Mature Pistachio Trees Research Articles

Contrasting allelic effects for pistachio salinity tolerance in juvenile and mature trees

Breeding perennial tree crops often requires prediction of mature performance from juvenile data. To assess the utility of juvenile screens to predict salinity tolerance of mature pistachio trees, we compared performance of 3-month ungrafted seedlings and 4-year-old grafted rootstocks under salinity stress. The QTL allele associated with higher salt exclusion from seedling leaves conferred lower growth in saline field conditions, suggesting that mapping QTL in seedlings may be easier than discerning the optimal allele for field performance.

Seasonal potassium dynamics in fruiting and non-fruiting branches of pistachio trees in relation to crop load

Under dry and warm environmental conditions, the main Tunisian pistachio cultivar Mateur does not show a normal ‘On/Off’ cycle with highly variable nut yield, which could be affected by the tree nutritional status. In this context, Potassium (K) is considered a key nutritional element for nut development and for yield. The current study investigated the effects of alternate bearing and flower bud removal on seasonal dynamics of potassium in fruiting and non-fruiting branches of mature pistachio trees (cv. Mateur) in arid land. Three disbudding treatments were considered in reference to untreated trees taken as a control (T0): removal of all flower buds for one year (T1), or two successive years (T2) and removal of 50% of flower buds each year (T3). Similar K concentrations were detected early in the season in leaves, current shoot and one-year-old wood for all treatments. Current shoot begin the cycle with higher K concentrations, which declined during the lignification of endocarp and seed growth stages to finally accumulate K during postharvest. Inversely, one-year-old wood stored a large amount of K during the stage I and II of nut development, and became the main sink for K of the bearing shoot. Leaf K concentration explained 75% of yield variation. Yearly removal of 50% of flower buds induced less variation of leaf K concentrations (ranged between 0.5-0.8% DM) with regular nut yield compared to bi-annual On-Off cycle. Thus, under severe climatic conditions, the annual pruning could be applied to improve the nutritional status of pistachio trees.

Olgun Antepfıstığı’nın (Pistacia vera L.) Stomatal ve Morfolojik Özellikleri Üzerine In vitro Mikropropagasyon Büyüme Koşullarının Etkisi

This research was conducted to reveal the stomatal anatomy, stomatal index and water loss (%) of mature pistachio leaves as well as the leaves of different phases (multiplication, rooting, hardening and regenerated plant) of micropropagation of mature pistachio trees obtained from the in vitro. Microscopic observations on surfaces of these leaves showed variety from elliptical to ovate stomata with length of 0.81-2.02 μm and width of 1.58-3.80 μm. An increase in stomatal index (SI) in the leaves of plants grown in vitro was observed most specifically in the hardening phase. (17.49±0.04). The stomatal index declined in the leaves of plantlets transferred to in vivo conditions subsequent to the hardening phase. In order to measure water loss, leaves obtained from all types of samples were dried in the oven between 30 minutes and 2 hours and weighed. The percent water loss of in vitro leaves of multiplication phase was greater than the other phases. The stomatal differentation was found to be influenced by the different hardening regimes applied. Hardening by covering the pots with polyethylene bags improved the survival rate. This study indicates that optmization of in vitro micropropagation stages is necessary to avoid transplantation stress.

Seasonal changes in starch content in pistachio organs as related to crop load

The alternate bearing in pistachio (Pistacia vera L.) results from inflorescence buds abscission differentiated on current season growth during the year of heavy crop. Inflorescence bud drop has been directly correlated with the presence of fruits on 1-year shoot, and in particular with the kernel grow that acts as the major sink of nutrients. Experimental evidences suggest the involvement of competition between reproductive organs for the available resources. The annual carbohydrates storage was analysed in mature pistachio trees characterized by low, medium and high crop load (about 1, 7 and 11 kg tree(-1) of dry in-shell nuts). The experiment was carried out in 2013 in a commercial pistachio orchard, using ‘Bianca’ grafted onto P. terebinthus L. in Sicily (Italy, 37°30’ Lat N). Starch concentration was measured in sample tissues of trunk wood, current-year shoot, one-year-old and two-year-old shoots throughout the season from the dormancy phase (March) until the post-harvest period (September). During dormancy, the trunk represented the main storage organ having starch concentration ranging from 60 to 120 mg g(-1) of dry weight, whereas the tissues of the other organs examined showed values below 20 mg g(-1) of dry weight. The deepest decrement of starch concentration after bud-break until bloom was observed in the trunk, whereas, starch concentration started increasing after the initial growth flush. The patterns of starch in the tissues varied according with the crop load; trees bearing the highest crop load (11 kg tree(-1)) showed a constant starch concentration during the growing season, in contrast with the trees characterized by lower crop load values. Before the onset of dormancy, starch rapidly increased in all the shoots type and in the trunk wood and no effects of tree crop load were observed.

