Botryosphaeria branch canker and dieback of avocado ( Persea americana Mill.) has expanded in avocado-growing areas in recent years. Twenty-one avocado groves in the major producing regions of California were surveyed in 2018 and 2019.... more
Botryosphaeria branch canker and dieback of avocado ( Persea americana Mill.) has expanded in avocado-growing areas in recent years. Twenty-one avocado groves in the major producing regions of California were surveyed in 2018 and 2019. Monthly inoculations of wounded, green, and lignified branches of ‘Hass’ and ‘Lamb Hass’ were conducted. Botryosphaeriaceae were the predominant fungi recovered from cankered tissues collected across the surveyed traditional and high-density orchards and caused symptoms on all six sampled cultivars. These fungi were also recovered in asymptomatic twigs and other organs and thus exist as a potential reservoir for future infections. Molecular analyses of 173 isolates showed that Neofusicoccum luteum had the greatest incidences across sites and cultivars, with 83 and 29% recovered from Hass and Lamb Hass, respectively. Pathogenicity tests on excised (Hass, GEM, and Hass mutants) and attached shoots from potted (Hass) and mature avocado trees (Hass and La...
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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... more
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 m...
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In July 2009 and October 2012, stems of young peach (Prunus persica) trees with cankers from Kings, Fresno and Yuba Counties, respectively, in California were submitted to our diagnostic laboratory. The cankered areas were discoloured... more
In July 2009 and October 2012, stems of young peach (Prunus persica) trees with cankers from Kings, Fresno and Yuba Counties, respectively, in California were submitted to our diagnostic laboratory. The cankered areas were discoloured brown in comparison with the creamy healthy bark and covered with gum galls. More than 30 trees were killed in Fresno and Kings Counties, and 6 trees in Yuba County. Scraping the cankers revealed large black pycnidia and brown discoloured wood. A fungus consistently isolated from the cankers was identified as Lasiodiplodia citricola based on morphological characteristics (Abdollahzadeh et al., 2010) and analyses of ITS, and TEF-1α gene regions. The sequence showed high identity (ITS, 100%; TEF-1α, 99%) with reference sequence (isolate: IRAN 1522C = CBS 124707, ex-type of L. citricola; accession Nos.: ITS, GU945354; TEF-1α, GU945340; β- tubulin, not available) for L. citricola (Abdollahzadeh et al., 2010). Sequences were deposited to GenBank (isolates: ...
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In California, aflatoxin contamination of almond, fig, and pistachio has become a serious problem in recent years due to long periods of drought and probably other climatic changes. The atoxigenic biocontrol product Aspergillus flavus... more
In California, aflatoxin contamination of almond, fig, and pistachio has become a serious problem in recent years due to long periods of drought and probably other climatic changes. The atoxigenic biocontrol product Aspergillus flavus AF36 has been registered for use to limit aflatoxin contamination of pistachio since 2012 and for use in almond and fig since 2017. New biocontrol technologies employ multiple atoxigenic genotypes because those provide greater benefits than using a single genotype. Almond, fig, and pistachio industries would benefit from a multi-strain biocontrol technology for use in these three crops. Several A. flavus vegetative compatibility groups (VCGs) associated with almond, fig, and pistachio composed exclusively of atoxigenic isolates, including the VCG to which AF36 belongs to, YV36, were previously characterized in California. Here, we report additional VCGs associated with either two or all three crops. Representative isolates of 12 atoxigenic VCGs signifi...
