Morpho-anatomical and microbiological analysis of kiwifruit roots with KVDS symptoms

Italy, one of the largest producers of kiwifruit in the world, has lost 10% of its production in recent years because of the spread of the kiwifruit vine decline syndrome (KVDS). Although the aetiology of KVDS has not been characterized, root rot symptoms are often associated with water stagnation and root asphyxia. To investigate causal factors and potential solutions to counter this syndrome, an experimental trial was undertaken in a kiwifruit orchard affected by KVDS in Latina (central Italy) in 2020. Root samples from healthy plants were collected and compared with samples taken from plants affected by KVDS. Macroscopically, the roots affected by KVDS were rotting, showing a loss of rhizodermis and cortical parenchyma. Microscopic analysis revealed damage to the root system with tissue breakdown and decomposition, flaking of the rhizodermis, cortical area with a clear loss of cell turgor, initial decay of the stele and evident detachment of the cortex from the central conducting tissues. Light microscopy, morphological and molecular analyses were carried out on the rhizodermis of roots showing decay and death symptoms. Total DNA extracted from the pure fungal colonies was amplified by PCR with ITS primers, amplicons directly sequenced, and the obtained nucleotide sequences were compared with those present in the GenBank database (NCBI) through BLAST analysis. Genomic analysis allowed the identification of three abundant fungi namely Ilyonectria vredenhoekensis, Fusarium oxysporum and Paraphaeosphaeria michotii. Further investigation is required to determine the role of these fungi in KVDS, whether they are species favoured by water stagnation and root asphyxia; their abundance and presence in other regions, orchards, and kiwifruit species; if they compromise roots functionality individually or conjunction with other microbial pathogens or abiotic factors; and if they contribute to plant death associated with KVDS

Moria del kiwi: alterazione della struttura anatomica e morfologica delle radici di actinidia sottoposte a condizioni di asfissia del suolo

produzione negli ultimi anni a causa della diffusione della sindrome del declino dell’actinidia (KVDS/moria). Sintomi simili al KVDS sono stati osservati in diversi ambienti e vengono spesso associati a ristagno idrico e asfissia radicale, con conseguente marciume radicale. Nell'ambito del progetto Zespri “Water and soil management of G3 in Italy”, nel 2020 è stata avviata la sperimentazione in actinidieti colpiti da moria a Latina (Lazio, - ET0 732 mm) al fine di indagare sulle possibili cause e suggerire delle soluzioni per contrastare questa fisiopatia. Sono stati raccolti campioni di radici da piante sane e confrontati con campioni raccolti da piante affette da KVDS. Per l’analisi microscopica, le radici sono state fissate in formalina al 10%, disidratate e incluse in paraffina. Ogni singolo campione è stato sezionato in sezioni dello spessore di 5 μm e colorate con diverse metodiche. Macroscopicamente, le radici affette da KVDS sono risultate marcescenti, mostrando una perdita di rizoderma e parenchima corticale. L’analisi microscopica ha rilevato danneggiamenti del sistema radicale con rottura e decomposizione tissutale, sfaldamento di rizoderma, area corticale con evidente perdita di turgore cellulare, disfacimento iniziale della stele ed evidente distacco della corteccia dai tessuti conduttori centrali. Nel campione di controllo, le radici hanno presentato un rizoderma con spessore di 13 μm e una dimensione media di cellule del parenchima di 44,5 μm, a differenza del campione KVDS, in cui lo spessore del rizoderma, quasi assente, è stato di 8,3 μm e la dimensione media delle cellule di 34,7 μm. Dall’analisi dei gas tellurici è emerso che, conseguentemente all'insorgenza del ristagno idrico nel suolo, nei suoli attorno alle piante colpite da KVDS, il potenziale redox, parametro inversamente correlato alla concentrazione di ossigeno, è risultato essere significativamente più basso (+331 vs. +368 mV; media 0-90 cm di profondità), mentre sono state riscontrate concentrazioni più elevate di CO2 (7467 vs. 5870 ppm; media 0-90 cm di profondità), un indicatore di condizioni anossiche del suolo. Per migliorare le qualità fisica del suolo e assicurare una crescita ottimale delle radici di actinidia, sarà applicata una gestione innovativa del suolo volta ad aumentarne la sostanza organica e ridurre la compattazione, facilitando il movimento orizzontale e verticale dell'acqua nel terreno per fornire alle radici di actinidia l'ossigeno necessario per mitigare gli effetti di microrganismi potenzialmente patogeni, molti dei quali proliferano in ambienti anaerobi. Sarà, infine, ottimizzata la gestione della chioma e dell’apparato radicale per bilanciare il rapporto tra radici e foglie e migliorare la capacità delle piante di riprendersi da questo declino fisiologico

