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Garcia-Lopez MT, Meca E, Jaime R, Puckett RD, Michailides TJ, Moral J. Sporulation and Dispersal of the Biological Control Agent Aspergillus flavus AF36 Under Field Conditions. Phytopathology 2024:PHYTO06230200KC. [PMID: 37581424 DOI: 10.1094/phyto-06-23-0200-kc] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/16/2023]
Abstract
Aflatoxins are carcinogens produced by the fungi Aspergillus flavus and A. parasiticus that contaminate pistachio crops. International markets reject pistachio when aflatoxins exceed permitted maximum levels. Releasing the atoxigenic strain AF36 of A. flavus is the leading aflatoxin pre-harvest control method. The product AF36 Prevail, sorghum grains coated with AF36 propagules, has been used in California since 2017. However, a high percentage of grains of the Prevail fail to sporulate in orchards. Here, the effect of soil moisture on the percentage of AF36 product grains sporulating (SG) and the quantity of spores per grain using a sporulation index (SI) was determined. Under controlled conditions, SG was higher than 85% when soil moisture was 13% or more, and SI increased with increasing soil moisture from 8.4 to 21%. The highest AF36 sporulation occurred near the micro-sprinklers when the grains were not impacted by the irrigation water drops. Arthropod predation was responsible for lost product grains, which was more pronounced in non-tilled soil than in tilled soil. Dispersal of the AF36 spores decreased markedly with the height and distance from the inoculum source, following a pattern of diffusion equations. However, AF36 spores easily reached canopies of pistachios located 10 m from the inoculum source. Our results indicate that AF36 Prevail should be applied close to the irrigation line in the moist soil area but avoiding the areas where excess irrigation causes water accumulation. The biocontrol of aflatoxins in California's pistachio production areas was optimized by improving the field realization of the biological control agent.
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Affiliation(s)
- M Teresa Garcia-Lopez
- Department of Agronomy, Maria de Maeztu Unit of Excellence, University of Cordoba. Edif. C4, Campus de Rabanales 14071, Cordoba, Spain
- Department of Plant Pathology, University of California-Davis, Kearney Agricultural Research and Extension Center, Parlier 93648, CA, U.S.A
| | - Esteban Meca
- Department of Applied Physics, University of Cordoba. Edif. C2, Campus de Rabanales 14071, Cordoba, Spain
| | - Ramon Jaime
- Department of Plant Pathology, University of California-Davis, Kearney Agricultural Research and Extension Center, Parlier 93648, CA, U.S.A
| | - Ryan D Puckett
- Department of Plant Pathology, University of California-Davis, Kearney Agricultural Research and Extension Center, Parlier 93648, CA, U.S.A
| | - Themis J Michailides
- Department of Plant Pathology, University of California-Davis, Kearney Agricultural Research and Extension Center, Parlier 93648, CA, U.S.A
| | - Juan Moral
- Department of Agronomy, Maria de Maeztu Unit of Excellence, University of Cordoba. Edif. C4, Campus de Rabanales 14071, Cordoba, Spain
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Singh P, Jaime R, Puckett RD, Lake J, Papangelis A, Gabri Martin VM, Michailides T. Ochratoxin A contamination of California pistachios and identification of causal agents. Plant Dis 2023. [PMID: 38115568 DOI: 10.1094/pdis-06-23-1233-re] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/21/2023]
Abstract
Ochratoxin A (OTA) is a potent mycotoxin produced by Aspergillus and Penicillium spp., which contaminates many crops, including pistachios. Pistachios contaminated with OTA may be subjected to border rejections resulting in significant economic losses to the United States agricultural revenues. The current study examined prevalence of OTA in California grown pistachios and identified its causal agents. OTA was detected in 20% samples from 2018-21 (n=809), with 18% samples exceeding the European Union regulatory limit of 5 µg/kg. Fungi potentially responsible for OTA contamination were isolated from leaves, nuts, and soil collected from 14 pistachio orchards across California. A total of 1,882 isolates of Aspergillus section Nigri and 85 isolates of section Circumdati were recovered. Within section Nigri, 216 (11.5%) isolates were identified as potential OTA producers using a boscalid-resistance assay. Phylogenetic analyses of partial gene sequences for β-tubulin and calmodulin genes resolved section Circumdati into four species: A. ochraceus (33%), A. melleus (28%), A. bridgeri (21%), and A. westerdijkiae (19%). Aspergillus westerdijkiae produced the highest levels of OTA in inoculated pistachios (47 µg/g), followed by A. ochraceus (9.6 µg/g) and A. melleus (3.3 µg/g). Aspergillus bridgeri did not produce OTA. OTA production by section Circumdati was optimal from 20 to 30ºC. All 216 boscalid-resistant isolates from section Nigri were identified as A. tubingensis and representative isolates (n =130) produced 3.8 µg/kg OTA in inoculated pistachios. This is the first detailed report on OTA contamination and causal fungi in California pistachios and will be helpful in devising effective management strategies.
