Shell Hardening Research Articles

Costs of induced defenses dissipate by maturity for diploid and triploid oysters

Oyster reef restoration efforts and on-bottom aquaculture are frequently plagued with high predation rates. Oysters are phenotypically plastic, and rearing juvenile oysters, Crassostrea virginica, with predator cues causes them to grow stronger shells that increases survivorship in the field. However, induced defenses (e.g., shell hardening in oysters) are often associated with cost-benefit trade-offs, and the extent the increased shell strength persists into adulthood and alters the growth of somatic and reproductive tissues remains unknown. We raised diploid oysters (used in reef restoration) and triploid oysters (used in aquaculture) with and without predator cues for one month before placing individuals on an oyster farm to grow to market size. Oyster shell characteristics, soft tissue mass, and reproductive investment were measured periodically over one year of culture and compared across treatments. Both diploid and triploid oysters had significantly stronger and smaller shells than controls at the end of their nursery period. However, while diploid shells became 15 % stronger and 17 % smaller than controls, triploid shells became 28 % stronger and 23 % smaller. Additionally, triploid oysters exposed to predator cues returned to the size of controls faster and maintained their shell strength differences longer than diploids. Differences in soft tissue mass between treatments mirrored the patterns exhibited in shell size and weight with greater initial physiological costs and faster recovery for triploid individuals. There was no significant difference in somatic or reproductive tissue mass between induced and control oysters of the same ploidy after seven months in the field. Triploid oysters were 15–110 % larger than diploids depending on the characteristic measured at maturity. Additionally, there was a significant interaction between treatment and ploidy because induced triploids had marginally greater growth than their control counterparts while induced diploids had marginally less growth than controls. These findings demonstrate that physiological costs of oysters reacting to predators in early life stages are minimal by the time individuals reach maturity. Early exposure to predator cues is a promising tool for improving oyster survivorship in restoration and aquaculture operations, especially in regions with high predation pressure.

Identification and functional analysis of the estradiol 17β-dehydrogenase gene on the shell hardness of Scylla paramamosain during the molting cycle

Estradiol 17 β-dehydrogenase (17E2DH) is an oxidoreductase gene involved in the metabolism of androgen and estrogen in mammals and birds, and is also associated with molting in crustaceans. However, neither the full-length estradiol 17 β-dehydrogenase nor its molecular mechanism during molting has been reported in crabs. In this study, the cDNA encoding 17-beta-dehydrogenase was cloned from the hepatopancreas of Scylla paramamosain and named Sp17E2DH. The full length Sp17E2DH consists of 922 bp with an open reading frame encoding 255 amino acids. Phylogenetic analysis showed that the predicted Sp17E2DH protein is conserved and clustered with the 17E2DH from other crustacean species. RT-qPCR and immunohistochemistry analyses indicated that the expression level of Sp17E2DH was lowest before molting (TQ), up-regulated at 3 h after molting (TH3h), and highest at 48 h after molting (TH48h) in the hepatopancreas and muscles. An RNA interference experiment showed that the mRNA expression level of Sp17E2DH was significantly down-regulated (P < 0.05) and the hardness of crab shells was significantly decreased (P < 0.05) at TH48h in the hepatopancreas and muscles after injection of Sp17E2DH-targeted dsRNA. Genes such as gastrolith protein (P = 0.045), cuticular protein 15 (P = 0.021), chitin synthase (P = 0.047) and troponin C2 (P = 0.013) were significantly suppressed at TH48h after Sp17E2DH dsRNA injection compared to the control groups, which were potentially regulated by Sp17E2DH to control shell hardness of S. paramamosain. In summary, the results suggest that Sp17E2DH plays a vital role in the molting cycle and shell hardening of the mud crab, and the dsRNA interference of Sp17E2DH may be used to prolong the marketing shelf life of live soft-shelled mud crabs.

