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Pecan (Carya illinoensis), an economically important deciduous tree, bears commercially valuable nutritional nuts. Spring freezes in April can severely injure pecan buds, decreasing bloom, and fruit set. This study determined how low temperatures affect pecan buds/flowers at different growth stages in several pecan scion/rootstock combinations. This study focused on three pecan scion/rootstock combinations: Pawnee/Peruque (PP), Kanza/Giles (KG), and Maramec/Colby (MC), grown at the Cimarron Valley Research Station, Perkins, Oklahoma. Branches at three different growth stages, i.e., outer bud scale shed, one week after bud break, and early bloom stages were collected from PP, MC, and KG. Branches were held in a Conviron E8 freezing unit at 4 temperatures (-2, 0, 2, and 4°C) for 4 and 8 hours; A total of 8 treatments. One sample set was kept as an untreated control. After 2–3 weeks, branch samples from all the temperature treatments were observed and categorized into two groups. Group one with number of branches had healthy buds/formation of healthy leaves/flowers and group two with number of dead branches. The carbohydrate content reserved from dormant was analyzed using an Anthrone reagent. Visual observations and carbohydrate analyses revealed differences in damage and carbohydrate content among the scion/rootstock combinations, low-temperature treatments, and growth stages. The MC combination had minimum visual damage to leaves, buds, and flowers and significantly lower soluble sugars and starch in bark phloem as well as significantly lower soluble sugars in woody tissue xylem. The KG combination had maximum visual damage and significantly higher soluble sugars and starches in the bark, and soluble sugars in the woody tissues. These results indicate the MC combination is more tolerant to spring freeze damage at all three growth stages compared to the other two pecan scion/rootstock combinations. The results also demonstrate the MC combination is using more non-structural carbohydrates, soluble sugars and starches, suggesting this is a possible mechanism in its freeze tolerance.

Spring freeze is among the problems threatening pecan bloom and production. Pecan tree height and structure make them difficult to protect from spring freezes. Some cultivars can compensate because the secondary buds can produce healthy flowers if the primary buds freeze. The mechanism that precipitates secondary budbreak is unknown. Our results show a correlation between successful secondary budbreak and 1-year-old shoot carbohydrate levels. ‘Kanza’ and ‘Pawnee’, with the higher secondary budburst, also had higher carbohydrate levels than ‘Maramec’. This suggests higher carbohydrate levels in the bud-bearing 1-year-old shoots promote successful secondary bud burst after spring freeze destruction of the primary buds.

Pistachio (Pistacia vera L.), an economically and nutritionally important tree crop, relies on winter chill for bud endodormancy break and subsequent blooming and nut production. However, insufficient winter chill poses an increasing challenge in pistachio growing regions. To gain a better understanding of the physiological and biochemical responses of endodormant pistachio buds to chilling accumulation, we investigated the global gene expression changes in flower buds of pistachio cv. Kerman that were cultivated at three different orchard locations and exposed to increasing durations of winter chill. The expression of genes encoding β-1,3-glucanase and β-amylase, enzymes responsible for breaking down callose (β-1,3-glucan) and starch (α-1,4-glucan), respectively, increased during the endodormancy break of pistachio buds. This result suggested that the breakdown of callose obstructing stomata as well as the release of glucose from starch enables symplasmic trafficking and provides energy for bud endodormancy break and growth. Interestingly, as chilling accumulation increased, there was a decrease in the expression of nine-cis-epoxycarotenoid dioxygenase (NCED), encoding an enzyme that uses carotenoids as substrates and catalyzes the rate-limiting step in abscisic acid (ABA) biosynthesis. The decrease in NCED expression suggests ABA biosynthesis is suppressed, thus reducing inhibition of endodormancy break. The higher levels of carotenoid precursors and a decrease in ABA content in buds undergoing endodormancy break supports this suggestion. Collectively, the temporal transcriptome and biochemical analyses revealed that the degradation of structural (callose) and non-structural (starch) carbohydrates, along with the attenuation of ABA biosynthesis, are critical processes driving endodormancy break in pistachio buds.

