Commercial Pistachio Orchards Research Articles

Genome assembly and association tests identify interacting loci associated with vigor, precocity, and sex in interspecific pistachio rootstocks.

Understanding the basis of hybrid vigor remains a key question in crop breeding and improvement, especially for rootstock development where F1 hybrids are extensively utilized. Full-sibling UCB-1 F1 seedling rootstocks are widely planted in commercial pistachio orchards that are generated by crossing 2 highly heterozygous outbreeding parental trees of Pistacia atlantica (female) and P. integerrima (male). This results in extensive phenotypic variability, prompting costly removal of low-yielding small trees. To identify the genetic basis of this variability, we assembled chromosome-scale genome assemblies of the parental trees of UCB-1. We genotyped 960 UCB-1 trees in an experimental orchard for which we also collected multiyear phenotypes. We genotyped an additional 1,358 rootstocks in 6 commercial pistachio orchards and collected single-year tree-size data. Genome-wide single marker association tests identified loci associated with tree size and shape, sex, and precocity. In the experimental orchard, we identified multiple trait-associated loci and a strong candidate for ZZ/ZW sex chromosomes. We found significant marker associations unique to different traits and to early vs late phenotypic measures of the same trait. We detected 2 loci strongly associated with rootstock size in commercial orchards. Pseudo-testcross classification of markers demonstrated that the trait-associated alleles for each locus were segregating in the gametes of opposite parents. These 2 loci interact epistatically to generate the bimodal distribution of tree size with undesirable small trees observed by growers. We identified candidate genes within these regions. These findings provide a foundational resource for marker development and genetic selection of vigorous pistachio UCB-1 rootstock.

Spatial and Temporal Population Dynamics of Aspergillus flavus in Commercial Pistachio Orchards in Arizona

Aspergillus flavus infects a wide range of crops, including pistachio, and subsequent aflatoxin contamination results in significant economic losses. Application of biocontrol products based on nonaflatoxigenic (atoxigenic) strains of A. flavus is one of the most effective tactics for controlling aflatoxins in crops. Both risk of aflatoxin contamination and effectiveness of biocontrol are influenced by the extent to which A. flavus spores move into pistachio tree canopies during periods of nut development. Thus, the purpose of this study was to evaluate spatial and temporal population dynamics of A. flavus, including the applied biocontrol strain AF36, in canopies of pistachio orchards in Arizona. Propagule densities of A. flavus were quantified on leaf samples collected from lower, middle, and upper canopies from spring through harvest in 2018 and 2019. A. flavus propagule densities peaked during periods of high temperature and rainfall in 2018 (up to 600 CFU/g) and 2019 (up to 23 CFU/g), which coincided with nut development and maturation. The applied biocontrol strain AF36 was detected at all canopy heights but overall propagule densities were greater in the upper and middle canopy (mean = 70 CFU/g) compared with the lower canopy (mean = 47 CFU/g). Results suggest that June to August is the period during which A. flavus inoculum increases in Arizona pistachio orchards and, to most effectively displace aflatoxin-producing fungi in tree canopies, biocontrol applications should precede this period. In addition, this study demonstrates that soil-applied biocontrol strains can successfully disperse throughout the canopies of commercial tree nut orchards.

Aetiology of branch dieback, panicle and shoot blight of pistachio associated with fungal trunk pathogens in southern Spain

