Pistachio Fruit Research Articles

Association of Botryosphaeria Panicle and Shoot Blight of Pistachio with Injuries of Fruit Caused by Hemiptera Insects and Birds.

Panicle and shoot blight of pistachio caused by species of Botryosphaeriaceae fungi remains one of the major diseases of pistachio in California, with the highest potential for crop destruction because buds and fruit clusters (panicles) are killed. Pistachio fruit can also be damaged by various insect pests. For instance, hemipteran insects are considered major pests of pistachio and can attack maturing fruit, causing necrotic areas on the fruit epicarp (epicarp lesion). Surveys in pistachio orchards showed a putative association of punctures of pistachio fruit with infection by Botryosphaeriaceae fungi, resulting in panicle and shoot blight. This study was undertaken to determine any association of Botryosphaeriaceae fungi with fruit bearing epicarp lesions and whether hemipteran insects can actively carry propagules of the pathogens to healthy fruit and cause disease. Three large insects of the order Hemiptera (Thyanta pallidovirens, Acrosternum hilare, and Leptoglossus clypealis) were used in pathogen-spread and infection experiments. The most frequently isolated species of the family Botryosphaeriaceae in pistachio, Neofusicoccum mediterraneum, was used in these transmission experiments. Significantly higher incidence of fruit infected by N. mediterraneum was recorded when pistachio clusters were sprayed with a spore suspension of N. mediterraneum and caged with the above insects than the level of infected fruit sprayed similarly with the pathogen but caged without any insects. Furthermore, increasing the number of insects caged with pistachio clusters resulted in an increase of insect feeding punctures and, subsequently, disease incidence. Similarly, increasing the number of wounds per fruit made with a needle, simulating injuries caused by the insect's stylet, resulted in significantly higher incidence of infected fruit than for wounded fruit with fewer injured sites. In addition, bird-injured fruit were also associated with higher incidence of panicle blight than fruit not injured by birds, especially in orchards with high disease incidence. In laboratory experiments, wounding or applying fruit sap to nonwounded fruit resulted in significantly higher incidence of infected fruit than in nonwounded fruit without sap. In field experiments, wounding of fruit before or after inoculation with N. mediterraneum resulted in higher disease incidence than nonwounded and inoculated fruit. Additionally, fruit sap enhanced initial mycelial growth of N. mediterraneum. Protecting fruit clusters from injuries by hemipteran insects or birds using mesh cages significantly reduced the incidence of panicle and shoot blight. The association of wounding by hemipteran insects and birds with high incidence of infected pistachio fruit may explain partially the broad distribution of Botryosphaeria panicle and shoot blight among pistachio orchards of the central San Joaquin Valley, even in areas where inoculum sources are not nearby.

Enzyme Activity, Cold Hardiness, and Supercooling Point in Developmental Stages of Acrosternum arabicum (Hemiptera: Pentatomidae).

Several species of pentatomid bugs feed on pistachio fruits in Iran. Acrosternum arabicum Wagner (Hemiptera: Pentatomidae) is one of the most important pests of pistachio in Rafsanjan, Iran. This study was carried out to investigate the carbohydrase activities, supercooling points, and cold hardiness profiles of different developmental stages of A. arabicum under laboratory conditions. The midgut amylolytic of A. arabicum showed an optimal pH at 7.0. The highest amylolytic activity was found in the female adults (35.41 ± 0.90 nmol/min/gut). The mean amylolytic activity measured in first instar nymph was 6.75 ± 0.54 nmol/min/gut. Midgut α- and β-glucosidase showed an optimal activity at pH 5 and 7, respectively. These activities increased from first (83 ± 5 and 54 ± 5 nmol/min, respectively) to fifth (881 ± 17 and 237 ± 14 nmol/min, respectively) instar nymphs. The enzyme activities increased in the adults. Midgut α- and β-galactosidase showed an optimal activity at pH 5. α- and β-galactosidase activities were low in the first instar nymphs (73 ± 5 and 21 ± 3 nmol/min, respectively). The level of α- and β-galactosidase activities in the female adults (533 ± 18 and 246 ± 6 nmol/min, respectively) was higher than the nymphs. The lowest super cooling points (−19 and −18.2 °C, respectively) and the highest cold hardiness (22 and 18% following 24 h exposure at − 20 °C, respectively) were recorded for the eggs and adult females.