Producción y viviparidad de nogal pecanero (Carya illinoinensis [Wangenh.] K. Koch) en relación con la humedad del suelo

Introduction: Viviparity in pecan nut (Carya illinoinensis [Wangenh.] K. Koch) has increased considerably. This genetic-environmental phenomenon can be controlled with soil moisture management and other quality variables.Objective: To determine the effect of soil moisture content on yield, nut size, kernel percentage and germinated nut on the tree.Materials and methods: Forty-year-old pecan nut trees were irrigated by 40 emitters with an output of 3.2 L∙h-1. From the phenological stage of shell hardening, irrigation time was 4, 6 and 8 h, corresponding to moisture levels of 0.257, 0.327 and 0.380 m3 of water per m3 of soil, at depths of 40 to 80 cm. Yield per tree, germinated nut percentage, fruit size and kernel percentage were evaluated during the production cycles of 2016 and 2017 production cycles.Results and discussion: During the two production cycles, when soil moisture level increased from 0.257 to 0.380 m3∙m-3, nut yield per tree, fruit length and diameter, and kernel percentage increased on average 23.8 %, 25.3 and 10 %, and 1.8 %, respectively; however, vivipary increased 11.2 %, which was reflected in the decrease of commercial pecan nut percentage. Treatments 0.327 and 0.380 m3∙m-3 had a similar effect (P &gt; 0.05) on these variables.Conclusions: The lower moisture level (0.257 m3∙m-3), starting at the kernel filling stage, decreased vivipary and increased commercial kernel percentage.

Increasing the Efficiency of Supplemental Foliar Nutrition on Improving Reproductive Disorders of Pistachio by Application of Plant Growth Regulators

Severe environmental stress and nutrient deprivation cause reproductive disorder in pistachio trees. In this study, the effect of some plant growth regulators on increment the efficiency of supplemental foliar nutrition on reducing these complications was investigated. A factorial experiment (4 × 2) was carried out with exogenous foliar spray of three plant growth regulators included control (without treatment), nitric oxide (DETA/NO, 0.05 mM), 24-epibrassinolide (0.1 mM), Spermine (1 mM), and supplemental foliar nutrition at two levels contained untreated (control) and foliar nutrition with urea (5 gL−1) + zinc chelate (2 gL−1)+calcium chelates (2 gL−1) + boric acid (0.5 gL−1) + KNO3 (40gL−1) + Ca(NO3)2 (20gL−1). Plant growth regulators were applied along with urea, zinc and calcium chelate and boric acid a week before full bloom and 2 weeks after full bloom. They were also used in combination with potassium and calcium nitrate at the shell hardening, beginning and middle of pistachio kernel filling, respectively. The interactive effect of 24-epibrassinolide with supplemental foliar nutrition had the greatest effect on the reduction of fruit abscission (19.1%), blank nuts (53.9%) and inflorescence bud abscission (20.6%) as the main effective variables in reducing the yield of ‘Ahmad-Aghai’ pistachio. This treatment had the highest effect on the increasing the efficiency of supplemental foliar nutrition on improving the reproductive disorders, decreasing the alternate bearing intensities (30.2%) and enhancing fruit yield per tree (79.1%) in ‘Ahmad-Aghai’ pistachio.

Industrially scalable complex coacervation process to microencapsulate food ingredients

