California Pistachio Research Articles

Investigating rootstock susceptibility and new Oomycota fungicides for the management of Phytophthora crown and root rot of pistachio in California

Investigating rootstock susceptibility and new <i>Oomycota </i>fungicides for the management of Phytophthora crown and root rot of pistachio in California

Ochratoxin A Contamination of California Pistachios and Identification of Causal Agents.

Ochratoxin A (OTA) is a potent mycotoxin produced by Aspergillus and Penicillium spp., which contaminates many crops, including pistachios. Pistachios contaminated with OTA may be subjected to border rejections resulting in significant economic losses to the United States agricultural revenues. The current study examined prevalence of OTA in California-grown pistachios and identified its causal agents. OTA was detected in 20% of samples from 2018 to 2021 (n = 809), with 18% of samples exceeding the European Union regulatory limit of 5 μg/kg. Fungi potentially responsible for OTA contamination were isolated from leaves, nuts, and soil collected from 14 pistachio orchards across California. A total of 1,882 isolates of Aspergillus section Nigri and 85 isolates of section Circumdati were recovered. Within section Nigri, 216 (11.5%) isolates were identified as potential OTA producers using a boscalid-resistance assay. Phylogenetic analyses of partial gene sequences for β-tubulin and calmodulin genes resolved section Circumdati into four species: A. ochraceus (33%), A. melleus (28%), A. bridgeri (21%), and A. westerdijkiae (19%). A. westerdijkiae produced the highest levels of OTA in inoculated pistachios (47 μg/g), followed by A. ochraceus (9.6 μg/g) and A. melleus (3.3 μg/g). A. bridgeri did not produce OTA. OTA production by section Circumdati was optimal from 20 to 30°C. All 216 boscalid-resistant isolates from section Nigri were identified as A. tubingensis, and representative isolates (n = 130) produced 3.8 μg/kg OTA in inoculated pistachios. This is the first detailed report on OTA contamination and causal fungi in California pistachios and will be helpful in devising effective management strategies.

Sporulation and Dispersal of the Biological Control Agent Aspergillus flavus AF36 Under Field Conditions.

Aflatoxins are carcinogens produced by the fungi Aspergillus flavus and A. parasiticus that contaminate pistachio crops. International markets reject pistachio when aflatoxins exceed permitted maximum levels. Releasing the atoxigenic strain AF36 of A. flavus is the leading aflatoxin pre-harvest control method. The product AF36 Prevail, sorghum grains coated with AF36 propagules, has been used in California since 2017. However, a high percentage of grains of the Prevail fail to sporulate in orchards. Here, the effect of soil moisture on the percentage of AF36 product grains sporulating (SG) and the quantity of spores per grain using a sporulation index (SI) was determined. Under controlled conditions, SG was higher than 85% when soil moisture was 13% or more, and SI increased with increasing soil moisture from 8.4 to 21%. The highest AF36 sporulation occurred near the micro-sprinklers when the grains were not impacted by the irrigation water drops. Arthropod predation was responsible for lost product grains, which was more pronounced in non-tilled soil than in tilled soil. Dispersal of the AF36 spores decreased markedly with the height and distance from the inoculum source, following a pattern of diffusion equations. However, AF36 spores easily reached canopies of pistachios located 10 m from the inoculum source. Our results indicate that AF36 Prevail should be applied close to the irrigation line in the moist soil area but avoiding the areas where excess irrigation causes water accumulation. The biocontrol of aflatoxins in California's pistachio production areas was optimized by improving the field realization of the biological control agent.

