Deficit irrigation strategies in grapevine (<i>Vitis vinifera</i> L): ecophysioloic responses, growth-yield balance, canopy and cluster microclimate for improving quality under Mediterranean climate

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UNIVERSITÀ DEGLI STUDI DI SASSARI

SCUOLA DI DOTTORATO DI RICERCA

Scienze dei Sistemi Agrari e Forestali

e delle Produzioni Alimentari

Indirizzo Agrometeorologia ed Ecofisiologia dei Sistemi Agrari e Forestali Ciclo XXIII

Quadriennio Accademico 2008 - 2011

DEFICIT IRRIGATION STRATEGIES IN GRAPEVINE (VITIS VINIFERA L). ECOPHYSIOLOGIC RESPONSES, GROWTH-YIELD BALANCE, CANOPY AND

CLUSTER MICROCLIMATE FOR IMPROVING QUALITY UNDER MEDITERRANEAN CLIMATE

Dr. Ana Sofia Parreira Cortez Fernandes de Oliveira

Direttore della Scuola: Prof. Giuseppe Pulina

Referente di Indirizzo: Prof. Donatella Spano

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Ana Fernandes de Oliveira - Deficit Irrigation Strategies in Grapevine (Vitis vinifera L). Ecophysiologic Responses,

Growth-Yield Balance, Canopy and Cluster Microclimate for Improving Quality under Mediterranean Climate i

ABSTRACT

Water stress is considered one of the most important factors limiting crop growth and quality worldwide, especially in the Mediterranean areas. During the last decades, farmers have increasingly relied on irrigation during water scarcity periods in order to maintain or even raise yield. There is still much debate concerning the positive and negative impacts of irrigation in vineyards, due to an incomplete understanding of the relationships between grapevine physiology, yield and berry quality. Experimental research can support reliable and objective assessment of irrigation strategies effects on vine physiology and production, for given agro-climatic contexts and varieties. Moreover, these studies can contribute to define criteria of high quality irrigation strategies.

The main objective of this study was to analyse, in Mediterranean climate areas, the effects of different drip-irrigation strategies on field-grown grapevine ecophysiology, vegetative growth and yield, as well as on canopy and cluster microclimate, in order to improve quality without compromising productivity or vine life-time. Therefore, three irrigation trials were established: a) the first trial, during 2008-2009 vintages, in a „Cannonau‟ vineyard of the Nurra wine region (Alghero, North-Western Sardinia), where drip-irrigation was applied with a sub-surface irrigation line; b) the second trial was conducted in 2009-2010 vintages, in a „Vermentino‟ vineyard of the Parteolla wine region (Serdiana, South Sardinia), using the same drip-irrigation system; c) the third trial was established in 2011 in a „Vermentino‟ vineyard of the Nurra wine region, using surface drip-irrigation lines.

For the three experimental sites, Full (FI), classic deficit (DI) and partial root-zone drying (PRD) irrigation strategies were set after fruit-set until harvest. Furthermore, two different irrigation scheduling methods were evaluated. The first method was based on maximum evapotranspiration estimation (ETm) and replenishment of ETm fractions, using DI or PRD strategies. In the „Cannonau‟ trial, four treatments were set: FI 100, DI 50, DI 25 (supplying 100%, 50% and 25% of ETm, respectively) and PRD (supplying 50% of ETm

to one side of the root system, allowing the other side to dry, alternating the watered side every 15 days); in the „Vermentino‟ Parteolla trial, the treatments were: DI 80, DI 40, PRD 80 and PRD 40. In the second scheduling method, used in the Vermentino‟ Nurra trial, irrigation time was set according to a plant water relations index, the midday stem water potential (Ψstem). A threshold of -0.8 MPa was defined for deficit irrigated plants to be re-watered. In this last experiment, four irrigation treatments were test: early deficit (ED), late deficit (LD), irrigated control (IC) and non irrigated control (NC).

In order to evaluate vegetative growth during the four year trials, empirical mathematical models were developed and validated, following a methodology for non-destructive estimation of primary and lateral leaf area per shoot. The validation showed very good fitting, for both primary and lateral leaf area estimation.

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Growth-Yield Balance, Canopy and Cluster Microclimate for Improving Quality under Mediterranean Climate ii

Moreover, these models can give accurate information on vegetative growth independently of the terroir, year, phenological stage and training system.

Significant differences between treatments in „Cannonau‟ trial were found as far as root-zone soil moisture is concerned, but small differences were observed in „Vermentino‟ of Parteolla. For both trials, plants response to irrigation was conditioned by the presence of a water table in deep soil layers, which seems to have contributed significantly to root water extraction during the entire summer. This sub-surface saturated level influenced plant water status, vegetative growth, vigour and yield.

Regarding plants water status during the irrigation seasons, stem water potential showed a nearly constant pattern in the first two trials, oscillating around values indicative of small/mild water stress; the most significant differences between treatments were observed after veraison. In the „Vermentino‟ trial of Nurra, where irrigation was scheduled using a stem water potential threshold, a decreasing trend in Ψstem was registered. Before veraison, ED and NC plants experienced severe water stress, while LD and IC plant remained at mild water stress levels. After veraison, LD and NC plant experienced severe water stress.

During every experimental trial, plants evidenced good performances of leaf gas exchanges; however, stomatal conductance was more sensitive than photosynthesis to mild and severe water stress conditions. Intrinsic water use efficiency was significantly higher in NC, ED and LD plants except when leaf photosynthesis was reduced.

In the first two trials, irrigation promoted vegetative growth and canopy density, even in PRD treatments. Total leaf area was highly composed by lateral shoots and cluster exposure was not significantly different between treatments, except after veraison, in DI 25 treatment. This lead to a improved light microclimate in DI 25 „Cannonau‟ plants, and to extremely shaded canopies in every treatment of „Vermentino‟ of Nurra trial. The differences between treatments regarding yield and vigour results were inconsistent and transitory in the first two experimental sites. However, when deficit irrigation was based on Ψstem re-watering threshold, significant differences on yield components were detected.

Irrigation treatments did not differ significant as far as light microclimate is concerned in the „Vermentino‟ of Parteolla trial. There was a strong reduction of PAR interception at the fruit-zone and in the upper canopy. The shaded microclimate had a negative impact on berry metabolism, since canopies remained thick during ripening,. Regarding „Cannonau‟ trial, DI 25 treatment and the east facing clusters of DI 50 were exposed to a better light microclimate, in terms of PAR and UV radiation, and also to a more favourable R:FR ratio. Conversely, in „Vermentino‟ of Parteolla the low R:FR ratio inside the canopy, might have exert a photosynthesis depressing effect at the canopy scale.

Significant differences between treatments were found regarding the exposure time to high temperatures (> 35°C). Important daily fluctuations of heat normalised hours (HNH) were registered in every

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Growth-Yield Balance, Canopy and Cluster Microclimate for Improving Quality under Mediterranean Climate iii

experimental site. HNH decreased sharply during midday and this have affected overall berry metabolism. The amplitude between maximum and minimum HNH was extremely high, with potential impact on thermal efficiency for berry metabolism, since maximum and minimum temperatures seem to notably account for berry anthocyanin synthesis and aroma formation.

Moreover, regarding thermal efficiency for anthocyanin and aromatic compounds synthesis, skin and flesh differ in their contribution. Ours results indicate that a better estimation of anthocyanin accumulation might be obtained using skin temperature data.

The irrigation treatments set caused small but significant differences in berry fresh weight and composition in the two varieties under analysis. The minor and mostly transitory effects of deficit irrigation on berry mass and soluble solids contents (TSS), as well as the higher pH and lower titratable acidity, are indicative of berry developmental delays. The 2011 „Vermentino‟ of Nurra berry juice reached significantly higher TSS values in every irrigation treatment (about 25-26 °Brix) as compared to that of Parteolla in 2009 and 2010 vintages, where TSS did not exceed 21.8 °Brix. This indicates a better cluster microclimate and source-sink balance of the plants in the third trial. In the red variety, DI 25 treatment determined lower total anthocyanin contents; however, both PRD and DI 25 favoured the accumulation of acetyl-glucoside and coumaroyl-glucoside forms as compared to mono-coumaroyl-glucosides anthocyanin derivates.

