Red and Blue Netting Alters Leaf Morphological and Physiological Characteristics in Apple Trees.

There is little information about the role of red and blue light on leaf morphology and physiology in fruit trees, and more studies have been developed in herbaceous plants grown under controlled light conditions. The objective of this research was to evaluate the effect of red and blue screens on morpho-anatomy and gas exchange in apple leaves grown under ambient sunlight conditions. Apple trees cv. Fuji were covered by 40% red and blue nets, leaving trees with 20% white net as control. Light relations (photosynthetic photon flux density, PPFD; red to far-red light ratio, R/FR and blue to red light ratio, B/R), morpho-anatomical features of the leaf (palisade to spongy mesophyll ratio, P/S, and stomata density, SD) and leaf gas exchange (net photosynthesis rate, An; stomatal conductance, g s; transpiration rate, E; and intrinsic water use efficiency, IWUE) were evaluated. Red and blue nets reduced 27% PPFD, reducing by 20% SD and 25% P/S compared to control, but without negative effects on An and g s. Blue net increased g s 21%, leading to the highest E and lowest IWUE by increment of B/R light proportion. These findings demonstrate the potential use of red and blue nets for differential modulation of apple leaf gas exchange through sunlight management under field conditions.

Single-Shot Convolution Neural Networks for Real-Time Fruit Detection Within the Tree.

Image/video processing for fruit detection in the tree using hard-coded feature extraction algorithms has shown high accuracy on fruit detection during recent years. While accurate, these approaches even with high-end hardware are still computationally intensive and too slow for real-time systems. This paper details the use of deep convolution neural networks architecture based on single-stage detectors. Using deep-learning techniques eliminates the need for hard-code specific features for specific fruit shapes, color and/or other attributes. This architecture takes the input image and divides into AxA grid, where A is a configurable hyper-parameter that defines the fineness of the grid. To each grid cell an image detection and localization algorithm is applied. Each of those cells is responsible to predict bounding boxes and confidence score for fruit (apple and pear in the case of this study) detected in that cell. We want this confidence score to be high if a fruit exists in a cell, otherwise to be zero, if no fruit is in the cell. More than 100 images of apple and pear trees were taken. Each tree image with approximately 50 fruits, that at the end resulted on more than 5000 images of apple and pear fruits each. Labeling images for training consisted on manually specifying the bounding boxes for fruits, where (x, y) are the center coordinates of the box and (w, h) are width and height. This architecture showed an accuracy of more than 90% fruit detection. Based on correlation between number of visible fruits, detected fruits on one frame and the real number of fruits on one tree, a model was created to accommodate this error rate. Processing speed is higher than 20 FPS which is fast enough for any grasping/harvesting robotic arm or other real-time applications. HIGHLIGHTS: Using new convolutional deep learning techniques based on single-shot detectors to detect and count fruits (apple and pear) within the tree canopy.

Apoplasmic and simplasmic phloem unloading mechanisms: Do they co-exist in Angeleno plums under demanding environmental conditions?

Biophysical fruit growth depends on a balance among the vascular and transpiration flows entering/exiting the fruit via phloem, xylem and through the epidermis. There is no information on vascular flows of Japanese plums, a species characterized by high-sugar content of its fruit at harvest. Vascular flows of Angeleno plums were monitored by fruit gauges during late fruit development, under the dry environment of the Goulburn Valley, Victoria, Australia. Phloem, xylem flows and skin transpiratory losses were determined, as well as diurnal leaf, stem and fruit pressure potentials. Fruit seasonal development, skin conductance and dry matter accumulation were also monitored. Fruit grew following a double-sigmoid pattern, but fruit size increased only 3.1 g over the last 3 weeks of development. Fruit grew very little in the morning, primarily due to phloem inflows (0.05 g fruit-1hr-1), while water left the fruit via the xylem. Negligible skin transpiration was recorded for vapour pressure deficit (VPD) values below 3 kPa. This growth pattern, in the absence of skin transpiration, suggests apoplastic phloem unloading. However, at VPD values over 3 kPa (e.g. from early afternoon to a peak around 18:00 h), transpiratory losses through the skin (up to 0.25 g fruit-1hr-1) caused fruit to shrink, leading to enhanced phloem and xylem inflows (ca. 0.15 g fruit-1hr-1), a scenario that would correspond to symplastic phloem unloading. Over 24 h the fruit showed a slightly negative total growth, consistent with fruit growth measured in situ during the season at weekly intervals. A few fruit species are known to alter their phloem unloading mechanism, switching from symplastic to apoplastic during the season. Our data support the coexistence in Japanese plum of different phloem unloading strategies within the same day.