Phenotypic Characteristics That May Contribute to Persistence of Salmonella Strains in the Pistachio Supply Chain

Salmonella enterica subsp. enterica strain diversity in California pistachios is limited; some strains have persisted in the pistachio supply chain for ≥10 years. Representative isolates of six persistent strains and three sporadic strains isolated from California pistachios were selected to evaluate copper resistance, growth in pistachio hull slurry, biofilm formation, desiccation tolerance, and survival during subsequent storage. The presence of a copper homeostasis and silver-resistance island sequence in three of the persistent strains was associated with an increase in tolerance to CuSO4 from 7.5 mM to 15 mM under anaerobic but not aerobic conditions; all isolates were resistant to ≥120 mM Cu-EDTA under both anerobic and aerobic conditions. When inoculated into pistachio hull slurry at 2.75 ± 0.04 log CFU/mL and incubated at 30 °C, the populations of Salmonella Enteritidis strain A (sporadic) increased to significantly lower levels than the other strains at 16, 20, 24, and 28 h but not at 40 and 48 h. Maximum populations of 8.70–8.85 log CFU/mL were observed for all strains at ≥40 h of incubation. All nine Salmonella strains produced weak to strong biofilms after 4 days at 25 °C; seven strains, including two sporadic strains, produced moderate biofilms, and Salmonella Liverpool strain A (persistent) produced a strong biofilm. The rdar+ and rdar- morphotypes were observed in both persistent and sporadic Salmonella strains. Population declines of 5.03 log were observed for Salmonella Enteritidis strain A within 18 h of drying on filter paper whereas reductions of 0.50–1.25 log were observed for the other eight Salmonella strains. Population reductions (3.98–5.12 log) of these eight strains were not significantly different after storage at 25 ± 1 °C and 35% relative humidity for 50 days. The phenotypic characteristics evaluated here do not independently account for the persistence of a small number of Salmonella strains associated with the California pistachio production chain.

Kaolin as a management alternative for insecticide-resistant navel orangeworm (Lepidoptera: Pyralidae).

The production of almonds and pistachios in California's Central Valley employs insecticides for the management of their primary pest, navel orangeworm. The pyrethroid Bifenthrin is commonly used, and now a strain of Amyelois transitella Walker (Lepidoptera: Pyralidae) (R347) obtained from Kern County almond orchards with a history of Bifenthrin use has acquired >110-fold resistance toward pyrethroids. One method to improve control is to use additives and spray adjuvants, which are applied simultaneously with an insecticide to increase coverage and/or duration of control. We tested 2 levels of the naturally occurring clay Kaolin as an additive, alone and in combination with either Bifenthrin or the diamide Chlorantraniliprole, to determine if it could reduce feeding damage and decrease survival of pyrethroid-resistant A. transitella on almonds in the laboratory and improve the efficacy of Chlorantraniliprole in the field. Larval performance was measured for the strains R347 and ALM (34.7-fold resistance compared to susceptible lab strain) reared on treated almonds. Strain R347 had 1.9-fold greater survival and caused 1.3-fold more feeding damage than strain ALM across all treatments, although both strains were susceptible to the combination of Kaolin + insecticide. Kaolin synergized Bifenthrin for R347, decreasing survival by 10.0%. Kaolin did not reduce feeding damage for either strain. When combined with insecticide, feeding damage was similar to insecticide alone, but the addition of Kaolin to the insecticide generally decreased survival more than the insecticide alone. In the field, the addition of Kaolin to Chlorantraniprole during application helped retain activity against this challenging pest.

Selection and validation of reference genes for quantifying gene expression in the Gill's mealybug.

The Gill's mealybug, Ferrisia gilli Gullan, (Hemiptera: Pseudococcidae) has emerged as a major pest of pistachio in California. Because F. gilli is only relatively recently described, there are no validated reference genes to normalize the expression data from real-time quantitative reverse transcription-polymerase chain reaction (qRT-PCR) in this species. We selected and validated 8 commonly used reference genes (RPS8, TBP, UBQE2, RPL7, RPL5, RPL40, RPLP1, and HEL) for expression stability in F. gilli. These genes were evaluated in 5 different geographical populations of F. gilli collected from organic and conventionally grown pistachio orchards. Candidate reference genes were also evaluated in F. gilli fed with 4 plant hosts: pistachio, almond, grapes, and lima beans. The stability of candidate genes was analyzed using 4 software algorithms: geNorm, NormFinder, BestKeeper, and RefFinder. Three genes RPS8, RPL40, and RPL7 encoding for ribosomal proteins were identified as the most stable across the treatments and thus were recommended for normalizing the qRT-PCR data. These findings will support resistance monitoring, molecular toxicology, and functional genomics research in F. gilli.