Demography of pistachio fruit hull borer moth, Arimania komaroffi (Lepidoptera: Pyralidae) under different constant temperatures

Recently, the pistachio fruit hull borer moth, Arimania komaroffi Ragonot (Lepidoptera: Pyralidae) has been emerged as a major pest of pistachio in Iran. Temperature is the most effective ecological factors on demography and life cycle of arthropods. The effect of temperature on the reproduction and population growth parameters of this pest was investigated in current study. Experiments were conducted at four constant temperatures 25, 27.5, 30 and 32.5 (±1) °C, on Ohadi cultivar in the laboratory. Based on the results, the immature development times were calculated as 56.37±0.53, 47.72±0.70, 42.03±0.39 and 39.10±0.46days at 25, 27.5, 30 and 32.5°C, respectively. The highest net fecundity rate was 25.34 eggs/female at 27.5°C, although no significant difference was observed between 27.5 and 30°C. Mean daily number of eggs laid by a female was the greatest at 30°C. The gross reproductive rate (GRR) and net reproductive rate (R0) of A. komaroffi were higher at 30 and 27.5°C. The highest intrinsic rate of increase (rm) was calculated as 0.056 at 30°C. Similarly no significant difference was observed in rm values between 27.5 and 30°C. The higher finite rates of increase (λ) ware achieved at 27.5 and 30°C. The longest mean generation time (T) was 59.9days at 25°C. Pest generation time decreased significantly with increasing temperature from 25°C to 30°C. Regarding the results, development and population increase of A. komaroffi at 27.5 and 30°C were more rapidly performed and this knowledge could be valuable in its monitoring and control.

Effects of Chitosan and Aloe Vera Gel Coating on Quality Characters of Pistachio

Iran is one of the largest pistachio producer and exporter in the world. Under unfavorable conditions during storage, pistachio quality will be reduced due to undesirable reactions. The objective of the present study was to evaluate the ability of Aloe vera gel to reduce/control the loss of post harvest fresh pistachio quality, compare with a natural polysaccharide-chitosan, as an established coating material with antifungal activity. Freshly harvested pistachio fruits were coated with A. vera gel (100% and 50%), chitosan (0.05% and 0.5%) and control (water). The coated and uncoated pistachio was stored at 4o RH for 1 month. The parameters analyzed included physiological water conservation (PWC), sensory analysis for pistachio quality (colour and marketability), degree of spoilage, and Peroxide value of oil extracted from them. Results indicate that chitosan and A. vera gel are potential candidates to preserve post-harvest quality of pistachio; either showed that for coating of pistachio, chitosan 0.05% is better than other coating; that followed by A. vera gel 50% and Chitosan 0.5% coating, and A. vera gel 100% is undesirable for coating of pistachio.

