California Pistachio Research Articles

New navel orangeworm sanitation standards could reduce almond damage

The navel orangeworm (NOW), a primary pest of almonds and pistachios in California, is controlled in part by sanitation, with a current threshold of two mummy nuts or fewer per tree. However, almond and pistachio acreage has increased dramatically since the tree mummy threshold was established. This study addresses the impact of this expansion and the possible need for a more stringent standard. Beginning in 2002, the Paramount Farming Company conducted a series of large-scale studies reevaluating the current tree mummy threshold in almond orchards, as well as the impact of ground mummies and proximity to pistachio orchards. The data supports a more stringent threshold of 0.2 mummies per tree. In addition, a new threshold for ground mummies of four per tree for ‘Nonpareil’ almonds is supported in Kern County, although this needs to be validated in other regions. Proximity to pistachios was an important risk factor for navel orangeworm damage of 2% or less in almonds. Likewise, the influence of pistachios extended 3 miles from the center of the 10-acre almond orchard sections in our experiments to the margin of the nearest pistachio orchard.

New pistachio varieties show promise for California cultivation

California pistachio growers have long relied on a single female (‘Kerman’) and single male (‘Peters’) cultivar. Despite their benefits, these cultivars present important production and marketing concerns. To evaluate new varieties for the pistachio industry, we conducted the first randomized and replicated pistachio variety trials in the San Joaquin Valley, where most U.S. pistachios are grown. After more than a decade of scientific evaluation, several varieties new to California (such as ‘Kalehghouchi’) or the world (such as ‘Golden Hills’) demonstrated commercial potential for the California pistachio industry and would complement the production characteristics of ‘Kerman’.

Postharvest survival of navel orangeworm assessed in pistachios

Controlling navel orangeworm, a key pistachio pest, is problematic because the moth overwinters in “mummy” nuts. After harvest, there may be more than 30,000 pistachio nuts (mummies) left behind per acre. To provide better information for winter sanitation decisions, we investigated the number of available mummies and their levels of navel orangeworm infestation from winter through early summer in California pistachio orchards. Navel orangeworm mortality was highest from late December through mid-February, and was also higher on the ground than in trees. Mortality on the ground was highest when mummies were tilled or mowed with the groundcover than when nuts were left on the raised berm. Our data indicates that, in contrast to almonds, it is more productive to focus on clearing pistachios from the ground than on removing them from trees. However, winter sanitation procedures also should be augmented in order to destroy more overwintering navel orangeworm.

Temperature-dependent development of Macrocentrus iridescens (Hymenoptera: Braconidae) as a parasitoid of the obliquebanded leafroller (Lepidoptera: Tortricidae): Implications for field synchrony of parasitoid and host

Obliquebanded leafroller (OBLR), Choristoneura rosaceana (Harris) (Lepidoptera: Tortricidae), is widely distributed in North America where it causes damage to several fruit and nut crops. Macrocentrus iridescens (French) (Hymenoptera: Braconidae) parasitizes OBLR in California pistachio orchards, but to date there is little published information on its biology or effectiveness. To determine its potential as a biological control agent, development of M. iridescens was evaluated at eight constant temperatures, ranging from 12.6 to 36.8 °C. Results show development times, from egg to adult eclosion, ranged from 115.8 to 36.5 days at 13.9 and 31.0 °C, respectively, the lowest and highest temperatures tested that permitted complete development. Fitting the data to a nonlinear model provided estimates of M. iridescens lower (9.8 °C), upper (34.3 °C), and optimal (23.7 °C) development temperatures. M. iridescens requires 625 degree-days to develop from egg to adult stage. To complement laboratory studies, OBLR and M. iridescens season-long field population dynamics were monitored in pistachio orchards, including overwintering behaviors. M. iridescens overwinters in the OBLR larva and produces one generation for each generation of the host.