AbstractPistachio represents an emerging nut crop across the Mediterranean basin. In Spain, pistachio has been traditionally cultivated in marginal‐dry areas with unfavourable climatic conditions for plant diseases. Consequently, little attention has been given to research on pistachio diseases until recently. Symptoms of branch dieback and cankers, and shoot and panicle blight have been recently observed in commercial pistachio orchards across southern Spain. In this study, 10 commercial pistachio orchards showing disease symptoms were surveyed between 2017 and 2018. Botryosphaeriaceae fungi were consistently isolated from affected shoots, among other fungal families with minor relevance. Representative isolates of each family were characterized based on colony and conidial morphology, optimum growth temperature, and the comparison of DNA sequence data (ITS, LSU, EF, TUB2, and ACT genomic regions). Detached and attached shoots, and attached panicles of pistachio cv. Kerman were inoculated with mycelial plugs or conidial suspensions to demonstrate the pathogenicity of the selected isolates. Botryosphaeria dothidea, Lasiodiplodia pseudotheobromae, Neofusicoccum mediterraneum, N. parvum, Diaporthe neotheicola, Diaporthe sp., Eutypa lata, Eutypa sp., Cytospora sp., and Phaeoacremonium minimum were identified. P. minimum had the highest optimum growth temperature (29.6 °C) and Cytospora sp. the lowest (21–22 °C). Botryosphaeriaceae isolates showed the largest lesions on inoculated shoots, with L. pseudotheobromae being the most aggressive, followed by Neofusicoccum species. Panicles inoculated with N. mediterraneum showed blight symptoms and canker formation 6 weeks after inoculation, without significant differences in aggressiveness between isolates. This work reports relevant information about this emerging disease in the novel Spanish pistachio‐growing areas.

Macrophomina Crown and Root Rot of Pistachio in California.

In this study, declining pistachio rootstocks were detected in newly planted commercial pistachio orchards in Kern County, California. Symptoms were characterized by wilted foliage combined with crown rot in the rootstock. From diseased trees, 42 isolates were obtained, and all had similar cultural and morphological characteristics of Macrophomina phaseolina. Analyses of nucleotide sequences of three gene fragments, the internal transcribed spacer region (ITS1–5.8S–ITS2), partial sequences of β-tubulin, and translation elongation factor 1-α (TEF1) confirmed this identification, and 20 representative isolates are presented in the phylogenetic study. Testing of Koch’s postulates showed that M. phaseolina, when inoculated to stems and roots of the pistachio rootstocks using mycelial plugs or a microsclerotial suspension, is indeed pathogenic to this host. The widely used clonal University of California Berkeley I (UCBI) rootstock appeared highly susceptible to M. phaseolina, suggesting that this pathogen is an emerging threat to the production of pistachio in California. This study confirmed the association of M. phaseolina with the decline of pistachio trees and represents the first description of this fungus as a crown rot-causing agent of pistachio in California.

Phenotypic and molecular characterization of resistance to the SDHI fungicide fluopyram in populations of Alternaria alternata from pistachio orchards in California

In this study, the sensitivity of 902 isolates of A. alternata collected before and after the commercial use of fluopyram were assessed using mycelial growth tests. Distribution of 50% effective concentration (EC50) values for 116 A. alternata isolates (population A), collected in 2011 from an experimental orchard that had been treated with fluopyram products or boscalid showed that 86% of the isolates displayed different levels of resistance to boscalid while 87 (76%) and 28 (24%) showed sensitivity and different levels of resistance to fluopyram, respectively. Among the last group of isolates, only 5 and 23 showed moderate (MR) and low (LR) resistance to fluopyram, respectively. The sensitivity to fluopyram was further evaluated in agar medium at the discriminatory dose of 5 μg/ml fluopyram for a total of 786 A. alternata isolates collected in 2012 from commercial pistachio orchards with (173 isolates, population B; 373 isolates, population C) or without a history of use of fluopyram products (240 isolates, population D). Among the 240 isolates from 31 boscalid-treated orchards, 93 and 7% showed sensitivity (S) and low resistance (LR) to fluopyram, respectively, while 65 and 33 were resistant (R) and LR to boscalid, respectively. Analyses of the sensitivities to boscalid and fluopyram of the 546 isolates from populations B and C collected from orchards exposed to fluopyram or other SDHIs showed fluopyram-resistant isolates did not occur at the same frequency as boscalid resistance. In both populations, the frequencies of boscalid resistance isolates in all plots, exposed or not to fluopyram products, were significantly higher than those observed for fluopyram. Sequence analyses of the A. alternata SDHB, C, and D proteins showed the presence of several amino acid substitutions (SDHB: H277Y/R/L, P230 A/R/I/F,D, N235D/T/E/G; SDHC: H134R, S135R; SDHD: D123E, H133P) in boscalid- and fluopyram-resistant phenotypes. Current data provided further evidences of the good performance of fluopyram and the various and interactive impacts of SDH mutations on the levels of resistance to SDHIs. Although their frequency is still very low, fluopyram-resistant phenotypes could quickly build up in Alternaria populations under continual selection pressure by SDHI-containing products and ultimately affect fluopyram efficacy. As fluopyram products become extensively used in pistachio orchards, continual monitoring of Alternaria sensitivities to fluopyram and other active ingredients in these mixtures (tebuconazole in particular) will be required to detect any shifts in sensitivity that could result in disease control failures.