Sweet cherry water relations and fruit production efficiency are affected by rootstock vigor.

Rootstock vigor is well known to affect yield and productive performance in many fruit crops and the dwarfing trait is often the preferred choice for modern orchard systems thanks to its improved productivity and reduced canopy volume. This work investigates the different physiological responses induced by rootstock vigor on cherry, by comparing shoot and fruit growth, water relations, leaf gas exchanges as well as fruit vascular and transpiration in/outflows of "Black Star" trees grafted on semi-vigorous (CAB6 P) and on semi-dwarfing (Gisela™6) rootstocks. The daily patterns of stem (Ψstem), leaf (Ψleaf) and fruit (Ψfruit) water potential, leaf photosynthesis, stomatal conductance and transpiration, shoot and fruit growth, fruit phloem, xylem and transpiration flows were assessed both in pre- and post-veraison, while productivity and fruit quality were determined at harvest. At both stages, no significant differences were found on Ψleaf, photosynthesis, fruit daily growth rates as well as fruit vascular and transpiration flows, while trees on Gisela™6 showed lower shoot growth rates and lower Ψstem and Ψfruit than trees on CAB6 P. The resulting decrease in stem-to-leaf Ψ gradient on Gisela™6 trees determined a reduction in shoot growth by decreasing shoot strength as sinks for water and carbohydrates. On the other hand, Gisela™6 fruit lowered their Ψfruit thanks to a higher osmotic accumulation and increased their competitiveness towards shoots, as confirmed by the higher productivity and fruit soluble solid content found at harvest for these trees. These results indicate that rootstock vigor alters resource competition between vegetative and reproductive growth, which can affect water use efficiency, yield, and fruit quality.

Photosynthetic Performance and Vegetative Growth in a New Red Leaf Pear: Comparison of Scion Genotypes Using a Complex, Grafted-Plant System.

Leaf photosynthetic performance of a new red-skinned inter-specific hybrid pear variety called 'PremP009' (PIQA®BOO®) is presently unknown and therefore was compared to the Asian pear variety 'Hosui'. The seasonal growth patterns and the final dry matter accumulation of all tree components were also investigated for both genotypes in their first year of growth after grafting. Leaf gas exchange and tree growth comparisons were assessed using an innovative grafted plant system, which involved a bi-axis tree with the presence of combinations of identical or mixed (one of each genotype) 'PremP009' and 'Hosui' scion genotypes grafted onto a single clonal rootstock ('Buerre Hardy' BA29). This experimental grafted plant system allowed a technique for comparing leaf photosynthesis of two scion genotypes on the same root system, thereby avoiding between-plant differences in plant water relations. 'PremP009' had higher leaf photosynthesis and higher leaf mass compared with 'Hosui.' However, by the end of the first year of growth, primary shoots of 'PremP009' were shorter with fewer nodes, corresponding to less dry weight gain in primary shoot leaves and stems. This vegetative behavior of 'PremP009' is likely a response to the smaller individual leaf area in the early season affecting light capture that greatly limits dry matter accumulation of young trees. HIGHLIGHTS - The bi-axis grafting technique never showed before in a scientific paper presents a strategic system for a comparative study of red/green leaf photosynthetic performance and related dry matter partitioning.

An integrated approach for increasing breeding efficiency in apple and peach in Europe.