ALTERNARIA BLIGHT INFECTIONS OF PISTACHIO FRUITS IN THE SOUTHEASTERN ANATOLIA REGION OF TURKEY

Pistacia vera L. is an important crop species in the Southeastern region of Turkey. Alternaria blight disease caused by Alternaria spp. has become epidemic for the last couple of years. Disease symptoms mainly develop on young fruits and infections continue until harvest. Repeated infections decrease fruit quantity and quality that in turn reduce the yield. Pistachio fruits with Alternaria blight symptoms were collected during 2010-2011 growing seasons. Infected fruits were sampled from Adiyaman, Gaziantep, Sanliurfa, Mardin, Kahramanmaras and Siirt provinces where large pistachio plantations are located. Sampling and pathogen isolations were started in April just after pollination and fruit set, and continued until October, which is the harvest time of pistachio in the Southeastern Anatolia region. Isolates obtained from tissues infected with Alternaria blight were characterized morphologically and analyzed with DNA sequences, the nuclear internal transcribed spacer region, ITS and allergen regions, ALT, for molecular confirmation. Twenty-three Alternaria spp. isolates were obtained and subjected to pathogenicity analysis on ‘Ohadi’ pistachios. All the Alternaria spp. isolates caused blight symptoms on mature pistachio fruits. Four isolates were found to be highly pathogenic and there was difference among isolates in virulence levels. One highly virulent isolate was used to test reactions of ‘Uzun’, ‘Ohadi’ and ‘Siirt’ cultivars under field conditions, and ‘Uzun’ was found to be the most tolerant cultivar followed by ‘Siirt’ and ‘Ohadi’.

Effects of salicylic acid onAspergillus flavusinfection and aflatoxin B1accumulation in pistachio (Pistacia veraL.) fruit

One of the most important saprophytic infections in fresh pistachio fruits after harvesting is Aspergillus flavus colonization, which significantly reduces fruit quality. Salicylic acid plays a crucial role in plant tissues and has a suppression effect on some fungi. The inhibitory effect of salicylic acid on the growth of A. flavus was assessed in vitro and in vivo. For this purpose, seven concentrations (0, 1, 3, 5, 7, 9 and 11 mmol L(-1)) of salicylic acid were used in both experiments. Also, aflatoxin B1 contents of the samples were analysed using immunoaffinity chromatography. The results obtained from in vitro experiments showed that salicylic acid significantly reduced Aspergillus growth at all concentrations, and at 9 mmol L(-1) growth was completely suppressed. In vivo evaluation showed relatively high levels of inhibition, though the intact treated fruits as compared with the injured treated fruits demonstrated higher inhibitory effects. Regarding the inhibitory effects of salicylic acid on the control of A. flavus contamination, its application on pistachio fruits after harvesting could be a promising approach to control the fungus infection and reduce aflatoxin production in treated fruits.

Effects of pyriproxyfen on some physiological aspects of the pistachio fruit hull borer, Arimania comaroffi Ragonot, pupae

The pistachio fruit hull borer, Arimania comaroffi (Lepidoptera: Pyralidae) is one of the minor pests of pistachio orchards. This pest passes the winter as pupae in silken cocoons in soil beside pistachio trees. In this study, effects of insect growth regulator pyriproxyfen were investigated on some physiological aspects of the pest by measuring glycogen, total sugar, lipid, protein, low-molecular-weight carbohydrates (trehalose and glucose) and polyols (sorbitol and myo-inositol) contents of the pupal body. Last larval instar was treated with 1 μl of the pesticide, and the effects on pupae were measured after one week. Glycogen content in treatment with 3.11 mg/g fresh body weight was significantly different from control with 8.51 mg/g fresh body weight, but no significant differences in protein and lipid contents (p > 0.05) were observed. Glucose content in treated pupae with 1.50 mg/g fresh body weight was significantly different from control with 2.99 mg/g fresh body weight. Trehalose and sorbitol contents in treated pupae with 0.52 and 0.04 mg/g fresh body weight, respectively, were significantly lower than control with 2.07 and 1.5 mg/g fresh body weight, while there were no significant differences in glucose and myo-inositol contents between treated and control pupae.

Biochemical characterisation of digestive proteases and carbohydrases of the pistachio fruit hull borer, Arimania komaroffi Ragonot (Lepidoptera: Pyralidae)

