocellara del Belice' (NB) and narrow-leaved 'Passulunara' (PA) and 'Biancolilla Siracusana' (BS) were studied to evaluate their responses to drought. In a greenhouse, two-year-old rooted cuttings were irrigated to field capacity (WW) or with 20% of WW evapotranspiration (DS) for over three months. Subsequently, all pots were rewatered to field capacity for 20 days. Gravimetric soil water content (SWC), leaf relative water content (RWC), stomatal conductance (gs), and leaf carbohydrates, percentage of leaf drop and shoot elongation were determined throughout the trial. In WW, SWC fluctuated between 80 and 100% of field capacity, whereas in DS, SWC decreased sharply reaching a minimum level around 30-35% of field capacity after two months of drought. At this time, drought induced a significant reduction of: (a) RWC in PA and BS, (b) gs in MN, NB, and PA, and (c) shoot elongation (-23%) in PA. Conversely, drought increased leaf drop in all genotypes, especially in MN and NB. RWC and gs levels were mostly restored after rewatering. Initially, drought induced an increase of mannitol and total carbohydrates in MN and a decrease in NB. At more advanced drought stages, mannitol and total carbohydrates decreased in PA and BS. NB exhibited a general increase of the (mannitol + glucose)/sucrose ratio in response to drought. The two broad-leaved genotypes (MN and NB) maintained similar leaf hydration levels in DS and WW plants proving to be generally intolerant to dehydration, whereas the two narrow-leaved genotypes (PA and BS) tolerated a fair degree of dehydration

Maturity Prediction in Yellow Peach (Prunus persica L.) Cultivars Using a Fluorescence Spectrometer

Technology for rapid, non-invasive and accurate determination of fruit maturity is increasingly sought after in horticultural industries. This study investigated the ability to predict fruit maturity of yellow peach cultivars using a prototype non-destructive fluorescence spectrometer. Collected spectra were analysed to predict flesh firmness (FF), soluble solids concentration (SSC), index of absorbance difference (IAD), skin and flesh colour attributes (i.e., a* and H°) and maturity classes (immature, harvest-ready and mature) in four yellow peach cultivars—‘August Flame’, ‘O’Henry’, ‘Redhaven’ and ‘September Sun’. The cultivars provided a diverse range of maturity indices. The fluorescence spectrometer consistently predicted IAD and skin colour in all the cultivars under study with high accuracy (Lin’s concordance correlation coefficient > 0.85), whereas flesh colour’s estimation was always accurate apart from ‘Redhaven’. Except for ‘September Sun’, good prediction of FF and SSC was observed. Fruit maturity classes were reliably predicted with a high likelihood (F1-score = 0.85) when samples from the four cultivars were pooled together. Further studies are needed to assess the performance of the fluorescence spectrometer on other fruit crops. Work is underway to develop a handheld version of the fluorescence spectrometer to improve the utility and adoption by fruit growers, packhouses and supply chain managers

Continuous determination of fruit tree water-status by plant-based sensors

Recently, climate change has caused shortages of water worldwide, especially in semi-arid and arid regions. Several irrigation strategies have been studied with the aim of saving water overuse in agriculture. In the past most of the attention was directed towards soil water content, but recently the focus has moved to plant responses to water deficit. In recent years, crop evapotranspiration (ETc) obtained from reference evapotranspiration (ET0) and crop coefficients (Kc), has become common for irrigation scheduling in several crops, but it does not provide precise insights on the tree water status. Today an increasing focus is being given to plant-based sensors for the continuous monitoring of plant water status to provide support to irrigation management strategies with a precision approach. In this work several plant-based (leaf, stem and fruit) devices used for plant water status sensing and for irrigation scheduling are reviewed. Scientists have managed to create and test a variety of small leaf-adapted sensors with the aim of 7collecting valuable information on water dynamics. Nondestructive continuous water status detection in leaves is difficult due to the intrinsic fragility of these organs. Yet, the data collected can provide insights on the actual status of one leaf, within a multitude of other leaves which might have a slightly different behavior because of factors such as age, sun exposure, canopy position and others. Leaf thickness sensors, leaf pressure and leaf thermal probes are discussed in this review. Stems and shoots establish the connection between climatic conditions and water availability in the soil. Continuous measurements of stem water status by non-destructive sensors provide information not only on the variations of soil water availability but also on the reserves of plant tissues. The use of stem dendrometers, sap flow probes, stem hygrometers and stem microtensiometers for continuous determination of plant water status and irrigation management is discussed. Moreover, it has been demonstrated that fruit water relations have key implication on horticultural production and quality. Measurements of fruit water status and fruit growth dynamics under different irrigation strategies might be crucial in order to reduce water use, maintain yield and/or improve fruit quality. Advantages and disadvantages of different sensors ranging from linear variable displacement transducers (LVDTs), strain-gauges, potentiometers and/or optoelectric sensors, are discussed. However, a unique methodology for continuous plant water status determination in fruit trees has yet to be found. An integrated approach, which considers contemporary use of sensors on different plant organs is proposed as effective strategy to collect exhaustive information on tree water status