Abstract Microencapsulation by conventional complex coacervation, though highly effective and achievable at the bench-scale, is challenging to scale-up because of the complexity of the process. A novel, industrially-scalable microencapsulation process by in situ complex coacervation during spray drying (the ‘CoCo process’) is introduced, where the multiple steps are collapsed into one, to form dry complex coacervated (CoCo) microcapsules by spray drying. The CoCo process was used to encapsulate d -limonene in CoCo microcapsules using alginate and gelatin as wall materials. Insoluble CoCo particles were produced without chemical cross-linking, with extents of complex coacervation of 75 ± 6% and 64 ± 6% for CoCo particles with and without d -limonene, respectively. Up to 82.7% of d -limonene was retained during spray drying; moreover, the CoCo matrix exhibited excellent barrier properties, retaining up to 80.0% of total d -limonene over 72-day storage in sealed vials at room temperature. Industrial relevance Commercialization of microencapsulation of bioactives by complex coacervation in agricultural and food applications is hindered by the high-cost and time-intensive multistep process consisting of emulsification, coacervation, shell hardening and drying. In this work, we overcome these limitations by developing an industrially scalable in situ complex coacervation process during spray drying (‘CoCo process’). One-step complex coacervation during spray-drying opens the door to cost-effective, high-throughput, high-volume production of bioactive-containing microcapsules. The protective matrix microcapsules formed by this novel process stabilize and protect the bioactive, while allowing controlled release of the cargo for various applications in the food and many other industries.

Theoretical Prediction of Crack Formation in Axisymmetric Multilayer Shell Molds

On the basis of the numerical method, the study has developed a general scheme for solving the problems on stress-strain state of axially symmetric shell molds. The study has developed a mathematical model for the process of casting melting metal into shell molds and hardening of castings. The results of the solution of the problem have showed that stresses of σ22 have the highest values, the stresses of σ11 have order of magnitude smaller values, and the stresses of σ33 vary over time and space like stresses of σ22, but they are 5-10% less in absolute values. The calculations show that the metal hardening in a shell mold starts in 31 seconds, and meanwhile, tensile stresses occur on the metal-mold surface and, therefore, metal tends to depart from the shell mold surface.

Cenosphere formation from heavy fuel oil: a numerical analysis accounting for the balance between porous shells and internal pressure

Heavy fuel oil (HFO) as a fuel in industrial and power generation plants ensures the availability of energy at economy. Coke and cenosphere emissions from HFO combustion need to be controlled by particulate control equipment such as electrostatic precipitators, and collection effectiveness is impacted by the properties of these particulates. The cenosphere formation is a function of HFO composition, which varies depending on the source of the HFO. Numerical modelling of the cenosphere formation mechanism presented in this paper is an economical method of characterising cenosphere formation potential for HFO in comparison to experimental analysis of individual HFO samples, leading to better control and collection. In the present work, a novel numerical model is developed for understanding the global cenosphere formation mechanism. The critical diameter of the cenosphere is modelled based on the balance between two pressures developed in an HFO droplet. First is the pressure (Prpf) developed at the interface of the liquid surface and the inner surface of the accumulated coke due to the flow restriction of volatile components from the interior of the droplet. Second is the pressure due to the outer shell strength (PrC) gained from van der Walls energy of the coke layers and surface energy. In this present study it is considered that when PrC ≥ Prpf the outer shell starts to harden. The internal motion in the shell layer ceases and the outer diameter (DSOut) of the shell is then fixed. The entire process of cenosphere formation in this study is analysed in three phases: regression, shell formation and hardening, and post shell hardening. Variations in pressures during shell formation are analysed. Shell (cenosphere) dimensions are evaluated at the completion of droplet evaporation. The rate of fuel evaporation, rate of coke formation and coke accumulation are analysed. The model predicts shell outer diameters of 650, 860 and 1040 µm, and inner diameters are 360, 410 and 430 µm respectively, for 700, 900 and 1100 µm HFO droplets. The present numerical model is validated with experimental results available from the literature. Total variation between computational and experimental results is in the range of 3–7%.