Effect of Exogenous Application of L-arginine and Sodium Nitroprusside on Fruit Abscission and Physiological Disorders of Pistachio (Pistacia Vera L.) Scions

Pistachio yield are often negatively affected by some physiological problems such as abscission of inflorescence buds and fruits, deformed or blank nuts, and non-split shells. In the present study the effect of exogenous application of arginine (Arg) (a substrate for nitric oxide (NO) synthase) and sodium nitroproside (SNP), as a NO-donor was investigated on yield production, fruit and inflorescence buds abscission, and physiological parameters of Pistacia vera. The experiment was conducted in randomized complete block design with factorial structure in a commercial pistachio orchard. Factors were included two levels of Arg (0.5 and 1 mM), two levels of SNP (50 and 100 μM) and their combination applied at two distinct time; one week before full bloom (first stage) and five weeks after full bloom (second stage). Comparing to SNP-treated trees, Arg was more effective on growth and physiological parameters of shoots and on fruit and inflorescence buds abscission, and on fruit parameters such as split and non-split shells, blank nuts, number of nuts per ounce. Effects of these treatments were considerably depending on the time of application and the concentrations of applied compounds. It is proposed that the effects of Arg and SNP may be related to the NO signaling and polyamines production.

Actual Evapotranspiration and Tree Performance of Mature Micro-Irrigated Pistachio Orchards Grown on Saline-Sodic Soils in the San Joaquin Valley of California

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.

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.

Spatially variable evapotranspiration over salt affected pistachio orchards analyzed with satellite remote sensing estimates

Recent prolonged droughts in California have emphasized the urgent need to implement more efficient water management practices for high value tree crops. Accurate estimation of evapotranspiration (ET), a main component of consumptive water use, is critical for improving management of micro-irrigated pistachio orchards grown in the San Joaquin Valley of California. We estimated ET of three mature commercial pistachio orchards on non-saline and increasingly saline soils in 2015 and 2016, using the Mapping Evapotranspiration at high Resolution with Internalized Calibration (METRIC) method and Landsat 8 satellite observations. Based on a comparison with field observations at 8 sites, we modified the parameterizations of the momentum roughness length and net radiation for pistachio tree crops and reduced the uncertainty of daily ET estimates. When compared with field data, the recalibrated METRIC ET estimates had an R2 of 0.59, a mean absolute error of 1.1 mm/day, and a RMSE of 1.4 mm/day during Landsat overpass dates (n = 72). The METRIC ET map captured the temporal dynamics and spatial heterogeneity both within and among the orchards. The mean annual crop season estimated ET (mid-March to mid-October in 2016) with remote sensing decreased by 32% from 1064 ± 99 mm in the non-salt affected control orchard to 725 ± 82 mm in the orchard with the highest level of soil-water salinity. The ET reduction was consistent with canopy volume differences among the study orchards, as shown by summer Normalized Difference Vegetation Index (NDVI) from Landsat observations, e.g., 0.72 ± 0.06 in the control vs. 0.52 ± 0.06 in the most saline orchard. The available energy was controlled mostly by canopy features and explained 64% of daily ET variation among all Landsat pixels and satellite overpass days. The normalized differenced water index (NDWI) could be considered as an important parameter to capture the partitioning of available energy for ET (R2 = 0.38), suggesting that the lower soil osmotic potential in saline orchards further reduced crop ET.