The irrigation treatments set in „Cannonau‟ plants did not induce significant differences in source-sink balance, but vines were source-limited due to low vigour. In „Vermentino‟ experiment conducted in Parteolla, vegetative growth lead to unbalanced canopies and high vigour in every irrigation treatment. The higher water use efficiency in „Cannonau‟ trial was observed in DI 25 treatment. In terms of water saving, in „Vermentino‟ the irrigation strategies that replenished less amount of water were the interesting, namely ED and LD. The lack of relevant irrigation effects on yield in our experimental trials, together with slight reversible reduction of photosynthetic rate in deficit irrigated plants, indicate that a substantial amount of water can be conserved, without negative impacts on fruit yield or quality, by reducing the fraction of ETm reintegrated with irrigation.

Although further research is necessary regarding the effects of irrigation strategies on berry metabolism, in „Cannonau‟, the DI 25 and PRD treatments proved to be better strategies for the studied terroir, giving good responses both from agronomic and crop quality points of view. „Vermentino‟ responded well to irrigation in early (prior to veraison) and late (after veraison) deficit. Nevertheless, additional years of trial would give sounder information about varietal adaptability to drought and to thermal stress, and also regarding the effects of irrigation scheduled according to stem water potential, on vine growth, yield and longevity.

Key words: grapevine, deficit irrigation, vegetative growth modelling, microclimate and berry

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RIASSUNTO

Lo stress idrico è uno dei fattori limitanti più importanti per la crescita e la qualità delle produzioni agricole, specialmente nelle aree Mediterranee. Negli ultimi decenni i produttori agricoli hanno fatto sempre più ricorso all‟irrigazione durante i periodi di siccità al fine di mantenere o accrescere le produzioni. Esiste ancora un dibattito aperto sugli impatti positivi e negativi indotti dall‟irrigazione nei vigneti, a causa dell‟incompleta comprensione delle interrelazioni tra la fisiologia della vite, la produzione e la qualità della bacca. In specifici contesti agro-climatici e varietali, le ricerche sperimentali, contribuiscono in modo determinante sia alla valutazione oggettiva ed affidabile degli effetti delle strategie di irrigazione sulla fisiologia e sulla produzione del vigneto, sia alla definizione dei criteri da adottare per perseguire strategie irrigue di qualità.

Il principale obiettivo di questo lavoro è stato quello di analizzare, in aree a clima mediterraneo, gli effetti che esercitano differenti strategie di irrigazione a goccia sull‟ ecofisiologia, sullo sviluppo vegetativo e sulla produzione della vite, così come sul microclima della chioma e dei grappoli.

Per tale ragione, sono state condotte tre prove sperimentali di irrigazione: a) la prima, durante le annate 2008-2009, in un vigneto della varietà „Cannonau‟ nella regione vitivinicola della Nurra (Alghero, Sardegna nord-occidentale), nel quale l‟irrigazione è stata applicata con un‟ala gocciolante sotterranea; b) la seconda è stata condotta nelle annate 2009-2010 in un vigneto della varietà „Vermentino‟ nella regione vitivinicola del Parteolla (Serdiana, Sardegna meridionale), facendo ricorso ad un sistema di irrigazione uguale al precedente; c) la terza è stata condotta nel 2011 in un vigneto di „Vermentino‟ della regione vitivinicola della Nurra, mediante l‟impiego di ali gocciolanti superficiali.

Per le tre prove sperimentali sono state applicate, dall‟allegagione alla vendemmia, le seguenti strategie irrigue: di piena irrigazione (FI), irrigazione deficitaria classica (DI) e disseccamento parziale del sistema radicale (PRD). Inoltre, sono stati valutati due distinti metodi di programmazione dell‟irrigazione. Il primo metodo si è basato sulla stima dell‟evapotraspirazione massima (ETm) e sulla restituzione di frazioni di ETm, facendo ricorso alle strategie DI o PRD. Nella prova sul „Cannonau‟, sono stati confrontati quattro trattamenti: FI 100, DI 50, DI 25 (con restituzione del 100%, 50% e 25% di ETm, rispettivamente) e PRD (con restituzione del 50% di ETm su un lato del sistema radicale, lasciando disidratare l‟altro lato, e alternando il lato irrigato ogni 15 giorni); nella prova sul „Vermentino‟, nel Parteolla, i trattamenti sono stati: DI 80, DI 40, PRD 80 e PRD 40. Nel secondo metodo di programmazione, utilizzato nella prova di „Vermentino‟ nella Nurra, la definizione del momento dell‟irrigazione si è basata sul potenziale idrico del germoglio (Ψstem), scelto tra gli indici delle relazione idriche nella pianta, utilizzando la soglia d‟intervento di -0.8 MPa. In quest‟ultima prova sperimentale, sono stati confrontati quattro trattamenti irrigui: deficit precoce (ED), deficit tardivo (LD), controllo irrigato (IC) e controllo non irrigato (CN).

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Con l‟obiettivo di valutare la crescita vegetativa, sono stati sviluppati e validati anche dei modelli matematici empirici, facendo ricorso ad una metodologia di stima non distruttiva dell‟area fogliare principale e di quella secondaria. La validazione ha evidenziato un buon accordo dei modelli empirici in merito alla stima dell‟ area fogliare principale e di quella delle femminelle. Questi modelli possono fornire, con un costo assi ridotto, indicazioni accurate sullo sviluppo vegetativo, a prescindere dal terroir, dall‟anno, dallo stato fenologico e dal sistema di allevamento.

Nella prova effettuata sul „Cannonau‟, relativamente al contenuto di umidità del suolo nella zona radicale, sono emerse differenze significative tra i trattamenti, mentre, viceversa, queste differenze sono apparse di scarsa entità sul „Vermentino‟ coltivato nel Parteolla. Per entrambe le prove, la risposta delle piante all‟irrigazione è stata condizionata dalla presenza di una falda freatica negli strati profondi del suolo, che sembrerebbe aver contribuito significativamente all‟estrazione di acqua da parte dell‟apparato radicale durante tutta l‟estate, influenzando conseguentemente lo stato idrico della pianta, la crescita vegetativa, la vigoria e la resa.

In merito allo stato idrico delle piante durante le stagioni irrigue, il potenziale idrico del germoglio ha mostrato un andamento quasi costante nelle prime due prove sperimentali, oscillando su valori di stress idrico ridotto o moderato; le differenze più significative fra trattamenti sono state riscontrate dopo l‟invaiatura. Nella prova sperimentale sul „Vermentino‟ coltivato in Nurra, in cui l‟irrigazione è stata programmata sulla base del potenziale idrico, si è registrata durante la stagione una tendenza decrescente dei valori di Ψstem. Prima dell‟invaiatura, ED e NC hanno manifestato stress idrico severo, mentre le piante LD e IC si sono mantenute su livelli di stress moderato, divenuto severo dopo l‟invaiatura.

In tutte le prove sperimentali, le piante hanno evidenziato buone performances in termini di scambi gassosi a livello fogliare; tuttavia, la conduttanza stomatica ha mostrato essere un parametro più sensibile della fotosintesi alle condizioni di stress idrico moderato e severo. L‟efficienza intrinseca dell‟uso dell‟acqua è stata significativamente più elevata nelle piante NC, ED e LD, eccetto quando la fotosintesi è risultata ridotta. Nelle due prime prove sperimentali, l‟irrigazione ha promosso la crescita vegetativa e la densità della chioma, perfino nei trattamenti PRD. L‟area fogliare totale è risultata composta da un elevato numero di femminelle e la percentuale di esposizione dei grappoli non è stata significativamente diversa tra i trattamenti, tranne che, dopo l‟invaiatura, nel trattamento DI 25. Questo ha portato ad ottenere, nelle piante di „Cannonau‟ DI 25, un migliore microclima luminoso e, nel „Vermentino‟, in tutti i trattamenti della prova sperimentale condotta nel Parteolla, una formazione di chiome ombreggiate.