Preliminary assesment of ABA concentration in roots of drip irrigated peach trees

Abscisic acid (ABA) is a phytohormone able to regulate the stomatal behaviour, transpiration and photosynthesis. ABA synthesis is usually associated to drought conditions. Based on the evidence that drip irrigation wets only 15-20% of soil surface and that 80% is dry during summer, this study tests the hypothesis that in a well drip irrigated tree the ABA concentration in roots located in the inter-row (non-irrigated) is higher than that measured in roots under the emitter line (irrigated row). Abscisic acid was determined by a competitive enzyme-linked immunosorbent assay in roots collected from a well irrigated tree (x 3) in summer at row and inter-row positions in a nectarine orchard grown in Southern Italy. Results show that leaf water potential was optimal (0.3 MPa at pre-dawn). However, ABA concentration was 3.74 pmol g-1 FW in roots from inter-row while it was 2.58 pmol g-1 FW in that growing along the row. Possible effects of the increased ABA levels at a part of the root-zone on leaf gas exchanges are discussed

Physical structure and chemical quality of soils in G3 kiwifruit orchards differentially managed

In the last years, a new physiopathy that hits kiwifruit plants (Kiwifruit Vines decline Syndrome; KVDS) is emerging. We hypothesize that soil compaction and asphyxia could have a priming effect in the emergence of KVDS. On this basis, we characterized soils from three areas of a kiwifruit orchard located in Latina (Central Italy): one with plants showing severe symptoms of KVDS (Mfield), another with plants having intermediate symptoms (Ifield), and the last with healthy plants (Cfield). Soils were characterized physically showing a gradient of compaction, clay/silt content and water content, with the highest values in M and the lowest in C, while not significant differences were found regarding the content of chemical parameters (e.g., organic matter, acidity, and macro- and micro-nutrients). From the analysis of telluric gases it emerged that, following the onset of waterlogging in the soil, the redox potential, a parameter that indicates reducing conditions and so inversely related to oxygen concentration, was found to be significantly lower in Mfield. Higher concentrations of CO2 and CH4, two indicators of anoxic soil conditions were found in Mfield. The microscope analysis of the soils showed that Mfield soils had fewer macropores, whose number is directly related to the oxygen content. To improve the physical qualities of the soil and ensure an optimal growth of kiwifruit roots, an innovative management of the soil is necessary, including the application of external organic matter up to a depth of 40 cm, the use of decompacting cover crops (e.g., Rafanus spp.), reducing soil compaction and in order to provide the oxygen necessary to mitigate the effects of potentially pathogenic microorganisms, many of which proliferate in anaerobic environments. An adequate soil management is also aimed at facilitating the horizontal and vertical movements of soil water. Our activity will be oriented to the optimization of root and canopy management to balance the relationship between roots and leaves and improve the ability of plants to recover from this physiological decline. Particularly in kiwifruit, where waterlogged and compacted soils are a serious issue, soil physicochemical quality has a key role not only in terms of fertility and productivity, but it also important to assure plant growth and production

Root−to−shoot signaling and leaf water−use efficiency in peach trees under localized irrigation