Voice-Controlled and Wireless Solid Set Canopy Delivery (VCW-SSCD) System for Mist-Cooling

California growers in the San Joaquin Valley believe that climate change will affect the pistachio yield dramatically. As the central valley fog disappears, insufficient dormant chill accumulation results in poor flowering synchrony, flower quality, and fruit set in this dioecious species. We have developed a novel, user-friendly, and low-cost Voice-Controlled Wireless Solid Set Canopy Delivery (VCW-SSCD) system to increase bud chill accumulation with evaporative cooling on sunny (winter) days. This system includes: (i) an automated solid-state canopy delivery (SSCD) system; (ii) a wireless weather-, crop-related data acquisition system; (iii) a Voice-Controlled (VC) system using Amazon Alexa; (iv) a mobile application to visualize the collected data and wirelessly control the SSCD system; and (v) a smart control system. The proposed system was deployed and evaluated in a commercial pistachio orchard in Bakersfield, CA. The system worked well with no reported errors. Results demonstrated the system’s ability to cool bud temperatures in a low relative humidity climate. At an ambient temperature of 10–20 °C, bud temperatures were lowered 5–10 °C.

First Report of Root Rot Caused by Phytopythium helicoides on Pistachio Rootstock in California

HomePlant DiseaseVol. 100, No. 11First Report of Root Rot Caused by Phytopythium helicoides on Pistachio Rootstock in California PreviousNext DISEASE NOTES OPENOpen Access licenseFirst Report of Root Rot Caused by Phytopythium helicoides on Pistachio Rootstock in CaliforniaE. J. Fichtner, G. T. Browne, M. Mortaz, L. Ferguson, and C. L. BlomquistE. J. FichtnerSearch for more papers by this author, G. T. BrowneSearch for more papers by this author, M. MortazSearch for more papers by this author, L. FergusonSearch for more papers by this author, and C. L. BlomquistSearch for more papers by this authorAffiliationsAuthors and Affiliations E. J. Fichtner , University of California Cooperative Extension Tulare Co., Tulare, CA 93274 G. T. Browne , USDA-ARS, CPGRU, Department of Plant Pathology, University of California Davis, CA 95616 M. Mortaz L. Ferguson , Department of Plant Sciences, University of California Davis, CA 95616 C. L. Blomquist , California Department of Food and Agriculture, Plant Pest Diagnostics Laboratory (CDFA-PPDC), Sacramento, CA 95832. Published Online:16 Aug 2016https://doi.org/10.1094/PDIS-12-15-1424-PDNAboutSections ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmailWechat Approximately 25 potted 2-year-old pistachio rootstock trees in a Kern County, CA, research plot maintained outdoors and irrigated to container capacity exhibited wilting in June 2013. Symptomatic plants gradually declined and died through November 2013. Extensive root necrosis was observed on symptomatic plants. Necrotic roots of seedling UCB-1 rootstock (Pistacia atlantica × Pistacia integerrima) submerged in CMA-PARP selective medium (Jeffers and Martin 1986) yielded a Pythium-like organism. On V8 juice agar, a representative isolate produced rapidly growing colonies (188 mm/day, radial) that produced subglobose, papillate sporangia measuring 25 to 42.5 × 25.0 to 37.5 µm (33.4 × 30.4 µm average). Sexual structures were not observed. DNA was extracted from the isolate and amplified by PCR with primers ITS1 and ITS4 (White et al. 1990). BLAST query of the sequence, GenBank accession no. KT901799 matched HQ643382, Phytopythium helicoides, with 98% identity. Diseases caused by P. helicoides have been reported on several plants and include root and stem rot on begonia (e.g., Yang et al. 2013) and rhizome rot on lotus (Yin et al. 2016). Phytopythium is a recently established genus containing organisms formerly classified as Pythium Clade K species (de Cock et al. 2015). For completion of Koch’s postulates, two isolates of P. helicoides were grown for 14 days on V8-oat-vermiculite substrate. UCB-1 clonal rootstock plants were purchased from a wholesale nursery, acclimatized in the greenhouse, grown to approximately 12 cm in height, and then transplanted into potting medium mixed with either uninfested substrate (the control) at a rate of 5% (v/v), or P. helicoides-infested substrate (2.5% v/v of each isolate). To induce zoospore release, pots were submerged in water for 4 h with the water surface maintained 1 cm above the soil. Control plants were treated identically to those in infested soil. The soil was then allowed to drain, and plants were watered daily. Two experimental runs included eight and 12 replicate plants of each treatment, respectively. Plants challenged with P. helicoides wilted within 1 week of inoculation. By 2 weeks after inoculation, 100% and 43% of inoculated plants died in the first and second experimental runs conducted in summer and winter, respectively. Control plants remained asymptomatic. By 6 weeks after inoculation, root mass of inoculated plants was only 28% and 65% of that of control plants in respective experimental runs. P. helicoides was consistently isolated from symptomatic plants and never from control plants. To our knowledge, this is the first report of root rot caused by P. helicoides on pistachio. The results indicate that the pathogen can be aggressive on UCB-1 rootstock, which is used for approximately half the commercial pistachio acreage in California. The greater mortality observed in summer than in winter suggests that variation in host or environmental factors may modulate disease development. The source of primary inoculum in the original symptomatic plants is unknown. Future work is needed to assess the importance and epidemiology of P. helicoides in commercial pistachio orchards.