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Research Interests: Microbiology, Horticulture, Plant Biology, Biology, Fungus, and 3 moreMancozeb, Fungicide, and Mycelium
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Alternaria late blight caused by Alternaria alternata is a major disease affecting pistachios grown in California and to some degree those grown in Arizona. Alternaria alternata is prone to quick fungicide resistance selection when... more
Alternaria late blight caused by Alternaria alternata is a major disease affecting pistachios grown in California and to some degree those grown in Arizona. Alternaria alternata is prone to quick fungicide resistance selection when single-mode of action fungicides are used. For the specific detection of five possible amino acid alterations associated with Alternaria alternata resistance to succinate dehydrogenase inhibitors used in California and Arizona pistachio orchards, we have designed five primer sets to be used as an allele-specific PCR assay (AS-PCR). Within a couple of hours from DNA extraction, the new specific-primers amplify the different PCR product sizes, according to the chosen target, allowing their differentiation on gel agarose. In our study, the AS-PCR assay consistently detected the mutations H277L and H277R at the AaSdhB gene, the mutations H134R and S135R at the AaSdhC gene, and the mutation D123E at the AaSdhD gene from A. alternata isolates collected from pis...
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Abstract In this study, 229 isolates of Alternaria alternata collected from commercial pistachio orchards with (n = 198) and without (n = 31) a prior history of Switch (cyprodinil + fludioxonil) applications were examined for their... more
Abstract In this study, 229 isolates of Alternaria alternata collected from commercial pistachio orchards with (n = 198) and without (n = 31) a prior history of Switch (cyprodinil + fludioxonil) applications were examined for their sensitivity to fludioxonil and cyprodinil using in vitro mycelial growth assays. The 50% effective dose (EC50) values for the baseline isolates for cyprodinil and fludioxonil ranged from 0.001 to 1.184 μg/mL (average = 0.214) and from 0.010 to 4.875 μg/mL (average = 0.770), respectively. Out of 72 isolates assayed from the exposed population, 93% had EC50 values for fludioxonil ranging from 0.001 to 5.370 μg/mL (average = 0.472), but five isolates were highly resistant to this fungicide (EC50 > 100 μg/mL). About 98.55% of these isolates were sensitive to cyprodinil (0009 10 μg/mL). No cross-resistance relationship between cyprodinil and fludioxonil was observed (P = 0.2925, r = −0.1074). To determine the occurrence of multiple resistances, the radial growths of 126 isolates, collected from orchards with a history of Switch, Pristine, and strobilurin exposures, were measured on agar media amended with a single discriminatory dose of 10 μg fungicide/mL. High proportions of these isolates were resistant to boscalid (86.3%) and pyraclostrobin (92.9%). Most isolates were still sensitive to fludioxonil (77.8%) and cyprodinil (89.7%), but some were found to be independently or simultaneously resistant to all fungicides tested. Under conditions of excessive exposure to Switch resistant phenotypes may develop in A. alternata populations and ultimately affect fungicide performance. Therefore, monitoring studies must be continued and strict adherence to anti-resistance strategies followed and implemented in at risk orchards.
Research Interests: Horticulture, Biology, EC, Alternaria alternata, Crop Protection, and 3 moreEc, Fludioxonil, and Fungicide
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Abstract The frequency of strains of Monilinia fructicola that are resistant to the demethylation inhibiting fungicide tebuconazole in Brazil was determined by three methods. The first involved testing 295 isolates for relative growth... more
Abstract The frequency of strains of Monilinia fructicola that are resistant to the demethylation inhibiting fungicide tebuconazole in Brazil was determined by three methods. The first involved testing 295 isolates for relative growth under a discriminatory dose of 0.3 µg mL−1. The second and the third methods involved testing 120 isolates for the effective concentration for 50% population inhibition (EC50); one method employed the discriminatory dose of 0.3 µg mL−1 and the other method utilized the baseline dose of 0.046 µg mL−1 to separate the strains based on sensitivity. The frequencies of resistance among the isolates based on the three methods were determined by measuring mycelial growth in fungicide-amended media. The shifts in M. fructicola sensitivities were determined by comparing the EC50 density distributions of the baseline (2000–2004, n=31), intermediate (2005–2008, n=88), and current (2009–2011, n=120) isolate populations. The frequency of resistance to tebuconazole varied according to the assessment method; the resistance frequencies were 18.3% for the relative growth method, 40% for the baseline EC50 method, and 8.33% for the EC50 method segregated by the dose of 0.3 µg mL−1. The application of the EC50 method involving the discriminatory dose of 0.3 µg mL−1 revealed a decrease in the frequency of resistant genotypes. However, the baseline EC50 method is recommended for future resistance surveys because this method was originally used to determine the mean sensitivity prior to the use of tebuconazole in Brazil. Additionally, a shift of the current population toward sensitivity was observed compared with the intermediate population. Finally, São Paulo was found to be the state with the highest EC50 values (0.186 µg mL−1) compared with Paraná (0.053 µg mL−1) and Rio Grande do Sul (0.026 µg mL−1). These results suggest that the build-up of fungicide resistance in Monilinia fructicola has been prevented by the use of anti-resistance strategies in the main peach production areas of Brazil; however, additional studies are required to demonstrate how resistance instability and fitness are affecting isolate sensitivity.