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Affiliation(s)
- Pummi Singh
- University of California Davis, 8789, Plant Pathology, 9240 South Riverbend Ave., Parlier, California, United States, 93648;
| | - Ramon Jaime
- UC-Davis, Plant Pathology, PARLIER, California, United States;
| | - Ryan D Puckett
- University of Caliofrnia, Kearney Plant Pathology, Parlier, California, United States;
| | | | | | | | - Themis Michailides
- University of California, Agriculture & Natural Resources, Kearney Agric. Research and Extesnion Center, 9240 South Riverbend Ave., Parlier, California, United States, 93648;
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Garcia-Lopez MT, Gordon A, Puckett RD, Chevailler C, Doster M, Michailides TJ, Moral J. Pistachio Male Inflorescences as an Alternative Substrate for the Application of Atoxigenic Strains of Aspergillus flavus. Plant Dis 2023:PDIS09222109RE. [PMID: 36401847 DOI: 10.1094/pdis-09-22-2109-re] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Aflatoxins are carcinogens mainly produced by Aspergillus flavus and A. parasiticus in susceptible crops, including pistachio. The primary inoculum sources of these pathogens are plant debris in the orchard soils. In Californian fields, one approach to controlling aflatoxin contamination is based on releasing the atoxigenic strain of A. flavus AF36 in inoculated (coated) sorghum grains (AF36 Prevail). However, this control method can fail due to poor sporulation of the AF36 strain or sorghum grain losses due to predation. In 2008 and 2018, we showed that toxigenic and atoxigenic isolates of Aspergillus spp. frequently colonized fallen inflorescences of male pistachio trees. Under controlled conditions, strain AF36 profusely colonized pistachio male inflorescences when humidity was higher than 90%. However, there were significant differences between types of inflorescence (aerial > fallen). In 2016, we considerably (P = 0.015) increased the population of AF36 on the canopies of trees when fallen inflorescences were inoculated with AF36, compared with untreated trees. In 2017 and 2018, these differences were not detected (P > 0.05) due to cross-contamination of strain AF36 between seasons and neighboring plots. In any case, the density of AF36 spores on the canopy of the inflorescence-treated trees was similar (P > 0.05) to that on trees treated with the commercial product. Here, we present a new method for applying strain AF36 based on using a natural, abundant, and uniformly distributed substrate in pistachio fields, and we discuss how it can be improved. Furthermore, our results indicate that, in pistachio orchards where biocontrol practices are not conducted, eliminating this important source of toxigenic Aspergillus inoculum is recommended.