Mid- and End-of-the-Century Estimation of Agricultural Suitability of California’s Specialty Crops

Specialty crops with long economic life cycles have lower adaptability and flexibility to climate change, making long-term planning crucial. This study examines the impact of climate change on almond, citrus, pistachio, and walnut production in California, using a machine learning approach to estimate crop suitability under current and future environmental conditions. We used recent satellite-observed cropland data to generate an occurrence dataset for these crops. Ecological data including bioclimatic variables derived from global circulation models developed under the Coupled Model Intercomparison Project Phase 6 (CMIP6) and surface variables were used to model suitability. The bioclimatic variables relating to temperature and precipitation had the largest effect on each crop’s suitability estimation. The results indicate that suitable areas for almonds, citrus, and walnuts will change significantly within 20 years due to climatic change, and the change will be even greater by the end of the century, indicating a potential loss of 94% of the current suitable area. The results for pistachios indicate change in the spatial distribution of suitable area but the total area is predicted to remain near the current suitable area. Policymakers, researchers, and farmers must work together to develop proactive adaptation strategies to mitigate the negative effects of climate change on specialty crop production. The application of a species distribution model for agriculture suitability provides critical information for future work on adaptation to climate change, identifying areas to target for further analysis.

Alterations in Ferrisia gilli (Hemiptera: Pseudococcidae) phenology in California pistachios and potential impacts on controls.

The mealybug, Ferrisia gilli Gullan, attacks important crops such as almonds, grapes, and pistachios in California. In pistachios, F. gilli has 3 generations per year, and a single insecticide application timed to the presence of first instars of the first or second generation provided sufficient control. This strategy has, recently, become less effective, and here we tested the possible explanation that F. gilli life stages are smeared, with different life stages present concurrently, reducing the efficacy of a single pesticide application. We monitored F. gilli populations and their natural enemies in central California pistachio orchards from 2021 through 2022. We found the first generation of F. gilli was synchronous, but occurred 3 wk earlier than previously reported. Subsequent generations were smeared. Increased yearly temperatures are a likely explanation for the changes observed in phenology. Almost all natural enemies found were lacewings (n > 10,000). Parasitoids were recovered from pistachios in 2021 (n = 4) and 2022 (n = 164), most were hyperparasitoids. Based on these studies, recommendations are made to monitor F. gilli in early May rather than late May to better target insecticide applications for the first instars.

Characterizing the Genetic Diversity of Salmonella Isolated from U.S. Raw Inshell Pistachios Using Whole Genome Sequencing

The genetic diversity of 169 Salmonella isolates from pistachios collected from California storage silos during the 2010, 2011, and 2012 harvests (silo survey isolates) was determined by analyzing the whole genome sequence data using the CFSAN SNP pipeline developed by the U.S. Food and Drug Administration’s Center for Food Safety and Applied Nutrition. Salmonella isolates clustered by serovars Agona, Enteritidis, Montevideo, Sandiego, Senftenberg, Liverpool, Tennessee, and Worthington in the phylogenetic tree. Within each serovar, isolates grouped into one or two clusters (≤14 SNPs). Two distinct clusters (>14 SNPs; A and B) were identified for Salmonella Enteritidis, Montevideo, and Liverpool for a total of 11 unique strains. Sequences of representative silo survey isolates clustered with sequences of Salmonella strains isolated from U.S. pistachio-associated samples collected between 2008 and 2018 available on the National Center for Biotechnology Information database, and, in all but two cases, not with sequences of Salmonella strains recovered from raw California almonds from 2001 through 2013. The genomic evidence suggests that strains of Salmonella Agona, Liverpool Cluster A, Montevideo Clusters A and B, Senftenberg, and Worthington have persisted in the California pistachio environment for ≥3 years and some of these strains have been reported exclusively in association with pistachios.