Bisphenol A and the related alkylphenol contaminants in crustaceans and their potential bioeffects

Bisphenol A is widely used in plastic and other industrial consumer products. Release of bisphenol A and its analogues into the aquatic environment during manufacture, use and disposal has been a great scientific and public concern due to their toxicity and endocrine disrupting effects on aquatic wildlife and even human beings. More recent studies have shown that these alkylphenols may affect the molting processes and survival of crustacean species such as American lobster, crab and shrimp. In this study, we have developed gas chromatography with flame ionization detection (GC-FID) and gas chromatography- mass spectrometric (GC-MS) methods for the determination of bisphenol A and its analogues in shrimp Macrobrachium rosenbergii, blue crab Callinectes sapidus and American lobster Homarus americanus samples. Bisphenol A, 2,4-bis-(dimethylbenzyl)phenol and 4-cumylphenol were found in shrimp in the concentration ranges of 0.67-5.51, 0.36-1.61, and < LOD (the limit of detection)-1.96 ng/g (wet weight), and in crab of 0.10-0.44, 0.13-0.62, and 0.26-0.58 ng/g (wet weight), respectively. In lobster tissue samples, bisphenol A, 2-t-butyl-4-(dimethylbenzyl)phenol, 2,6-bis-(t-butyl)-4-(dimethylbenzyl)phenol, 2,4-bis- (dimethybenzyl)phenol, 2,4-bis-(dimethylbenzyl)-6-t-butylphenol and 4-cumylphenol were determined at the concentration ranges of 4.48-7.01, 1.23-2.63, 2.71-9.10, 0.35-0.91, 0.64-3.25, and 0.44-1.00 ng/g (wet weight), respectively. At these concentration levels, BPA and its analogs may interfere the reproduction and development of crustaceans, such as larval survival, molting, metamorphosis and shell hardening.

Shell hardening of unalloyed steel cylinders by high speed quenching

AbstractKobasko et al. have primarily shown that rapid water quenching can create compressive residual stresses near the surface and thereby a significant increase in the fatigue-limit (Intensive Quenching). Such processes result in an increase in hardness. Depending on steel grade, dimensions of the component and quenching intensity through hardening or only shell hardening will result. In this work, shell hardening processes were investigated in a more detailed manner for cylinders made of two different unalloyed steels. The goal of the work was discovering the general requirements to reach, on the one hand, a sufficient surface hardness paired with a non-through hardened hardening profile. On the other hand, compressive residual stresses in the near surface area should be as high as possible to achieve huge lifetime cycles for the heat treated work pieces. The experiments were carried out with a device that was especially developed for high speed quenching. As a quenching medium only tap water or water...

INCIDENCE OF DAMAGE BY NUT WEEVIL ON DIFFERENT HAZELNUT CULTIVARS IN NORTHWESTERN ITALY

The nut weevil Curculio nucum L. (Coleoptera: Curculionidae) is one of the major hazelnut pests, responsible for high yield losses in Europe and Turkey. However, some hazelnut cultivars seem to be more resistant to the nut weevil attacks, even if mechanisms involved in the resistance are not yet altogether known. In a previous study on two cultivars and four selections of hazelnut, the susceptibility to nut weevil appeared to be related to the timing of shell hardening. Therefore, a three-year study on 15 hazelnut cultivars was carried out to assess their susceptibility to the nut weevil. In addition, nut and kernel development stages and shell hardening were detected. At harvest, nut weevil damage was significantly different between the cultivars. Despite their different earliness, ‘Hall’s Giant’, ‘Tonda di Giffoni’ and ‘Tonda Gentile delle Langhe’ were the least damaged (<5.0%), whereas the latest ‘Cosford’ showed the highest damage (35%). Thus, the earliness of nut development resulted not to be the only factor affecting the rate of nut weevil damage at harvest.