Detection of isolates of Alternaria alternata with multiple-resistance to fludioxonil, cyprodinil, boscalid and pyraclostrobin in California pistachio orchards

In this study, 229 isolates of Alternaria alternata collected from commercial pistachio orchards with (n = 198) and without (n = 31) a prior history of Switch (cyprodinil + fludioxonil) applications were examined for their sensitivity to fludioxonil and cyprodinil using in vitro mycelial growth assays. The 50% effective dose (EC50) values for the baseline isolates for cyprodinil and fludioxonil ranged from 0.001 to 1.184 μg/mL (average = 0.214) and from 0.010 to 4.875 μg/mL (average = 0.770), respectively. Out of 72 isolates assayed from the exposed population, 93% had EC50 values for fludioxonil ranging from 0.001 to 5.370 μg/mL (average = 0.472), but five isolates were highly resistant to this fungicide (EC50 > 100 μg/mL). About 98.55% of these isolates were sensitive to cyprodinil (0009 < EC50 < 0.415 μg/mL; average = 0.098). Only one isolate was resistant to cyprodinil (EC50 > 10 μg/mL). No cross-resistance relationship between cyprodinil and fludioxonil was observed (P = 0.2925, r = −0.1074). To determine the occurrence of multiple resistances, the radial growths of 126 isolates, collected from orchards with a history of Switch, Pristine, and strobilurin exposures, were measured on agar media amended with a single discriminatory dose of 10 μg fungicide/mL. High proportions of these isolates were resistant to boscalid (86.3%) and pyraclostrobin (92.9%). Most isolates were still sensitive to fludioxonil (77.8%) and cyprodinil (89.7%), but some were found to be independently or simultaneously resistant to all fungicides tested. Under conditions of excessive exposure to Switch resistant phenotypes may develop in A. alternata populations and ultimately affect fungicide performance. Therefore, monitoring studies must be continued and strict adherence to anti-resistance strategies followed and implemented in at risk orchards.

Crop Loss Relationships and Economic Injury Levels for Ferrisia gilli (Hemiptera: Pseudococcidae) Infesting Pistachio in California.