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Brown rot is a devastating disease of stone fruits caused by Monilinia spp. This study was conducted to investigate the disease aetiology on blossoms and fruit in peach, apricot, sweet cherry and plum orchards, in Greece. In total, 1433... more
Brown rot is a devastating disease of stone fruits caused by Monilinia spp. This study was conducted to investigate the disease aetiology on blossoms and fruit in peach, apricot, sweet cherry and plum orchards, in Greece. In total, 1433 isolates obtained from orchards located in the main stone fruit production regions of Greece were identified to species based on the presence/size of a cyt b intron. Monilinia laxa and M. fructicola were detected at frequencies of 59 and 41%, respectively, while M. fructigena was absent. Monilinia fructicola was more common on fruit whereas M. laxa occurred in similar frequency on blossoms and fruit. Monilinia laxa was replaced by M. fructicola in fruit infections of peach in both regions investigated and in fruit infections of plum in the Imathia region. Assessments of aggressiveness of 30 isolates of both species on the petals and fruits of the hosts showed that M. fructicola isolates were more aggressive. This suggests that the predominance of M. ...
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Samples of leaves, buds, fruits and fruit clusters of pistachio (Pistacia vera) were collected during the middle crop season from different localities in Central Valley, California, USA. Washings of the plant samples were sprayed on... more
Samples of leaves, buds, fruits and fruit clusters of pistachio (Pistacia vera) were collected during the middle crop season from different localities in Central Valley, California, USA. Washings of the plant samples were sprayed on acidified potato dextrose agar (PDA), and fungal isolates ...
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A total of 185 isolates of Botryosphaeriaceae and Phomopsis spp. were collected from 13 counties in California such as Butte, Colusa, Fresno, Kings, Glenn, Merced, San Benito, Stanislaus, Sutter, Tulare, Ventura, Yolo, and Yuba.... more
A total of 185 isolates of Botryosphaeriaceae and Phomopsis spp. were collected from 13 counties in California such as Butte, Colusa, Fresno, Kings, Glenn, Merced, San Benito, Stanislaus, Sutter, Tulare, Ventura, Yolo, and Yuba. Identification of the isolates was based on morphological features of the cultures and DNA sequence comparisons of ITS, TEF-1α, and β-tubulin gene regions, 10 species of Botryosphaeriaceae and two species of Diaporthe (anamorph Phomopsis, Diaporthaceae) were identified. These species include Botryosphaeria dothidea, Diplodia seriata, Diplodia mutila, Dothiorella iberica, Lasiodiplodia citricola, Neofusicoccum mediterraneum, Neofusicoccum nonquaesitum, Neofusicoccum parvum, Neofusicoccum vitifusiforme, Neoscytalidium dimidiatum, Diaporthe rhusicola and Diaporthe neotheicola. Neofusicoccum mediterraneum was widely distributed in 10 of the 13 sampled counties. Pathogenicity on three walnut cultivars, Chandler, Tulare, and Vina, using a mycelial-plug inoculation...