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Affiliation(s)
- M Teresa Garcia-Lopez
- Department of Agronomy, Maria de Maeztu Unit of Excellence, University of Cordoba, Edif. C4, Campus de Rabanales, 14071 Cordoba, Spain
- Department of Plant Pathology, University of California-Davis, Kearney Agricultural Research and Extension Center, Parlier, CA 93648, U.S.A
| | - Ana Gordon
- Department of Agronomy, Maria de Maeztu Unit of Excellence, University of Cordoba, Edif. C4, Campus de Rabanales, 14071 Cordoba, Spain
| | - Ryan D Puckett
- Department of Plant Pathology, University of California-Davis, Kearney Agricultural Research and Extension Center, Parlier, CA 93648, U.S.A
| | - Coralie Chevailler
- Department of Plant Pathology, University of California-Davis, Kearney Agricultural Research and Extension Center, Parlier, CA 93648, U.S.A
| | - Mark Doster
- Department of Plant Pathology, University of California-Davis, Kearney Agricultural Research and Extension Center, Parlier, CA 93648, U.S.A
| | - Themis J Michailides
- Department of Plant Pathology, University of California-Davis, Kearney Agricultural Research and Extension Center, Parlier, CA 93648, U.S.A
| | - Juan Moral
- Department of Agronomy, Maria de Maeztu Unit of Excellence, University of Cordoba, Edif. C4, Campus de Rabanales, 14071 Cordoba, Spain
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Luo Y, Niederholzer FJA, Felts DG, Puckett RD, Michailides TJ. Inoculum quantification of canker-causing pathogens in prune and walnut orchards using real-time PCR. J Appl Microbiol 2020; 129:1337-1348. [PMID: 32406554 DOI: 10.1111/jam.14702] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2020] [Revised: 05/05/2020] [Accepted: 05/06/2020] [Indexed: 11/30/2022]
Abstract
AIMS A real-time quantitative PCR (qPCR) assay was established to quantify the inoculum densities in the air and rainwater for six canker-causing pathogen groups in prune and walnut orchards in California. METHODS AND RESULTS The previously published DNA primers to target six pathogen groups including Botryosphaeria dothidea, Cytospora spp., Diplodia spp., Lasiodiplodia spp., Neofusicoccum spp. and Phomopsis spp. were used in a qPCR assay. Air samples from Burkard spore traps and rain samples from special rain collector devices were collected periodically from various prune and walnut orchards. Using the qPCR approach, we were able to quantify the concentrations of these pathogen groups in rainwater and air samples and study the dynamics of pathogen inoculum in orchards showing severe canker potential. Phomopsis spp. and Diplodia spp. were not found in all rain samples in prune orchards, although they were detected in the 2016 in the walnut orchard. The other four pathogen groups were quantified at varying concentrations in the prune and walnut orchards. Cytospora spp. in some cases showed higher concentrations in the rainwater in prune orchards. CONCLUSIONS The rainy season during winter and early spring is a highly risky period of time for infection by the pathogens when the inoculum of these pathogens can easily spread by air and rain water, thus serving as an important inoculum source for disease initiation. The different studied pathogen groups showed different concentrations during the growing season, indicating the complexity of the components of canker-causing species in various tree crops. SIGNIFICANCE AND IMPACT OF THE STUDY This study showed the applicability of the qPCR assay in the quantification of inoculum in tree orchards to help reveal the mechanisms of canker disease epidemics and to help design disease management strategies.
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Affiliation(s)
- Y Luo
- Department of Plant Pathology, University of California-Davis, Kearney Agricultural Research and Extension Center, Parlier, CA, USA
| | | | - D G Felts
- Department of Plant Pathology, University of California-Davis, Kearney Agricultural Research and Extension Center, Parlier, CA, USA
| | - R D Puckett
- Department of Plant Pathology, University of California-Davis, Kearney Agricultural Research and Extension Center, Parlier, CA, USA
| | - T J Michailides
- Department of Plant Pathology, University of California-Davis, Kearney Agricultural Research and Extension Center, Parlier, CA, USA
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Ortega-Beltran A, Moral J, Picot A, Puckett RD, Cotty PJ, Michailides TJ. Atoxigenic Aspergillus flavus Isolates Endemic to Almond, Fig, and Pistachio Orchards in California with Potential to Reduce Aflatoxin Contamination in these Crops. Plant Dis 2019; 103:905-912. [PMID: 30807246 DOI: 10.1094/pdis-08-18-1333-re] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
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 significantly (P < 0.001) reduced (>80%) aflatoxin accumulation in almond and pistachio when challenged with highly toxigenic isolates of A. flavus and A. parasiticus under laboratory conditions. Isolates of the evaluated VCGs, including AF36, constitute valuable endemic, well-adapted, and efficient germplasm to design a multi-crop, multi-strain biocontrol strategy for use in tree crops in California. Availability of such a strategy would favor long-term atoxigenic A. flavus communities across the affected areas of California, and this would result in securing domestic and export markets for the nut crop and fig farmer industries and, most importantly, health benefits to consumers.