Pecan [Carya illinoinensis (Wangenh.) K. Koch] is a member of the Juglandaceae family. During spring, pecan trees break their bud dormancy and produce new leaves and flowers. Carbohydrates stored in roots and shoots are thought to support the bloom and early vegetative growth during this time until new leaves start the full photosynthetic activity. Spring freeze is known for its damaging effects on pecan bud and flower growth and development. Pecan shoots with leaves and flowers from five scion–rootstock combinations were collected hours before and after a recent spring freeze (below 0 °C for 6 hours, 21 Apr 2021, Perkins, OK, USA). Morphologies of the leaf, bud, and catkin were visually observed, and the morphologies of the anther and pollen in paraffin sections were investigated by light microscopy. Soluble sugar and starch from bark and wood were analyzed using the anthrone reagent method. The Kanza–Mount showed the maximum damage to terminal leaves, buds, and catkins, whereas Maramec–Colby had the minimum damage only to leaves. Pollen grains were shrunk and reduced in number in the anthers in the protandrous Pawnee scions, whereas no pollen damage was observed in the protogynous Kanza scion. Furthermore, bark soluble sugar levels increased in all the scion–rootstock combinations after the freeze, which may indicate a physiological response to the cold stress. Overall, the extent of spring freeze damage of pecans is affected by the growth stage, types of scion and rootstock, and the scion–rootstock interactions. Furthermore, in addition to low temperature, scion–rootstock interactions also affected the starch and soluble sugar contents in wood and bark tissues.

Tree source-sink ratio has a predominant and complex impact on tree performance and can affect multiple physiological processes including vegetative and reproductive growth, water and nutrient use, photosynthesis, and productivity. In this study, we manipulated the branch level source-sink ratio by reduction of photosynthetic activity (partial branch defoliation) or thinning branch fruit load early in the growing season (after fruit set) in pistachio (Pistacia vera) trees. We then characterized the leaf photosynthetic light response curves through leaf aging. In addition, we determined changes in leaf non-structural carbohydrates (NSC) and nitrogen (N) concentrations. In leaves with high source-sink ratios, there was a gradual decrease in maximum net photosynthetic rate (ANmax) over the growing season, while in branches with low source-sink ratios, there was a sharp decline in ANmax in the first two weeks of August. Branches with high-sink showed an up-regulation (increase) in photosynthesis toward the end of July (at 1,500 growing degree days) during the period of rapid kernel growth rate and increased sink strength, with ANmax being about 7 μmol m-1 s-1 higher than in branches with low-sink. In August, low source-sink ratios precipitated leaf senescence, resulting in a drastic ANmax decline, from 25 to 8 μmol m-1 s-1 (70% drop in two weeks). This reduction was associated with the accumulation of NSC in the leaves from 20 to 30 mg g-1. The mechanisms of ANmax reduction differ between the two treatments. Lower photosynthetic rates of 8-10 μmol m-1 s-1 late in the season were associated with lower N levels in high-sink branches, suggesting N remobilization to the kernels. Lower photosynthesis late in the season was associated with lower respiration rates in low-source branches, indicating prioritization of assimilates to storage. These results can facilitate the adaptation of management practices to tree crop load changes in alternate bearing species.