Impacts of water stress, environment and rootstock on the diurnal behaviour of stem water potential and leaf conductance in pistachio (Pistacia vera L.)

Little information is available on the diurnal behaviour of water potential and leaf conductance on pistachio trees despite their relevance to fine tune irrigation strategies. Mature pistachio trees were subject to simultaneous measurements of stem water potential (Ψx) and leaf conductance (gl) during the day, at three important periods of the irrigation season. Trees were grown on three different rootstocks and water regimes. An initial baseline relating Ψx to air vapor pressure deficit (VPD) is presented for irrigation scheduling in pistachio. Ψx was closely correlated with VPD but with a different fit according to the degree of water stress. No evidence of the variation of Ψx in relation to the phenology of the tree was observed. Furthermore, midday Ψx showed more accuracy to indicate a situation of water stress than predawn water potential. Under well irrigated conditions, gl was positively correlated with VPD during stage II of growth reaching its peak when VPD reached its maximum value (around 4 kPa). This behaviour changed during stage III of fruit growth suggesting a reliance of stomatal behaviour to the phenological stage independently to the tree water status. The levels of water stress reached were translated in a slow recovery of tree water status and leaf conductance (more than 40 days). Regarding rootstocks, P. integerrima showed little adaptation to water shortage compared to the two other rootstocks under the studied conditions.

EFFECTIVE HYDROGEN CYANAMIDE (DORMEX®) APPLICATION FOR BUD BREAK, FLOWERING AND NUT YIELD OF PISTACHIO TREES CV. MATEUR IN WARM GROWING AREAS

SUMMARYClimate change characterized by global warming is expected to have an incidence on fruit trees’ development and production. The severity of these effects depends on lack of chilling. The current study focused on the research of an optimal dose of hydrogen cyanamide (Dormex®) treatment which can advance the bud break of female pistachio trees (Pistacia veraL.) to ensure better blooming synchronization with pollinators. A field experiment was conducted in northern Tunisia (36°49′N, 9°48′E) on mature pistachio trees. Two hydrogen cyanamide treatments at 2% and 4% Dormex® were applied with reference to the control untreated trees. The flowering time, vegetative growth, starch content, productivity and nut characters were followed. Results show that 4% Dormex® advanced the normal bud break by 15 days and flowering by 11 days and improved natural pollination by synchronization of male and female flowers. Consequently, fresh yield and nut quality as split and blank rates and nut weight were improved. However, shoot growth, leaf area and starch content in current shoot seemed unaffected by hydrogen cyanamide applications. In conclusion, hydrogen cyanamide could be used as 4% Dormex® and sprayed 45 days before bud break to improve pistachio productivity and prevent anomalies of lack of chilling due to global warming that could be more frequent in the Mediterranean areas.

MICROPROPAGATION OF PISTACHIO: "THE WAVE OF THE FUTURE?"

The aim of this review is concerned with the novel in vitro methods published for micropropagation and conservation of pistachio. Since the first publication by Barghchi in 1982, there have been considerable biotechnological advances in both micropropagation and conservation of pistachio germplasm. All of those studies revealed that the success of biotechnological approaches is dependent on regeneration of mature pistachio trees following successful culture initiation, generally by micropropagation. This review is focused upon the novel in vitro methods published for micropropagation and conservation of pistachio in which contributions of Barghchi, Abousalim, Onay, Parfitt, Tilkat and Ozden-Tokatli and others are discussed in a historical perspective. Examples of all aspects of micropropagation (shoot tip culture, somatic embryogenesis and adventive organogenesis) and currently employed uses of pistachio tissue culture, especially practical applications of micropropagation, which enable the pistachio industry to transition into an evaluation of what lies ahead, are also presented. Our work of over 20 years of experience will be presented in relation to past accomplishments, while presenting newer technologies and developments that may provide researchers with knowledge allowing them to determine the practicality and economic validity for micropropagation to become the wave of the future for large-scale commercial propagation of pistachios.