Ferrisia gilli Gullan (Hemiptera: Pseudococcidae) is a new pest in California pistachios, Pistacea vera L. We conducted a 3-yr field study to determine the type and amount of damage caused by F. gilli. Using pesticides, we established gradients of F. gilli densities in a commercial pistachio orchard near Tipton, CA, from 2005 to 2007. Each year, mealybug densities on pistachio clusters were recorded from May through September and cumulative mealybug-days were determined. At harvest time, nut yield per tree (5% dried weight) was determined, and subsamples of nuts were evaluated for market quality. Linear regression analysis of cumulative mealybug-days against fruit yield and nut quality measurements showed no relationships in 2005 and 2006, when mealybug densities were moderate. However, in 2007, when mealybug densities were very high, there was a negative correlation with yield (for every 1,000 mealybug-days, there was a decrease in total dry weight per tree of 0.105 kg) and percentage of split unstained nuts (for every 1,000 mealybug-days, there was a decrease in the percentage of split unstained of 0.560%), and a positive correlation between the percentage of closed kernel and closed blank nuts (for every 1,000 mealybug-days, there is an increase in the percentage of closed kernel and closed blank of 0.176 and 0.283%, respectively). The data were used to determine economic injury levels, showing that for each mealybug per cluster in May there was a 4.73% reduction in crop value associated with quality and a 0.866 kg reduction in yield per tree (4.75%).

Characterization of Aspergillus section Flavi from pistachio soils in Iran

Abstract During 2012, soil samples from commercial pistachio orchards in three major production regions include Rafsanjan (Kerman Province, center of Iran), Damghan (Semnan Province, north-central Iran) and Feyz-Abad (Khorasan-e Razavi Province, northeastern Iran), were assayed on Dichloran Rose-Bengal Chloramphenicol agar (DRBC) and Aspergillus flavus-parasiticus agar media to quantify populations of Aspergillus species from the section Flavi. The mean propagule density of Aspergillus species from the Flavi section [log10 (CFU/g soil)] was higher in Feyz-Abad (3.06, 2.88–3.24), compared to Damghan (2.55, 2.44–2.65) and Rafsanjan (2.40, 2.26–2.54). A. flavus (69.7, 65.3 and 57.9%), A. parasiticus (19.6, 25.4, and 29.3%), and A. nomius (10.7, 9.3, and 12.8%) were the predominant species in the regions of Rafsanjan, Damghan, and Feyz-Abad, respectively. There were significant differences among sclerotia producing isolates of A. flavus in the sampling regions (p &lt; 0.05). The percentage of sclerotium-producing isolates of A. flavus from Rafsanjan (14.5%) was much lower than Damghan (39.5%) and Feyz-Abad (41.4%). The A. flavus isolates from Damghan, Rafsanjan, and Feyz-Abad were toxigenic at 53.7%, 61.6%, and 60.4%, respectively. In Rafsanjan, aflatoxin B1 (AFB1), and AFB1 + AFB2 (aflatoxin B2) ranged from 274 to 553 ppb (393±17.11) and 394 to 3745 ppb, respectively, while AFB1, and AFB1 + AFB2 ranged from 257 to 392 ppb (285±13.18) and 415 to 1658 ppb, respectively, in Damghan. We found 16 and 20 vegetative compatibility groups (VCGs) for 41 and 37 nit mutant producing isolates of A. flavus from Rafsanjan and Damghan, respectively. From Damghan the VCG diversity for A. flavus isolates was greater (54%) than from Rafsanjan (39%). Because there were a few number of sclerotium-producing isolates of A. flavus, we did not determine the relationships between sclerotium production with VCGs and/or geographical distribution in the three pistachio production regions. This study was the first to determine the strain and VCG diversity of A. flavus soil isolates from Iranian pistachio orchards.

Evaluation of the Atoxigenic Aspergillus flavus Strain AF36 in Pistachio Orchards.

The atoxigenic strain Aspergillus flavus AF36, which has been extensively used as a biocontrol agent in commercial corn and cotton fields to reduce aflatoxin contamination, was applied in research pistachio orchards from 2002 to 2005 and in commercial pistachio orchards from 2008 to 2011. AF36 was applied as hyphae-colonized steam-sterilized wheat seed (the same product and same application rate as used in cotton fields). In all orchards, applying the wheat-AF36 product substantially increased the proportion of vegetative compatibility group (VCG) YV36, the VCG to which AF36 belongs, within A. flavus soil communities. Application of the AF36 product in additional years further increased YV36 in the soil until it composed 93% of the A. flavus isolates in treated commercial orchards. Nonetheless, application of the AF36 product did not result in increased incidence of kernel decay of the nuts. For nuts harvested from commercial orchards, reductions in percentages of samples contaminated with aflatoxin from treated orchards (relative to that for untreated orchards) ranged from 20 to 45%, depending on the year. Because of the high value of pistachio nuts and the costs associated with rejection of shipments due to aflatoxin contamination, these reductions are significant and valuable to the pistachio industry.