Frequency of Alternaria Genotypes Resistant to SDHI Fungicides in California Pistachio Orchards Determined by Real-Time PCR.

Real-time PCR methods were developed to quantify the frequency of SDHC-H134R and SDHB-H277Y mutants associated with succinate dehydrogenase inhibitors (SDHI) resistance in Alternaria populations from pistachio. The linearity of the standard curves demonstrated the applicability in the quantification of the assays. The accuracy and reliability of the qPCR protocols to determine the frequency of mutants in real samples were corroborated. Orchards visibly affected by Alternaria late blight were sampled. The frequency of mutants was determined using the qPCR assays, while the frequency of resistant phenotypes was determined using a single discriminatory dose. The statistical analysis showed that the frequencies of the mutation SDHC-H134R determined with the qPCR assay were highly correlated with those estimated with the conventional method. The survey also evidenced that resistance to boscalid is still widespread in California. Results also indicated the possible contribution of other mutations to SDHI resistance. Our results confirmed the prevalence of SDHC-H134R mutants and the occurrence of mutation SDHB-H277Y at low frequencies. The real-time PCR methods developed in this study were able to detect differences in the frequencies of resistant mutants caused by the use of chemical fungicides. Finally, the effects of two fungicide programs on the frequency of mutants resistant to SDHI and quinone outside inhibitors fungicides were studied using qPCR assays. The experiments demonstrated that the use of anilinopyrimidine and demethylation inhibitors fungicides in the same program reduced the frequency of these mutations in Alternaria populations. The qPCR methods developed and used in this study can be used to track resistance levels in the pistachio orchards on a large scale.

Nut factors associated with navel orangeworm, Amyelois transitella (Lepidoptera: Pyralidae) damage to pistachio (Pistacia vera) in California (2007-2017) and implication for control.

Amyelois transitella is the primary pest of pistachios in California. The first A. transitella outbreak of the twenty-first century occurred in 2007 and a total of five outbreaks occurred between 2007 and 2017 (total insect damage >1%). This study used processor information to identify the nut factors associated with the outbreaks. Processor grade sheets were used to explore the relationship between the variables time of harvest, percent nut split, percent nut dark staining, percent nut shell damage, and percent adhering hull for Low Damage (82,537 loads) and High Damage years, (92,307 loads). Total insect damage (±SD) for the Low Damage years averaged 0.005 ± 0.01 and in High Damage years was three times higher, 0.015 ± 0.02. In Low Damage years the strongest correlation was between total insect damage and two variables, percent adhering hull and dark stain (0.25, 0.23) while in High Damage years the correlation between total insect damage and percent dark stain was the highest (0.32) followed by percent adhering hull (0.19). The linkage of these nut factors to insect damage suggests that outbreak prevention depends on early identification of premature hull split/breakdown in addition to the traditional emphasis on treating the standing population of A. transitella.

Baseline Susceptibility and Evidence of Resistance to Acetamiprid in Gill's Mealybug, Ferrisia gilli Gullan (Hemiptera: Pseudococcidae).