Ambered Kernels in Stenospermocarpic Fruit of Eastern Black Walnut

“Ambers” is a term used to describe poorly filled, shriveled eastern black walnut (Juglans nigra L.) kernels with a dark brown or black-colored pellicle that are unmarketable. Studies were conducted to determine the incidence of ambered black walnut kernels and to ascertain when symptoms were apparent in specific tissues. The occurrence of ambered kernels was evaluated in fruit harvested from mature ‘Football’ trees growing at three sites within a commercial black walnut orchard in 2008 to 2010. Mature walnut fruit sampled from trees at Site 2 had greater odds for ambered kernels than those on trees at two other sites within the same orchard with 27% of the walnuts sampled exhibiting symptoms when examined in October. Also, black walnut fruit in 2010 had more ambered kernels than those examined in Oct. 2008 or 2009. Cropload, soil type, ambient temperatures, or precipitation was not apparently associated with a high incidence of ambered kernels. When black walnut fruit from trees at Site 2 were examined from 25 June to 6 Oct. 2011, embryos were visible in 50% of the fruit without discoloration on the first date. Stenospermocarpy (e.g., aborted or rudimentary embryos after fertilization) was observed in fruit with discolored or ambered kernels as early as 7 July. Stenospermocarpic fruit with ambered kernels had shorter embryo axis lengths (root apex to shoot apex) than fruit with non-ambered kernels on 7 July and at successive sampling dates. Cotyledon widths of ambered kernels in stenospermocarpic fruit were narrower than those of non-ambered kernels on 21 July, but symptomatic cotyledons continued to enlarge until 15 Sept. All fruit enlarged during the growing season and nut diameters varied by only 3.4 mm at harvest. Thus, visible embryo degeneration, which was associated with ambered kernels in black walnut fruit, was detected in early July when shell hardening occurs and kernel tissues are enlarging.

Modeling shell disease in American lobster (Homarus americanus) as individual-based health trajectories

The emergence of epizootic shell disease in American lobsters (Homarus americanus) has presented many new challenges to understanding the interface between disease and the management of the lobster fishery. While a variety of the potentially causative and correlative factors for shell disease have been explored, a clear etiological agent remains elusive. The recency of this disease and the lack of identifiable causal agents have hindered the development of conceptual models that can yield testable predictions. Here, a model originally developed for human–parasite interactions was applied to lobster shell disease as a means to unify the broad experimental and field observations. The model is a graphical means to understand the onset and severity of shell disease and is a function of the length of the molt cycle and the rate of the decrease of health both before and after lesion formation as a function of bacterial abundance and pathogenicity. The model also accounts for shell hardening and passive and active portals of entry for the bacteria. The timing for a conceptual understanding of the epidemiology of shell disease is critical because its prevalence is increasing in key fishing areas. Ideally, such a model will help researchers create hypothesis-driven predictive experiments from which we can further our understanding of an important disease to a critical member of the Gulf of Maine ecosystem.

Simultaneous identification and quantification of 4-cumylphenol, 2,4-bis-(dimethylbenzyl)phenol and bisphenol A in prawn Macrobrachium rosenbergii

Bisphenol A (BPA), 4-cumylphenol (4-CP) and 2,4-bis-(dimethylbenzyl)phenol (2,4-DCP) are all high production volume chemicals and widely used in plastic and other consumer products. During the past two decades, BPA has attracted a great deal of scientific and public attention due to its presence in the environment and estrogenic property. Although 4-CP and 2,4-DCP are much more estrogenic and toxic than BPA, little information is available about their occurrence and fate in the environment. In this study, a rapid, selective, accurate and reliable analytical method was developed for the simultaneous determination of 4-CP, 2,4-DCP and BPA in prawn Macrobrachium rosenbergii. The method comprises an ultrasound-accelerated extraction followed by capillary gas chromatographic (GC) separation. The detection limits range from 1.50 to 36.4ngkg−1 for the three alkylphenols. The calibration curves are linear over the concentration range tested with the coefficients of determination, R2, greater than 0.994. The developed method was successfully applied to the simultaneous determination of 4-CP, 2,4-DCP and BPA in prawn samples. The peak identification was confirmed using GC–MS. Bisphenol A, 2,4-bis-(dimethylbenzyl)phenol and 4-cumylphenol were found in prawn samples in the concentration ranges of 0.67–5.51, 0.36–1.61, and 0.00–1.96ngg−1 (wet weight), respectively. All relative standard deviations are less than 4.8%. At these environmentally relevant concentration levels, 4-CP, 2,4-DCP and BPA may affect the reproduction and development of aquatic organisms, including negative influence on crustaceans’ larval survival, molting, metamorphosis and shell hardening. This is the first study reported on the occurrence of 4-CP, 2,4-DCP and BPA in prawn M. rosenbergii.