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Research Interests: Microbiology, Horticulture, Plant Biology, Biology, Medicine, and 5 moreRosaceae, Prunus, Plant Disease, Orchard, and Fruit Tree
The effects of osmotic potential (T) and temperature on mycelial growth, sporulation, and survival of Monilinia fructicola were determined us- ing potato-dextrose agar (PDA) amended with KC1 and sucrose. Comparatively, KC1 facilitated the... more
The effects of osmotic potential (T) and temperature on mycelial growth, sporulation, and survival of Monilinia fructicola were determined us- ing potato-dextrose agar (PDA) amended with KC1 and sucrose. Comparatively, KC1 facilitated the spor- ulation and sucrose facilitated the mycelial growth and survival of the fungus. Optimal mycelial growth occurred at -1 MPa and 25 C and sporulation at -3 MPa and 20 C. Sporulation decreased more rapidly than mycelial growth as osmotic potential and tem- perature became less conducive. Significant interac- tions between osmotic potential and temperature were observed on affecting the mycelial growth and sporulation. Moniliniafructicola did not grow in PDA amended with KC1 at T < -11 MPa (20 and 25 C), -9 MPa (15 and 30 C), or -7 MPa (10 C) after 6-d incubation; it also did not grow in PDA amended
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Alternaria rot has been recently described as an emerging fungal disease of citrus causing significant damage in California groves. A survey was conducted to determine latent infections on fruits, twigs, and leaves and investigate their... more
Alternaria rot has been recently described as an emerging fungal disease of citrus causing significant damage in California groves. A survey was conducted to determine latent infections on fruits, twigs, and leaves and investigate their seasonal patterns during 2019 and 2020. On fruits, latent infections were more associated with the stem end than with the stylar end, except during spring when a significantly high percentage of flowers (86%) had latent infections. Latent infections on twigs varied markedly between years (28% in 2019 and 9.5% in 2020), while Alternaria spp. were also recovered from citrus leaves. Alternaria isolates collected during the survey were identified based on multigene sequence analysis, confirming that Alternaria alternata and Alternaria arborescens are the two species associated with infections of citrus fruits. Of the 23 isolates, 19 were identified as A. alternata and demonstrated the dominance of this species over A. arborescens. Isolates representing populations of these two species were selected as representative isolates for physiological and morphological studies. A. alternata and A. arborescens showed similar conidial dimensions but differed in the number of conidia produced. Growth rates demonstrated that A. alternata grows faster than A. arborescens at all the temperatures evaluated, except at 25 and 35 °C. The growth patterns were similar for both species. The sporulation rate of the Alternaria isolates was influenced differently by temperature. This parameter also influenced conidial germination and appressorium formation, and no significant differences were observed between Alternaria species. Pathogenicity and aggressiveness tests on detached fruit demonstrated the ability of A. alternata and A. arborescens to cause internal lesions and produce fruit drop in the orchards with no quantitative differences between them (disease severity indexes of 58 and 68%, respectively). The fungicide sensitivity tests showed that DMI fungicides are the most effective fungicides in reducing mycelial growth. The SDHI fungicides had intermediate activity against the mycelial growth but also suppressed spore germination. The spore germination assay suggested that some of the isolates included in this study might have some level of resistance to QoI and SDHI fungicides. The findings of this study provide new information about the pathogens associated with the excessive fruit drop recently observed in some California citrus groves.