Gill's mealybug, Ferrisia gilli (Gullan) (Hemiptera: Pseudococcidae), is a major pest of pistachio in California. Insecticide treatment is the primary control method and acetamiprid is widely used to control this pest. However, there have been numerous reports of control failures for F. gilli after field applications of recommended insecticides in recent years. The purpose of this study was to develop a method for routine monitoring of F. gilli susceptibility and quantify current levels of F. gilli susceptibility to acetamiprid. A leaf-dip bioassay method using lima bean leaves was established and baseline susceptibility responses of 5 field populations were determined. Lethal concentrations to kill 50% of population (LC50) for second instar nymphs at 48 h ranged from 0.367 to 2.398 µg(AI)ml-1 of acetamiprid. Similarly, lethal concentrations to kill 90% of population (LC90) for second instar nymphs at 48 h ranged from 2.887 to 10.752 µg(AI)ml-1 of acetamiprid. The F. gilli population collected from Hanford area showed up to 6.5-fold significantly decreased mortality to acetamiprid compared to other populations. The resistance identified in this study, although relatively low, indicates that there has been repeated pressure to select for acetamiprid resistance and resistance levels can further magnify if effective management steps are not taken. The baseline susceptibility established in this study can be used to investigate potential cause of recent acetamiprid failures against F. gilli. In the long-term, results of this study will support the development of resistance management strategies by monitoring shifts in the susceptibility of F. gilli populations.

Diel Periodicity in Males of the Navel Orangeworm (Lepidoptera: Pyralidae) as Revealed by Automated Camera Traps.

Navel orangeworm, Amyelois transitella (Walker), is a key pest of walnuts, pistachio, and almonds in California. Pheromone mating disruption using timed aerosol dispensers is an increasingly common management technique. Dispenser efficiency may be increased by timing releases with the active mating period of navel orangeworm. Past work found that the peak time of sexual activity for navel orangeworm females is 2 h before sunrise when temperatures are above 18°C. Inference of male responsiveness from data collected in that study was limited by the necessity of using laboratory-reared females as a source of sex pheromone emission to attract males and the inherent limitations of human observers for nocturnal events. Here we used camera traps baited with artificial pheromone to observe male navel orangeworm mating response in the field over two field seasons. Male response to synthetic pheromone exhibited diel patterns broadly similar to females, i.e., they were active for a brief period of 2–3 h before dawn under summer conditions and began responding to pheromone earlier and over a longer period of time during spring and fall. But contrary to the previous findings with females, some males were captured at all hours of the day and night, and there was no evidence of short-term change of pheromone responsiveness in response to temperature. Environmental effects on the response of navel orangeworm males to an artificial pheromone source differ in important ways from the environmental effects on female release of sex pheromone.

First Report of Phytophthora parsiana Causing Crown and Root Rot on Guayule in the United States.