Using real-time PCR to survey frequency of azoxystrobin-resistant allele G143A in Alternaria populations from almond and pistachio orchards in California

Alternaria spp. cause leaf spot of almond and Alternaria late blight of pistachio in California, and azoxystrobin is a strobilurin fungicide that has been registered for the control of these diseases. To date, only a single point mutation of G143A in cytochrome b resulting to azoxystrobin resistance in Alternaria spp. was found in California. Based on this single point mutation, a real-time PCR assay was developed to quantify the frequency of the resistant allele G143A (FA) in pathogen samples taken from orchards. Forty-one almond and pistachio orchards were arbitrarily selected in eight counties of California. Fifty leaf lesions caused by Alternaria spp. per orchard were cut to extract the fungal DNA for a real-time PCR assay to determine the FA. About 88% of 41 surveyed orchards had Alternaria spp. with FA > 0.90, while six pistachio orchards showed a FA < 0.90. Therefore, azoxystrobin-resistant Alternaria populations are predominant in almond and pistachio orchards in California, and sprays of azoxystrobin to control Alternaria diseases are not recommended in these orchards. This study shows a potential use of a real-time PCR assay to efficiently quantify the frequency of azoxystrobin-resistant Alternaria spp. from large number of samples.

Using Nutrigenomic Techniques to Determine Anti‐inflammatory Effects of Pistachio Oil in Mouse Macrophage Cells

Pistachios beneficially affect the lipid/lipoprotein profile, however, less is known about their potential anti-inflammatory effects. The present study was conducted to better understand the effects of pistachio oil (PO) on inflammation. Mouse macrophages (RAW 264.7 cells) were treated with PO (5.5 mg/ml) and gene expression microarray analyses were performed. Our results showed that a total of 43 genes were significantly regulated by PO treatment. Interferon-induced protein with tetratricopeptide repeats (Ifit) was significantly repressed (P<0.05). Ifit is a gene family induced by interferon, lipopolysaccharide (LPS) and involved in many inflammatory and immunologic processes. Plasmids with different lengths (1.5 kb, 1 kb and 0.5 kb) of 5′ flanking region of Ifit promoter upstream of the luciferase reporter gene were constructed. In the 1.5 kb construct, LPS induced Ifit promoter activity, which was decreased by treatment with either PO (−31%) or lipid extract from the PO (PE, −62%; P<0.05). The corresponding changes in expression of the 0.5 kb construct were −13% and −35%, respectively. The data suggest that pistachios decrease the expression of the inflammatory gene Ifit by affecting its transcription rate. Supported by: California Pistachio Commission

Use of Bayesian Methods to Improve Prediction of Panicle and Shoot Blight Severity of Pistachio in California

ABSTRACT Panicle and shoot blight, caused by a Fusicoccum sp., is one of the major aboveground diseases of pistachio in California. The effects of temperature, number of continuous rainy days in April and May, irrigation system, and incidence of latent infection of the Fusicoccum sp. on severity of panicle and shoot blight of pistachio leaves and fruit have been quantified previously, using data collected from 1999 through 2001. A predictive model for leaves and another model for fruit with good explanatory power were generated. In 2003 and 2004, newly collected data were used to evaluate the two models with non-Bayesian and Bayesian methods. The 95% credible (i.e., confidence) intervals of initial (before modification with non-Bayesian and Bayesian methods) and updated parameter estimates were used to investigate their prognostic validity. In 2003, the non-Bayesian analysis resulted in all parameter estimates, with the exception of cumulative daily mean temperature from 1 June until harvest, having different 95% confidence intervals than the parameter estimates of the original models. In addition, the parameter estimates for drip irrigation for the leaf infection and the parameter estimates for drip irrigation and number of continuous rainy days in April and May for fruit infection were not statistically significant. With Bayesian methods, the reestimated model parameters had overlapping 95% credible intervals with the initial estimated parameters, except for the number of continuous rainy days in April and May. When the two sets of modified parameter estimates were used to predict disease severity, statistically significant (alpha = 0.05) differences between observed and predicted disease severities were found with non-Bayesian analysis for leaf infection in three locations and with Bayesian analysis for fruit infection in one orchard. The parameter estimates were modified again at the end of the 2004 season and were all statistically significant with both non-Bayesian and Bayesian methods. Both sets of parameter estimates gave predictions that were not significantly different from observed disease severity on leaves and fruit in all monitored orchards in 2004. In summary, Bayesian methods gave more consistent results when used to update parameter estimates with new information and yielded predictions not statistically different from observed disease severity in more cases than the non-Bayesian analysis.