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Las aflatoxinas son micotoxinas producidas por hongos de suelo del<br> género Aspergillus, principalmente A. flavus y A. parasiticus. Por su<br> alta toxicidad, están reguladas en numerosos alimentos para consumo<br>... more
Las aflatoxinas son micotoxinas producidas por hongos de suelo del<br> género Aspergillus, principalmente A. flavus y A. parasiticus. Por su<br> alta toxicidad, están reguladas en numerosos alimentos para consumo<br> humano y animal. Ambas especies crecen sobre restos de material<br> vegetal produciendo un gran número de conidios aerovagantes<br> que pueden colonizar y contaminar diferentes cultivos como maíz,<br> cacahuete, algodón y frutos secos, entre otros. La contaminación<br> por aflatoxinas en almendro y pistachero, sus causas y control, han<br> sido intensamente estudiados en California en los últimos 25 años.<br> En España, la situación es menos conocida y está siendo abordada<br> en el marco de dos proyectos de investigación entre la Universidad<br> de Córdoba y la Universidad de California, Davis. Aquí, revisamos la<br> importancia actual, la etiología, biología, y control de esta problemática<br&g...
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Fig limb dieback is a cosmopolitan disease caused by Neoscytalidium dimidiatum (Botryosphaeriaceae), characterized by branch and shoot cankers, discoloration of woody tissues, and dieback. The present study investigated the etiology of... more
Fig limb dieback is a cosmopolitan disease caused by Neoscytalidium dimidiatum (Botryosphaeriaceae), characterized by branch and shoot cankers, discoloration of woody tissues, and dieback. The present study investigated the etiology of the disease in California that seems to have become prevalent among fig orchards in the last several years. During orchard surveys in Fresno, Kern, and Madera Counties over 3 years, we isolated consistently and evaluated the pathogenicity of N. dimidiatum under laboratory and field conditions. The effect of summer and winter pruning on the disease severity and the effects of different environmental and mechanical stresses, such as sunburn and wounding by mallets, were assayed. In addition, the susceptibility of six different cultivars and the effects of eradicating cankered shoots from the fig trees as a method to combat the spread of the disease were studied. Pathogenicity tests demonstrated that N. dimidiatum induces cankers on fig, mainly on wounde...
Research Interests: Microbiology, Horticulture, Plant Biology, Biology, Medicine, and 7 moreCultivar, Ficus, Plant Disease, Canker, Pruning, Orchard, and Shoot
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Alternaria late blight (ALB) caused by Alternaria spp. is an annual disease problem in California pistachio and requires repeated applications of fungicides to prevent significant losses of pistachio foliage and nut quality. From 2003... more
Alternaria late blight (ALB) caused by Alternaria spp. is an annual disease problem in California pistachio and requires repeated applications of fungicides to prevent significant losses of pistachio foliage and nut quality. From 2003 onward, the succinate dehydrogenase inhibiting fungicide boscalid has played a key role in ALB management. The development of boscalid resistance in A. alternata populations was monitored from 2005 to 2012 in pistachio producing areas in California. A total of 1,765 single-spore isolates, collected from commercial and experimental pistachio orchards with or without a history of boscalid exposure, were tested in a radial growth assay in agar media amended with the discriminatory dose of 10 µg/ml of boscalid. The frequency of boscalid-resistant isolates in 2005 was 12% but increased significantly and remained stable toward the end of the survey period. Most of the resistant isolates exhibited a high level of resistance (R) to boscalid with percent of myc...