Knowing a tree crop’s seasonal growth and development as a function of heat accumulation can facilitate scheduling of irrigation, pesticide applications, and harvest. Our objective was to compare the goodness of fit of applied models and determine which provides the best description of pistachio nut growth as a function of thermal unit accumulation. Three fruit growth traits of pistachio—pericarp (hull) + endocarp (shell) size, endocarp thickening and hardening, and embryo (kernel) size—exhibited clear nonlinear dependence on heat accumulation. We tested three nonlinear models—Michaelis–Menten, three-parameter logistic, and Gompertz—fitted to fruit development data to create a tool to forecast pest susceptibility and harvest timing. Observation of development began at full bloom and ended at harvest. Data were collected from six pistachio cultivars in one experimental and eight commercial orchards over 3 years. Analyses of residual distribution, parameter standard errors, coefficient of determination (R2) and the Akaike information criterion (AIC) all demonstrated the Gompertz function was the best model. Cultivars differed significantly in all the three parameters (Asym, b, and c) for all three traits with the Gompertz model, demonstrating the Gompertz model can adjust to incorporate cultivar differences. The growth curve of the three traits together provided integrated information on nut biomass accumulation that facilitates predicting the critical timing for multiple orchard management practices.

Salinity’s many stresses may not kill a relatively salt-tolerant perennial in one season, but they can still deplete or modify nonstructural carbohydrate (NSC) pools. Any change to the quantity or quality of NSC reserves may have detrimental effects on phenology and reproduction, as well as yield, in tree crops. This study integrates salinity’s infringement on the energy margins of pistachio rootstock ‘UCB-1’ (an interspecific hybrid of Pistacia atlantica and P. integerrima) at senescence by measuring sugar and starch pools in wood, bark, and roots after treatment with ≈100 days of moderate to high salinity (50–100 mm NaCl and 10–20 mm CaCl2). Supported by a second experiment using sodium orthovanadate (NaOV) to block active xylem retrieval in the same hybrid pistachio rootstock, we conclude that retrieval of Na+ from xylem sap may allow for the preservation of NSC pools (particularly, starch) in mature xylem tissues by limiting the demand for carbon-based osmoticum (sugars). In contrast, younger growing tissues (bark and fine roots) were found to counteract salinity by degrading carbon-dense starch into osmotically active sugars at the expense of total NSC reserves, suggesting a physiological shift toward protection/isolation from environmentally pervasive but potentially toxic salts in these tissues.

Production of California table olives has declined significantly in recent years due to hand harvesting costs, often over 60% of gross return. Mechanical harvesting could sharply decrease harvest costs, increasing economic viability. Mechanical harvester efficiency is a combination of the percentage of the total fruit on a tree removed by a harvester, and the time required to do so. A comparison between an experimental canopy contact shaker and a commercial trunk shaker demonstrated low harvest efficiencies and no significant differences in harvester efficiency between the two, averaging no more than 8%. However, simultaneously combining both shaking methods increased fruit removal to an economically feasible 75% and produced better fruit quality. Combining both shaking methods increased the price per ton by 63% versus trunk shaking and 35% versus canopy shaking. These results suggest a mechanical olive harvester that simultaneously combines trunk and canopy shaking is more efficient than either shaking method alone, and, has potential for economically feasible mechanical table olive harvesting.

Pecan is the only native north American tree nut. The USA produces approximately 80% of the world’s pecans. Pecan trees have an extended juvenility, 10 years to the first nut crop. With mature bearing they begin alternate bearing; alternating large and small crops. Theoretically, a heavy crop inhibits flower induction in the current year resulting in a low crop the following year. The flowering of perennial trees involves a complex interplay of multiple hormones. The possible molecular mechanisms regulating tree flowering can be revealed by endogenous plant hormone quantification, exogenous hormone application and RNA-sequencing. In this review, we synthesize the investigations of transcriptomic analysis and exogenous hormone treatments on bud break and flowering in fruit/nut trees with a focus on pecan. Knowledge of how hormones regulate flowering suggest they are a potential tool for improving return bloom and mitigating alternate bearing.

