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Olive quick decline syndrome (OQDS) is a severe disease, first described in Italy in late 2013, caused by strains ofXylella fastidiosasubsp.pauca (Xfp)in susceptible olive cultivars. Conversely, resistant olive cultivars do not develop OQDS but present scattered branch dieback, which generally does not evolve to severe canopy decline. In the present study, we assessed the physiological responses ofXfp-infected olive trees of susceptible and resistant cultivars. Periodic measurements of stomatal conductance (gs) and stem water potential (Ψstem) were performed using a set of healthy andXfp-infected plants of the susceptible “Cellina di Nardò” and resistant “Leccino” and “FS17” cultivars. Strong differences in Δgsand ΔΨstem amongXfp-infected trees of these cultivars were found, with higher values in Cellina di Nardò than in Leccino and FS17, while no differences were found among healthy plants of the different cultivars. Both resistant olive cultivars showed lower water stress uponXfpinfections, compared to the susceptible one, suggesting that measurements of gsand Ψstem may represent discriminating parameters to be exploited in screening programs of olive genotypes for resistance toX. fastidiosa.

Despite irrigation being one of the most powerful tools to increase yields and maintaining profitability in fruit production, most farm operations are not following sound irrigation management tools, although there are many available to them, even through the Internet. As societal pressure is on agriculture to reduce its use of the water resource, ecophysiological studies are elucidating the mechanisms underpinning the interplay between leaf, fruit and stem water relations, and how these affect fruit growth. Daily variations in water potentials of these organs are involved (in different manners for different species) in the process of fruit growth but more interestingly, the possibility arises of manipulating the gradients between these potentials that occur during the day, enhancing the fruit's capacity to attract dry matter and water, that are needed to grow, while saving water.

There has been very little literature on the spatial variability of fruit production in horticulture crops published to date. Most of the existing literature refers to data collected at picking time. Crop load data taken prior to hand thinning and prior to harvest were collected in 3 blocks of a commercial apple (Malus domestica Borkh.) orchard in the Po valley (Ferrara, Italy). The purpose of the survey was to characterize the within field variability of crop load, using spatial statistics, and assess the effectiveness of the hand-thinning treatment to eliminate this variability. Crop load estimations were taken at 156 sites pre and post hand-thinning over a defined distance (0.8 m) and the data used to model a variogram and associated spatial analysis. Variation in the spatial distribution of the fruit load prior to the hand-thinning was observed, indicating a possibility to spatially differentially manage the orchard. No spatial variation in fruit number was observed prior to harvest (post thinning), indicating that thinning had removed the previously observed spatial variation in crop load. However, the spatial variation observed prior to thinning may indicate that a differential crop load management strategy may be optimal for maximizing quality in the orchard.

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

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

Net photosynthesis, at the base of plant productivity, increases with irradiance till a saturating point. All the extra absorbed energy may be considered excessive and can emphasize the photoprotective and photoinactivation mechanisms with a consequent decrease of plant dry matter accumulation. Several areas in which peach is commonly grown the excessive light is often associate with water limitation that can in turn exacerbate the loss due to photoinhibition increase and net photosynthesis reduction. In this study the ameliorative consequences of light reduction of about 40% trough a neutral shading net were pointed out. Light reduction, associate with temperature mitigation did not affect leaf net photosynthesis but it reduced water consumption and the amount of inactive photosynthetic complexes to be repaired at expense of dry matter accumulation. Under the shading net the entity of the photoprotective mechanisms decreased since leaves were less exposed to light excess. The consequence of this favourable state was probably the increase of dry matter accumulation, including fruit production.