Global climate change is affecting important natural resources including water. Increasing temperature will change rate of evaporation and transpiration, leading to variations in water availability, ground water recharge, and water consumption by plants. Thus, competition for water will be a major future challenge for agriculture. Increasing water productivity at farm level is necessary to increase the efficiency of the irrigation system, plant water−use efficiency (WUE) and to optimize irrigation management. We test the hypothesis that in field−grown, drip−irrigated nectarine trees, the roots in the un−irrigated inter−row soil produce chemical signals that increase in summer to induce stomatal closure and so increase WUE. Concentrations of abscisic acid (ABA) were determined in leaf, root, and xylem sap of drip−irrigated (D) trees in which only about 25% of the soil volume was wetted and compared with those of trees irrigated using microjets (M) in which the whole soil volume was wetted. We also examined the effects of increased ABA on root−to−shoot dry matter ratio, the ratio ABA to indole−3−acetic acid (IAA), sap pH, and fruit and shoot growth. Both D and M trees were maintained at optimal water status as judged by pre−dawn leaf water potentials (about −0.3 MPa). There were no significant differences between treatments in mean fruit size (fruit diameter) or in tree yield (total fruit weight). However, shoot length was strongly reduced in D trees (to 75%) compared to M trees (100%). The concentrations of ABA in the inter−row roots of D trees were increased by 59% and that in the leaves by 13% compared to in the M trees. Despite the similar water status of D and M trees, a clear chemical signal was triggered in terms of a significant increase in the ABA/IAA ratio. This signal influenced leaf stomatal conductance which was 40% lower in D trees than in M trees. The associated responses in photosynthesis and transpiration raised the WUE of D trees by 7%–10% compared to M trees. This field study shows that in drip−irrigated trees, an ABA root−to−shoot signal issues from the inter−row roots growing in soil that dries out during a Mediterranean summer (hot, low rainfall). This ABA−induced WUE increase was achieved principally through reduced stomatal conductance and reduced transpiration

Water use of yellow-fleshed kiwifruit during an annual cycle

Irrigation is particularly important in Italian kiwifruit orchards because of high summer evapotranspiration demand and very low rainfall totals. To date, very little research has been done to define the water needs of kiwifruit (Actinidia chinensis var. chinensis 'Zesy002' commonly known as Gold3) vines. In this project, we are studying the water balance of a kiwifruit orchard during an annual cycle in Italy using a measurement and modelling approach. Field experiments were carried out in an orchard of 6-year-old vines planted in 5.0-m wide rows at a trunk spacing of 2.0 m. Trunk sap flow (T) was measured using the heat-pulse method and soil moisture was measured using time domain reflectometry (TDR). T peaked at 5.5 L h‐1 during the middle of the day. Corresponding values of the daily sap flow peaked at almost 60 L d‐1, on average. The equivalent rate of vine transpiration, ETC, equalled 6.0 mm d‐1. Mid-summer values of the reference evapotranspiration, ETO, were up to 8 mm d‐1 during June and July and they dropped back to about 2 mm d‐1 during late autumn (October). Results from this study are contributing to the development of guidelines for growers on irrigation best practice that will help overcome reduced productivity resulting from poor orchard irrigation practices

Physical structure and chemical quality of waterlogged soils in a kiwifruit orchard

In the last years, kiwifruit vines have been affected by the kiwifruit vine decline syndrome (KVDS), which is damaging the Italian kiwifruit industry. We hypothesize that soil compaction and asphyxia could have a priming effect in the emergence of KVDS. On this basis, we characterized soils from three areas of a kiwifruit orchard in Latina (Lazio region, Italy): one with vines showing severe symptoms of KVDS (Kfield), another with vines having intermediate symptoms (Ifield), and the last with healthy vines (Cfield) as control. Soils were characterized physically showing a gradient of compaction, clay/silt content and water content, with the highest values in Kfield and the lowest in Cfield, while soil chemical properties were not significantly different. The soil gas redox potential after the onset of waterlogging was significantly lower in Kfield than in the other treatments. This parameter indicates reducing soil conditions and it is negatively correlated to oxygen concentration. Higher CO2 and CH4 concentrations, two indicators of anoxic soil conditions, were found in Kfield, compared to Cfield. The microscope analysis of the soils showed that Kfield soils had fewer macropores than Cfield, whose number is positively correlated to the oxygen content. Implementation of soil and water management strategies could improve kiwifruit roots growth and vine productivity, and also help reduce symptoms of KVDS in impacted vineyards

