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Hazelnut (Corylus avellana) cultivation is increasing worldwide. A 3D model of its structure could improve the managerial techniques such as pruning. This study aims to analyse, over two successive years, hazelnut architectural development to implement a functional structural plant model. 104 one-year-old shoots of own-rooted hazelnut trees were selected and analyzed in winter 2020 and 2021. Exploratory analyses, generalized linear models, and multinomial regression models were used to describe the architectural processes. The existence of sylleptic shoots on hazelnut one-year-old shoots, characterized by the presence of the male inflorescence on apical position, was detected. Along proleptic shoots the branching pattern was described by (1) blind nodes located in the proximal part (2) sylleptic shoots and mixed buds in the median part (3) vegetative buds in the distal part. Apical bud died during the growing season, suggesting that Tonda di Giffoni has a sympodial branching. The models revealed dependencies among buds located at the same node, in the case of proleptic shoots. Especially, the probability of a bud to burst depended on both its type (i.e., mixed or vegetative) and the presence of other buds, either mixed or vegetative. Based on these local models and on a flow diagram, which defines the steps that lead to the construction of hazelnut tree architecture, a first functional-structural plant model of hazelnut tree architecture was built. Further experiments will be needed and should be repeated over following years to extend this study toward the juvenility phase and tree architecture over time.

Dark respiration (Rd) is a fundamental process in plant physiology. It reduces the carbohydrates gained via photosynthesis to CO2 and produces energy that can be used to satisfy the maintenance needs of organs and contribute to their growth. Because Rd is involved in the formation of new organs, it is also driven by the size and growth stage of each organ. In this work, we aimed at investigating how changes in temperature and relative growth rate (RGR) impact Rd in leaves, stems and fruits of filbert (Corylus avellana), and to assess if there are critical stages during which respiration peaks can pose a limitation to the fruit set. Rd was measured on leaves, stems and fruits of "Tonda di Giffoni" during the spring and summer of 2021. Rd in filbert leaves, stems and fruits widely varied according to temperature and RGR. The results indicate that when the nut shell grows, the carbon demand, in terms of Rd, was two-fold compared to other organs. High carbon demands have significant consequences on carbon partitioning among organs and the occurrence of possible carbon shortages limiting nut yield. Rd relationships with temperature and RGR are fundamental for the parametrization of future Rd models for filbert, and the optimization of appropriate horticultural techniques to reduce the carbon limitation to fruit set.

Vapor pressure deficit (VPD) is the driving force of leaf transpiration and it is positively related to air temperature and negatively related to relative humidity. Hazelnut is considered a species able to withstand limited increase of VPD. High VPD during the summer can induce significant stomatal limitations with significant short-term effects on leaf photosynthesis and long-term damage to the leaf apparatus. We investigated the leaf sensitivity to VPD in three C. avellana cultivars, ‘Tonda Gentile delle Langhe’ (TGL), ‘Tonda Romana’ and ‘Tonda di Giffoni’, and on leaves borne on long shoots, non-fruiting short shoots and fruiting short shoots of ‘Tonda di Giffoni’. TGL was the most sensitive to VPD and leaf temperature. Leaves on short shoots were more sensitive to VPD than leaves on long shoots. Leaves on fruiting short shoots had lower leaf gas exchange rates than those on non-fruiting short shoots and long shoots, respectively. Part of this variability was related to higher leaf mass per area of leaves borne on short shoots and to different osmotic potential. Leaf sensitivity to VPD can be an important physiological parameter influencing the adaptability of cultivars to scenarios of climate change and limiting the capability of leaves located on short shoots where nuts are borne to export carbohydrates.

Relative growth rate (RGR) is a standardized measure of growth that accounts for the difference in initial organ size. Relative growth rate sets the sink strength potential that, in combination with dark respiration (Rd), determines the carbon need of organs. Total Rd is the sum of maintenance respiration and growth respiration (Rg). The first provides energy for the maintenance of the existing cell structures, while the latter provides energy for growth. Dark respiration is mainly driven by temperature, but it varies during the season according to temperature acclimation and organ growth. Temperature acclimation is defined as the variation of Rd following the exposure to short or long periods of different temperatures. Temperature strongly affects growth and drives the Rg component of Rd. We hypothesized that RGR has a fundamental role in Rd variation during the season. The aims of the study were to determine the following: (i) if there was a variation of leaf Rd over the season and if such variation could be due to acclimation and/or RGR; (ii) the type of acclimation (i.e., Type I or II) on fully expanded leaves and newly formed leaves; and finally, (iii) if acclimation or RGR should be included to model Rd variation over the season. Leaf Rd was measured in field-grown plants from bud break to summer. Different cohorts of leaves were used to test the effect of exposure to different temperature regimes during leaf formation. The only case of acclimation was found in fully expanded leaves. It was an acclimation of Type II. Under field conditions, acclimation of filbert leaves, Rd to temperature was limited since most of the Rd variation during the season was explained by RGR. Our work suggests that RGR is a fundamental parameter that should be included in addition to temperature to model seasonal Rd pattern.