Pistachio fruit hull borer, Arimania komaroffi Ragonot (Lep.: Pyralidae), is one the most important pests of pistachio in Iran. The larvae spin web as well as bore into young fruits, and the infested fruits fall off the trees. The second-generation adult moths appear in August and September, and their offspring feed on the fruit hull. Results indicated the presence of α-amylase, α-glucosidase, β-glucosidase, α-galactosidase, β-galactosidase and some proteases in the digestive tract of the pest. Highest activities of α-amylase, α-glucosidase, β-glucosidase, α-galactosidase and β-galactosidase were at pH 10, 7, 7, 6 and pH 6, respectively. Highest activities of trypsin, chymotrypsin and elastase of larval midgut were at pH 11. Zymogram analysis of α-amylase, α-glucosidase, β-glucosidase, tryptic, chymotryptic and elastase using native-PAGE revealed 1, 1, 2, 3, 3 and 2 bands of activity respectively, in A. komaroffi. One band was disappeared in the presence of the inhibitor TLCK, but no further inhibition by the inhibitors TPCK was observed. The results can be of help for designing new strategies for controlling the pistachio fruit hull borer based on natural proteases and carbohydrase inhibitors.

Effect of different rootstocks on PAL activity and phenolic compounds in flowers, leaves, hulls and kernels of three pistachio (Pistacia vera L.) cultivars

Phenylalanine ammonia-lyase (PAL) is a biochemical marker of environmental stress and plays a pivotal role in phenolic synthesis. Lower ROS levels and oxidative damage were observed in grafted plants; moreover, the rootstocks have a profound influence on the biochemical composition, especially of phenolic compounds. Regarding the importance of the effect rootstocks have on scion in pistachio trees, this study was carried out to assess and compare three pistachio cultivars (Ahmadaghaii, Ohadi and Kallehghuchi) on four rootstocks (Mutica, Ahli, Sarakhs and Atlantica). PAL activity, phenolic compounds, and flavonoid and anthocyanin contents in leaves, flowers and fruits were measured for the selection of the most suitable and compatible rootstock/scion resistant to environmental stresses. The results showed that PAL activity was different among the cultivars and organs. A positive correlation was observed between PAL activity and phenolic compounds in the leaves and flowers of Mutica-Ahmadaghaii, suggesting that it was more resistant than the others to environmental stresses. PAL activity and total phenolics in pistachio fruits suffered a decrease when the maturation processes began. The hulls of the pistachio fruits contained high levels of phenolic compounds, especially in Mutica-Ahmadaghaii, suggesting its function as a protective layer and a defense chemical against ultraviolet radiation and pathogens. Our results indicated the presence of a number of bioactive compounds in kernels with the highest amount belonging to Mutica-Ahmadaghaii. Therefore, we concluded that pistachio rootstocks mighy affect the antioxidant compounds in kernels.

Biological parameters of Elasmus nudus (Hymenoptera, Eulophidae), a parasitoid of the pistachio fruit hull borer moth, Arimania komaroffi (Lepidoptera, Pyralidae)

Elasmus nudus (Nees) is known as a synovigenic, gregarious ectoparasitoid of the pistachio fruit hull borer moth, Arimania komaroffi Ragonot in pistachio plantations in southern Iran. The biological parameters of this parasitoid were studied using the Mediterranean flour moth, Ephestia kuehniella Zeller as a host and the resulting data were compared with that of its native host, A. komaroffi. The parasitoid developed successfully from egg to adult over a temperature range of 17–35°C. The developmental times of the parasitoid on A. komaroffi and E. kuehniella were not significantly different. The threshold value at which the development rate of E. nudus was zero was estimated to be 9.2°C and the estimated number of degree days (°D) for development from egg to adult was 238 above this threshold. The reproductive potential of E. nudus was similar on both hosts at 30°C. The intrinsic rate of natural increase (r m ) for E. nudus did not vary much between 25°C and 32.5°C. In addition, the clutch size of the parasitoid on the two hosts was not statistically different. The present study provides some basic information on the biological characteristics of E. nudus.