Multiple factors in marine environments affecting lobster survival, development, and growth, with emphasis on alkylphenols: a perspective

A major die-off of the American lobster (Homarus americanus) population in Long Island Sound (LIS) occurred in 1999, involving multiple causes, including increases of temperatures, decreasing oxygen concentrations, and pollutants. Other possible affectors were stress to their immune system, microbial population changes, which may have induced shell disease, water acidification, and insecticides. We examined LIS alkylphenol pollution. Alkylphenols, alkylphenol ethoxylates, and bisphenol A (BPA) are produced in excessive amounts, with BPA estimated at 8 billion pounds per year (1 lb = 0.453 kg). Sixty percent of alkylphenols enter the marine environment and have estrogenic endocrine-disrupting effects on vertebrates. We found multiple effects of alkylphenols on lobsters, on larval survival, molting and postlarval molting, shell hardening, and interference in metamorphosis causing larval–juvenile intermediates. We also found evidence for a basic molecular mechanism of action for alkylphenols through juvenile hormone (JH) and ecdysone receptors. Alkylphenols appear to have contributed to the decrease in the LIS lobster population. We recommend remediation, reducing, or eliminating alkylphenols from the marine environment to protect lobsters as well as other organisms.

Effects of salinity on growth, molt and energy utilization of juvenile swimming crab Portunus trituberculatus

We evaluated the effects of salinity on the growth,molt,and energy utilization of juvenile Portunus trituberculatus.The crabs were held at five salinities(15,20,25,30,and 35) and cultured in rectangular aquari-ums.Each treatment group was quadruplicated,with each replicate consisting of 3 stages(7 juveniles/stage).During the 50-day experiment,mortalities and incidence of "molt death syndrome" were recorded daily,while the intermolt period,carapace length,carapace width,and wet weight were measured at each molt.Salinity had a sig-nificant effect on growth and energy utilization.At salinities of 20,25,and 30,food intake(FId) was lower and food conversion efficiency(FCEd) was higher than in the control.At 30,FCEd was significantly higher than in crabs held at 15 and 35,but not different from those held at 20 and 25.The assimilation efficiency(K1) and net growth efficiency(K2) of crabs held at 20,25,and 30 were significantly higher than in the remaining groups.At the end of the experiment,crabs held at 25 and 30 had a higher wet body weight,relative body weight gain,and SGR.The difference was significant when compared to crabs held at 15 and 35 ppt,but not 20 and 25 ppt.Re-gression analysis suggested that maximum SGRd would occur at salinity 26.3.The molt recycle(MC) between instars VII–X ranged from 18.9 to 23.5 d,and was not different among the groups.Nevertheless,MC was 3.1-4.6 d shorter in crabs held at 30 than the remaining groups.MDS was observed at 15,suggesting that the lower salin-ity plays a role in inhabiting the molt of P.Trituberculatus.Conversely,new shell hardening was inhibited by higher salinity.Our results indicate that the culture water should be maintained at about 25 salinity to improve growth and molt success.