Despite the availability of whole genome sequences of apple and peach, there has been a considerable gap between genomics and breeding. To bridge the gap, the European Union funded the FruitBreedomics project (March 2011 to August 2015) involving 28 research institutes and private companies. Three complementary approaches were pursued: (i) tool and software development, (ii) deciphering genetic control of main horticultural traits taking into account allelic diversity and (iii) developing plant materials, tools and methodologies for breeders. Decisive breakthroughs were made including the making available of ready-to-go DNA diagnostic tests for Marker Assisted Breeding, development of new, dense SNP arrays in apple and peach, new phenotypic methods for some complex traits, software for gene/QTL discovery on breeding germplasm via Pedigree Based Analysis (PBA). This resulted in the discovery of highly predictive molecular markers for traits of horticultural interest via PBA and via Genome Wide Association Studies (GWAS) on several European genebank collections. FruitBreedomics also developed pre-breeding plant materials in which multiple sources of resistance were pyramided and software that can support breeders in their selection activities. Through FruitBreedomics, significant progresses were made in the field of apple and peach breeding, genetics, genomics and bioinformatics of which advantage will be made by breeders, germplasm curators and scientists. A major part of the data collected during the project has been stored in the FruitBreedomics database and has been made available to the public. This review covers the scientific discoveries made in this major endeavour, and perspective in the apple and peach breeding and genomics in Europe and beyond.

Application of a sensory-instrumental tool to study apple texture characteristics shaped by altitude and time of harvest.

BACKGROUND: Texture is important in the preferences of apple consumers. Of the pre-harvest factors affecting fruit quality and especially texture, altitude and subsequent climatic conditions are crucial, determining differences in the physiological mechanisms of fruit growth, ripening stage and chemical composition, as demonstrated by several studies. This work applies a detailed sensory-instrumental protocol developed in a previous paper to investigate the impact of altitude, time of harvest and their cross-effect on sensory characteristics of apple, with a focus on texture. RESULTS: Sensory differences were found in relation to altitude, although the profile results were mainly affected by the time of harvest. Fruit from lower altitude was described as juicier, crunchier and sweeter than samples from higher altitude, which were floury, sourer and more astringent. Texture performance, soluble solids content and titratable acidity corroborated this sensory description. Moreover, anatomical data showed that fruit from lower altitude had a larger volume, a higher number of cells and a higher percentage of intercellular spaces. CONCLUSION: We demonstrated that differences between fruit from various altitudes can be perceived through human senses, and that the proposed sensory-instrumental tool can be used to describe such differences. This study brings more understanding about the impact of altitude and time of harvest on apple sensory properties. This work could support apple producers, from semi-mountainous regions (Alps, Tyrol, etc.), in advertising and valorising their products with their specific characteristics in a more efficient manner. © 2017 Society of Chemical Industry.

A multivariate approach for assessing leaf photo-assimilation performance using the IPL index.

The detection of leaf functionality is of pivotal importance for plant scientists from both theoretical and practical point of view. Leaves are the sources of dry matter and food, and they sequester CO2 as well. Under the perspective of climate change and primary resource scarcity (i.e. water, fertilizers and soil), assessing leaf photo-assimilation in a rapid but comprehensive way can be helpful for understanding plant behavior under different environmental conditions and for managing the agricultural practices properly. Several approaches have been proposed for this goal, however, some of them resulted very efficient but little reliable. On the other hand, the high reliability and exhaustive information of some models used for estimating net photosynthesis are at the expense of time and ease of measurement. The present study employs a multivariate statistical approach to assess a model aiming at estimating leaf photo-assimilation performance, using few and easy-to-measure variables. The model, parameterized for apple and pear and subjected to internal and external cross validation, involves chlorophyll fluorescence, carboxylative activity of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCo), air and leaf temperature. Results prove that this is a fair-predictive model allowing reliable variable assessment. The dependent variable, called IPL index, was found strongly and linearly correlated to net photosynthesis. IPL and the model behind it seem to be (1) reliable, (2) easy and fast to measure and (3) usable in vivo and in the field for such cases where high amount of data is required (e.g. precision agriculture and phenotyping studies).

Increasing water stress negatively affects pear fruit growth by reducing first its xylem and then its phloem inflow.