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Abstract In this study, the sensitivity of 902 isolates of A. alternata collected before and after the commercial use of fluopyram were assessed using mycelial growth tests. Distribution of 50% effective concentration (EC50) values for... more
Abstract In this study, the sensitivity of 902 isolates of A. alternata collected before and after the commercial use of fluopyram were assessed using mycelial growth tests. Distribution of 50% effective concentration (EC50) values for 116 A. alternata isolates (population A), collected in 2011 from an experimental orchard that had been treated with fluopyram products or boscalid showed that 86% of the isolates displayed different levels of resistance to boscalid while 87 (76%) and 28 (24%) showed sensitivity and different levels of resistance to fluopyram, respectively. Among the last group of isolates, only 5 and 23 showed moderate (MR) and low (LR) resistance to fluopyram, respectively. The sensitivity to fluopyram was further evaluated in agar medium at the discriminatory dose of 5 μg/ml fluopyram for a total of 786 A. alternata isolates collected in 2012 from commercial pistachio orchards with (173 isolates, population B; 373 isolates, population C) or without a history of use of fluopyram products (240 isolates, population D). Among the 240 isolates from 31 boscalid-treated orchards, 93 and 7% showed sensitivity (S) and low resistance (LR) to fluopyram, respectively, while 65 and 33 were resistant (R) and LR to boscalid, respectively. Analyses of the sensitivities to boscalid and fluopyram of the 546 isolates from populations B and C collected from orchards exposed to fluopyram or other SDHIs showed fluopyram-resistant isolates did not occur at the same frequency as boscalid resistance. In both populations, the frequencies of boscalid resistance isolates in all plots, exposed or not to fluopyram products, were significantly higher than those observed for fluopyram. Sequence analyses of the A. alternata SDHB, C, and D proteins showed the presence of several amino acid substitutions (SDHB: H277Y/R/L, P230 A/R/I/F,D, N235D/T/E/G; SDHC: H134R, S135R; SDHD: D123E, H133P) in boscalid- and fluopyram-resistant phenotypes. Current data provided further evidences of the good performance of fluopyram and the various and interactive impacts of SDH mutations on the levels of resistance to SDHIs. Although their frequency is still very low, fluopyram-resistant phenotypes could quickly build up in Alternaria populations under continual selection pressure by SDHI-containing products and ultimately affect fluopyram efficacy. As fluopyram products become extensively used in pistachio orchards, continual monitoring of Alternaria sensitivities to fluopyram and other active ingredients in these mixtures (tebuconazole in particular) will be required to detect any shifts in sensitivity that could result in disease control failures.
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Procedures were developed to permit screening pistachio for resistance to infection by Botryosphaeria dothidia panicle and shoot blight. A method of growing B. dothidea in liquid culture was developed and two inoculation procedures,... more
Procedures were developed to permit screening pistachio for resistance to infection by Botryosphaeria dothidia panicle and shoot blight. A method of growing B. dothidea in liquid culture was developed and two inoculation procedures, direct injection of inoculum into shoots at the base of leaf petioles and a leaf scratch assay, were used to test selected pistachio (Pistacia vera L.) clones for resistance to B. dothidea. Both the direct injection and the scratch test procedures provided easily scored symptoms. Both solid and liquid cultures produced visible infections. Sources of resistance were identified in an F1 interspecific P. vera cv. Sfax × P. integerrima hybrid cross and P. integerrima genotypes. P. integerrima may be a valuable source of resistance for cultivar improvement, but resistant P. vera genotypes were not found. No correlation between Alternaria alternata resistance and B. dothidea resistance was found in P. vera.
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Research Interests: Botany, Microbiology, Horticulture, Plant Biology, Biology, and 9 moreCultivar, Pathogen, Blight, Inoculation, Pistacia, Botryosphaeria, Phoma, Shoot, and Mycelium
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The Botrytis cinerea species complex comprises two cryptic species, originally referred to Group I and Group II based on Bc-hch gene RFLP haplotyping. Group I was described as a new cryptic species B. pseudocinerea. During a survey of... more
The Botrytis cinerea species complex comprises two cryptic species, originally referred to Group I and Group II based on Bc-hch gene RFLP haplotyping. Group I was described as a new cryptic species B. pseudocinerea. During a survey of Botrytis spp. causing gray mold in blueberries and table grapes in the Central Valley of California, six isolates, three from blueberries and three from table grapes, were placed in Group I but had a distinct morphological character with conidiophores significantly longer than those of B. cinerea and B. pseudocinerea. We compared these with B. cinerea and B. pseudocinerea by examining morphological and physiological characters, sensitivity to fenhexamid and phylogenetic analysis inferred from sequences of three nuclear genes. Phylogenetic analysis with the three partial gene sequences encoding glyceraldehyde-3-phosate dehydrogenase (G3PDH), heat-shock protein 60 (HSP60) and DNA-dependent RNA polymerase subunit II (RPB2) supported the proposal of a new ...