Seasonal irrigation volumes and water footprint in a Mediterranean peach orchard

The water footprint of a product (WFP) has been proposed as indicator for quantifying the impact of production or consumption of goods and a tool to drive consumers' choices. Also it may serve to encourage the efficient use of fresh water. This is highly desirable in agriculture because of its high demand for fresh water, reaching 80% of total use. This study provides an assessment of the total water footprint (WFPtot) and its blue, green and grey components, at the orchard gate of a drip irrigated Mediterranean peach orchard located in southern Italy. The area has dry summers and an average of 590 mm of annual rainfall. The orchard was managed according to conventional (C) (soil tillage, mineral fertilization, empirical irrigation) and innovative (IN) practices (cover crops, recycle of pruning material, compost application and postharvest regulated deficit irrigation). The mean annual irrigation volume was 27.2% higher for C than IN. Six-year field data and ten-year weather data were analyzed through a soil, plant atmosphere computer model (SPASMO) in order to calculate mechanistically WFP (m3 t-1) as the amount of the annual water consumption (m3) per unit of yield (t). Total water footprint was 46.5% higher for C than IN. The blue component of the water footprint (WFPblue) was the dominant component, accounting for ~70% of the WFPtotal in both treatments. Possible use of WFP analysis within a certification scheme as marketing tool is discussed

Tecniche innovative per l’ottimizzazione dell’irrigazione in frutticoltura

L’acqua è tra le principali risorse naturali disponibili sul pianeta. Il settore agricolo gioca un ruolo fondamentale rispetto alle richieste idriche mondiali, utilizzandone più del 70% (UNEP, 2007). L’impronta idrica (Water Footprint, WF) è un valido strumento per pianificare l’appropriata gestione idrica di un territorio. Tale valore, riferito ad un prodotto, indica il volume di acqua utilizzato per produrlo, ed è espresso in m3/t. All’interno della WF si distinguono tre componenti: blu, verde e grigia. La componente blu si riferisce al volume di acqua irrigua evaporato e/o traspirato; la verde indica il volume di pioggia evaporato e/o traspirato, mentre la componente grigia si riferisce al volume necessario per diluire i contaminanti prodotti dall’agricoltura, riportandone i valori ai livelli qualitativi standard. Obiettivo del lavoro è fare una disamina dei principali risultati ottenuti applicando tecniche innovative finalizzate a ridurre i volumi idrici impiegati in frutticoltura per diminuire l’impatto della produzione sul sistema delle acque. In primo luogo, è possibile ridurre l’incidenza della componente blu intervenendo sui seguenti aspetti: • Aumentare la capacità di immagazzinamento idrico da parte del suolo (es. lavorazione minima, interramento dei residui colturali e aggiunta di materiale organico); • Migliorare l’assorbimento e il trasporto idrico da parte della pianta (es. simbiosi tra funghi micorrizici e radici ); • Integrare le attuali conoscenze di fisiologia sul trasporto xilematico e sul controllo della traspirazione al fine di aumentare l’efficienza dell’uso dell’acqua (es. segnali biochimici e non per il controllo stomatico, modulazione dell’attività delle acquaporine). • Migliorare la gestione dei “contenitori”, intesi come il volume di suolo esplorato dalle radici e bagnato dall’irrigazione (contenitore 1) e il volume di suolo esplorato dalle radici e non interessato dall’irrigazione (contenitore 2), programmando lo svuotamento del contenitore 2 (tardivo o precoce). L’applicazione di tali tecniche innovative in frutticoltura permetterà di garantire la sostenibilità del processo di produzione in relazione alla tutela ambientale