The Effect of Alkylphenols on Lobster Shell Hardening

Alkylphenols, anthropogenic estrogenic endocrine disruptors in vertebrates, have been found in lobsters (Homarus americanus) in New England sites. We hypothesize that alkylphenols interfere in the shell hardening during molting. We used an in vitro cuticle bioassay to investigate the effects of 2 alkylphenolic compounds—2,4-bis-(dimethylbenzyl) phenol (compound 3) and bisphenol A (BPA; 4,4#-dihydroxy-2,2-diphenylpropane (also referred to as 4,4#-(propan-2-ylidene) diphenol))—on tyrosine incorporation during the hardening of new cuticle following lobster molting. During sclerotization, both alkylphenols and cold tyrosine competed with C 14 -tyrosine incorporation in a concentration-dependent manner. This process was also phenoloxidase dependent, as treatment with phenylthiourea (PTU; a phenoloxidase inhibitor) significantly decreased C 14 -tyrosine incorporation. We also found that incorporation of C 14 -2,4-bis-(dimethylbenzyl) phenol during the shell hardening process was inhibited by cold alkylphenol, cold tyrosine, or PTU, and competition was concentration dependent. Furthermore, incorporation of tyrosine and derivatives into new cuticle decreased with time after molting from 27% incorporation 1 day after a molt to 6% by 4 days after a molt. In nonmolting cuticles, there was no incorporation of alkylphenol or tyrosine derivatives. When lobsters were injected with 2,4-bis-(dimethylbenzyl) phenol during the premolt stage, it took the shells 12 ± 1 days to harden sufficiently to resist deflection by 5 lb pressure exerted by a pressure gauge, compared with 7 ± 1 days for control shells. Thus, shell hardening is delayed significantly by the presence of 2,4-bis-(dimethylbenzyl) phenol. The effects of this compound on shell hardening may result in lobsters susceptibility to microbial invasion and, therefore, may contribute to the onset of shell disease.

Characterizing the Subharmonic Response of Phospholipid-Coated Microbubbles for Carotid Imaging

The subharmonic vibration of BR14 (Bracco Research S.A., Geneva, Switzerland) contrast agent microbubbles is investigated within the preferable frequency range for carotid ultrasound imaging (8–12 MHz). The response of the bubbles was recorded optically with an ultra-fast recording camera (Brandaris 128) at three acoustic pressures (50, 100 and 120 kPa). The vibration of the microbubbles was measured as a function of the excitation frequency and its frequency content was determined. Among 390 recordings, 40% showed subharmonic oscillations. It was observed that for smaller microbubbles (diameter < 3 μm) the frequency of the maximum subharmonic response increases for increasing pressures (shell hardening) opposite to what has been reported for larger microbubbles (3 μm < diameter < 15 μm). These findings are well predicted by the model proposed by Marmottant et al. (2005) after including the dilatational shell viscosity of the microbubbles measured by Van der Meer et al. (2007), which indicates a marked shear-thinning behavior of the phospholipid shell.

Water relations of pistachio ( Pistacia vera L.) as affected by phenological stages and water regimes

Pistachio is a drought tolerant fruit tree that can be cultivated in rainfed and irrigated conditions. The water requirements of the tree, however, are considerable so in most of the commercial orchards deficit irrigation is a common practice. Regulated deficit irrigation in pistachio trees has been described in several works, which reported that the phenological stage of shell hardening, so called stage II, is the most drought tolerant. This paper proposes that such drought resistance is related to changes in water relations linked to the phenological stages, even in conditions of no water stress. In order to evaluate such changes, the daily pattern of stem water potential and gas exchange (net photosynthesis, P n, and leaf conductance, g s) was measured, determining also the pressure–volume curves, in three different phenological stages of mature pistachio trees ( Pistacia vera cv Kerman on P. terebinthus L. rootstock.). The daily pattern of stem water potential and gas exchange were performed in three different irrigation treatments: control, regulated deficit irrigation and rainfed. The pressure–volume curves were made only in the control and rainfed treatments. Significant differences were found in the daily pattern of stem water potential in all the phenological stages considered, while only in the last one the net photosynthesis was affected by water stress. The daily pattern of gas exchange at the beginning of the season was not affected by the evaporative demand, with a constant value when radiation was not limiting. Moderate levels of water stress during the last measurement date reduced the maximum values of g s and P n resulting also in a clear change in the pattern of the daily curve, with maximum values only at the beginning of the day. The relationships between stem water potential and gas exchange parameters were different during stage II and almost the same in stages I and III. The parameters drawn from the pressure–volume curves also indicated a change in the elastic modulus of the leaf cells in stage II. In addition, differences in the osmotic adjustment (OA) index suggested different degree of osmotic adjustment of the phenological stages in the response to water stress. The results showed that different mechanisms of drought resistance are operating in the different phenological stages in pistachio trees.