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Affiliation(s)
- Alejandro Ortega-Beltran
- 1 Department of Plant Pathology, University of California, Davis, and Kearney Agricultural Research and Extension Center, Parlier, CA 93648; and
| | - Juan Moral
- 1 Department of Plant Pathology, University of California, Davis, and Kearney Agricultural Research and Extension Center, Parlier, CA 93648; and
| | - Adeline Picot
- 1 Department of Plant Pathology, University of California, Davis, and Kearney Agricultural Research and Extension Center, Parlier, CA 93648; and
| | - Ryan D Puckett
- 1 Department of Plant Pathology, University of California, Davis, and Kearney Agricultural Research and Extension Center, Parlier, CA 93648; and
| | - Peter J Cotty
- 2 United States Department of Agriculture-Agricultural Research Service, School of Plant Sciences, The University of Arizona, Tucson, AZ 85721
| | - Themis J Michailides
- 1 Department of Plant Pathology, University of California, Davis, and Kearney Agricultural Research and Extension Center, Parlier, CA 93648; and
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Ortega-Beltran A, Moral J, Puckett RD, Morgan DP, Cotty PJ, Michailides TJ. Fungal communities associated with almond throughout crop development: Implications for aflatoxin biocontrol management in California. PLoS One 2018; 13:e0199127. [PMID: 29924839 PMCID: PMC6010285 DOI: 10.1371/journal.pone.0199127] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2018] [Accepted: 06/03/2018] [Indexed: 11/18/2022] Open
Abstract
Interactions between pathogenic and nonpathogenic fungal species in the tree canopy are complex and can determine if disease will manifest in the plant and in other organisms such as honey bees. Seasonal dynamics of fungi were studied in an almond orchard in California where experimental release of the atoxigenic biopesticide Aspergillus flavus AF36 to displace toxigenic Aspergillus strains has been conducted for five years. The presence of the vegetative compatibility group (VCG) YV36, to which AF36 belongs, in the blossoms, and the honey bees that attend these blossoms, was assessed. In blossoms, A. flavus frequencies ranged from 0 to 4.5%, depending on the year of study. Frequencies of honey bees carrying A. flavus ranged from 6.5 to 10%. Only one A. flavus isolate recovered from a blossom in 2016 belonged to YV36, while members of the VCG were not detected contaminating honey bees. Exposure of pollinator honey bees to AF36 was detected to be very low. The density of several Aspergillus species was found to increase during almond hull split and throughout the final stages of maturation; this also occurred in pistachio orchards during the maturation period. Additionally, we found that AF36 effectively limited almond aflatoxin contamination in laboratory assays. This study provides knowledge and understanding of the seasonal dynamics of Aspergillus fungi and will help design aflatoxin management strategies for almond. The evidence of the low levels of VCG YV36 encountered on almond blossoms and bees during pollination and AF36's effectiveness in limiting aflatoxin contamination in almond provided additional support for the registration of AF36 with USEPA to use in almond in California.