Potential for classical biological control of the potato bug Closterotomus norwegicus (Hemiptera: Miridae): description, parasitism and host specificity of Peristenus closterotomae sp. n. (Hymenoptera: Braconidae).

The potato bug, Closterotomus norwegicus (Gmelin) (Hemiptera: Miridae) is an introduced pest of lucerne, white clover and lotus seed crops in New Zealand and a key pest of pistachios in California, USA. Efforts were made to identify potential biological control agents of C. norwegicus in Europe. A total of eight parasitoids, including six primary parasitoids from the genus Peristenus (Hymenoptera: Braconidae) and two hyperparasitoids from the genus Mesochorus (Hymenoptera: Ichneumonidae), were reared from C. norwegicus nymphs collected in various habitats in northern Germany. With a proportion of more than 85% of all C. norwegicus parasitoids, Peristenus closterotomae (Hymenoptera: Braconidae), a new species, was the most dominant parasitoid, whereas other parasitoid species only occurred sporadically. Peristenus closterotomae did not fit in the keys to any described species and is described as new to science. Parasitism caused by P. closterotomae was on average 24% (maximum 77%). To assess the host specificity of parasitoids associated with C. norwegicus, the parasitoid complexes of various Miridae occurring simultaneously with C. norwegicus were studied. Peristenus closterotomae was frequently reared from Calocoris affinis (Herrich-Schaeffer), and a few specimens were reared from Calocoris roseomaculatus (De Geer) and the meadow plant bug, Leptopterna dolobrata (Linnaeus) (all Hemiptera: Miridae). The remaining primary parasitoids associated with C. norwegicus were found to be dominant in hosts other than C. norwegicus. Whether nymphal parasitoids may potentially be used in a classical biological control initiative against the potato bug in countries where it is introduced and considered to be a pest is discussed.

Effects of Latent Infection, Temperature, Precipitation, and Irrigation on Panicle and Shoot Blight of Pistachio in California

ABSTRACT Panicle and shoot blight, caused by a Fusicoccum sp., is an economically important disease of pistachio in California. Between 1999 and 2001, the disease severity was monitored throughout the growing season in 10 pistachio orchards, irrigated with drip, microsprinklers, low-angled (12 degrees ) sprinklers, or flood. The effect of temperature, precipitation pattern, irrigation system, and incidence of Fusicoccum sp. latent infection on panicle and shoot blight severity was quantified with a generalized linear model for repeated measures. The number of continuous rainy days in April and May and the cumulative daily mean temperatures from June to early September had a significant positive effect on panicle and shoot blight of pistachio leaves and fruit. Drip irrigation significantly decreased disease risk. Other factors, such as the number of discontinuous rainy days in April and May, the cumulative deviation from the 30-year average temperature during the dry days of April and May, the incidence of latent infection (only on leaves), and irrigation with microsprinklers or lowangled (12 degrees ) sprinklers were weak explanatory variables of panicle and shoot blight severity. Knowledge of panicle and shoot blight risk may contribute significantly to decisions regarding the appropriate application of fungicides, especially in years or fields of low risk.