Drought stress negatively affects many physiological parameters and determines lower yields and fruit size. This paper investigates on the effects of prolonged water restriction on leaf gas exchanges, water relations and fruit growth on a 24-h time-scale in order to understand how different physiological processes interact to each other to face increasing drought stress and affect pear productive performances during the season. The diurnal patterns of tree water relations, leaf gas exchanges, fruit growth, fruit vascular and transpiration flows were monitored at about 50, 95 and 145 days after full bloom (DAFB) on pear trees of the cv. Abbé Fétel, subjected to two irrigation regimes, corresponding to a water restitution of 100% and 25% of the estimated Etc, respectively. Drought stress progressively increased during the season due to lower soil tensions and higher daily vapour pressure deficits (VPDs). Stem water potential was the first parameter to be negatively affected by stress and determined the simultaneous reduction of fruit xylem flow, which at 95 DAFB was reflected by a decrease in fruit daily growth. Leaf photosynthesis was reduced only from 95 DAFB on, but was not immediately reflected by a decrease in fruit phloem flow, which instead was reduced only at 145 DAFB. This work shows how water stress negatively affects pear fruit growth by reducing first its xylem and then its phloem inflow. This determines a progressive increase in the phloem relative contribution to growth, which lead to the typical higher dry matter percentages of stressed fruit.

Changes in vascular and transpiration flows affect the seasonal and daily growth of kiwifruit (Actinidia deliciosa) berry.

BACKGROUND AND AIMS: The kiwifruit berry is characterized by an early stage of rapid growth, followed by a relatively long stage of slow increase in size. Vascular and transpiration flows are the main processes through which water and carbon enter/exit the fruit, determining the daily and seasonal changes in fruit size. This work investigates the biophysical mechanisms underpinning the change in fruit growth rate during the season. METHODS: The daily patterns of phloem, xylem and transpiration in/outflows have been determined at several stages of kiwifruit development, during two seasons. The different flows were quantified by comparing the diurnal patterns of diameter change of fruit, which were then girdled and subsequently detached while measurements continued. The diurnal courses of leaf and stem water potential and of fruit pressure potential were also monitored at different times during the season. KEY RESULTS: Xylem and transpiration flows were high during the first period of rapid volume growth and sharply decreased with fruit development. Specific phloem import was lower and gradually decreased during the season, whereas it remained constant at whole-fruit level, in accordance with fruit dry matter gain. On a daily basis, transpiration always responded to vapour pressure deficit and contributed to the daily reduction of fruit hydrostatic pressure. Xylem flow was positively related to stem-to-fruit pressure potential gradient during the first but not the last part of the season, when xylem conductivity appeared to be reduced. CONCLUSIONS: The fruit growth model adopted by this species changes during the season due to anatomical modifications in the fruit features.

The positive effect of skin transpiration in peach fruit growth.

The effect of fruit transpiration on the mechanisms driving peach (Prunus persica (L.) Batsch) daily growth was investigated. In peach, fruit water losses increase during the season and might play a key role in determining fruit growth. Skin transpiration was reduced during the cell expansion stage by enclosing fruit in plastic bags fitted with holes. In the first year, diameter changes of bagged and control fruit were precisely monitored for 15 days, and percentage dry matter and soluble solids content were determined during the experiment and at harvest. In the second year, midday fruit water potential, daily patterns of fruit growth and of vascular and transpiration flows were monitored. Bagging reduced fruit daily growth on some days, and negatively affected both fruit dry matter percentage and soluble solids content. Fruit transpiration rate was reduced during the midday hours, thus increasing midday fruit water potential and lowering xylem inflows. In accordance with the Münch hypothesis on traslocation, these conditions likely decreased the necessary gradient needed for the transport of phloem sap to sink organs, as in the afternoon, bagged fruit showed lower phloem inflows. These data suggest that skin transpiration in peach has a positive effect on fruit growth, as it enhances fruit phloem import.

Modulating the light environment with the peach 'asymmetric orchard': effects on gas exchange performances, photoprotection, and photoinhibition.