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Affiliation(s)
- Alejandro Ortega-Beltran
- Department of Plant Pathology, University of California Davis, Davis, California, United States of America
- Kearney Agricultural Research and Extension Center, Parlier, California, United States of America
| | - Juan Moral
- Department of Plant Pathology, University of California Davis, Davis, California, United States of America
- Kearney Agricultural Research and Extension Center, Parlier, California, United States of America
| | - Ryan D. Puckett
- Department of Plant Pathology, University of California Davis, Davis, California, United States of America
- Kearney Agricultural Research and Extension Center, Parlier, California, United States of America
| | - David P. Morgan
- Department of Plant Pathology, University of California Davis, Davis, California, United States of America
- Kearney Agricultural Research and Extension Center, Parlier, California, United States of America
| | - Peter J. Cotty
- USDA-ARS, School of Plant Sciences, University of Arizona, Tucson, Arizona, United States of America
| | - Themis J. Michailides
- Department of Plant Pathology, University of California Davis, Davis, California, United States of America
- Kearney Agricultural Research and Extension Center, Parlier, California, United States of America
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Luo Y, Gu S, Felts D, Puckett RD, Morgan DP, Michailides TJ. Development of qPCR systems to quantify shoot infections by canker-causing pathogens in stone fruits and nut crops. J Appl Microbiol 2016; 122:416-428. [PMID: 27862716 DOI: 10.1111/jam.13350] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2016] [Revised: 11/06/2016] [Accepted: 11/07/2016] [Indexed: 11/29/2022]
Abstract
AIMS To develop real-time PCR assays for quantification of shoot infection levels of canker disease of stone fruits and nut crops caused by six fungal pathogen groups. METHODS AND RESULTS This study focused on six major canker-causing fungal pathogen groups: Phomopsis sp., Botryosphaeria dothidea, Lasiodiplodia sp., Cytospora sp., Neofusicoccum sp. and Diplodia sp., occurring in stone fruits and nut crops in California. DNA primers were designed to specifically target each of the six pathogen groups after the specificity tests using canker-causing and non-canker-causing pathogens and by using DNA sequences of other species from GenBank using blast. The quantitative real-time PCR (qPCR) systems were developed and used to quantify the infection levels of inoculated dried plum shoots. CONCLUSIONS For Neofusicoccum sp. and Phomopsis sp., which were used in inoculation of walnut shoots, the values of the molecular severity ranged from 5·60 to 6·94 during the 16 days of latent infection period. The qPCR assays were more efficient, accurate and precise to quantify latent infections caused by canker-causing pathogens as compared to the traditional plating methods. SIGNIFICANCE AND IMPACT OF THE STUDY This study demonstrated the potential of using the developed qPCR systems for epidemiological studies on canker diseases of woody plants.
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Affiliation(s)
- Y Luo
- Department of Plant Pathology, University of California-Davis, Kearney Agricultural Research and Extension Center, Parlier, CA, USA
| | - S Gu
- Department of Plant Pathology, University of California-Davis, Kearney Agricultural Research and Extension Center, Parlier, CA, USA
| | - D Felts
- Department of Plant Pathology, University of California-Davis, Kearney Agricultural Research and Extension Center, Parlier, CA, USA
| | - R D Puckett
- Department of Plant Pathology, University of California-Davis, Kearney Agricultural Research and Extension Center, Parlier, CA, USA
| | - D P Morgan
- Department of Plant Pathology, University of California-Davis, Kearney Agricultural Research and Extension Center, Parlier, CA, USA
| | - T J Michailides
- Department of Plant Pathology, University of California-Davis, Kearney Agricultural Research and Extension Center, Parlier, CA, USA
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Donner M, Lichtemberg PSF, Doster M, Picot A, Cotty PJ, Puckett RD, Michailides TJ. Community Structure of Aspergillus flavus and A. parasiticus in Major Almond-Producing Areas of California, United States. Plant Dis 2015; 99:1161-1169. [PMID: 30695944 DOI: 10.1094/pdis-05-14-0450-re] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Several nut crops, including almond, pistachio, and walnut, can become contaminated with mycotoxins. Of greatest economic significance are aflatoxins, which are mainly produced by members of Aspergillus section Flavi. The distribution of the two sclerotial-size morphotypes of Aspergillus flavus (i.e., S and L strains) and A. parasiticus, the main species responsible for aflatoxin production among section Flavi, was monitored in the soil of almond orchards in California over a 5-year period from 2007 to 2011, excluding 2009. In total, 4,349 Aspergillus isolates were collected from 28 almond orchards located in the northern, central, and southern Central Valley in California. Overall, A. flavus L strain was the most frequent, followed by A. parasiticus and A. flavus S strain. However, variations in the spatial distribution of these three taxa were found between the three regions. Over the 5-year period, higher frequencies of L strain were more often observed in the southern region (79.9 to 95.1%, depending on year) compared with the northern region (21.4 to 47.1%). In the north, A. parasiticus was the most common strain, with frequencies of 28.5 to 61% for the various years. In addition, the frequency of aflatoxin-producing isolates among L strains fluctuated from year to year. A significant increase (P = 0.0001) was observed from 2008 (75% of the isolates produced aflatoxins) to 2007 (59%), and a decrease was observed from 2010 (61%) to 2011 (53%). Aflatoxin-producing L strain isolates were significantly more prevalent than atoxigenic isolates in each region during the 5-year survey, except in 2011 in the north, where more isolates were atoxigenic (56%) than aflatoxin-producing (44%). Our results indicate that the structure of A. flavus and A. parasiticus communities in the soil and the proportion of toxigenic isolates vary across regions and years. Such knowledge may help devise appropriate aflatoxin control strategies, including the use of atoxigenic isolates as biological control agents adapted to the soil environments in each region.