Biology ofMacrocentrus iridescens(Hymenoptera: Braconidae): A Parasitoid of the Obliquebanded Leafroller (Lepidoptera: Tortricidae)

Abstract Macrocentrus iridescens French is a polyembryonic parasitoid with a wide host and geographic range in North America. In a survey of California pistachio orchards, M. iridescens was the most common parasitoid species reared from the obliquebanded leafroller, Choristoneura rosaceana Harris. To determine its potential as a biological control agent of the obliquebanded leafroller, we conducted laboratory studies and described M. iridescens immature development. We evaluated adult female longevity, brood size, sex ratio, and host stage preference for oviposition. The parasitoid egg develops polyembryonically. At 26.8°C, larval development required 25–30 d, and pupal development 10–12 d. There was a positive relationship between mandible size and development time, although individual stages could not be determined. Adult females survived on average 15.9, 1.6, and 0.9 d at 25°C when provided with honey and fructose solution, water only, or neither, respectively. Oviposition of fertilized eggs was observ...

Characterization of iprodione-resistant Alternaria isolates from pistachio in California

Alternaria late blight caused by Alternaria spp. in the alternata, tenuissima, and arborescens species-groups is one of the most common fungal diseases of pistachio in California. In this study, a field iprodione-resistant (FIR) isolate of the arborescens species-group and a laboratory-induced iprodione-resistant (LIIR) isolate of the alternata species-group were characterized by fungicide and osmotic sensitivity, virulence on detached pistachio leaflets, and sequence of the coiled-coil region (six repeats of approximately 90-amino-acid domain) of the two-component histidine kinase ( HK) gene. Both FIR and LIIR isolates were sensitive to azoxystrobin and tebuconazole, and azoxystrobin-resistant isolates were sensitive to iprodione and tebuconazole. The LIIR isolate showed more sensitivity to osmotic stress than its wild-type parent. However, the FIR isolate did not show higher osmotic sensitivity compared to field iprodione-sensitive (FIS) isolates. Laboratory inoculation tests showed that both FIR and LIIR isolates remained highly virulent on pistachio. Analysis of DNA sequences of the HK coiled-coil region showed that there were no differences in deduced amino acid sequence of this region from the LIIR, FIR, and FIS Alternaria isolates from pistachio in California.

An Allele‐specific PCR Assay for Detecting Azoxystrobin‐resistant Alternaria Isolates from Pistachio in California

AbstractAlternaria late blight caused by Alternaria spp. in the alternata, tenuissima and arborescens species‐groups is one of the most common fungal diseases of pistachio in California. A single point mutation resulting in the replacement of a glycine by an alanine at codon 143 (G143A) in the mitochondrial cytochrome b (cyt b) has been found in all azoxystrobin‐resistant isolates of these three species from California pistachio. In this study, a pair of allele‐specific polymerase chain reaction (PCR) primers was developed to detect this point mutation. The allele‐specific PCR assay coupled with a rapid DNA extraction method could detect azoxystrobin‐resistant Alternaria isolates in a few hours. The allele‐specific PCR method was also reliable for detecting azoxystrobin‐resistant Alternaria directly in both laboratory‐inoculated and naturally infected pistachio leaves.

Panicle and Shoot Blight of Pistachio: A Major Threat to the California Pistachio Industry