L‟irrigazione deficitaria non ha influenzato significativamente la produttività e la vigoria tranne nei casi in cui è stata utilizzata una soglia di Ψstem per l‟adacquamento.

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In termini di microclima lumonoso, i trattamenti irrigui non hanno presentato differenze significative nella prova su „Vermentino‟ coltivato nel Parteolla. Si è osservata una forte riduzione della PAR intercettata nella zona fruttifera e nel livello vegetativo sovrastante. Il microclima ombreggiato ha avuto impatti negativi sul metabolismo della bacca, anche durante la maturazione. Per quanto riguarda la prova su „Cannonau‟, il trattamento DI 25 e i grappoli sul lato est del DI 50 sono stati esposti ad un migliore microclima luminoso, sia in termini di PAR sia di radiazione UV, con un rapporto R:FR all‟interno della chioma più favorevole. Al contrario, nel „Vermentino‟ coltivato nel Parteolla, il rapport R:FR registrato negli estrati interni della chioma ha un effetto depressivo sulla fotosintesi, a scala di intera chioma.

Ulteriori differenze significative fra i vari trattamenti sono state riscontrate sui tempi di esposizione ad elevate temperature (> 35°C), poiché in tutte le tre prove sono state registrate importanti fluttuazioni giornaliere nelle ore di caldo normalizzate (HNH). Le HNH sono diminuite marcatamente intorno a mezzogiorno, e ciò ha influito sul metabolismo dell‟acino, mentre l‟escursione fra valori massimi e minimi di HNH è stata estremamente elevata, con un potenziale impatto sull‟efficienza termica sul metabolismo della bacca, considerato che le temperature massime e minime sembrerebbero esercitare un effetto notevole sulla sintesi degli antociani e sulla formazione degli aromi nella bacca.

L‟indagine ha consentito di verificare che una migliore stima dell‟accumulo antocianico può essere ottenuta usando dati di temperatura della buccia, rispetto a quelli dell‟intera bacca considerando il contributo specifico dell‟epidermide alla sintesi degli antociani e dei composti aromatici.

In entrambe le varietà studiate i trattamenti irrigui applicati hanno determinato piccole ma significative differenze sul peso e sulla composizione dell‟acino. Così, il mosto di „Vermentino‟ coltivato nella Nurra, nel 2011, ha raggiunto valori di TSS significativamente più elevati in tutti i trattamenti irrigui (circa 25-26 °Brix) rispetto a quello prodotto nel Parteolla nelle annate 2009 e 2010, in cui i TSS non hanno superato 21.8 °Brix. Questo aspetto é indicativo di un migliore microclima dei grappoli e di un migliore bilancio source-sink nelle piante utilizzate durante la terza prova.

Nella varietà a bacca rossa, il trattamento DI 25 ha determinato minori contenuti in antociani totali alla vendemmia; tuttavia, sia nella PRD sia nella DI 25 la dinamica di formazione dei derivati di antociani ha favorito un maggiore accumulo della forme acetil-glucoside e cumaril-glucoside rispetto ai monoglucosidi.

I trattamenti irrigui applicati nelle piante di „Cannonau‟ non hanno indotto differenze significative in termini di bilancio source-sink, ma la produzione di fotosintetati è stata probabilmente limitata a causa di una bassa vigoria. Nella prova sperimentale su „Vermentino‟ condotta nel Parteolla, la crescita vegetativa ha indotto la formazione di chiome sbilanciate ed elevata vigoria su tutti i trattamenti irrigui.

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Nella prova sul „Cannonau‟, la maggiore efficienza di uso dell‟acqua, è stata osservata con il trattamento DI 25. In termini di risparmio idrico, sul „Vermentino‟ sono risultate le più interessanti le strategie irrigue che hanno reintegrato un minore volume di acqua, in particolare la ED e la LD.

La scarsità di effetti dell‟irrigazione sulla produttività in queste prove sperimentali, insieme alla leggera e reversibile riduzione del tasso fotosintetico nelle piante sottoposte a irrigazione deficitaria indicano che, riducendo la frazione della ETm da reintegrare tramite l‟irrigazione, può essere conservata una quantità sostanziale di acqua, senza che ciò comporti impatti negativi sulla resa e sulla qualità dei frutti,

Nonostante sia necessario approfondire le ricerche sugli effetti delle strategie di irrigazione sul metabolismo della bacca, nel „Cannonau‟ i trattamenti, DI 25 e PRD si sono rivelati le migliori strategie irrigue per il terroir studiato, fornendo buone risposte dai punti di vista agronomico ed enologico. Il „Vermentino‟ ha risposto positivamente all‟irrigazione deficitaria precoce (pre invaiatura) e tardiva (post invaiatura). In ogni caso, ulteriori anni di prove sperimentali potranno fornire informazioni più consistenti sull‟adattabilità varietale alla siccità e allo stress termico, ed anche in merito agli effetti dell‟irrigazione programmata sulla base del potenziale idrico del germoglio, sullo sviluppo vegetativo, la resa e la longevità della vite.

Parole chiave: vite, irrigazione deficitaria, modellizzazione della crescita vegetativa, microclima e

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ACKNOWLEDGMENTS

There are many people I would like to express my gratitude for helping me, in several ways during the past four year. I wish to thank everyone who contributed to the research activities reported in this thesis, for they have made possible the accomplishment of this work.

First of all, I would like to thank Professor Sandro Dettori, Chair of the Department of Economics and Woody Plants Ecosystems (DESA), University of Sassari, and the referent of the PhD School, Professor Donatella Spano, for giving me the opportunity to develop my research activities at the department and to work with a great team of experts and colleagues.

I express deep gratitude to my supervisor Professor Giovanni Nieddu for all the help and encouragement , guidance and advices given during the entire duration of the PhD studies, as for the reviewing of the thesis. I also thank Professor Nieddu, as scientific coordinator of the project “Per un Salto di Qualità della

Filiera Vitivinicola della Sardegna”, founded by the CONVISAR s.c.a.r.l., Consorzio Vino e Sardegna and the

Regione Autonoma della Sardegna, for having me in the working group and giving me the chance to conduct research activities with such a good “core” of Sardinia working people.

I am thankful to the work team I have met at the University of Sassari, Dr. Luca Mercenaro, Dr. Giampaolo Usai, Dr. Nicola Tedde and Dr.ssa Marcella Betza, for all the days of hard field work together, as for their useful contributions and suggestions. Most of all, I thank them for the friendship, sacrifices and good moments shared. I really appreciate them!

I thank the researchers at the AGRIS Sardegna, Dr. Daniela Satta, Dr. Massimiliano Mameli and Dr. Luciano De Pau, and the technical people, especially Lorenzo Zucca and Dr. Gianluca Ventroni, for all the work developed together, experience and knowledge shared to establish and carry out the experimental trials. Especially to Dr. Massimiliano Mameli, scientific responsible of the project “Risparmio Idrico ed Irrgazione Sostenibile‟ of the Regione Autonoma della Sardegna, for having conducted the irrigation scheduling at Sella & Mosca and in the Argiolas irrigation experiments, as well as for having me in his team, and for contributing with many data. To Dr. Luca Mercenaro, I also would like to express my gratitude for having conducted the experimental trial at Santa Maria La Palma vineyard, and for helping me complete the data analysis on time. Grazie Mille!

To my friends and colleagues of the DESA, I am thankful. Especially to Pasquangela, who‟s opinions are so inspiring. It is great to be your friend! To Anna Paola, Marina, Lalla, Valentina Bacciu, Patrizia, Matteo

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and Giuseppe for being such nice colleagues and friends. Also to Valentina Mereu, for caring and giving always information and help for PhD classes, reports and deadline! Grazie davvero!

To Professor Carlos Lopes, Instituto Superior de Agronomia de Lisboa (ISA), I express great gratitude, for the detailed and complete revision of my thesis and for having always been available to help me, teaching and advising, and most of all for his friendship. I also thank Professor Lopes for having me at the ISA, and for is work and support on the validation of models. Muito obrigado pela ajuda!