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The epiphytic plant Hylocereus undatus, locally known as pitahaya, is endemic to Mexico. Recently, small-scale farming of this plant has begun and the harvested fruit exported to distant markets. In 2001 and 2002, samples of H. undatus... more
The epiphytic plant Hylocereus undatus, locally known as pitahaya, is endemic to Mexico. Recently, small-scale farming of this plant has begun and the harvested fruit exported to distant markets. In 2001 and 2002, samples of H. undatus with stem spots were collected from ...
Research Interests: Botany, Microbiology, Plant Biology, Biology, Plant, and 3 moreSpots, Plant Pathology, and Botryosphaeria
California is a major almond (Prunus dulcis) producer in the world. In September 2012, 2-year-old almond trees from an orchard in Fresno Co. with stem cankers were submitted for disease diagnosis. In a survey of the orchard, 12 ha (1,500... more
California is a major almond (Prunus dulcis) producer in the world. In September 2012, 2-year-old almond trees from an orchard in Fresno Co. with stem cankers were submitted for disease diagnosis. In a survey of the orchard, 12 ha (1,500 Nonpareil and 1,800 Monterey almond trees) of 48 ha trees had been killed apparently due to a stem canker. The cankers developed above the graft union, were covered with amber sap, and often girdled the trunk. Isolations made from tissues at the canker margins onto acidified potato dextrose agar (PDA) yielded two fungi, Macrophomina phaseolina (Tassi) Goid and Lasiodiplodia theobromae (Pat.) Griffon & Maubl (1). M. phaseolina and L. theobromae were isolated from eight and two of 10 cankered trees, respectively. No mixed infections were found. M. phaseolina isolates were characterized by gray hyphae that turned black with developing microsclerotia. L. theobromae isolates were characterized by white, aerial mycelium that turned mouse gray after 5 days...
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Traditional olive orchards in Spain have been planted at a density of 70 to 80 trees per ha with three trunks per tree. During the last decade, the hedgerow orchard, in which planting density is approximately 2,000 trees per ha, was... more
Traditional olive orchards in Spain have been planted at a density of 70 to 80 trees per ha with three trunks per tree. During the last decade, the hedgerow orchard, in which planting density is approximately 2,000 trees per ha, was developed. In 2006 and 2007, we noted a severe outbreak of fruit rot in FS-17, a new cultivar from Italy, in an experimental hedgerow planting in Córdoba, southern Spain. The incidence of fruit rot in ‘FS-17’ was 80% in January of 2006 and 24% in January of 2007. Cvs. Arbosana, IRTA-i18 (a selected clone from ‘Arbequina’), and Koroneiki had no symptoms in either year of the study. Disease incidence in ‘Arbequina’ was <0.1% only in 2006. Affected fruits were soft with gray-white skin and they eventually mummified. Black-green sporodochia were observed on the surface of diseased fruits. A fungus was isolated from diseased fruits on potato dextrose agar (PDA) and incubated at 22 to 26°C with a 12-h photoperiod. After 8 days of growing on PDA, fungal colo...
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In August 1996, a commercial retailer of high quality cherries from the Okanagan Valley of British Columbia, Canada, reported severe losses in at least 150 boxes (11.3 kg per box) of packed cherries cv. Stella. Upon examination of a... more
In August 1996, a commercial retailer of high quality cherries from the Okanagan Valley of British Columbia, Canada, reported severe losses in at least 150 boxes (11.3 kg per box) of packed cherries cv. Stella. Upon examination of a representative box of these cherries, it was found that approximately 80% of the fruit was affected by what appeared to be Mucor spp. The decayed cherries were concentrated below the surface layer and small pockets of cherries had prominent salt-and-pepper-colored whiskers emanating from individual cherries. Counting the exact number of rotten cherries was difficult because they disintegrated on handling. Several infected cherries were surface sterilized by immersing in a 0.5% NaClO solution for 1 min and rinsing with sterile, distilled water. Pieces of the surface-sterilized cherries were plated onto dishes containing potato dextrose agar and incubated at 6°C for 10 days. Ten typical isolates derived from single spores from these dishes were all identif...