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.

Effects of immaturity on productivity and nut quality in pistachio (Pistacia vera L.)

SummaryImmature trees of pistachio (Pistacia vera L.), a dioecious species, exhibit major cropping problems; in particular, insufficient male bloom and low yields of poor quality nuts. The aims of this research were to elucidate the extent of pollen limitation and factors that affect pollination and fruit-set during this precarious period. The experiment was conducted in a 4 year-old, 57 ha orchard, in the southwest of the San Joaquin Valley, California. Female trees of the cultivar ‘Kerman’ and trees of the male cultivar ‘Peters’ were interplanted at a ratio of 1:24. Bloom phenology was recorded visually. Supplementary pollination treatments, using electrostatic and non-electrostatic methods, were applied to the female trees and compared to open-pollination. Pollen density in the air was analysed during the application of the treatments. The following results were found: male and female bloom completely overlapped, although pollen availability became a limiting factor early in the flowering period; supplementary pollination significantly increased pollen flow, while pollen levels were extremely low in open-pollination; supplementary pollination, and electrostatic pollination in particular, significantly increased pollen germination on the stigma, and reduced the level of blank nuts. In conclusion, pollination was found to be a limiting factor in immature pistachio trees. It is suggested that, in some cases, electrostatic pollination could supplement natural pollination, thereby ensuring higher yields with better nut quality. However, poor levels of pollen alone could not account for all the differences in cropping between immature and mature pistachio trees.

Regulated deficit irrigation effects on yield, nut quality and water-use efficiency of mature pistachio trees

SummaryRegulated deficit irrigation (RDI) was evaluated on deep rooted, mature pistachio trees grown under high evaporative demand in the low rainfall southern San Joaquin Valley of California. The focus of this work was to assess the impact of deficit irrigation during various parts of the season with the goal of determining which period was most stress tolerant in terms of nut production. Pistachio nuts have a unique fruit growth pattern in which rapid kernel growth does not begin until about six weeks after full shell size has been attained. Our hypothesis was that irrigation could be reduced during this period with limited negative effects on production. The season was divided into three preharvest periods: leafout to full shell expansion (Stage 1), full shell expansion to the onset of rapid kernel growth (Stage 2), and rapid kernel growth to harvest (Stage 3). Water deprivation during Stage 1 applied 7.2% less water than the near-fully irrigated Control without any yield loss, based on mean values for the last “on” and “off” alternate bearing years of this study. Shell splitting (endocarp dehiscence) at harvest (a positive impact) was significantly higher (10.4% relative to the Control) but this was offset by a nut weight reduced by 9.4%. Stage 3 water deprivation (53% less applied water than the Control) significantly reduced nut size, shell splitting, mechanical nut removal by tree shaking, and yield, while increasing kernel blanking and abortion. Postharvest water deprivation (5.0% less applied water than the Control) had no significant negative effects on yield components. Six irrigation regimes that applied water at various rates were used to investigate Stage 2 behaviour. While there were no significant differences in yield components among these regimes, the best production occurred with deficit irrigation during Stage 2 at 50% of near-potential ETc during Stage 2 and 25% of near-potential ETc after harvest. This RDI regime saved about 180 mm of water (23.2% of the Control) and water use efficiency was significantly higher (4.69 versus 3.61 kg marketable fruit per mm water, for this RDI regime and the Control, respectively). We believe RDI during Stage 2 and postharvest is a viable irrigation strategy to save water while maintaining top yields of high quality pistachio nuts. Further work is needed to determine if the improved shell splitting harvest that occurred with Stage 1 stress can be exploited to improve grower profits.