Crop water stress index is a sensitive water stress indicator in pistachio trees

Regulated deficit irrigation (RDI) strategies, often applied in tree crops, require precise monitoring methods of water stress. Crop water stress index (CWSI), based on canopy temperature measurements, has shown to be a good indicator of water deficits in field crops but has seldom been used in trees. CWSI was measured on a continuous basis in a Central California mature pistachio orchard, under full and deficit irrigation. Two treatments—control, returning the full evapotranspiration (ETc) and RDI—irrigated with 40% ETc during stage 2 of fruit grow (shell hardening). During stage 2, the canopy temperature—measured continuously with infrared thermometers (IRT)—of the RDI treatment was consistently higher than the control during the hours of active transpiration; the difference decreasing after irrigation. The non-water-stressed baseline (NWSB), obtained from clear-sky days canopy–air temperature differential and vapour pressure deficit (VPD) in the control treatment, showed a marked diurnal variation in the intercept, mainly explained by the variation in solar radiation. In contrast, the NWSB slope remained practically constant along the day. Diurnal evolution of calculated CWSI was stable and near zero in the control, but showed a clear rising diurnal trend in the RDI treatment, increasing as water stress increased around midday. The seasonal evolution of the CWSI detected large treatment differences throughout the RDI stress period. While the CWSI in the well-irrigated treatment rarely exceeded 0.2 throughout the season, RDI reached values of 0.8–0.9 near the end of the stress period. The CWSI responded to irrigation events along the whole season, and clearly detected mild water stress, suggesting extreme sensitivity to variations in tree water status. It correlated well with midday leaf water potential (LWP), but was more sensitive than LWP at mild stress levels. We conclude that the CWSI, obtained from continuous nadir-view measurements with IRTs, is a good and very sensitive indicator of water stress in pistachio. We recommend the use of canopy temperature measurements taken from 1200 to 1500 h, together with the following equation for the NWSB: (T c − T a) = −1.33·VPD + 2.44. Measurements of canopy temperature with VPD < 2 kPa are likely to generate significant errors in the CWSI calculation and should be avoided.

Early nut development as a resistance factor to the attacks of Curculio nucum (Coleoptera: Curculionidae)

AbstractThe nut weevil Curculio nucum (Coleoptera: Curculionidae) is responsible for high yield losses in several hazelnut‐growing areas of Europe and Turkey, if not regularly controlled using pesticides. The resistance of hazelnut varieties to the nut weevil is known but poorly investigated so far. Thus a 2‐year study was carried out to investigate factors affecting C. nucum attacks on two cultivars [Tonda Gentile delle Langhe (TGL), Ennis] and four selections (Daria, 101, B6, L35) in a 15‐year‐old orchard of northwestern Italy. Nut developmental stages and shell characteristics, such as hardness and thickness, were measured and correlated to the biological cycle of the nut weevil and to the damage by its larvae. During the 2‐year sampling, nut weevil adults were collected on all cultivars and selections, but in greater quantities on TGL and Daria, and in lower quantities on 101 and B6. In 2005, by female dissection, mature eggs were observed from late June, when the mean temperature exceeded 18°C. Differences between cultivars and selections were found in nut and kernel development, and in shell hardening; in particular, the kernel development was directly related with the shell hardness. At harvest, the damage varied on average from 2.57% in cultivar TGL to 51.84% in selection 101 of total nuts harvested, so independently of the numbers of the collected weevil adults. These two varieties were the earliest and the latest in kernel development and shell hardening, respectively. Therefore, the susceptibility to nut weevil attacks was strictly related to shell hardening; in fact, a rapid hardening of the shell can hamper the oviposition of C. nucum females. By contrast, no correlation was found between shell thickness and damage at harvest.