The comprehension of one-year-old-shoot architecture provides useful information for improving crop management, such as pruning or vegetative/reproductive equilibrium. This work aimed to investigate one-year-old hazelnut shoot structures, in three different treatments: own-rooted plants at two ages (6 or 35 years old) or 6-year-old plants grafted to Corylus colurna seedlings. The experiment was conducted in January 2020 in Deruta, Perugia (Italy). In each treatment, 120 one-year-old shoots of C. avellana ‘Tonda di Giffoni’ were sampled. In each shoot, the position and the number of axillary buds (vegetative (V) or mixed (M)), the presence of blind nodes (B), or male inflorescences (S) were recorded. The frequency of each observation was computed per rank from the base to the tip of the one-year-old shoots. In the 6-year-old plants (either own-rooted or grafted), blind nodes were followed by male inflorescences, mixed buds and then vegetative buds. Grafting seems to change the percentage of mixed and vegetative buds. New shoots borne by the grafted plants seem to be longer than those from own-rooted plants. The length of the shoots is not related to the nut yield in grafted plants while, in own-rooted ones, the longer the shoot the higher the fruit set. Tree aging is not only reflected in shorter shoots. Indeed, 35-year-old own-rooted plants were characterized by the presence of male inflorescences in all the ranks and an average percentage of vegetative buds less than 30%. The different patterns of vegetative and mixed buds, observed along one-year-old shoots, suggest that different strategies for canopy management could be adopted in grafted or own-rooted trees.

The nut set process depends on the availability of viable pollen and the amount of resources, particularly carbohydrates, available during the period of nut growth. One of the usual responses of the plant to pruning is an increase in the rate of nut set. The aim of this work was to investigate the role of shoot leaf area formed by the elongation of the vegetative part of the glomerule on the rate of nut set. Three experiments were carried out on ‘Tonda Gentile delle Langhe’ (TGL) and ‘Negret’ hazelnuts. In the first one, one out of three branches of TGL bushes was removed in addition to current pruning to test the effect of heavy pruning on fruit set. In the second experiment, single glomerules were targeted. Glomerules of different lengths and with different leaf areas were chosen. Some of them were partially defoliated removing 33% (LR33) and 66% (LR66) of the shoot leaf area. In the third experiment, the effect of shoot heading was tested by removing the top 3 nodes (trimming) and heading 2 nodes above the distal glomerule (topping). The pruning treatment resulted in a significant increase of fruit set from 0.54 nuts glomerule-1 in control plants to 1.28 in additionally pruned plants. In the second experiment, nut set rate was 0.92, 1.25 and 1.63 nuts glomerule-1 in control, LR33 and LR 66, respectively. The topping treatment increased glomerule shoot length by 47% and nut set by 78%. These data suggest that the application of horticultural techniques to force the growth of glomerule shoots could improve nut set, which can be considered one of the major barriers to achieving maximum yield potential in hazelnut.

Yield reduction over the years is a phenomenon that affects many fruit tree species, including hazel (Corylus avellana). Studying plant architecture could provide useful information for improving crop management, such as pruning, to reduce the impact of yield reductions. This study aimed to compare the relationship between bud composition and shoot length in hazel shoots. The experiment was carried out in January 2020 and 2021 in Deruta, Perugia (Italy). In 2020, 120 1-year-old shoots of C. avellana ‘Tonda di Giffoni’ were sampled. In 2021, the same observations were performed on lateral and apical 1-year-old shoots that had burst from parental buds in spring 2020. Depending on its length, each shoot was sorted into four categories: short (Sh) when shorter than 5 cm, medium (Me) when between 5 and 20 cm, long (Lo) when between 20 and 40 cm, and very long (VLo) when longer than 40 cm. For each shoot, shoot length, axillary and apical bud fate was recorded at each node: vegetative bud, latent bud, catkin, and mixed bud (V, B, C, and M, respectively). Percentage of lateral mixed buds was higher in longer shoots than in shorter ones while that of vegetative buds remained constant whatever the length. Fruit set, computed as the ratio between the number of nuts and the number of mixed buds, was significantly higher in Lo and VLo shoots. It was observed that the length of lateral proleptic shoots, developed in 2021, was related to the length of the bearer shoot from which it was developed. Proleptic lateral Sh shoots were the most frequent among all length categories while longer proleptic shoots (Lo and VLo) were originated only from Lo and VLo shoots. Managing tree architecture, considering a good balance between long and short shoots, and mixed and vegetative buds, could help control and prevent yield decrease in hazelnut trees.