To my friends Dr. Isabel Andrade, Ing. Rosa Guilherme, Ing. Vanda Pedroso, Ing. Sergio Martins, Dr. Pedro Rodrigues and Dr. João Paolo Gouveia, I thank for all the years of help, training and friendship. Muito Obrigado!

I thank very much Professor Gregory Jones, Southern Oregon University, for his kindness and the comments on my thesis and for having taken time reviewing it. Thank you so much!

Many thanks also to my sister Isabel, for revising so accurately my thesis many times, with so much care and attention. Obrigado Mana!

I also thank Angela, Caterina, Pietro, Marcello e Mario and all the Professors, researchers, administrative and technical staff of the DESA, who have been so kind on helping me and advising at work. I am thankful to Giovanni Ligios and Filippo Virdis for helping with the laboratory analysis and to Filippo Rossi and the GMR Strumenti for the technical support regarding research devices.

I wish to thank the wineries Sella & Mosca, and Argiolas, as well as to Dr. Renzo Peretto, Agenzia LAORE Sardegna, for providing information on the vineyards and for the collaboration given to caring out the experimental trials in their vineyards.

I express my gratitude also to the Fundação para a Ciência e a Tecnologia, Ministério da Ciência, Tecnologia e Ensino Superior, that founded my research with a scholarship during the last three years.

My special thanks to Michele, for his unconditional support, care and love, for all the help and wise advices, and for being there from the beginning, with much patience!

I would like to dedicate this thesis to my family, especially to my Father and Mother, for their essential sustain, love, encouragement and understanding. Thank you, I fell your support everytime!

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ACRONYMS

Acronyms Units

ABA abscisic acid

AEs ultrasonic acoustic emissions ANOVA analysis of variance

AOC Controlled Appellation of Origin

AWC available water capacity %

Ci sub-stomatal CO2 concentration ppm

CNN Vitis vinifera cv. Cannonau

CWSI CWSI – crop water stress index DI deficit irrigation

DI 25 deficit irrigation, supplying 25% ETm

E transpiration rate mmol H2O m-2 s-1

ED early deficit irrigation

ELA exposed leaf area m2

Es irrigation system efficiency %

ET Evapotranspiration

ETc crop evapotranspiration mm

ETm maximum crop evapotranspiration mm

ET0 reference evapotranspiration mm

ETp potential evapotranspiration mm

FI full irrigation, supplying 100% ETm

GDD growing degree days

gs stomatal conductance mmol H2O m-2 s-1

HNH heat normalised hours hours

HNHc cumulated heat normalised hours hours

I solar irradiance W m-2 IC irrigated control Kc crop coefficient Kd deficit coefficient Ks stress coefficient La air temperature °C LA leaf area m2

LD late deficit irrigation LLN leaf layer number

LSD less significant difference

LT leaf temperature °C

MP Methoxypyrazine NC Non irrigated control

PAL phenylalanine ammonia-lyase PAR photosynthetic active radiation

Pe effective precipitation mm

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Acronyms (cont.) Units

Pn/E evaporative efficiency μmol CO2/mol H2O

PPFD Photosynthetic photon flux density μmol photons m-2_s-1

PRD partial root-zone drying

PRD partial root-zone drying, applying 50% ETm

PRD 40 partial root-zone drying, applying 40% ETm PRD 80 partial root-zone drying, applying 80% ETm

R:FR Red/Far red ratio

RDI regulated deficit irrigation

Rg global solar radiation W m-2

RH relative humidity %

RWC relative water content % (vol./vol.)

Sψ water stress integral MPa day

T temperature °C

TA titratable acidity g tart. ac. L-1

Tb berry temperature °C

Tc canopy temperature °C

Tcmax maximum cardinal temperature °C

Tcmin minimum cardinal temperature °C

Topt optimum temperature °C

Td dew point °C

TSS total soluble solids °Brix

UV ultraviolet radiation W m-2

UV-A ultraviolet A radiation W m-2

UV-B ultraviolet B radiation W m-2

V watering volume mm

VPD vapour pressure deficit kPa

VRM Vitis vinifera cv. Vermentino

WUE water use efficiency gberry L-1

WUEi intrinsic water use efficiency μmol CO2/mol H2O

θ volumetric soil water content % (vol/vol) θg gravimetric soil moisture content % (mg/mg)

λ wavelength nm

Ψ water potential MPa

Ψleaf leaf water potential MPa

Ψmid midday leaf water potential MPa

Ψpd predawn water potential MPa

Ψsoil soil water potential MPa

Ψstem stem water potential MPa

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Growth-Yield Balance, Canopy and Cluster Microclimate for Improving Quality under Mediterranean Climate Page 1 of 234

GENERAL INDEX

ABSTRACT i RIASSUNTO iv ACKNOWLEDGMENTS viii ACRONYMS x GENERAL INDEX 1

FIGURES AND TABLES INDEX 4

1. INTRODUCTION 8

1.1 Overview on Viticulture Sector 8

1.1.1 Broad Scale 8

1.1.2 Sardinia Context 10

1.2 Viticulture in Mediterranean Climate 11

1.3 Assessment Techniques of Grapevine Water Requirements 14

1.3.1 Requisites of Irrigation Scheduling 15

1.3.2 Soil Water Balance Approach 16

1.3.2.1 Evapotranspiration Estimation 17

1.3.2.2 Evapotranspiration Measurement 17

1.3.3 Soil Water Monitoring 21

1.3.3.1 Gravimetric Method 22

1.3.3.2 Indirect Methods 23

1.3.4 Plant-based Methods 26

1.3.4.1 Plant Water Status 28

1.3.4.2 Sap Flow 32

1.3.4.3 Xylem Cavitation 33

1.3.4.4 Stomatal Conductance and Thermal Sensing 34

1.4 Deficit Irrigation Strategies. Effects on Vine Physiology, Growth, Yield and Berry Composition

under Mediterranean Climate 35

1.4.1 Vine Physiology 35

1.4.1.1 Gas Exchanges 36

1.4.1.2 Water Relations 38

1.4.1.3 Long Distance Signalling Mechanisms 40

1.4.2 Vine Growth, Vigour and Fruitfulness 41

1.4.3 Source-Sink Relations 46

1.4.4 Canopy and Cluster Microclimate 48

1.4.4.1 Light Microclimate 49

1.4.4.2 Thermal Microclimate 52

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1.4.6 Berry Ripening and Quality 57

1.4.6.1 Sugars 58

1.4.6.3 Phenolic Compounds 61

1.4.6.4 Aroma 67

1.4.6-2 Acids 60

2. OBJECTIVES 70

3. MATERIAL AND METHODS 72

3.1 Plant Material 72

3.1.1 Vitis vinifera L. „Cannonau‟ 72

3.1.2 Vitis vinifera L. „Vermentino‟ 72

3.2 Experimental Sites and Irrigation System 73

3.3 Experimental Design 76

3.4 Methodologies 77

3.4.1 Irrigation Management and Scheduling 77

3.4.1.1 Water Requirements and Irrigation Plans 77

3.4.1.2 Soil Water Content 79

3.4.2 Plant Physiological Status 80

3.4.2.1 Stem Water Potential 80

3.4.2.2 Leaf Gas Exchanges 80

3.4.3 Vegetative Growth and Canopy Structure 80

3.4.3.1 Leaf Area Modelling and Estimation 80

3.4.3.2 Main and Lateral Leaf Area Assessment 81

3.4.3.3 Canopy Dimensions and Exposed Leaf Area 81

3.4.3.4 Canopy Density and Leaf Layers Number 81

3.4.4 Light Microclimate 82

3.4.4.1 Light Intensity 82

3.4.4.2 Light Spectral Composition 82

3.4.5 Moisture and Thermal Microclimate 82

3.4.5.1 Skin and Flesh Temperature 82

3.4.5.2 Modelling and Calibration 83

3.4.5.3 Canopy Temperature and Moisture 84

3.4.5.4 Heat Normalised Hours and Physiological Efficiency for Anthocyanin Biosynthesis 84

3.4.6 Ripening Controls and Berry Composition Analysis 86

3.4.7 Yield Components 86

3.4.8 Pruning Weight 86

3.4.9 Statistical Analysis 86

4. RESULTS AND DISCUSSION 87

4.1 Leaf Area Modelling 87

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4.1.2 Data analysis and Models Description 88