Guayule (Parthenium argentatum A. Gray) is a perennial shrub plant (approximately 50 cm in height) cultivated in the southwestern United States. It produces natural low-allergenic latex, resins and high-energy biofuel feedstock. During August 2021, a crown and root rot disease was observed on 2-year-old plants of direct-seeded guayule cultivar 'Az 2' in research plots located in Pinal county, Arizona, where a record 36 cm of rainfall fell during monsoon season. Symptoms included yellowing of leaves, wilting, and plant death. Average disease incidence was 16%. Isolation from necrotic crown and root tissues on 10% clarified V8-PARP (Jeffers and Martin 1986) yielded Phytophthora-like colonies. Three isolates were subcultured on V8 agar and chlamydospores and hyphal swellings were abundant in 2-week-old cultures. All three isolates produced abundant noncaducous and nonpapillate sporangia ranging from 33 to 54 μm × 20 to 39 μm (average 45.5 × 28.5 μm, n = 20) in soil water extract solution. Isolates did not produce oospores after 2 weeks on carrot agar at 20°C in the dark. Isolates had optimum vegetative growth at 30 oC and grew well at 35 oC. There was no growth at 5 and 40 oC. Genomic DNA was extracted from the mycelia of three isolates using DNeasy Plant Pro Kit (Qiagen Inc., Valencia, CA) according to the manufacturer's instructions. The internal transcribed spacer (ITS) region of rDNA, mitochondrially encoded cytochrome c oxidase 1 (cox 1) gene, and beta-tubulin (β-tub) gene were amplified with primers ITS1/ITS4 (White et al., 1990), COXF4N/COXR4N and TUBUF2/TUBUR1 (Kroon et al., 2004) and the resulting 3 amplicons were sequenced (GenBank Accession No. OK438221, OK484426, and OK484427). A BLASTn search of 811-bp amplicon (OK438221) revealed 99% match (762/766) with ITS sequences MG865562 which was Phytophthora parsiana Ex-type CPHST BL 47 from Iran. BLAST analysis of the 867-bp amplicon (OK484427) showed 99% identity (866/867) with the COX 1 sequence of P. parsiana (KC733455) from Virginia. BLAST analysis of the 941-bp amplicon (OK484426) showed 99% identity (928/938) with the β-tub sequence of P. parsiana (AY659746). To fulfill Koch's postulates, pathogenicity tests were conducted twice on 2-week-old 'Az 2' guayule seedlings grown in 10 plants per 1.9-liter pot filled with a steam-disinfested potting mix. Pots were placed in a plastic container and watered three times a week by flooding, to create waterlogged conditions. Plants were maintained in a greenhouse with 12 h day/12 h night (15-28 oC) and fertilized weekly with a 20-20-20 fertilizer at 1mg/ml. Fifty plants in 5 pots were challenged with a P. parsiana isolate by drenching each pot with 50 ml of a 1×105 zoospore/ml suspension. Fifty plants in 5 pots, serving as a control, received each 50 ml of distilled water. Symptoms of wilting, root rot, and plant death were observed 1 week afterward in inoculated plants, whereas control plants remained asymptomatic. P. parsiana was reisolated from necrotic roots of inoculated plants but not from control plants. To our knowledge, this is the first report of crown and root rot in guayule caused by P. parsiana in Arizona. P. parsiana is a species known for causing root rot on woody plants such as pistachio in California (Fichtner et al., 2016) and Iran (Mostowfizadeh-Ghalamfarsa et al., 2008). Arizona is home of desert woody guayule plant. P. parsiana may represent a significant barrier to commercialization of guayule for rubber in low desert areas of Arizona. The origin, distribution, and virulence of the pathogen on Arizona guayule is currently unknown. Disease resistance evaluation may help identify resistance in guayule germplasm that are useful in breeding for resistant cultivars.

Comparative Life History Parameters of Three Stink Bug Pest Species.

California pistachios are threatened by several stink bug species (Hemiptera: Pentatomidae), including the native Thyanta pallidovirens (Stål) and Chlorochroa uhleri (Stål), as well as the invasive Nezara viridula (L.). In pistachio, control tactics often target specific life stages, which makes knowledge about life histories fundamental to successful IPM programs. For that purpose, life history parameters of these stink bug species were assessed. Nymphal development and survivorship at seven constant temperatures, upper and lower development thresholds, thermal constants, adult longevity and fecundity, and life table parameters were evaluated. No species completed development at 15°C or 35°C. For N. viridula, egg to adult development was fastest at 30°C, whereas for T. pallidovirens there was no significant difference between 27.5 and 30°C and C. uhleri development was similar between 25 and 30°C. Egg to adult survival was highest at 22.5°C and 27.5°C. The thermal requirements as degree-days (DD) to complete immature development were estimated to be 714.3, 370.4, and 434.8 for C. uhleri, T. pallidovirens, and N. viridula, respectively. For C. uhleri, life table calculations produced a value of 56.7 d for mean generation time (To), 24.89 for net reproductive rate (Ro) and 0.057 for the intrinsic rate of increase (r). Thyanta pallidovirens had a To of 39.9 d, a Ro of 81.10 and a r of 0.11. The results are discussed with respect to the improvement of IPM in California pistachios, and the information presented may contribute to the control of these pest species in other ecosystems.