Moisture and fat content, fatty acid profile, and volatile terpenes were measured for the first time for ‘Kalehghouchi’, ‘Pete 1’, and ‘Lost Hills’ pistachios grown at two California microclimates: Lost Hills and Parlier. ‘Kalehghouchi’ had the highest moisture content, followed by ‘Pete 1’ and ‘Lost Hills’, respectively. While the moisture content of ‘Kalehghouchi’ was not significantly affected by location, it was lower for ‘Pete 1’ grown at Parlier (40.8 vs. 40.8 g/100 g) and higher for ‘Lost Hill’ grown there (48.2 vs. 45.2 g/100 g). ‘Pete 1’ grown at the Parlier site had a higher fat content compared with ‘Lost Hills’ (47.7 vs. 43.0 g/100 g). ‘Kalehghouchi’ had a lower fat content at Parlier compared with Lost Hills (42.0 vs. 44.9 g/100 g), and ‘Lost Hills’ was unaffected by location. The main fatty acid measured in the pistachio samples was oleic acid (52% to 58%), followed by linoleic (26% to 33%) and palmitic acids (11% to 13%). While oleic acid content of ‘Lost Hills’ and ‘Kalehghouchi’ was higher for pistachios grown in Parlier, no impact of location was observed for ‘Pete 1’. The fatty acid profiles of all three cultivars appeared to be more dependent on genotype and less affected by microclimate. α-pinene (95–1682 ng/kg), limonene (37–741 ng/kg), and α-terpinolene (1–368 ng/kg) were the most abundant volatiles among all the cultivars and locations. Microclimate was the primary factor in determining volatile terpenes concentration in pistachio kernels.

Abstract Understanding the mechanisms of stress tolerance in diverse species is needed to enhance crop performance under conditions such as high salinity. Plant roots, in particular in grafted agricultural crops, can function as a boundary against external stresses in order to maintain plant fitness. However, limited information exists for salinity stress responses of woody species and their rootstocks. Pistachio (Pistacia spp.) is a tree nut crop with relatively high salinity tolerance as well as high genetic heterogeneity. In this study, we used a microscopy‐based approach to investigate the cellular and structural responses to salinity stress in the roots of two pistachio rootstocks, Pistacia integerrima (PGI) and a hybrid, P. atlantica x P. integerrima (UCB1). We analyzed root sections via fluorescence microscopy across a developmental gradient, defined by xylem development, for sodium localization and for cellular barrier differentiation via suberin deposition. Our cumulative data suggest that the salinity response in pistachio rootstock species is associated with both vacuolar sodium ion (Na+) sequestration in the root cortex and increased suberin deposition at apoplastic barriers. Furthermore, both vacuolar sequestration and suberin deposition correlate with the root developmental gradient. We observed a higher rate of Na+ vacuolar sequestration and reduced salt‐induced leaf damage in UCB1 when compared to P. integerrima. In addition, UCB1 displayed higher basal levels of suberization, in both the exodermis and endodermis, compared to P. integerrima. This difference was enhanced after salinity stress. These cellular characteristics are phenotypes that can be taken into account during screening for sodium‐mediated salinity tolerance in woody plant species.

The production and consumption of nuts are increasing in the world due to strong economic returns and the nutritional value of their products. With the increasing role and importance given to nuts (i.e., walnuts, hazelnut, pistachio, pecan, almond) in a balanced and healthy diet and their benefits to human health, breeding of the nuts species has also been stepped up. Most recent fruit breeding programs have focused on scion genetic improvement. However, the use of locally adapted grafted rootstocks also enhanced the productivity and quality of tree fruit crops. Grafting is an ancient horticultural practice used in nut crops to manipulate scion phenotype and productivity and overcome biotic and abiotic stresses. There are complex rootstock breeding objectives and physiological and molecular aspects of rootstock–scion interactions in nut crops. In this review, we provide an overview of these, considering the mechanisms involved in nutrient and water uptake, regulation of phytohormones, and rootstock influences on the scion molecular processes, including long-distance gene silencing and trans-grafting. Understanding the mechanisms resulting from rootstock × scion × environmental interactions will contribute to developing new rootstocks with resilience in the face of climate change, but also of the multitude of diseases and pests.