Study on the physiology of diapause, cold hardiness and supercooling point of overwintering pupae of the pistachio fruit hull borer, Arimania comaroffi

The pistachio fruit hull borer, Arimania comaroffi (Ragonot) (Lepidoptera: Pyralidae), is a key pest of pistachio orchards in Iran. This pest passes the winter as diapausing pupae. In this study, some physiological changes in relation to environmental temperature were investigated in field collected pupae. The relationship between supercooling point, cold hardiness and physiological changes of a wild population of this pest was also investigated. The glycogen content decreased with decrease in environmental temperature. Decrease in glycogen content was proportional to increase in total body sugar, trehalose, myo-inositol and sorbitol contents. In January with mean ambient temperature of 5.4°C, glycogen (5mg/g fresh body weight) content was at the lowest level whereas total body sugar (10.3mg/g fresh body weight), trehalose (8.6mg/g fresh body weight), myo-inositol (5.3mg/g fresh body weight) and sorbitol (2.6mg/g fresh body weight) were at the highest levels. Total body sugar, trehalose, myo-inositol and sorbitol contents increased as mean temperature decreased from 22.7°C in October to 5.4°C in January. Total body lipid decreased during overwintering and reached to the lowest level at the end of March. Supercooling points were decreased from October to January and reached to the lowest level (−16°C) in January with minimum ambient temperature of −10°C. Survival at low temperature after 24h was also greatest in January with 72% survival at −10°C, 39% survival at −15°C and 0% survival at −20°C. Increase in temperature from February onward, was proportional with increase in supercooling points and decrease in survival rate. Regardless of sampling date, all pupae died after 24h at −20°C, whereas none pupae died after 24h at −5°C. This indicates that this insect is freeze-intolerant.

OCCURRENCE OF ALTERNARIA SPECIES INVOLVED IN FRUIT BLIGHT OF PISTACHIO IN TUNISIA

During summer 2007-2010, a new disease was observed on pistachio (Pistacia vera L.) cv. Mateur in several orchards of Tunisia. Symptoms on the nuts consisted of black lesions with red halos, resulting in yield losses often exceeding 20%. A fungus recovered on potato dextrose agar (PDA) from surface-disinfected symptomatic nuts, produced cottony colonies characterized by an abundant branched, brownish, septate mycelium which, with time, turned olive-green to dark olive-green due to abundant sporulation. Conidiophores were simple or branched, septate, straight or flexuous, pale olivaceous-brown, and bore several conidial scars. Conidia were 100-200 mm in size, obclavate to ellipsoid, multiseptate and formed in single or, more often, branched chains. Based on these morphological characters, the fungus was identified as Alternaria sp. (Fr.) Keissler (Ellis, 1971). Pathogenicity tests were carried out on detached fresh pistachio nuts inoculating the hull with 5 μl conidial suspensions prepared from actively growing colonies (105 conidia/ml sterile distilled water). All isolates induced symptoms similar to those observed in the field after 15 days. An Alternaria sp. was reisolated from symptomatic fruits. To identify the fungus at the species level, the ITS1-5.8S-ITS2 region was amplified with primers ITS1 and ITS4 (White et al., 1990) and the amplicons were directly sequenced. A BLAST search of GenBank database revealed 99% homology with both A. alternata (accession No. HQ873733.1) and A. tenuissima (HQ916330.1). To our knowledge this is the first report of an Alternaria species of the alternata species-group, as the causal agent of pistachio fruit blight in Tunisia.

THE INVESTIGATION OF THE EFFECTS OF 17 FERTILIZERS TREATMENTS IN THE FORM OF FOLIAR APPLICATION ON QUALITATIVE CHARACTERISTICS OF PISTACHIO NUT CULTIVAR 'OUHADI'

ISHS V International Symposium on Pistachios and Almonds THE INVESTIGATION OF THE EFFECTS OF 17 FERTILIZERS TREATMENTS IN THE FORM OF FOLIAR APPLICATION ON QUALITATIVE CHARACTERISTICS OF PISTACHIO NUT CULTIVAR 'OUHADI'