Introduction - Tree architecture is a fundamental part of a functional structural plant model. This is particularly evident in perennial tree crops where the structure of the plant influences the position of source and sink organs, as well as light interception inside the canopy, and serves as storage pool for exceeding carbohydrates. Therefore, a precise description of tree 3D structure is essential to realistically allocate carbohydrates in a FSPM (Costes et al., 2006). Hazelnut tree architecture has different characteristics compared to other fruit tree crops that have been modelled (i.e., peach, mango, apple, and kiwi). It is a monoecious species. Female flowers are grouped into inflorescences located into mixed buds, while male flowers are arranged into inflorescences in the apical position of sylleptic shoots. Each node could bear more than one bud and, the following year, the new shoots are much shorter than the shoots from which they were born. The present study aimed to analyse hazelnut one-year-old shoots 'architecture in order to build the structural part of L-HAZELNUT: a functional structural plant model of hazelnut (Corylus avellana). Material and Methods - Own-rooted tree clones of C.avellana, cultivar “Tonda di Giffoni”, were chosen, during winter, in 2020 and 2021 in Deruta (Italy). Plants were normally irrigated and fertilized. No pruning occurred during the two years. 104 one-year-old proleptic shoots were sampled according to four length categories: short (Sh) when shorter than 5 cm, medium (Me) when they were between 5 and 20 cm, long (Lo) when they were between 20 and 40 cm, and very long (VLo) when longer than 40 cm. For each shoot, diameter, length, and number of nodes were recorded. From the base of the shoot to its tip, the fate of each node was noted. Four fates are distinguished in C.avellana: blind nodes, vegetative buds, sylleptic shoots and mixed buds. In the year subsequent to sampling, the same measurements were repeated on the latera

At springtime, the formation of stem somatic traits (stem elongation and leaf growth) and reproductive activity (flowering and fruit set) occur simultaneously. They are all competing carbon sinks, with an extremely high demand for carbohydrates. The shoot growth rate is strongly related to environmental temperature, which, according to climate change scenarios, is expected to increase also in extremes. Our hypothesis was that the increase in temperature during budburst could increase the vegetative carbon sink strength reducing the carbon stock available for the reproductive activity jeopardizing flowering of the next year. In our experiment, we artificially conditioned grapevine budburst by exposing the growing shoots to different temperature regimes. Higher temperatures during the spring vegetative growth favored shoot stem extension at the detriment of shoot leaf area. This caused a reduction in vine CO2 assimilation, which, combined with the competition of the growing vegetative organs, affected the concurrent reproductive activity, with carry-over effects on the following year, resulting in a limited flower initiation in dormant buds. These results suggest that the increase in springtime temperature can alter canopy development and vine physiology, resulting in the reduction in reproductive activity with an economical negative impact on grapevine productivity.

Functional structural plant models of tree crops are useful tools that were introduced more than two decades ago. They can represent the growth and development of a plant through the in silico simulation of the 3D architecture in connection with physiological processes. In tree crops, physiological processes such as photosynthesis, carbon allocation and growth are usually integrated into these models, although other functions such as water and nutrient uptake are often disregarded. The implementation of the 3D architecture involves different techniques such as L-system frameworks, pipe model concepts and Markovian models to simulate branching processes, bud fates and elongation of stems based on the production of metamers. The simulation of root architecture is still a challenge for researchers due to a limited amount of information and experimental issues in dealing with roots, because root development is not based on the production of metamers. This review aims to focus on functional–structural models of fruit tree crops, highlighting their physiological components. The potential and limits of these tools are reviewed to point out the topics that still need more attention.

Dark respiration (Rd) is a fundamental plant process used to gain biomass and maintain plant physiological activity. It accounts for the metabolization of a large share of the carbon fixed by photosynthesis. However, Rd during conditions of severe plant water stress is still poorly understood. The decrease in leaf transpiration increases temperature, one of the most important drivers of leaf Rd. On the other hand, water stress decreases the pool of leaf carbohydrates, which are the most important substrate for respiration. The aim of the present work was to determine the impact of water shortage on leaf Rd in grapevine and understand the driving factors in modulating leaf Rd response under plant water stress conditions. Water stressed vines had lower Rd as the water shortage severity increased. Rd was correlated with leaf temperature in well-watered vines. Instead, in water stressed vines, Rd correlated with leaf soluble sugars. The decrease of leaf Rd in water stressed vines was due to the decrease of leaf non-structural carbohydrate that, under water stress conditions, exerted a limiting effect on Rd.

Understanding the interaction between insects and microclimate can be essential in order to plan informed and efficient treatments against agricultural pests. Microclimatic factors such as humidity and temperature can influence the population dynamics of the invasive agricultural pest Halyomorpha halys, the brown marmorated stink bug. The aim of this work was to evaluate the level of transpiration of H. halys in dry, normal and humid microclimates according to the sex, physiological conditions and developmental stage of individuals. Water loss during diapause and the effect of population density on insects’ transpiration were also assessed, as were the nutritional preferences of adults upon exiting diapause. Our data demonstrate that microclimatic conditions significantly influence the transpiration of this pest species. The effect of sex and feeding status on insects’ water loss is marked, while population density does not influence water loss in diapausing individuals. The first nutritional need of the overwintering generations is represented by hydration, likely due to the water loss during diapause.