Potassium Fertilization Affects Soil K, Leaf K Concentration, and Nut Yield and Quality of Mature Pistachio Trees

A field experiment was conducted from 1996 to 1998 to examine the effects of K fertilization on leaf K, nut yield, and quality in pistachio (Pistacia vera L.). There were six treatments, including four annual rates of K application (0, 110, 220, and 330 kg·ha-1) and three K sources (K2SO4, KCl, and KNO3). Pistachio trees exhibited highly fluctuating seasonal leaf K levels. Leaf K concentration was low (<10 g·kg-1) during spring flush, increased dramatically during fruit development, and declined rapidly after harvest. Leaf K concentration increased following K fertilization. Potassium fertilization at the rate of 110 to 220 kg·ha-1 K significantly increased nut yield and quality, but nut yield tended to decrease when the annual rate exceeded 220 kg·ha-1 K. There were no significant differences among the K sources in their effects on leaf K concentration, nut yield, and quality. The use of KCl as a K source for 3 years did not increase leaf Cl concentration. There was a significant, positive correlation between nut yield and leaf K concentration during nut fill. The critical leaf K value for optimal pistachio production determined from 3 years' cumulative data was 16.9 g·kg-1. For sustained production in highly productive pistachio orchards, we recommend annual application rates of 110 to 220 kg·ha-1 K, using K2SO4, KCl, or KNO3.

Leaf Zinc and Copper Concentrations of Mature Pistachio Trees in Response to Fertigation

Mature `Kerman' pistachio (Pistacia vera L.) trees, located on the west side of the San Joaquin Valley of California on an alkaline clay-loam soil, were fertigated in 1997 and 1998 with three combinations of zinc (Zn) and copper (Cu) sulfate. Seasonal applications of Zn and Cu were injected at three separate times starting in spring and ending in summer. Efficacy of the treatments were compared by measuring the concentration of Zn and Cu in leaf tissue. Fertigated treatments were compared to trees receiving no supplemental Zn or Cu and to trees receiving a single foliar treatment of Zn and Cu each year. Soil Zn and Cu concentrations increased in the fertigated plots. Plots receiving the highest rates of Zn and Cu showed the greatest increase. However, at the recommended August leaf sampling period, only the foliar treated pistachio trees showed a significant increase in leaf Zn and Cu. The results demonstrate that after two seasons, a foliar application of Zn and Cu in April, two to three weeks after flowering, increased leaf-tissue concentrations of Zn and Cu to sufficiency levels. These foliar applications were more effective than fertigating with Zn and Cu sulfate.

Alternate Bearing Affects Nitrogen, Phosphorus, Potassium and Starch Storage Pools in Mature Pistachio Trees

The relationship between crop load and the functional storage of selected macronutrients and starch was assessed to develop nutrient budgets and best management fertilization practices in orchards. Functional storage represents the amount of nutrients and starch redistributed from perennial tree parts in support of the spring growth flush. Functional storage was influenced by:(a)nutrient and starch accumulation prior to dormancy; and(b)nutrient and starch demand by vegetative and reproductive organs in spring. Lightly cropping (off-year) trees stored 7, 14 and 2 times as much N, P and K, respectively, as heavily cropping (on-year) trees. Similar to many biennial plant species, nutrients that accumulated during the vegetative phase in off-year trees were used to support reproductive growth during the subsequent on-year. Soil nutrient uptake contributed more to storage pools than leaf nutrient resorption in off-year-trees, while the reverse was true in on-year trees. Net nutrient resorption from senescing leaves accounted for all of the N and P and a third of the K stored in on-year trees. Only between 20–33% of the N, P and K stored in perennial tissues of off-year trees could be attributed to leaf nutrient resorption. This is the first study to determine the amounts of nutrients stored in the perennial parts of mature, field-grown trees and the relative contributions of leaf nutrient resorption and soil nutrient uptake to functional storage in trees.