Introduction Pistachio cultivation dates back to the Holy Lands of the Middle East, where they grew wild in the high desert regions. The history of pistachios includes aspects of royalty, perseverance, and pride. Legend has it that lovers met beneath the trees to hear the pistachios crack open on moonlit nights for the promise of good fortune. A rare delicacy, pistachios were a favorite of the Queen of Sheba, who demanded all her land's production for herself and her court. The royal nut was imported by American traders in the 1880s, primarily for U.S. citizens of Middle Eastern origin. Some 50 years later, pistachios became a popular snack food, introduced in vending machines. These imported nuts were dyed red to draw attention and to cover stains from antiquated harvesting and drying techniques. The inception of the California pistachio industry occurred in 1929, when the American plant scientist William E. Whitehouse spent a lonely six months in Persia (Iran), collecting seed and going through piles of product to find the most distinctive pistachios. He returned with 20 pounds of seed to start a breeding program. With pistachios requiring from 7 to 10 years to mature, it was 1950 before a successful cultivar emerged from that program. The variety was named Kerman for the famous carpet-making city near where the original seed was collected by Dr. Whitehouse. University of California scientists then budded (grafted) the Kerman to more vigorous rootstocks. Thus the dream of a California pistachio industry became a reality. Word of the new crop spread, plantings expanded throughout the state in the 1960s, and the first commercial crop of 1.5 million pounds was harvested in 1976 from less than 1500 acres. By 1990, approximately 50,000 bearing acres yielded 120 million pounds, by 2000 approximately 75,000 acres yielded a total of 240 million pounds, and by 2002 a total of 300 million pounds were produced. With their acreage and production expanding, California pistachio growers united in their efforts to promote the industry. In 1981 the California Pistachio Commission (CPC) was established to provide support through public relations, marketing, and production research. By 2000, the CPC became one of the most successful agricultural industries in California. The CPC is funded by an assessment (cents) per pound of pistachios produced in the State. Pistachio is a dioecious plant with fruit drupes born in taxianthies called panicles (clusters).

Resistance to azoxystrobin in Alternaria isolates from pistachio in California

Failure to control Alternaria late blight in a few California pistachio orchards was observed after only 3–4 years of consecutive applications of azoxystrobin-based fungicide programs. A total of 72 isolates of Alternaria alternata, Alternaria tenuissima, and Alternaria arborescens, the causal organisms of Alternaria late blight, were collected from pistachio orchards with (58 isolates) and without (14 isolates) a prior history of azoxystrobin applications. The sensitivity to azoxystrobin was determined in conidial germination assays. Isolates from orchards with a history of azoxystrobin applications had EC 50 values greater than 100 μg/ml, whereas isolates from orchards without a prior history of azoxystrobin usage had EC 50 values ranging from 0.008 to 0.045 μg/ml. Azoxystrobin resistance correlated with a single mutation in the cytochrome b (cyt b) gene causing a change of glycine to alanine at amino acid position 143. A pair of PCR primers AF and AR was developed that amplified a 226-bp DNA fragment of the cyt b gene containing the mutation site from all three Alternaria species but not from 30 other fungal species frequently found on pistachio. PCR-restriction fragment length polymorphism (PCR-RFLP) analysis using the restriction enzyme Fnu4HI allowed differentiation of the PCR fragment of wild type cyt b gene from that of mutated gene. This method will aid in a fast detection of azoxystrobin resistance in these three Alternaria species.

Nested PCR Assays for Detection of Monilinia fructicola in Stone Fruit Orchards and Botryosphaeria dothidea from Pistachios in California

AbstractNested polymerase chain reaction (PCR) assays were developed based on microsatellite regions for detection of Monilinia fructicola, the causal agent of brown rot of stone fruits, and Botryosphaeria dothidea, the causal agent of panicle and shoot blight of pistachio. The nested PCR primers specific to M. fructicola were developed based upon the sequence of a species‐specific DNA fragment amplified by microsatellite primer M13. The external and internal primer pairs EMfF + EMfR and IMfF + IMfR amplified a 571‐ and a 468‐bp fragment, respectively, from M. fructicola, but not from any other fungal species present in stone fruit orchards. The nested PCR primer pairs specific to B. dothidea were developed based upon the sequence of a species‐specific 1330‐bp DNA fragment amplified by microsatellite primer T3B. The external and internal primer pairs EBdF + EBdR and IBdF + IBdR amplified a 701‐ and a 627‐bp fragment, respectively, from B. dothidea, but not from any other fungal species associated with pistachio. The nested PCR assays were sensitive enough to detect the specific fragments in 1 fg of M. fructicola or B. dothidea DNA or in the DNA from only two conidia of M. fructicola or B. dothidea. The nested PCR assays could detect small numbers of M. fructicola conidia caught on spore‐trap tapes and detect visible infections of B. dothidea in pistachio tissues. Microsatellite regions with high numbers of copies are widely dispersed in eukaryotic genomes. The results of this study indicate that microsatellite regions could be useful in developing highly sensitive PCR detection systems for phytopathogenic fungi.