La produttività degli alberi da frutto è linearmente legata alla quantità di luce intercettata; tuttavia tale relazione diviene meno stretta quando il livello di luce intercettata supera il 50% della radiazione disponibile. In questo lavoro vengono presentati i risultati di studi riguardanti la gestione della radiazione incidente da parte di piante di pesco, attraverso misure di intercettazione luminosa e scambio gassoso su chiome intere, combinate con rilievi di scambio gassoso e fluorescenza della clorofilla a livello di singola foglia. La prova è stata condotta su alberi appartenenti ad un frutteto sperimentale denominato “Pescheto Asimmetrico”, dove diverse combinazioni di orientamento dei filari ed inclinazione delle chiome hanno permesso la sussistenza di tre differenti profili radiativi (C, E, O) nelle medesime condizioni di campo. I livelli di fotosintesi netta (NCU) e traspirazione (TRWP) della chioma misurati sulle piante di controllo (C) sono risultati simili a quelli della tesi O, sebbene quest’ultima abbia intercettato la quantità più alta di luce, soprattutto al mattino. Gli alberi sottoposti ad alta irradianza al pomeriggio (E) hanno mostrato i valori di NCU e TRWP più alti, mantenendo un efficienza d’uso dell’ acqua (WUE) simile alle rimanenti tesi poste a confronto. Nei peschi della tesi O il fotodanno è stato più alto che in C e E, rispettivamente del 29% e 8%. L’analisi della ripartizione dell’energia assorbita ha evidenziato che la dissipazione termica (non photochemical quenching, NPQ) è risultata il meccanismo fotoprotettivo principale per la dissipazione degli eccessi luminosi, anche se alle radiazioni medio-basse sembrerebbe limitata dalla bassa concentrazione di H+ nel lumen dei tilaciodi. I trasporti elettronici alternativi (NC) hanno mostrato una maggiore efficienza fotoprotettiva a livelli luminosi medio-bassi facilitando, inoltre, l’instaurarsi di un pH ottimale per la piena attivazione del NPQ. I risultati ottenuti suggeriscono che in molti casi, specie nelle zone con alti livelli luminosi e bassa disponibilità idrica, la radiazione luminosa è eccessiva e può causare limitazioni termiche e stomatiche in aggiunta all’aumento del fotodanno, la cui riparazione richiede energia in forma di assimilati sottratti all’accumulo di sostanza secca ed alla produttività.

The energetic basis of orchard productivity lies in the interaction between the tree and sunlight. The light intercepted by a plant is linearly related to the amount of dry matter it produces. This concept drew the evolution of the new, intensive orchard planting systems, although this dependence seems to be more subordinate to planting system rather than light intensity. At whole plant level not always the increase of irradiance determines productivity improvement. One of the reasons can be the plant intrinsic un-efficiency in using energy. Generally in full light only the 5–10% of the total incoming photosynthetic photon flux density (PPFD) is allocated to net photosynthesis. Therefore preserving or improving this efficiency becomes pivotal for scientist and fruit growers. Net photosynthesis increases with light until the saturation point and additional PPFD doesn’t improve carboxylation. In several parts of the world, under clear sky the PPFD reaches commonly 2000 μmol photons m-2 s-1 or above, and about 50% of the incoming light is enough for reaching the saturating point in most plant species. On the other hand, about half of the available light may be in excess. Even tough a conspicuous energy amount is reflected or transmitted, plants can not avoid to absorb photons in excess. The chlorophyll over-excitation promotes the reactive oxygen species (ROS) production increasing the photoinhibition (photo-damage) risks. The dangerous consequences of photoinhibition forced plants to evolve a complex and multilevel machine able to dissipate the energy excess quenching heat (Non Photochemical Quenching), moving electrons (water-water cycle, cyclic transport around PSI, glutathione-ascorbate cycle and photorespiration) and scavenging the generated ROS. The price plants must pay for this equipment is the use of CO2 and reducing power with a consequent decrease of the photosynthetic efficiency, both because some photons are not used for carboxylation and an effective CO2 and reducing power loss occurs. The wide photo-protective apparatus, although is not able to cope with the excessive incoming energy, therefore photo-damage occurs. Each event increasing the photon pressure and/or decreasing the efficiency of the described photo-protective mechanisms (i.e. thermal stress, water and nutritional deficiency) can emphasize the photoinhibition. Likely in nature a small amount of not damaged photo-systems is found because of the effective, efficient and energy consuming recovery system. Since the damaged PSII is quickly repaired with energy expense, it would be interesting to investigate how much PSII recovery costs to plant productivity. This review purposes to improve the knowledge about the several strategies accomplished for managing the incoming energy and the light excess implication on photo-damage in plants. Furthermore the chlorophyll fluorescence measure technique is described. This is the most useful method, particularly because it can be used in vivo as well and it is possible to quantify and discriminate the contribution of pathways in which the incoming photon pressure is engaged. Finally some cases of light excess linked with abiotic stresses and particular physiological condition on fruit species are reported.