Macronutrient Allocation to Leaves and Fruit of Mature, Alternate-bearing Pistachio Trees: Magnitude and Seasonal Patterns at the Whole-canopy Level

Estimates of leaflet and fruit macronutrient (N, P, K, Ca, and Mg) accumulation and resorption were developed in six (three heavily cropping, on-year and three noncropping, off-year) mature pistachio (Pistacia vera L. `Kerman') trees over three growing seasons during three stages of phenology [the spring growth flush (April to June); seed fill (late June to September); and leaf senescence (September to November)]. Crop load influenced total nutrient content per tree in annual organs (leaves and fruit), the relative allocation of nutrients between leaves and fruit, temporal patterns of nutrient accumulation in annual organs, and the magnitude of net leaf nutrient resorption per tree prior to leaf fall. In off-year trees, macronutrient accumulation in annual organs (leaves) was concentrated during the spring flush of growth. In contrast, significant macronutrient accumulation in annual organs of on-year trees (leaves plus fruit) occurred not only during the spring flush of growth but also during seed fill. Duration and magnitude of macronutrient accumulation were greater in on-year vs. off-year trees. Fruit N and P demand during seed fill was partially met by a net decrease in the N and P contents of the pericarp. These decreases in pericarp nutrient content during seed fill were equivalent to 32% and 26% of embryo accumulation of N and P, respectively. Fruit demand for N, P, and K during the spring flush of “on” years was accompanied by reduced leaf N, P, and K contents per tree. Net leaf N, Ca, and Mg resorption per tree during leaf senescence differed with crop load. Net leaf N resorption was significantly greater in off-year trees than on-year trees. Leaf N resorption presumably represents an important component of the N pool stored in perennial tree parts during dormancy. The greater leaf N resorption following “off” years was a function of greater leaf N concentration and greater leaf biomass per tree. In contrast, net leaf resorption of Ca and Mg was greater in on-year vs. off-year trees. Experimental validation of the magnitude and periodicity of nutrient uptake by mature pistachio trees is needed during the alternate-bearing cycle, especially in light of the potential contribution of current fertilization practices to groundwater contamination.

Assessment of Nitrogen Uptake Capacity in Mature Alternate-bearing Pistachio (Pistacia vera) Trees

The interrelationships between crop load, root growth, and nutrient uptake in mature, pistachio trees were examined in this study. Nutrient uptake was determined during the spring, summer, and fall using labeled nitrogen (15N) and boron (10B) and by differences in whole-tree accumulation between tree harvests for other nutrients (e.g., P, K, Ca, Zn). Nitrogen and boron uptake were double in fruiting compared with nonfruiting trees in the spring. Most of the labeled N was found in the developing fruits and leaves. Total labeled N recovery during the spring flush period, however, was low, indicating that much of the N in the fruit came from N reserves from within the tree rather than uptake from the soil. In contrast, significant amounts of N were taken up from the soil during the summer uptake period. Thus, our data support the hypothesis that sink demand (i.e., fruit development) conditions N uptake in pistachio. The relationship between root growth and N uptake was also examined in this study. Root observation chambers were constructed, and root growth determined by tracing roots growing up against the glass windows. Root length, root growth rate, relative root growth rate, and total tree fine root weight were all greater in nonfruiting compared to fruiting trees during the fruit development period (late May to mid-July). Surprisingly, fruiting trees had less root growth, but greater N uptake than nonfruiting trees during this period. This evidence suggests that N uptake is decoupled from root growth in mature pistachio trees.

Alternate bearing influences annual nutrient consumption and the total nutrient content of mature pistachio trees

The influence of alternate bearing on nutrient utilization and total tree nutrient content was investigated in mature pistachio (Pistacia vera L. cv Kerman trees). Removal of N, P and Zn in fruit and abscised leaves of cropping (‘on’) trees averaged 5, 6, and 2 times, respectively, the removal in abscised leaflets of the non-fruiting, ‘off’ year trees. One hundred and thirty-five kg N, 131 kg K, 86 kg Ca, 39 kg Mg and 18 kg P per hectare were removed in fruits and abscised leaves in ‘on’ year trees. Tree nutrient contents and, presumably, the size of nutrient storage pools in dormant trees varied between ‘on’ and ‘off’ years. There was 22% and 14% more N and P, respectively, in dormant trees following ‘off’ than ‘on’ years. The greater N and P accumulation in ‘off’ year trees is depleted in support of the large fruit demand for N and P during ‘on’ years. In contrast to N and P, there was greater K and Ca accumulation in perennial tree parts during ‘on’ years than during ‘off’ years. The greater K accumulation in perennial tree parts and approximately 30% greater removal of K in annual organs during ‘on’ than ‘off’ years suggests that K uptake could be 4 times higher in ‘on’ year trees than in (non-cropping), ‘off’ year trees.