4.1.3 Estimation of Main Leaf Area per Shoot 90

4.1.4 Estimation of Lateral Leaf Area per Shoot 90

4.2 Deficit Irrigation Strategies. Effects on Vine Ecophysiology, Growth, Yield and Berry Quality

under Mediterranean Climate 93

4.2.1 Weather Conditions and Plants Evapotranspiration 93

4.2.2 Soil Water Content 106

4.2.3 Effects of the Irrigation Strategies on Plant Physiological Status 117

4.2.3.1 Stem Water Potential 117

4.2.3.2 Leaf Gas Exchanges 124

4.2.4 Effects of the Irrigation Strategies on Canopy Structure, Growth and Yield 132

4.2.4.1 Main and Lateral Leaf Area 132

4.2.4.2 Canopy Dimensions and Exposed Leaf Area 135

4.2.4.3 Canopy Density and Leaf Layers Number 137

4.2.4.4 Yield, Pruning Weight and Vigour 139

4.2.5 Effects of the Irrigation Strategies on Light Microclimate 143

4.2.5.1 Light Intensity 143

4.2.5.2 Light Spectral Composition 145

4.2.6 Thermal Microclimate and Moisture During Ripening 149

4.2.6.1 Seasonal Patterns of Berry and Canopy Temperature 149

4.2.6.2 Cluster Exposition to Critical Ranges of Temperature 151

4.2.6.3 Daily and Cumulative Heat Normalised Hours 153

4.2.6.4 Berry Skin ad Flesh Effects on Heat Normalised Hours Estimation 156

4.2.6.5 Canopy Moisture 165

4.2.7 Effects of the Irrigation Strategies on Ripening and Berry Composition 165

4.2.7.1 Berry Weight and Main Composition 165

4.2.7.2 Must Anthocyanin Profile 178

4.2.8 Effects of the Irrigation Strategies Source-Sink Balance and on Water Productivity 180

4.2.8.1 Source-Sink Ratios 180

4.2.8.2 Water Use Efficiency 182

5. CONCLUSIONS 185

6. BIBLIOGRAPHIC REFERENCES 194

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FIGURES AND TABLES INDEX

FIGURES

Figure 1 – World wine producing regions. Source: Schiller, C.G.E. “A global view: Who makes and who drinks wine?”

Schiller-Wine. 9 Sept. 2011. http://schiller-wine.blogspot.com 11.Sept. 2011. ... 9

Figure 2 – Sardinia AOCs. Source: Schiller, C.G.E. “DOC e DOCG. Le DOC della Sardegna”. Lavinium. Rivista di vino e cultura online. http://www.lavinium.com/denom/sardeden.shtml 11.Sept. 2011. ... 11

Figure 3 – Flux diagram of the climate – terroir – varieties of the studied system. Interacting variables, technical and scientific tools for planning and scheduling quality irrigation. ... 14

Figure 4 – Experimental sites location maps. Source: Wikimapia, http://www.wikimapia.org; Google Earth, http://www.google.com/intl/it/earth/download/ge/agree.html. ... 73

Figure 5 – Picture of berry skin and flesh temperature sensors installed in a „Cannonau‟ cluster. ... 83

Figure 6 – Calibration curve obtained for the thermal microclimate monitoring system. ... 84

Figure 7 – Shape of mathematical function used to convert the hourly berry temperature in heat normal hours. ... 85

Figure 8 – Illustration of single leaf measurements: main (L1), lateral left (L2lft) and right (L2r) veins. ... 88

Figure 9 – Relationship between observed and estimated values of mail leaf area per shoot in „Cannonau‟. ... 91

Figure 10 – Relationship between observed and estimated values of main leaf area per shoot in „Vermentino‟. ... 91

Figure 11 – Relationship between observed and estimated values of lateral leaf area per shoot in „Cannonau‟. ... 92

Figure 12 – Relationship between observed and estimated values of lateral leaf area per shoot in „Vermentino‟. ... 92

Figure 13 – Alghero weather conditions during the period from May to September 2008 and 2009. Daily Average Maximum and Minimum Temperature and Precipitation. ... 95

Figure 14 – Alghero weather conditions during the period from May to September 2008 and 2009. A) Daily Average Mean Temperature and Precipitation. B) Daily Average Precipitation and Potential Evapotranspiration. ... 96

Figure 15 – Serdiana weather conditions during the period from May to September 2009 and 2010. Daily Average Maximum and Minimum Temperature and Precipitation. ... 99

Figure 16 – Serdiana weather conditions during the period from May to September 2009 and 2010. A) Daily Average Mean Temperature and Precipitation. B) Daily Average Precipitation and Potential Evapotranspiration. ... 101

Figure 17 – Alghero weather conditions during the period from May to September 2011. A) Daily Average Maximum, Mean and Minimum Temperature and Precipitation. B) Daily Average Precipitation and Potential Evapotranspiration ... 105

Figure 18 – Pattern of the Average Soil Moisture Content and Soil Profile Moisture Content during 2008 ripening period in experimental site 1 – „Cannonau‟. Mean values (4 replicates/treatment). ... 108

Figure 19 – Pattern of the Average Soil Moisture Content and Soil Profile Moisture Content during 2009 ripening period in experimental site 1 – „Cannonau‟. Mean values (4 replicates/treatment). ... 111

Figure 20 – Pattern of the Average Soil Moisture Content and Soil Profile Moisture Content during 2009 ripening period in experimental site 2 – „Vermentino‟. Mean values (4 replicates/treatment). ... 113

Figure 21 – Pattern of the Average Soil Moisture Content and Soil Profile Moisture Content during 2010 ripening period in experimental site 2 – „Vermentino‟. Mean values (4 replicates/treatment). ... 115

Figure 22 – Effect of irrigation treatments on „Cannonau‟ stem water potential during the seasons 2008 (A) and 2009 (B) in experimental site 1. Mean values (4 replicates/plot) and standard error (P<0.05). ... 119

Figure 23 – Effect of irrigation treatments on „Vermentino‟ stem water potential during the seasons 2008 (A) and 2009 (B) in experimental site 2. Mean values (4 replicates/plot) and standard error (P<0.05). ... 121

Figure 24 – Effect of irrigation treatments on „Vermentino‟ stem water potential during the seasons 2011 in experimental site 3. Mean values (4 replicates/plot) and standard error (P<0.05). ... 123

Figure 25 – Effect of irrigation treatments on „Cannonau‟ leaf gas exchanges during season 2009 in site 1. Photosynthetic rate (Pn), stomatal conductance (gs), transpiration rate (E) and intrinsic water use efficiency (WUEi). Mean values (4 replicates/plot) and standard error (P<0.05). ... 126

Figure 26 – Effect of irrigation treatments on „Vermentino‟ leaf gas exchanges during the seasons 2009 and 2010 in site 2. Photosynthetic rate (Pn), stomatal conductance (gs) and transpiration rate (E). Mean values (4 replicates/plot) and standard error (P<0.05). Mean values (4 replicates/plot) and standard error (P<0.05). ... 128