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Following prolonged spring rains and cool summer weather in 2010, mature weeping willow trees (Salix babylonica L.) growing next to a manmade lake in Marin County, CA, showed symptoms of a previously undescribed disease. During summer,... more
Following prolonged spring rains and cool summer weather in 2010, mature weeping willow trees (Salix babylonica L.) growing next to a manmade lake in Marin County, CA, showed symptoms of a previously undescribed disease. During summer, small branches developed dark brown to black, sunken cankers. Canker lengths ranged from 3 to 20 cm. Within the cankered areas, affected twigs, shoots, and leaves turned brown, collapsed, and died. The distal portions of infected branches also died, giving the trees a blighted appearance. Acervuli and pink sporulation were observed in the canker tissue. When placed on acidified potato dextrose agar (A-PDA), canker tissues consistently yielded one type of fungal organism. On A-PDA, isolates produced gray aerial mycelium, acervuli, and single-celled fusiform conidia. Two isolates were identified as Colletotrichum acutatum based on sequence analysis of the ITS region of the ribosomal DNA and the 1-kb intron of the glutamine synthase gene (1) and fungal m...
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Postharvest Pathology and Mycotoxins Aspergillus Molds and Aflatoxins in Pistachio Nuts in California MA Doster and TJ Michailides Department of Plant Pathology, University of California, Davis, Kearney Agricultural Center, 9240 S.... more
Postharvest Pathology and Mycotoxins Aspergillus Molds and Aflatoxins in Pistachio Nuts in California MA Doster and TJ Michailides Department of Plant Pathology, University of California, Davis, Kearney Agricultural Center, 9240 S. Riverbend Ave., Parlier 93648. ...
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... Phytopathology, 100, 1340–1351. Okie, WR, & Pusey, PL (1996). USDA peach breeding inGeorgia: current status and breeding for resistance to Botryosphaeria. Acta Horticulturae, 374, 151–158. Pantidou, EM (1973). List of fungi and... more
... Phytopathology, 100, 1340–1351. Okie, WR, & Pusey, PL (1996). USDA peach breeding inGeorgia: current status and breeding for resistance to Botryosphaeria. Acta Horticulturae, 374, 151–158. Pantidou, EM (1973). List of fungi and hosts in Greece (pp. 223–234). ...
Research Interests: Microbiology, Horticulture, Plant Biology, Biology, Cultivar, and 4 moreBlight, Inoculation, First Year, and Shoot
Research Interests:
Research Interests:
Aflatoxin contamination of important food and feed crops occurs frequently in warm tropical and subtropical regions. The contamination is caused mainly by Aspergillus flavus and A. parasiticus. Aflatoxin contamination negatively affects... more
Aflatoxin contamination of important food and feed crops occurs frequently in warm tropical and subtropical regions. The contamination is caused mainly by Aspergillus flavus and A. parasiticus. Aflatoxin contamination negatively affects health and trade sectors and causes economic losses to agricultural industries. Many pre- and post-harvest technologies can limit aflatoxin contamination but may not always reduce aflatoxin concentrations below tolerance thresholds. However, the use of atoxigenic (non-toxin producing) isolates of A. flavus to competitively displace aflatoxin producers is a practical strategy that effectively limits aflatoxin contamination in crops from field to plate. Biocontrol products formulated with atoxigenic isolates as active ingredients have been registered for use in the US, several African nations, and one such product is in final stages of registration in Italy. Many other nations are seeking to develop biocontrol products to protect their crops. In this r...