The relation between the intercepted light and orchard productivity was considered linear, although this dependence seems to be more subordinate to planting system rather than light intensity. At whole plant level not always the increase of irradiance determines productivity improvement. One of the reasons can be the plant intrinsic un-efficiency in using energy. Generally in full light only the 5 – 10% of the total incoming energy is allocated to net photosynthesis. Therefore preserving or improving this efficiency becomes pivotal for scientist and fruit growers. Even tough a conspicuous energy amount is reflected or transmitted, plants can not avoid to absorb photons in excess. The chlorophyll over-excitation promotes the reactive species production increasing the photoinhibition risks. The dangerous consequences of photoinhibition forced plants to evolve a complex and multilevel machine able to dissipate the energy excess quenching heat (Non Photochemical Quenching), moving electrons (water-water cycle , cyclic transport around PSI, glutathione-ascorbate cycle and photorespiration) and scavenging the generated reactive species. The price plants must pay for this equipment is the use of CO2 and reducing power with a consequent decrease of the photosynthetic efficiency, both because some photons are not used for carboxylation and an effective CO2 and reducing power loss occurs. Net photosynthesis increases with light until the saturation point, additional PPFD doesn’t improve carboxylation but it rises the efficiency of the alternative pathways in energy dissipation but also ROS production and photoinhibition risks. The wide photo-protective apparatus, although is not able to cope with the excessive incoming energy, therefore photodamage occurs. Each event increasing the photon pressure and/or decreasing the efficiency of the described photo-protective mechanisms (i.e. thermal stress, water and nutritional deficiency) can emphasize the photoinhibition. Likely in nature a small amount of not damaged photosystems is found because of the effective, efficient and energy consuming recovery system. Since the damaged PSII is quickly repaired with energy expense, it would be interesting to investigate how much PSII recovery costs to plant productivity. This PhD. dissertation purposes to improve the knowledge about the several strategies accomplished for managing the incoming energy and the light excess implication on photo-damage in peach. The thesis is organized in three scientific units. In the first section a new rapid, non-intrusive, whole tissue and universal technique for functional PSII determination was implemented and validated on different kinds of plants as C3 and C4 species, woody and herbaceous plants, wild type and Chlorophyll b-less mutant and monocot and dicot plants. In the second unit, using a “singular” experimental orchard named “Asymmetric orchard”, the relation between light environment and photosynthetic performance, water use and photoinhibition was investigated in peach at whole plant level, furthermore the effect of photon pressure variation on energy management was considered on single leaf. In the third section the quenching analysis method suggested by Kornyeyev and Hendrickson (2007) was validate on peach. Afterwards it was applied in the field where the influence of moderate light and water reduction on peach photosynthetic performances, water requirements, energy management and photoinhibition was studied. Using solar energy as fuel for life plant is intrinsically suicidal since the high constant photodamage risk. This dissertation would try to highlight the complex relation existing between plant, in particular peach, and light analysing the principal strategies plants developed to manage the incoming light for deriving the maximal benefits as possible minimizing the risks. In the first instance the new method proposed for functional PSII determination based on P700 redox kinetics seems to be a valid, non intrusive, universal and field-applicable technique, even because it is able to measure in deep the whole leaf tissue rather than the first leaf layers as fluorescence. Fluorescence Fv/Fm parameter gives a good estimate of functional PSII but only when data obtained by ad-axial and ab-axial leaf surface are averaged. In addition to this method the energy quenching analysis proposed by Kornyeyev and Hendrickson (2007), combined with the photosynthesis model proposed by von Caemmerer (2000) is a forceful tool to analyse and study, even in the field, the relation between plant and environmental factors such as water, temperature but first of all light. “Asymmetric” training system is a good way to study light energy, photosynthetic performance and water use relations in the field. At whole plant level net carboxylation increases with PPFD reaching a saturating point. Light excess rather than improve photosynthesis may emphasize water and thermal stress leading to stomatal limitation. Furthermore too much light does not promote net carboxylation improvement but PSII damage, in fact in the most light exposed plants about 50-60% of the total PSII is inactivated. At single leaf level, net carboxylation increases till saturation point (1000 – 1200 μmolm-2s-1) and light excess is dissipated by non photochemical quenching and non net carboxylative transports. The latter follows a quite similar pattern of Pn/PPFD curve reaching the saturation point at almost the same photon flux density. At middle-low irradiance NPQ seems to be lumen pH limited because the incoming photon pressure is not enough to generate the optimum lumen pH for violaxanthin de-epoxidase (VDE) full activation. Peach leaves try to cope with the light excess increasing the non net carboxylative transports. While PPFD rises the xanthophyll cycle is more and more activated and the rate of non net carboxylative transports is reduced. Some of these alternative transports, such as the water-water cycle, the cyclic transport around the PSI and the glutathione-ascorbate cycle are able to generate additional H+ in lumen in order to support the VDE activation when light can be limiting. Moreover the alternative transports seems to be involved as an important dissipative way when high temperature and sub-optimal conductance emphasize the photoinhibition risks. In peach, a moderate water and light reduction does not determine net carboxylation decrease but, diminishing the incoming light and the environmental evapo-transpiration request, stomatal conductance decreases, improving water use efficiency. Therefore lowering light intensity till not limiting levels, water could be saved not compromising net photosynthesis. The quenching analysis is able to partition absorbed energy in the several utilization, photoprotection and photo-oxidation pathways. When recovery is permitted only few PSII remained un-repaired, although more net PSII damage is recorded in plants placed in full light. Even in this experiment, in over saturating light the main dissipation pathway is the non photochemical quenching; at middle-low irradiance it seems to be pH limited and other transports, such as photorespiration and alternative transports, are used to support photoprotection and to contribute for creating the optimal trans-thylakoidal ΔpH for violaxanthin de-epoxidase. These alternative pathways become the main quenching mechanisms at very low light environment. Another aspect pointed out by this study is the role of NPQ as dissipative pathway when conductance becomes severely limiting. The evidence that in nature a small amount of damaged PSII is seen indicates the presence of an effective and efficient recovery mechanism that masks the real photodamage occurring during the day. At single leaf level, when repair is not allowed leaves in full light are two fold more photoinhibited than the shaded ones. Therefore light in excess of the photosynthetic optima does not promote net carboxylation but increases water loss and PSII damage. The more is photoinhibition the more must be the photosystems to be repaired and consequently the energy and dry matter to allocate in this essential activity. Since above the saturation point net photosynthesis is constant while photoinhibition increases it would be interesting to investigate how photodamage costs in terms of tree productivity. An other aspect of pivotal importance to be further widened is the combined influence of light and other environmental parameters, like water status, temperature and nutrition on peach light, water and phtosyntate management.