An Experimental Study and Mathematical Modeling of Vibration Transfer in Pistachio Trees Using an Inertia-Type Trunk Shaker and Field-Adapted Wireless Sensors

Trunk shakers are the most widely used mechanical harvesting machines for harvesting nut trees, including pistachio in California. Improvement of these machines requires a better understanding of the shaking dynamics of the existing trunk shakers during harvest. In this study, the effects of four different shaking patterns on three sizes of pistachio trees of different ages, shapes, and sizes were investigated under field conditions. The vibration acceleration of the real pistachio tree was measured using a wireless network of 3-axis accelerometers installed on the shaker head and different parts of the trees during the shaking harvest. Changes in acceleration and the effect of tree morphology on the magnitude of acceleration in each pattern are presented and discussed. A new location index λ, which is based on the distance of the sensor from the shaking point and diameter of the branch at each sensor location, is introduced. This study focused on mathematical modeling of the variation and distribution of the acceleration throughout the tree canopy. The sensor location index, relative force ratio (RFR), and relative kinetic energy ratio (RKER) were defined to better understand the energy damping in each part of the tree. The results showed that the relationship between the acceleration peaks and the sensor location index could be expressed by a third-degree polynomial function with an acceptable coefficient of determination. Under different shaking patterns, similar changes in the RFR of the tree at different locations and for different trees were observed. This finding indicates that the vibration force is significantly damped as the distance from the shaker clamps increases. However, the RKER values at the same shaking pattern result in different effects at different points on the branches according to tree morphology.

Evaluating Flight Performance of Mass-Reared and Irradiated Navel Orangeworm (Lepidoptera: Pyralidae) for Sterile Insect Technique.

Navel orangeworm (Pyralidae: Amyelois transitella) is a key pest of almonds and pistachios in California. Moths directly infest nuts which leads to reduced crop yield and quality, and infestation can predispose nuts to fungal pathogens that produce aflatoxins. While several integrated pest management strategies have been developed for A. transitella, studies have recently been initiated to explore the use of sterile insect technique (SIT) as an additional control tool. Mass-rearing, sterilization, and transportation methods originally developed for Pectinophora gossypiella (Lepidoptera: Gelechiidae) are currently being used for production of A. transitella in a mass-rearing facility, but the impacts of these processes on performance of A. transitella remain unclear. In this study, computerized flight mills were used to evaluate multiple flight parameters of mass-reared and irradiated A. transitella males and females relative to non-irradiated mass-reared moths and two strains of locally reared moths which were neither mass-reared nor irradiated. Mass-reared non-irradiated females performed similarly to both strains of locally reared females, flying a mean 9.4-11.8 km per night, whereas mass-reared and irradiated males and mass-reared non-irradiated males all flew shorter distances, in the range of 3.0-6.7 km per night. All of the mass-reared moths compared to locally reared moths had significantly more non-fliers that did not engage in more than two minutes of continuous flight. Findings from this study suggest that mass-rearing conditions reduce A. transitella flight capacity, while irradiation interacts with moths in a sex-specific manner.

Quantification of the Aflatoxin Biocontrol Strain Aspergillus flavus AF36 in Soil and in Nuts and Leaves of Pistachio by Real-Time PCR.

The species Aspergillus flavus and A. parasiticus are commonly found in the soils of nut-growing areas in California. Several isolates can produce aflatoxins that occasionally contaminate nut kernels, conditioning their sale. Strain AF36 of A. flavus, which does not produce aflatoxins, is registered as a biocontrol agent for use in almond, pistachio, and fig crops in California. After application in orchards, AF36 displaces aflatoxin-producing Aspergillus spp. and thus reduces aflatoxin contamination. Vegetative compatibility assays (VCAs) have traditionally been used to track AF36 in soils and crops where it has been applied. However, VCAs are labor intensive and time consuming. Here, we developed a quantitative real-time PCR (qPCR) protocol to quantify proportions of AF36 accurately and efficiently in different substrates. Specific primers to target AF36 and toxigenic strains of A. flavus and A. parasiticus were designed based on the sequence of aflC, a gene essential for aflatoxin biosynthesis. Standard curves were generated to calculate proportions of AF36 based on threshold cycle values. Verification assays using pure DNA and conidial suspension mixtures demonstrated a significant relationship by regression analysis between known and qPCR-measured AF36 proportions in DNA (R2 = 0.974; P < 0.001) and conidia mixtures (R2 = 0.950; P < 0.001). Tests conducted by qPCR in pistachio leaves, nuts, and soil samples demonstrated the usefulness of the qPCR method to precisely quantify proportions of AF36 in diverse substrates, ensuring important time and cost savings. The outputs of this study will serve to design better aflatoxin management strategies for pistachio and other crops.