The productivity of fruit trees is a linear function of the light intercepted, although the relationship is less tight when greater than 50% of available light is intercepted. This paper investigates the management of light energy in peach using the measurement of whole-tree light interception and gas exchange, along with the absorbed energy partitioning at the leaf level by concurrent measurements of gas exchange and chlorophyll fluorescence. These measurements were performed on trees of a custom-built 'asymmetric' orchard. Whole-tree gas exchange for north-south, vertical canopies (C) was similar to that for canopies intercepting the highest irradiance in the morning hours (W), but trees receiving the highest irradiance in the afternoon (E) had the highest net photosynthesis and transpiration while maintaining a water use efficiency (WUE) comparable to the other treatments. In the W trees, 29% and 8% more photosystems were damaged than in C and E trees, respectively. The quenching partitioning revealed that the non-photochemical quenching (NPQ) played the most important role in excess energy dissipation, but it was not fully active at low irradiance, possibly due to a sub-optimal trans-thylakoid DeltapH. The non-net carboxylative mechanisms (NC) appeared to be the main photoprotective mechanisms at low irradiance levels and, probably, they could facilitate the establishment of a trans-thylakoid DeltapH more appropriate for NPQ. These findings support the conclusion that irradiance impinging on leaves may be excessive and can cause photodamage, whose repair requires energy in the form of carbohydrates that are thereby diverted from tree growth and productivity.

A rapid, whole-tissue determination of the functional fraction of PSII after photoinhibition of leaves based on flash-induced P700 redox kinetics.

Assaying the number of functional PSII complexes by the oxygen yield from leaf tissue per saturating, single-turnover flash, assuming that each functional PSII evolves one oxygen molecule after four flashes, is one of the most direct methods but time-consuming. The ratio of variable to maximum Chl fluorescence yield (F(v)/F(m)) in leaves can be correlated with the oxygen yield per flash during a progressive loss of PSII activity associated with high-light stress and is rapid and non-intrusive, but suffers from being representative of chloroplasts near the measured leaf surface; consequently, the exact correlation depends on the internal leaf structure and on which leaf surface is being measured. Our results show that the average F(v)/F(m) of the adaxial and abaxial surfaces has a reasonable linear correlation with the oxygen yield per flash after varied extents of photoinactivation of PSII. However, we obtained an even better linear correlation between (1) the integrated, transient electron flow (Sigma) to P700+, the dimeric Chl cation in PSI, after superimposing a single-turnover flash on steady background far-red light and (2) the relative oxygen yield per flash. Leaves of C3 and C4 plants, woody and herbaceous species, wild-type and a Chl-b-less mutant, and monocot and dicot plants gave a single straight line, which seems to be a universal relation for predicting the relative oxygen yield per flash from Sigma. Measurement of Sigma is non-intrusive, representative of the whole leaf tissue, rapid and applicable to attached leaves; it may even be applicable in the field.

Carbohydrate availability affects growth and metabolism in peach fruit.

Along with sucrose, sorbitol represents the main photosynthetic product and form of translocated carbon in peach. This study aimed at determining whether peach fruit carbohydrate metabolism is affected by changes in source-sink balance, and specifically whether sorbitol or sucrose availability regulates fruit enzyme activities and growth. In various trials, different levels of assimilate availability to growing fruits were induced in vivo by varying crop load of entire trees, leaf : fruit ratio (L:F) of fruiting shoots, or by interrupting the phloem stream (girdling) to individual fruits. In vitro, fruit tissue was incubated in presence/absence of sorbitol and sucrose. Relative growth rate (RGR), enzyme activities and carbohydrates were measured at different fruit growth stages of various peach cultivars in different years. At stage III, high crop load induced higher acid invertase (AI, EC 3.2.1.26) activities and hexose : sucrose ratios. Both sorbitol and sucrose contents were proportional to L:F, while sorbitol dehydrogenase (SDH, EC 1.1.1.14) activity was the only enzyme activity directly related to L:F in both fruit growth stages. Girdling reduced fruit RGR and all major carbohydrates after 4 days and SDH activity already after 48 h, but it did not affect sucrose synthase (SS, EC 2.4.1.13), AI and neutral invertase (NI, EC 3.2.1.27). Fruit incubation in sorbitol for 24 h induced higher SDH activities than in buffer alone. In general, assimilate availability affected both sorbitol and sucrose metabolism in peach fruit, and sorbitol may function as a signal for modulating SDH activity. Under highly competitive conditions, AI activity may be enhanced by assimilate depletion, providing a mechanism to increase fruit sink strength by increasing hexose concentrations.