English

Pistacia L. belongs to the family of Anacardiaceae. It contains nine species and five subspecies. P. vera L. (cultivated pistachio) is the economically most important species in the genus. It has edible seeds and considerable commercial importance. Iran, the United States, Turkey and Syria are the main pistachio producers in the world. Gaziantep province is the main producer and exporter of pistachio in Turkey. Samples of leaves, branches and fruits of pistachio (P. vera L.) were collected between 2009 and 2010 from different localities in Gaziantep province. Cytospora sarothamni Sacc., Phoma pulchella (Berk. and Broome) Sacc. and Steganosporium irregulare Lambotte and Fautrey are new records for Turkish mycobiota. For the first time in literature, Bispora antennata (Pers.) E.W. Mason, Coniothecium complanatum Nees (Sacc.) and Rosellinia pulveracea (Ehrh.) Fuckel were found on P. vera L., and P. vera L. is now defined as a new host plant for these three species. Key Words: Microfungi, new record, new host, Pistacia vera L., Turkey.

Evaluation of Two Disease Warning Systems for Botryosphaeria Panicle and Shoot Blight of California Pistachio and Efficient Control Based on Early-Season Sprays.

Two empirical models to predict infection events were evaluated for control of Botryosphaeria panicle and shoot blight, caused by a Fusicoccum sp., as well as the effectiveness of early-season fungicide sprays on the control of this disease of pistachio. A model incorporating wetness duration was superior to one based solely on duration of rains ≥1 mm/h for ≥4 h and with temperature ≥11°C. The wetness duration threshold (W) for rain events ≥4 mm at a given temperature (T) for high-risk infection events was W = -7.8 + 397/T and the threshold for medium-risk events was W = -6.9 + 220/T. Wet periods interrupted by ≤12 h were added together to calculate W. In two orchards with high levels of inoculum, one high-risk event resulted in 20 to 23% blighted fruit at harvest and two or three high-risk events resulted in 31 to 80% blighted fruit. Latent infections were 0 to 1% in instances where only low-risk events (one to two events) occurred prior to collection of pistachio fruit for determination of latent infections and were 17 to 36% with one to three high-risk events. Early-season fungicide sprays in April to May effectively controlled panicle and shoot blight when applied up to 12 days before predicted infection events or 5 days after.

تاثیر میزان آفلاتوکسین تولیدی توسط آسپرژیلوس فلاووس بر کاهش بازاریابی پسته در جهان

Pistachio product makes a special importance in the agricultural production of Iran and is one of the main portion of non-petroleum exportation. Aflatoxin as secondary metabolites produced by the fungus Aspergillus flavus on pistachio fruits is toxic and reduces our competition in global pistachio markets.. It is necessary that Iran observe international standards and make investments in marketing . We have to find new target markets for this product, particularly by eliminating fungal infection and aflatoxin production . In this study, existing position and challenges of major pistachio producing and its exporting in Iran and other countries are considered and a number of strategies are recommended. Keyword: Pistachio, Aflatoxin, Aspergillus, exporting

Parasitoid complex of the pistachio twig borer moth, Kermania pistaciella, in Iran

The parasitoid complex of the pistachio twig borer moth, Kermania pistaciella Amsel (Lepidoptera: Tineidae), a native pest of pistachio trees, was investigated at 27 pistachio plantation sites in Kerman province, the major pistachio growing area of Iran. The present study was conducted to document the naturally established parasitoid complex and to assess the need for improving the biological control of this species. In total, 22,390 moth cocoons were collected from 186 samples collected from commercial orchards during 2006–2008 and kept singly in controlled conditions to rear immature insects. An average of 2.8% of moth cocoons had been attacked by predators at time of sampling. Of the collected cocoons, on average 46.7% completed development and emerged as adult moths, no insects emerged from 8%, suggesting that the moth or wasp died before maturing, and parasitoids emerged from the remaining 42.5%. The overall percentage of host cocoons from which wasps emerged ranged from 25.6 to 59%. Fifteen hymenopterous parasitoid species were recovered from cocoons, of which three species were primary parasitoids, two were obligatory hyperparasitoids and the remaining 10 species were facultative hyperparasitoids. The primary parasitoid, Chelonus kermakiae (Tobias) (Hymenoptera: Braconidae), was the most abundant comprising almost 85% of the total emerging parasitoids. In addition, a further four species of larval parasitoid developed within the PTBM's larval tunnels in pistachio fruit cluster-stem tissue. Conservation of these parasitoids in the pistachio growing areas is recommended since a high level of parasitized moths’ cocoons was found at the majority of experimental sites.