Pecan is native to the United States. The US is the world’s largest pecan producer with an average yearly production of 250 to 300 million pounds; 80 percent of the world’s supply. Georgia, New Mexico, Texas, Arizona, Oklahoma, California, Louisiana, and Florida are the major US pecan producing states. Pecan trees frequently suffer from spring freeze at bud break and bloom as the buds are quite sensitive to freeze damage. This leads to poor flower and nut production. This review focuses on the impact of spring freeze during bud differentiation and flower development. Spring freeze kills the primary terminal buds, the pecan tree has a second chance for growth and flowering through secondary buds. Unfortunately, secondary buds have less bloom potential than primary buds and nut yield is reduced. Spring freeze damage depends on severity of the freeze, bud growth stage, cultivar type and tree age, tree height and tree vigor. This review discusses the impact of temperature on structure and function of male and female reproductive organs. It also summarizes carbohydrate relations as another factor that may play an important role in spring growth and transition of primary and secondary buds to flowers.

The effects of passive- and active-modified atmosphere packaging (passive- and active-MAP) were investigated on the physio-chemical and quality attributes of fresh in-hull pistachios stored at 4 ± 1 °C and 90 ± 5% R.H. Fresh pistachios were packaged under each of the following gas combinations: active-MAP1 (AMA1) (5% O2 + 5% CO2), AMA2 (5% O2 + 25% CO2), AMA3 (5% O2 + 45% CO2), AMA4 (2.5% O2 + 5% CO2), AMA5 (2.5% O2 + 25% CO2), and AMA6 (2.5% O2 + 45% CO2), all balanced with N2, as well as passive-MAP (PMA) with ambient air (21% O2 + 0.03% CO2 + 78% N2). Changes in quality parameters were evaluated after 0, 15, 30 and 45 days of storage. Results demonstrated that AMA6 and PMA had significantly lower (7.96 Log CFU g−1) and higher (9.81 Log CFU g−1) aerobic mesophilic bacteria counts than the other treatments. However, the AMA6 treatment decreased, kernel chlorophyll and carotenoid content, hull antioxidant capacity, and anthocyanin content. The PMA treatment produced a significant weight loss, 0.18%, relative to the other treatments. The active-MAP treatments were more effective than the passive-MAP in decreasing weight loss, microbial counts, kernel total chlorophyll (Kernel TCL), and kernel carotenoid content (Kernel CAC). The postharvest quality of fresh in-hull pistachios was maintained best by the AMA3 (5% O2 + 45% CO2 + 50% N2) treatment.

In California, a significant percentage of the pistachio acreage is in the San Joaquin Valley on saline and saline-sodic soils. However, irrigation management practices in commercial pistachio production are based on water-use information developed nearly two decades ago from experiments conducted in non-saline orchards sprinkler-irrigated with good quality water. No information is currently available that quantify the effect of salinity or combined salinity and sodicity on water use of micro-irrigated pistachio orchards, even though such information would help growers schedule irrigations and control soil salinity through leaching. To fill this gap, a field research study was conducted in 2016 and 2017 to measure the actual evapotranspiration (ETa) from commercial pistachio orchards grown on non-saline and saline-sodic soils in the southern portion of the San Joaquin Valley of California. The study aimed at investigating the functional relations between soil salinity/sodicity and tree performance, and understanding the mechanisms regulating water-use reduction under saline and saline-sodic conditions. Pistachio ETa was measured with the residual of energy balance method using a combination of surface renewal and eddy covariance equipment. Saline and saline-sodic conditions in the soil adversely affected tree performance with different intensity. The analysis of field data showed that ETa, light interception by the tree canopy, and nut yield were highly and linearly related (r2 > 0.9). Moving from non-saline to saline and saline-sodic conditions, the canopy light interception decreased from 75% (non-saline) to around 50% (saline) and 30% (saline-sodic), and ETa decreased by 32% to 46% relative to the non-saline orchard. In saline-sodic soils, the nut yield resulted around 50% lower than that of non-saline orchard. A statistical analysis performed on the correlations between soil physical-chemical parameters and selected tree performance indicators (ETa, light interception, and nut yield) revealed that the sodium adsorption ratio (SAR) adversely affected tree performance more than the soil electrical conductivity (ECe). Results suggest that secondary effects of sodicity (i.e., degradation of soil structure, possibly leading to poor soil aeration and root hypoxia) might have had a stronger impact on pistachio performance than did salinity in the long term. The information presented in this paper can help pistachio growers and farm managers better tailor irrigation water allocation and management to site-specific orchard conditions (e.g., canopy features and soil-water salinity/sodicity), and potentially lead to water and energy savings through improved irrigation management practices.