Microclimate Engineering for Climate Change Adaptation in Agriculture: The Case of California Pistachios

Can farmers adapt to climate change by altering effective weather conditions on their fields? Existing technologies allow farmers to cool down plants by a few degrees during critical periods, reducing the damage from excess heat. With nonlinear effects of high temperatures on yields, slight cooling can bring significant gains in many crops. We call this approach “microclimate engineering” (MCE) and note that it could be useful as a climate change adaptation concept. Our case study deals with California pistachios, threatened by warming daytime temperatures in the winter. A new solution for sunlight reflection, based on products already used in other contexts and crops, could potentially help deal with this challenge. We develop a model to analyze grower choice and market outcomes with MCE for California pistachios. The expected increase in welfare for the period of 2020–2040 is assessed at 0.49–1.42 billion dollars under several scenarios. Simulation results show increases in consumer surplus and total welfare when MCE is available but decreases in aggregate grower profits. We also introduce market power to test its potential effects on the gains from MCE, finding mixed effects.

Evaluating Response of Mass-Reared and Irradiated Navel Orangeworm, Amyelois transitella (Lepidoptera: Pyralidae), to Crude Female Pheromone Extract.

Simple SummaryThe navel orangeworm is an important pest of almonds and pistachios in California. Sterile insect technique (SIT) is being explored as an additional component of management of this pest. Preliminary field releases of sterile navel orangeworm shipped from a facility in Phoenix, AZ resulted in poor recovery of males in pheromone traps, raising concerns about the mass-reared male moths’ quality. In this study, a wind tunnel was used to evaluate the response of irradiated and non-irradiated mass-reared navel orangeworm males to pheromone extract from females, and their performance was compared to two strains of locally reared non-irradiated navel orangeworm. Initial responses were similar for all moths tested. A lower proportion of mass-reared moths contacted the pheromone source. The underlying mechanism for this reduction remains unclear, but is likely related to damage incurred during the mass-rearing and shipping process. Our findings indicate navel orangeworm in the current program is generally competent to locate a sex pheromone source, but the rearing and transportation protocols may need refining.The navel orangeworm, Amyleois transitella (Lepidoptera: Pyralidae), is a key pest of almonds and pistachios in California. Larvae directly feed on nuts, reducing quality and yield, and adults can introduce fungi that produce aflatoxins. The development of sterile insect technique (SIT) is currently being explored as a management tool for this pest. Large quantities of A. transitella are mass-reared, irradiated, and shipped to California from a USDA APHIS facility in Phoenix, AZ. Preliminary field releases of sterile A. transitella from this facility resulted in poor recovery of males in pheromone traps, raising concerns that mass-reared male A. transitella may not be responding to pheromone from virgin females. In this study, a wind tunnel was used to evaluate the response of both irradiated and non-irradiated mass-reared A. transitella males to crude pheromone extract from females, and their performance was compared to two strains of locally reared non-irradiated A. transitella. While initial responses associated with pheromone detection where similar between mass-reared and locally reared moths, a lower proportion of the mass-reared moths ultimately made contact with the pheromone source. Surprisingly, the addition of irradiation did not further decrease their performance. While mass-reared moths respond to pheromone, their ability to locate and make contact with the pheromone source appears to be impeded. The underlying mechanism remains unclear, but is likely related to damage incurred during the mass-rearing and shipping process.