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Figure 27 – Effect of irrigation treatments on „Vermentino‟ leaf gas exchanges during the seasons 2009 and 2010 in site 2. Intrinsic water use efficiency (WUEi). Mean values (4 replicates/plot) and standard error (P<0.05). ... 129 Figure 28 – Effect of irrigation treatments on „Vermentino‟ leaf gas exchanges during 2011 in the experimental site 3. Photosynthetic rate (Pn), stomatal conductance (gs), transpiration rate (E) and intrinsic water use efficiency (WUEi). Mean values (4 replicates/plot) and standard error (P<0.05). ... 131 Figure 29 – Effect of irrigation treatments on main and lateral leaf area development in „Cannonau‟ during 2008 and 2009 seasons and in „Vermentino‟ during 2009 and 2010 (C and D). Mean values (4 replicates/plot). ... 134 Figure 30 – Effect of irrigation treatments on the exposed leaf area (ELA) in „Cannonau‟ during 2008 and 2009 seasons and in „Vermentino‟ during 2009 and 2010. Mean values (4 replicates/plot). ... 136 Figure 31 – Effect of irrigation treatments on canopy leaf layer number (LLN), percentage of internal leaves, exposed clusters and porosity in „Cannonau‟ plants during 2008 and in „Vermentino‟ during 2010. Mean values (4 replicates/plot). ... 138 Figure 32 – Effect of irrigation treatments on „Vermentino‟ canopy and fruit zone PAR interception during the seasons 2009 and 2010 in experimental site 2. Mean values (6 replicates/plot). ... 144 Figure 33 – Effect of irrigation treatments on „Cannonau‟ and „Vermentino‟ light microclimate during the seasons 2009 and 2010. Global solar radiation (Rg), Ultraviolet-A and B (UV-A and UV-B) and Red/Far red ratio (R:FR). Mean values (6 replicates/plot) and standard error (P<0.05). ... 146 Figure 34 – Effect of irrigation on „Vermentino‟ canopy and fruit zone light microclimate during the seasons 2009 and 2010 in site 2. Irradiance (I) spectrum from 350 – 1800 nm wave bands. Mean values (6 replicates/plot). ... 148 Figure 35 – Effect of irrigation treatments on „Cannonau‟ and „Vermentino‟ thermal microclimate during the seasons 2009, 2010 and 2011. Daily pattern of the difference between berry and canopy average temperature. Mean values (4 replicates/treatment) ... 150 Figure 36 – Effect of irrigation treatments on „Cannonau‟ berries thermal microclimate during the seasons 2009. Percentage of berry exposure time to critical temperature ranges during ripening. Mean values (2 replicates/ side). ... 152 Figure 37 – Effect of irrigation treatments on „Vermentino‟ berries thermal microclimate during the seasons 2009, 2010 and 2011. Percentage of berry exposure time to critical temperature ranges. Mean values (2 replicates/ side). ... 153 Figure 38 – „Cannonau‟ and „Vermentino‟ thermal microclimate during the seasons 2009 and 2010. Daily pattern of average heat normalised hours (HNH), berry maximum (T max) and minimum (T min) temperature, mean canopy temperature (T c) and optimum cardinal (T opt) for anthocyanin synthesis and accumulation. Mean values (4 replicates/treatment). ... 155 Figure 39 – Seasonal pattern of mean, maximum and minimum berry skin and flesh HNH in „Cannonau‟ and „Vermentino‟ during 2009 and 2010. Mean values (4 replicates/treatment). ... 158 Figure 40 – Seasonal pattern of mean, maximum and minimum berry HNH in „Vermentino‟ at experimental site 3 during 2011. Mean values (4 replicates/treatment). ... 159 Figure 41 – Seasonal pattern of mean, maximum and minimum berry skin and flesh cumulative HNH in „Cannonau‟ and „Vermentino‟ during 2009 and 2010. Mean values (4 replicates/treatment). ... 161 Figure 42 – Seasonal pattern of mean, maximum and minimum berry cumulative HNH in „Vermentino‟ at experimental site 3 during 2011. Mean values (4 replicates/treatment). ... 162 Figure 43 – Relationship between maximum, minimum berry skin and flesh cumulative HNH and the average cumulative HNH in „Vermentino‟ during 2009 and 2010. Mean values (4 replicates/treatment)... 164 Figure 44 – Effect of irrigation on „Vermentino‟ canopy temperature and moisture during ripening 2010. Daily patterns of average canopy relative humidity (RH), mean temperature (Tc) and dew point (Td). Mean values (2 replicates/treatment). .. 165 Figure 45 – Effect of irrigation treatment (DI 50, PRD, DI 25) on the relationships between TSS, TA and Total anthocyanins and Berry Fresh Weight in „Cannonau‟ berries during ripening seasons 2008 and 2009. Mean values (3 replicates/plot) ... 172 Figure 46 – Effect of irrigation treatment on „Cannonau‟ berry anthocyanin accumulation pattern during 2009. Anthocyanin derivate forms dynamics. Mean values (3 replicates/plot) and standard error (P<0.05). ... 180 Figure 47 – Effect of irrigation treatment on source-sink indexes in „Cannonau‟ and „Vermentino‟ during 2008, 2009 and 2010. Exposed leaf are to total leaf area ratio (ELA/LA), total leaf area per yield (LA/Yield) and Yield per pruning weight (Ravaz Index). Mean values (4 replicates/plot) and standard error (P<0.05)... 181

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TABLES

Table 1 – Soil characteristics in experimental site 1 – „Cannonau‟. ... 74

Table 2 – Soil characteristics in experimental site 2 – „Vermentino‟. ... 75

Table 3 – Soil characteristics in experimental site 3 – „Vermentino‟. ... 75

Table 4 – Plant water needs estimation and watering supplies for experimental site 1 – „Cannonau‟. ... 77

Table 5 – Plant water needs estimation and watering supplies for experimental site 2 – „Vermentino‟. ... 78

Table 6 – Watering supplies per treatment and phenological stage during 2008 in experimental site 1 – „Cannonau‟. ... 78

Table 7 – Watering supplies per treatment and phenological stage during 2009 in experimental site 1 – „Cannonau‟. ... 78

Table 8 – Watering supplies per treatment and phenological stage in experimental site 2 – „Vermentino‟. ... 79

Table 9 – Watering supplies per treatment and phenological stage in experimental site 3 – „Vermentino‟. ... 79

Table 10 – Statistical data from the validation of the models for the estimation of grapevine leaf area per shoot. ... 91

Table 11 – Canopy growth and yield in 2008 and 2009 growing seasons in the site 1 – „Cannonau‟. Canopy Surface data regards harvest. Mean values (4 replicates/block) and ANOVA. * - significant for P<0.05; ns - not significant. ... 141

Table 12 – Canopy growth and yield in 2009 and 2010 seasons in site 2 – „Vermentino‟. Canopy Surface data regards harvest. Mean values (4 replicates/block) and ANOVA. * - significant for P<0.05; ns - not significant. ... 142

Table 13 – Yield components in 2011 growing season in experimental site 3 – „Vermentino‟. Canopy Surface data regards harvest. Mean values (4 replicates/block) and ANOVA. * - significant for P<0.05; ns - not significant. ... 143

Table 14 – Berry fresh and dry weight and main composition during ripening 2008 in experimental site 1 -„Cannonau‟ . Mean values (3 replicates/block) and ANOVA. * - significant for P<0.05; ns - not significant. ... 168

Table 15 – Berry fresh, dry weight and main composition during ripening 2009 in experimental site 1 -„Cannonau‟. Mean values (3 replicates/block) and ANOVA. * - significant for P<0.05; ns - not significant. ... 170

Table 16 – Berry fresh and dry weight and main composition during ripening 2009 in experimental site 2 -„Vermentino‟. Mean values (3 replicates/block) and ANOVA. * - significant for P<0.05; ns - not significant. ... 174

Table 17 – Berry fresh weight and main composition during ripening 2010 in experimental site 2 - „Vermentino‟. Mean values (3 replicates/block) and ANOVA. * - significant for P<0.05; ns - not significant. ... 175

Table 18 – Berry fresh weight and main composition during ripening 2011 in experimental site 3 - „Vermentino‟. Mean values (3 replicates/block) and ANOVA. * - significant for P<0.05; ns - not significant. ... 177

Table 19 – Effect of irrigation treatments on anthocyanin forms in „Cannonau‟ berry homogenates during ripening – experimental site 1 – 2009. Mean values (3 replicates/block) and ANOVA for P-values< 0.05; ns - not significant. ... 179

Table 20 – Effect of irrigation treatment on Water Use Efficiency in experimental site 1 – Cannonau – during 2008 and 2009. Mean values (4 replicates/block) and ANOVA. * - significant for P<0.05; ns - not significant. ... 183