Il carico di frutti, oltre a determinare quantità e qualità delle produzioni, risulta essere in molte specie un regolatore fotosintetico. Abbassando il numero e/o la forza dei sink, infatti, i prodotti della fotosintesi permangono più a lungo nel ciclo costipando il sistema che rallenta il suo tasso di carbossilazione. La pressione fotonica in entrata viene utilizzata in minima parte per la fotosintesi mentre la quota restante è dissipata tramite meccanismi di fotoprotezione (Non Photochemical Quenching, trasporti alternativi e fotorespirazione) e Foto-ossidazione, con la formazione di Specie Attive dell’Ossigeno. In condizioni di ridotta fotosintesi le vie di difesa ed i meccanismi di Foto-ossidazione risultano essere enfatizzati dall’ eccesso energetico non utilizzato per la carbossilazione; si incrementa, così, il rischio di formazione di specie radicaliche e di insorgenza del foto-danno. Vista la vitale importanza dei fotosistemi, la pianta mette in atto meccanismi efficaci ed efficienti per la repentina riparazione delle componenti danneggiate. Nel presente lavoro viene quantificata e confrontata l’entità delle diverse vie di utilizzazione dell’energia captata da foglie di piante di pesco (cv Stark RedGold) sottoposte ad alto e basso carico di frutti, in presenza o meno di riparazione del foto-danno. Consentendo la riparazione, i due carichi imposti non hanno determinato alcuna differenza sulla fotosintesi e sugli altri trasporti energetici. Quando la riparazione è stata bloccata, le piante sottoposte a basso carico hanno subito una sensibile flessione della fotosintesi ed un notevole innalzamento della quantità di energia dispersa dai fotosistemi danneggiati. Un basso carico produttivo, quindi, provocherebbe un rallentamento del tasso fotosintetico ed un conseguente incremento del foto-danno. La riparazione dei fotosistemi distrutti nasconderebbe tale fenomeno poiché il danno sarebbe riparato usando i fotosintati rilasciati dal ciclo carbossilativo che viene così de-costipato.

Nei giorni 20-22 giugno scorso si è tenuta presso la Facoltà di Agraria dell’Università di Bologna la 2a General Assembly del Progetto integrato europeo Isafruit, con il concreto sostegno della Facoltà di Agraria, della Regione Emilia Romagna e delle principali organizzazioni di produttori frutticoli italiani. Questo progetto è, tra quelli dedicati esclusivamente alla frutta, il maggiore sia per entità del budget totale, sia per entità del finanziamento Ue, nonché per il numero di partner partecipanti.