Composition and Enantiomeric Analysis of the Essential Oil of the Fruits and the Leaves of Pistacia vera from Greece

The essential oils of the fruits and the leaves of pistachio (Pistacia vera L.) were analyzed by GC and GC/MS. Fresh unripe pistachio fruits were richer in essential oil (0.5%, w/w) than the leaves (0.1%, w/w). Twenty one compounds were identified in the essential oil of the fruits and the major components were (+)-alpha-pinene (54.6%) and terpinolene (31.2%). The enantiomeric ratio of the major constituents of the essential oil of the fruits was determined using chiral GC/MS and it was found that the (+)/(-)-alpha-pinene ratio was 99.5:0.5, (+)/(-)-limonene 80:20, (+)/(-)-beta-pinene 96:4, and (+)/(-)-alpha-terpineol 0:100. Thirty three compounds were identified in the essential oil of the leaves and the major components were found to be alpha-pinene (30.0%), terpinolene (17.6%) and bornyl acetate (11.3%).

Gibberellic acid and benzyladenine reduce hull-splitting and aflatoxin levels in pistachio kernels

SummaryThe effects of gibberellic acid and a cytokinin on hull-splitting and aflatoxin levels in pistachio (Pistacia vera L. cv. ‘Owhadi’) were studied in a commercial orchard over 2 years. Gibberellin (GA3) at 25, 50 and 100 mg l–1 and benzyladenine (BA) at 50 and 100 mg l–1 reduced hull-splitting and infection by Aspergillus spp. with a strong correlation between splitting and infection (R2 = 0.88). GA3 and BA at high concentrations reduced hull-splitting to 0.6% and 0.3%, respectively. Kernels from trees treated with GA3 and BA at 50 or 100 mg l–1 had no aflatoxins compared with 4.7 ng g–1 in non-treated trees. BA also increased crude fat and chlorophyll levels in the kernels of pistachio fruit. Applications of GA3 or BA are recommended for commercial pistachio production.

Relationships Among Propagule Numbers of Botryosphaeria dothidea, Latent Infections, and Severity of Panicle and Shoot Blight in Pistachio Orchards.

Experiments were conducted between 1999 and 2001 to monitor the presence of propagules of Botryosphaeria dothidea and frequencies of latent infections on pistachio leaves and fruit clusters and to determine their relationships to panicle and shoot blight severity in commercial orchards. Numbers of B. dothidea propagules recovered from washing leaves and fruit clusters varied among the growing seasons and sampling dates. Lower numbers of B. dothidea propagules were obtained in 1999 and 2001 than in 2000. For the orchard in Glenn County, up to 75 propagules per leaf and 21 propagules per fruit cluster were recorded in 1999, compared with 365 and 248 propagules per leaf and fruit cluster, respectively, in 2000. Although more propagules were detected per leaf, the infection levels were higher on fruit clusters, suggesting that pistachio fruit is more susceptible to B. dothidea infection than leaves. Latent infections were detected as soon as leaves or fruit clusters started to expand and more infections were obtained in 2000 than 1999 or 2001. Significant (P < 0.05) relationships between propagules on leaves or frequency of infections on leaves (independent variables) and propagules on fruit clusters or frequency of infected fruit clusters (dependent variables) with r values ≥ 0.50 provide support for the role of latent infection in panicle and shoot blight later in the season. Propagules on leaves and fruit clusters were not significantly correlated to disease severity, but frequencies of latent infection on leaves and fruit clusters were positively correlated (P ≥ 0.05) with leaf and fruit disease severity under field conditions with r2 ranging between 0.25 and 0.42. Quantitative relationships between latent infections and disease severity may be incorporated in a prediction model for disease development or be used to develop a risk assessment method to guide growers in their effort to control panicle and shoot blight of pistachio.