Table 21 – Effect of irrigation treatment on Water Use Efficiency in the sites 2 and 3 – Vermentino – during 2009, 2010 and 2011. Mean values (4 replicates/block) and ANOVA. * - significant for P<0.05; ns - not significant. ... 184

APPENDIXES Appendix 1 – Experimental design in site 1 – „Cannonau‟ – Sella & Mosca winery. ... 224

Appendix 2 – Experimental design in site 2 – „Vermentino‟ – Argiolas winery. ... 224

Appendix 3 – Experimental design in site 3 – „Vermentino‟ – Santa Maria la Palma winery. ... 225

Appendix 4 – Effect of irrigation treatments on growth, vigour, and canopy structure and dimensions of „Cannonau‟ in experimental site 1 during the seasons 2008. Mean values (4 replicates/block) and ANOVA for P<0.05. ns - not significant. ... 225

Appendix 5 – Effect of irrigation treatments on growth, vigour, and canopy structure and dimensions of „Cannonau‟ in experimental site 1 during the seasons 2009. Mean values (4 replicates/block) and ANOVA for P<0.05. ns - not significant. ... 225

Appendix 6 – Effect of irrigation treatments on stem water potential and soil water content of „Cannonau‟ in experimental site 1 during the seasons 2008. Mean values (4 replicates/block) and ANOVA for P<0.05. ns - not significant. ... 226

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Appendix 7 – Effect of irrigation treatments on stem water potential, soil water content and leaf gas exchange parameters of „Cannonau‟ in site 1 during the season 2009. Mean values (4 replicates/block) and ANOVA for P<0.05. ns - not significant. ... 227 Appendix 8 – Effect of irrigation treatments on growth, vigour, and canopy structure and dimensions of „Vermentino‟ in experimental site 2 during the seasons 2009. Mean values (4 replicates/block) and ANOVA for P<0.05. ns - not significant. ... 227 Appendix 9 – Effect of irrigation treatments on stem water potential, soil water content and leaf gas exchanges of „Vermentino‟ in site 2 during the season 2009. Mean values (4 replicates/block) and ANOVA for P<0.05. ns - not significant. ... 228 Appendix 10 – Effect of irrigation treatment on growth, vigour, and canopy structure and dimensions of „Vermentino‟ in experimental site 2 during the seasons 2010. Mean values (4 replicates/block) and ANOVA for P<0.05. ns - not significant. ... 229 Appendix 11 – Effect of irrigation treatment on stem water potential, soil water content and leaf gas exchanges of „Vermentino‟ in site 2 during 2010. Mean values (4 replicates/block) and ANOVA for P<0.05. ns - not significant. ... 229 Appendix 12 – Effect of irrigation treatment on stem water potential, soil water content and leaf gas exchanges of „Vermentino‟ in the experimental site 3 during 2011. Mean values (4 replicates/block) and ANOVA for P<0.05. ns - not significant. ... 231 Appendix 13 – Effect of irrigation treatment (DI 50, PRD and DI 25) on anthocyanin derivatives in „Cannonau‟ berry homogenates during ripening – experimental site 1 – 2009. Mean values (3 replicates/block) and ANOVA for P<0.05 . ns - not significant. ... 232 Appendix 14 – Effect of irrigation treatments on „Cannonau‟ light microclimate at the fruit zone during ripening 2009. Global solar radiation (Rg), Ultraviolet-A and B (UV-A and UV-B), PAR interception and Red/Far red ratio (R:FR). Mean values (6 replicates per treatment and canopy side) and ANOVA for P<0.05. ns - not significant. ... 234 Appendix 15 – Effect of irrigation treatments on „Vermentino light microclimate at the fruit zone during 2009 and 2010 ripening period. Global solar radiation (Rg), Ultraviolet-A and B (UV-A and UV-B), PAR interception and Red/Far red ratio (R:FR). Mean values (6 replicates per treatment and canopy side) and ANOVA for P<0.05. ns - not significant. ... 234

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1. INTRODUCTION

1.1 Overview on Viticulture Sector

1.1.1 Broad Scale

The vast majority of the world's wine producing regions are found between the temperate latitudes of 30° and 50° in the Northern and the Southern hemispheres (Fig. 1). Within these bands, the annual mean temperatures are between 10 and 20°C. Roughly, vines need approximately 1300-1500 hours of sunshine during the growing season and around 700 mm of rainfall throughout the year in order to produce grapes suitable for winemaking. Yet, Jones and Davis (2000) have shown that onsets of grapevine growth stages vary significantly with rainfall, hours of insolation, and the number of very hot days. Occasionally, grapes are grown outside the 30 – 50 latitude boundaries for example in Northern Europe, where the Gulf Stream keeps the climate warmer than it normally would be. In some countries, grapes can be grown at lower latitudes, but normally these areas are located at a high altitude, where the climate is cooler, such as Australia's Granite Belt in Queensland, at 28° S and Jujuy region at 23° S, in north-western Argentina.

Some of the well known wine producing regions, namely France and Italy, Spain and Portugal, California, South Africa and South-eastern Australia are located near large bodies of water: Atlantic, Pacific and Indian Oceans, Mediterranean sea and several important rivers: Loire, Rhone, Garonne, Mosel, Douro, Dão, etc. The coastal areas are, in fact, considered lifelines to those important viticulture areas, as they moderate the extremes in the climate. They are regarded as the best locations for growing grapes. New Zealand, for instance, is one of the coolest wine regions in the New World. As the two islands are long and narrow, vineyards are grown near the coast. This makes the climate cool and steady allowing the grapes to ripen evenly.

Grapes are grown all over the world because they are among the most versatile and adaptable of all small fruits. Approximately 71% of world grape production is used for wine, 27% as fresh fruit, and 2% as dried fruit (O.I.V, 2011). The total world vineyard area stands at 7.550.000 hectares and although it has been suffering a decrease in recent years (less 61.000 ha in 2010 and 90.000 in 2009), the New World viticulture areas continue to grow (in spite of the Australian and South African latest drops in terms of total area), with a steady increase in Chilean vineyard areas

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Growth-Yield Balance, Canopy and Cluster Microclimate for Improving Quality under Mediterranean Climate Page 9 of 234 and a solid growth in China, with 5.000 ha. Meanwhile, European producing countries seem to be reducing planted areas, due to the implementation of new community regulations in the EU. Indeed, since 2008/2009 the market structure promotes grubbing-up in Member States by indiscriminately allowing producers to receive a premium for permanent abandonment, which lead to an overall grub up of 175.000 ha over three years (O.I.V., 2011). Although Spain remains the most affected country, the Italian vineyard has also suffered an overall estimated reduction of 14.000 ha (-1.7%), of which approximately 11.000 ha can be attributed to the EU premium. UE vineyards are expect to be reduced by approximately 64.000 ha in 2011, even though European viticulture still accounts for nearly 48% of the world‟s total viticulture area (O.I.V., 2011). Vineyard surface areas outside Europe have exceeded within Europe vines area since 1999 (O.I.V, 2003), and should stand stable with 3920.000 ha against the 3630.000 ha of European producing countries (2010 forecast; O.I.V., 2011). Italy comes third place in the 10 biggest global vineyard areas ranking, with nearly 798.000 ha (10.7% of the world vineyard area) and 44.840 hl of wine produced in 2010. The leader is Spain, with approximately 14% of the global area and 33.999 hl, followed by France, with 11% of total area and 44.963 hl produced.

Figure 1 – World wine producing regions. Source: Schiller, C.G.E. “A global view: Who makes and who drinks wine?” Schiller-Wine. 9 Sept. 2011. http://schiller-wine.blogspot.com 11.Sept.