Seasonal Phenology of &lt;I&gt;Ferrisia gilli&lt;/I&gt; (Hemiptera: Pseudococcidae) in Commercial Pistachios

The mealybug Ferrisia gilli Gullan is a serious new pest of pistachios in California. It was first found near the town of Tulare in the late 1990s and has since spread to orchards in most pistachio-producing regions of the state. The seasonal phenology of F. gilli was evaluated in a commercial pistachio orchard in Tulare County during 2005 and 2006. During both seasons E gilli overwintered as small nymphs and had three complete generations per year. Mealybug population densities were low and remained as immatures in March and April; by late May adult females formed and averaged (+/- SE) 1.3 +/- 0.3 and 1.2 +/- 0.3 per 0.75 m of sample branch in 2005 and 2006, respectively. The first in-season generation occurred from early June through mid-July, with mealybug densities ranging from 17.6 +/- 5.6-26.4 +/- 6.2 mealybugs per 0.75 m sample branch. The second in-season generation occurred from late July through September and had peak densities of 408.6 +/- 93.9 and 182.0 +/- 34.2 mealybugs per branch. In March and April mealybugs were located primarily on the buds and branch wood; in May the population was on branch wood as well as the rachis; from June through September the population was located primarily in the pistachio cluster. F. gilli's seasonal phenology described herein was used to develop a management program.

Free endogenous growth regulators in Pistachio (Pistacia vera L.)

This research was carried out in order to observe seasonal changes of internal plant growth regulators in pistachio. This research was conducted during three years at a commercial pistachio orchard located in FA±rat valley in Nizip, Gaziantep. ‘KA±rmA±zA±’ pistachio cultivar trees grafted on Pistacia vera L. were used as plant material. Changes in auxin (IAA), cytokinin (Zeatin), gibberellin (GA3) and abscisic acid (ABA) were observed in leaves in May, July and September of the first (heavy cropping year - 'on'-year) and second (subsequent light cropping year ' off '-year) years. Besides, yield and flower bud abscission rate were observed during three years to determine the relationships among the level of plant growth regulator, yield and flower bud abscission. It was observed that the IAA, zeatin and ABA levels in the leaf were high in the first year, and was low in the second year. The annual GA3 levels were lower in the ‘on’ year and higher in the alternate bearing, ‘off’ year. The correlation analysis between the hormones and fruit bud abscission rates showed that increase in the ABA levels caused also increase in fruit bud abscission at all months in the first year. Key words: Auxin, zeatin, gibberellic acid, abscisic acid, pistachio.

Quantifying reductions in consumptive water use under regulated deficit irrigation in pistachio ( Pistacia vera L.)

The reduction in agricultural water use in areas of scarce supplies can release significant amounts of water for other uses. As improvements in irrigation systems and management have been widely adopted by fruit tree growers already, there is a need to explore the potential for reducing irrigation requirements via deficit irrigation (DI). It is also important to quantify to what extent the reduction in applied water through DI is translated into net water savings via tree evapotranspiration (ET) reduction. An experiment was conducted in a commercial pistachio orchard in Madera, CA, where a regulated deficit irrigation (RDI) program was applied to a 32.3-ha block, while another block of the same size was fully irrigated (FI). Four trees were instrumented with six neutron probe access tubes each, in the two treatments and the soil water balance method was used to determine tree ET. Seasonal irrigation water in FI, applied through a full-coverage microsprinkler system, amounted to 842 mm, while only 669 mm were applied in RDI. Seasonal ET in FI was 1024 mm, of which 308 mm were computed as evaporation from soil ( E s). In RDI, seasonal ET was reduced to 784 mm with 288 mm as Es. The reduction in applied water during the deficit period amounted to 147 mm. The ET of RDI during the deficit period was also reduced relative to that of FI by 133 mm, which represented 33% of the ET of FI during the deficit irrigation period. There was an additional ET reduction in RDI of about 100 mm that occurred in the post-deficit period.