First Report of Botryosphaeria rhodina Causing Shoot Blight of Pistachio in California.

In the summers of 2000 and 2001, shoot blight was observed in pistachios (Pistacia vera L.) grown in Kern County, California. Black, necrotic lesions developed at the base of shoots originating from contaminated or partially infected buds. Infection moved upward resulting in a progressive wilting and blighting of leaves. Leaf blades on infected shoots withered, and petioles became necrotic. Symptoms have been considered characteristic of infection by Botryosphaeria dothidea (Moug.:Fr.) Ces. & de Not., but this pathogen causes panicle and shoot blight of pistachio (1). However, there were no symptoms of any fruit panicle infections on trees we observed. Isolations on acidified potato dextrose agar from the base of blighted shoots in both years revealed a fast-growing fungus producing pycnidia which was identified as the anamorph Lasiodiplodia theobromae (Pat.) Griffon & Maubl. of B. rhodina Berk. & Curt. Arx. Identification of the pathogen was based on characteristic dark brown, oval pycnidiospores with striations on the surface of the spore along the long axis. Pathogenicity tests were performed on 12 Kerman pistachio trees grown at Kearney Agricultural Center, in Parlier, CA, using three isolates recovered from pistachios grown in two locations. Six to 16 current season shoots of pistachio trees (1 to 2 shoots per tree) were wounded with a 5-mm-diameter cork borer, and a mycelial plug of 5-day-old cultures of B. rhodina was inserted in each wound. Shoots were wrapped with Parafilm to prevent desiccation of inoculum. Six other shoots (one per tree) were inoculated similarly with mycelial agar plugs of a pistachio isolate of B. dothidea and served as positive controls, while six similar shoots were inoculated with only agar plugs and served as negative controls. Wilting of lower leaves in the majority of inoculated shoots started within 4 days for B. rhodina and 7 days for B. dothidea. Depending on the isolate of B. rhodina, 1 to 5 shoots and 50 to 80% of leaves were blighted within 7 days after inoculation. All inoculated shoots were left on the trees until 3 to 4 months after inoculation, pruned and assessed again. For inoculations done in September 2001, 33 to 71% of shoots were blighted, and the rest had cankers ranging from 22.5 to 28 mm long and 13.5 to 23.5 mm wide. A majority (67 to 100%) of shoots had pycnidia of the pathogen present. For inoculations done in October 2001, none of the shoots was blighted, but cankers ranged from 5 to 55.4 mm long and 6 to 22 mm wide and 33.3 to 100% developed pycnidia. B. rhodina was isolated from all inoculated shoots but not from negative controls or those inoculated with B. dothidea. Inoculations of shoots with B. dothidea produced similar symptoms as those of B. rhodina. Shoots that served as negative controls did not develop symptoms. Because panicle and shoot blight of pistachio caused by B. dothidea has developed to epidemic levels in commercial pistachio orchards and is of concern to the pistachio industry in California, it would be of interest to monitor how much shoot blight caused by B. rhodina would eventually develop over the years in commercial pistachio orchards. A survey was initiated in 2002 to determine how widespread B. rhodina is in California pistachios. To our knowledge, this is the first report worldwide of B. rhodina causing shoot blight of pistachio. Reference: (1) T. Michailides. Panicle and shoot blight. Page 68 in: Compendium of Nut Crop Diseases in Temperate Zones. B. L. Teviotdale, T. J. Michailides, and J. W. Pscheidt, eds. American Phytopathological Society, St. Paul, MN 2002.

CALIFORNIA PISTACHIO ROOTSTOCKS EVALUATIONS

CALIFORNIA PISTACHIO ROOTSTOCKS EVALUATIONS

A PCR-based Technique for Identification of Fusicoccum sp. from Pistachio and Various Other Hosts in California.