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1.1.2 Sardinia Context

The historical legacy and the numerous archaeological findings first date winemaking in Sardinia at the beginning of the Phoenician colonisation (IX-VIII cent. B.C.) and the broader diffusion of viticulture during the following Cartagine and then Roman dominations (VI cent. B.C. and III cent. B.C., respectively). The evidence of its ancestral origin in Sardinia is also well documented by the presence of Vitis vinifera silvestris, largely diffused all over the territory (Sanges, 2010). Nevertheless, it is after Spanish domination (XIV-XVII cent. A.D.) that viticulture becomes, after wheat, the second culture in terms of diffusion and economical importance (Ferrante, 2010). Indeed, in spite of the controversy in attributing varietal origin, encouraged by lack of scientific prove as far as varieties ancestry is concerned, the classic hypothesis indicates a Spanish origin for several of the actual cultivated varieties, as for instance: Cannonau, Bovali, Cagnulari, Carignano, Vermentino and Nasco (Lovicu, 2010).

Nowadays, viticulture represents a strategic economical sector in Sardinia‟s agriculture (Nieddu, 2006). In this region, vineyards occupy 26.652 hectares of land distributed all over the island in its eight provinces: 22.2% in Cagliari, 10.4% in Olbia-Tempio, 6.3% in Medio Campidano, 13.1% in Oristano, 15.0% in Nuoro, 7.3% in Ogliastra, 16.4% in Sassari and 9.4% Carbonia-Iglesias (RAS, 2009).

In this region, 10 are the main varieties currently cultivated, but many others are considered suitable for cultivation and of those 28 are traditionally cultivated. Despite the great number of varieties found, few are the leading under cultivation. The first Vitis vinifera cultivars in order of importance are: Cannonau, Monica, Vermentino and Nuragus, which represent 70% of the Sardinian vineyard area (Nieddu, 2006).

For the past six decades, vineyards area has been decreasing, from nearly 75.000 ha in the 70‟s to less than 30.000 in 2009. Yet, yield and quality have substantially improved during recent years, due to the renewal of a great deal of old vineyards and an increase in the percentage of fine quality wines, namely of AOC (Controlled Appellation of Origin) wines produced (Fig. 2). The six main Sardinian AOCs in order of importance are, in terms of white wines: “Vermentino di Sardegna” with 75.378 hl; “Vermentino di Gallura” with 36.322 hl and “Nuragus”, 17.537 hl. The red wines are mainly represented by the AOC: “Cannonau” prevailing with 90.978 hl; “Monica” with 22.423 hl; and

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“Cagnulari del Sulcis” with 19.607 hl. Yet, there are many other fine quality wines that represent

nearly 38.691 hl of the total AOC production of the Island (Ruju, 2010).

In spite of the tradition of wine production, great part of vineyards suffers a number of ecological fragilities, namely low water resources and soil slope (A.A.R.A.P., 2002). Improving irrigation management is an import key in both the valorisation of these ecosystems, the sustainability of the vine and the increase of a high quality wine production.

Figure 2 – Sardinia AOCs. Source: Schiller, C.G.E. “DOC e DOCG. Le DOC della Sardegna”. Lavinium. Rivista di vino e cultura online. http://www.lavinium.com/denom/sardeden.shtml

11.Sept. 2011.

1.2 Viticulture in Mediterranean Climate

Grapevine (Vitis vinifera L.) is traditionally a non-irrigated crop cultivated in a quite extensive world area, mainly in semi-arid regions. In these regions grapevines are frequently exposed to drought due to high evaporative demand and low soil water availability (Cifre et al., 2005). Due to their large and deep root system and to an efficient stomatal control of transpiration vines are able to adjust their physiology in order to avoid or limit the negative impacts of drought. However, the

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Growth-Yield Balance, Canopy and Cluster Microclimate for Improving Quality under Mediterranean Climate Page 12 of 234 combined effect of water scarcity, high air temperature and evaporative demand during vegetative and reproductive stages is known to limit grapevine yield and berry quality (Escalona et al., 1999).

Water stress is considered to be one of the most important factors limiting plant growth and quality worldwide, especially in the Mediterranean areas. Viticulturists have begin to rely on irrigation during water scarcity periods in order to increase yield but there is still much controversy concerning the positive and negative impacts of irrigation in vineyards, due to an incomplete understanding of the relationships between grapevine physiology, yield and quality (Patakas et al., 2005; Souza et al., 2005).

The global warming predictions and almost all future climate scenarios indicate a decrease of the annual precipitation in Southern Europe, with potential decreases in summer and with higher frequency of extreme events such as warm spells, heat waves and heavy rain (IPCC, 2007). In the Mediterranean Basin this will likely lead to drier and warmer conditions and to an increase of the evapotranspiration. Furthermore, these factors will reduce soil water availability in most of the Mediterranean region, with great impacts on vineyards, particularly on its physiology (Schultz, 2000; Payan et al., 2006). Although vines have regulation mechanisms that improve the water use efficiency (for instance, increasing stomatal resistance), the frequency of water stress events will likely be higher and overall the phenological states will take place more rapidly. As a result, ripening will occur earlier, in the middle of the summer, with great risks of affecting grape organoleptic characteristics (Lebon, 2000; Cortázar, 2006; Jones et al., 2005).

This new agro-physiological balance and the aggravation of water use restrictions, due to the lack of available water resources and to deficient irrigation practices, compel us to extend the knowledge of efficient strategies for water use in vineyard that can contribute to stabilise and even improve the quality of wines.

Regulated Deficit Irrigation (RDI) has been proposed as a judicious water management tool for the vineyard (Chalmers et al., 1981; Kriedemann and Goodwin, 2004). It consists on applying amounts of water inferior to the maximum consumption of the vine at key stages of the growth season, reducing or even withholding the watering inputs for specific periods of time (Lopes et al., 1999; Battilani, 2000; Poni, 2004).

In Mediterranean climate conditions a specific type of deficit irrigation (DI) has been studied, the so-called Partial Root-zone Drying (PRD). Through this technique, the water is applied

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Growth-Yield Balance, Canopy and Cluster Microclimate for Improving Quality under Mediterranean Climate Page 13 of 234 at alternate sides of the root system. While one half of the root is exposed to dry soil conditions, the other is simultaneously exposed to wet soil conditions. The watered roots maintain the plant water status while the dehydrating roots send chemical signals (e.g. abscisic acid – ABA) to the shoots and leaves via the xylem, reducing the stomatal conductance (aperture) (Souza et al., 2005). This technique allows for a better control of the vegetative vigour and plants transpiration, without the unsuitable severe water stress periods that can occur in the RDI (Dry and Loveys, 1998). In fact, several studies have indicated that PRD might improve yield and berry quality in semi-arid regions (Dry and Loveys, 1998; 1999; Dry et al., 2000; Santos et al., 2003).

The effects of water deficit on the light and thermal environment within the fruit zone, and thus on the grape quality, vary within cultivars and field-growth conditions. Nevertheless, it is well known that dense canopies promote competition between shoots and fruits and reduce the lightning of the clusters zone, affecting the synthesis and accumulation of sugars, anthocyanins and phenols. Furthermore, when the exposure is too high and the temperature reaches values above the optimums for anthocyanins synthesis, this might be reduced or even inhibited (Bergqvist et al. 2001; Spayd et al., 2002; Santos et al., 2005; Yamane et al., 2006).

Based on projections for 21st_{century, using SRES scenarios, IPCC (2007) reports as virtually} certain the likelihood of warmer and fewer cold days and nights for the future together with warmer and more frequent hot days and nights. It is of utmost importance to assess the impact of the changing daily and seasonal thermal patterns also on berry metabolism and overall ripening dynamics.

Therefore, it is important to enhance the knowledge and to establish a reliable and objective assessment of irrigation strategies effects on vine physiology and production. For instance, developing robust correlations between water stress indicators and their critical values, and grape and wine quality parameters, as aromatic profiles, flavour and colorant matters for given varieties and agro-climatic contexts. Furthermore, these studies can contribute to define criteria of high quality irrigation strategies and to give a sustained answer to questions such as: “Does irrigation change the terroir of delimited production areas (AOC wines)?” or “Which effects does irrigation have on wine typicity characters?”

Experimental research, study and optimization of a management technique like irrigation in a given terroir requires the collections and analysis of a great deal of data of many different kinds,