With climate change and decreased water supplies, interest in irrigation scheduling based on plant water status is increasing. Stem water potential (ΨSWP) thresholds for irrigation scheduling in olive have been proposed, however, a physiologically-based evaluation of their reliability is needed. A large dataset collected at variable environmental conditions, growing systems, and genotypes was used to characterize the relation between ΨSWP and gas exchanges for olive. Based on the effect of drought stress on the ecophysiological parameters monitored, we described three levels of stress: no stress (ΨSWP above about −2 MPa), where the high variability of stomatal conductance (gs) suggests a tight stomatal control of water loss that limit ΨSWP drop, irrigation volumes applied to overcome this threshold had no effect on assimilation but reduced intrinsic water use efficiency (iWUE); moderate-stress (ΨSWP between about −2.0 and −3.5 MPa), where iWUE can be increased without damage to the photosynthetic apparatus of leaves; and high-stress (ΨSWP below about −3.5 MPa), where gs dropped below 150 mmol m−2 s−1 and the intercellular CO2 concentration increased proportionally, suggesting non-stomatal limitation to photosynthesis was operative. This study confirmed that olive ΨSWP should be maintained between −2 and −3.5 MPa for optimal irrigation efficiency and to avoid harmful water stress levels.

The olive fruit fly was first detected in Los Angeles in 1998 and in all the olive-growing regions of California soon after. Following its initial detection, UC researchers and Cooperative Extension farm advisors, county agricultural commissioners and the California Department of Food and Agriculture Pest Detection and Emergency Project established a statewide monitoring program to determine the extent of the olive fruit fly's occurrence, track its seasonal biology and evaluate monitoring tools. Fly populations and infestations can reach high levels throughout California but tend to be lower in the San Joaquin Valley. Trap captures typically exhibit a bimodal distribution with peaks in the spring and fall. Olive infestation is related to fly densities, climate and fruit size. Gravid, mated females vary in density throughout the year but are present at some level year-round. The data is being used to develop models that will better predict when the adults are active and olives are at risk.

Until the 1940s, when production economics and labor shortages became pressing, olives around the world were hand harvested. Despite 60 years of research, mechanical. There are two major reasons for this. First, trees over 20 years old are too tall and poorly structured for mechanical harvesting. Second, mechanical harvesting research for table olive production has not been sufficiently focused on the final goal, processed fruit quality. For oil olives, which are physiologically mature at harvest and require less removal force, advances in both trunk shaking and picker head technology are advancing rapidly. Also, as olive oil is enjoying a renaissance around the world new orchards are being planted in the hedgerows that facilitate mechanical harvesting. For table olives however, mechanical harvesting is still in the developmental stage. The research being done now, unlike earlier work, focuses on the parallel goals of efficient fruit removal and final processed product quality. Within 10 years most olive oil orchards of suitable tree size and shape will be mechanically harvested. When table olives will be routinely harvested mechanically cannot be predicted.

Topically applied 'Sevillano' olive pollen increased the percentage of normal fruit set and reduced incidence of worthless shotberry 'Manzanillo' olives. Applications were effective up to 90 feet from the pollen source.