Botryosphaeria panicle and shoot blight of pistachio, caused by Fusicoccum sp. is a destructive disease in California. In this study, a pair of group-specific polymerase chain reaction (PCR) primers BDI and BDII, was developed for identification of Fusicoccum sp. from pistachio and other hosts in California based on the sequences of the rDNA internal transcribed spacer (ITS) region. The primers amplified a 356-bp DNA fragment for all 73 tested isolates of Fusicoccum sp. collected from pistachio and other hosts throughout California in different years, but not for the other 33 fungal species isolated from pistachio and the eight isolates of Fusicoccum sp. obtained from pistachio trees in Greece. The PCR assay using this pair of primers was sensitive enough to detect 5 pg of genomic DNA of Fusicoccum sp. A simple DNA extraction procedure was developed that led to the rapid identification of Fusicoccum sp. from pistachio and other host plants in California.

Characterization of Botryosphaeria dothidea Isolates Collected from Pistachio and Other Plant Hosts in California

ABSTRACT Eighty-six isolates of Botryosphaeria dothidea, the causal agent of Botryosphaeria panicle and shoot blight of pistachio, were collected from pistachio and other plant hosts in California. The isolates were characterized by microsatellite-primed polymerase chain reaction (MP-PCR), sequences of the nuclear ribosomal DNA internal transcribed spacer region (ITS1, 5.8S gene, and ITS2), morphological and cultural characters, osmotic and fungicide sensitivity, and pathogenicity on pistachio. Three groups of these isolates were identified based upon analysis of MP-PCR data and ITS sequences. Group I contained 43 pycnidiospore-derived isolates collected from pistachio and other hosts. Group II consisted of 20 ascosporic isolates obtained from a single sequoia plant. Group III consisted of 20 ascosporic isolates from three shoots on a single blackberry plant, two pycnidiospore-derived isolates from incense cedar, and one from pistachio. Group I predominated over the other two groups in California pistachio orchards. B. dothidea isolates of group III grew faster on acidified potato dextrose agar (APDA) than the isolates of groups I and II. Isolates of group III produced pycnidia on both APDA and autoclaved pistachio shoots, but the isolates of the other two groups produced pycnidia on only autoclaved pistachio shoots. Additionally, significant differences in osmotic and fungicide sensitivities were observed among these three groups. Results from lathhouse inoculations demonstrated that the representative isolates for each of the three groups were all capable of infecting pistachio and producing characteristic disease symptoms of Botryosphaeria blight. The virulence of group II isolates on pistachio was, however, significantly lower than that of group I isolates.

Sensitivity of Botryosphaeria dothidea from California pistachio to tebuconazole

Botryosphaeria blight of pistachio, caused by Botryosphaeria dothidea, is a devastating disease in California. Baseline sensitivity of B. dothidea to tebuconazole (Elite ®) was determined using 105 wild-type single-spore isolates collected in 1999 and 2000 from a commercial pistachio orchard without a previous history of fungicide exposure in Glenn County, California. The 50% effective concentration (EC 50) values of tebuconazole for these 105 isolates ranged from 0.019 to 0.159 μg/ml, and the mean EC 50 was 0.080 μg/ml. In 2000, 277 single-spore isolates were collected from a fungicide trial orchard with 4 years of multi-sprays of tebuconazole in Glenn County, California. The EC 50 values of these 277 isolates ranged from 0.037 to 0.291 μg/ml. The mean EC 50 (0.099 μg/ml) of these 277 isolates was significantly higher ( F=62.2, P<0.0001) than that of wild-type isolates. The isolate PB22 from the fungicide trial orchard showed reduced-sensitivity to tebuconazole with an EC 50 of 0.291 μg/ml significantly higher ( F=114.21, P<0.0001) than those of 381 other tested isolates. PB22 also showed low sensitivity to propiconazole and benomyl. PB22 retained relatively high virulence on pistachio, but the efficacy of tebuconazole in controlling PB22 was not significantly different from that its efficacy against sensitive isolates.