Effects of Single-Drop Impactions and Natural and Simulated Rains on the Dispersal of Botryosphaeria dothidea Conidia

ABSTRACT Laboratory and field experiments were conducted to study the dispersal of Botryosphaeria dothidea conidia using single-drop impactions and natural and simulated precipitations. For laboratory studies, 200 single drops were released from a height of 1 m on infected pistachio nuts. On pieces of photographic film, 50% of the droplets were collected within 20 mm (average droplet travel distance) of the target area, and the droplets ranged from 0.041 to 3.19 mm in diameter, with an average of 0.3 mm. Each droplet carried an average of 23 B. dothidea conidia. In 3 years of field experiments, rainwater was collected in funnels connected to bottles positioned at different heights inside the tree canopy and at different distances away from the edge of tree canopy in three commercial pistachio orchards in San Joaquin, Yolo, and Glenn counties in California. Numbers of conidia in rainwater varied among and within sampling seasons by sampling dates and orchards. Up to 67,000 conidia/ml were obtained in rainwater samples collected from an orchard in Yolo County. Rainwater from orchards in Yolo and Glenn counties contained a consistently higher number of conidia than rainwater collected from the orchard in San Joaquin County. Variation in numbers of conidia also existed among heights where bottles were located. There were significantly more conidia in rainwater collected inside than outside tree canopies. Inside tree canopies, bottles located at 100 and 150 cm above ground collected more B. dothidea conidia than those placed at 50 and 200 cm. Conidia were collected as far as 1 m from the tree canopy edge. Based on data from the Glenn County orchard, a linear relationship between number of conidia (Y) and rainfall amount (X) in millimeters was determined as Y = 240X - 3,867, with r(2) = 0.91, which meant that a minimum of 16.1 mm of rain was needed to disperse conidia of B. dothidea. The power law model best described the dispersal gradients of B. dothidea propagules in the 1999-2000 and 2001-02 sampling seasons, with r(2) values of >/=0.73, whereas the exponential law model fit best for the 2000-01 data, with r(2) values of >/=0.81. In a rain simulation experiment, the intensity of the rain generated by a nozzle at 138 kPa of pressure inside the tree canopy was approximately five times higher than rain recorded outside the tree canopy. Rain removed up to 65% of conidia from infected fruit. These results confirmed that B. dothidea is a splash-dispersed pathogen with relatively short distances of spore dispersal within pistachio orchards. Only pycnidia are present in pistachio orchards; therefore, the results also indicate that inoculum of B. dothidea should be entirely splashed dispersed.

Spatiotemporal Changes in the Population Structure of Botryosphaeria dothidea from California Pistachio Orchards

ABSTRACT Spatiotemporal changes in the population structure of Botryosphaeria dothidea, causal agent of panicle and shoot blight of pistachio, were analyzed by using microsatellite-primed polymerase chain reaction (MPPCR), partial sequences of the RNA polymerase II (RPB2) gene, and vegetative compatibility groups (VCGs). We examined 390 isolates, 378 recovered from pistachio in seven counties of California from 1990 to 2001 and 12 recovered from peach, apple, and sycamore in Georgia, North Carolina, South Carolina, Illinois, and Pennsylvania. Six microsatellite primers generated 116 polymorphic bands. Based on MP-PCR data, we observed very high (>98%) levels of genetic identity among populations of B. dothidea collected from the commercial pistachio orchards in California. The near identity of these populations was supported by VCGs and partial sequences of the RBP2 gene. These findings suggest that populations of B. dothidea from commercial pistachio orchards are spatially and temporally stable, at least in the past 5 years.