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Affiliation(s)
- Matthias Donner
- Department of Plant Pathology, University of California, Davis, Kearney Agricultural Research and Extension Center, Parlier 93648
| | - Paulo S F Lichtemberg
- Department of Crop Protection, Federal University of Paraná State, Curitiba, PR 80035-050, Brazil
| | - Mark Doster
- Department of Plant Pathology, University of California, Davis, Kearney Agricultural Research and Extension Center
| | - Adeline Picot
- Department of Plant Pathology, University of California, Davis, Kearney Agricultural Research and Extension Center
| | - Peter J Cotty
- Department of Plant Science, University of Arizona, United States Department of Agriculture-Agricultural Research Service, Division of Plant Pathology and Microbiology, Tucson 85721
| | - Ryan D Puckett
- Department of Plant Pathology, University of California, Davis, Kearney Agricultural Research and Extension Center
| | - Themis J Michailides
- Department of Plant Pathology, University of California, Davis, Kearney Agricultural Research and Extension Center
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Palumbo JD, Mahoney NE, Light DM, Siegel J, Puckett RD, Michailides TJ. Spread of Aspergillus flavus by Navel Orangeworm (Amyelois transitella) on Almond. Plant Dis 2014; 98:1194-1199. [PMID: 30699615 DOI: 10.1094/pdis-09-13-1015-re] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Navel orangeworm (NOW) damage to almond is correlated with increased incidence of aflatoxin contamination caused by Aspergillus flavus. However, no reports demonstrate a causative relationship between NOW feeding and A. flavus infection. To demonstrate the potential of NOW to act as a vector of A. flavus on almond, NOW eggs were dusted with A. flavus and incubated in microchambers adjacent to but not touching agar plates or almond kernels. Following egg hatch, A. flavus colonies developed on agar along trails left by NOW larvae. Almond kernels damaged with A. flavus-carrying NOW showed higher incidence of A. flavus colonization and aflatoxin contamination than control treatments. Interestingly, levels of aflatoxin in NOW-damaged, A. flavus-infected almond were significantly higher than control treatments, even in the absence of visible fungal growth. Commercial almond orchards had a relatively low level of contamination with Aspergillus section Flavi in spring and early summer and a high level during summer, corresponding with the higher level of NOW infestation of the crop. Our study demonstrates that NOW is capable of vectoring A. flavus to almond, and that monitoring and sorting of almond kernels for insect damage is warranted to limit aflatoxin contamination potential both before and after harvesting.
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Affiliation(s)
- Jeffrey D Palumbo
- Plant Mycotoxin Research Unit, Western Regional Research Center, United States Department of Agriculture-Agricultural Research Service (USDA-ARS) Albany, CA 94710
| | - Noreen E Mahoney
- Plant Mycotoxin Research Unit, Western Regional Research Center, United States Department of Agriculture-Agricultural Research Service (USDA-ARS) Albany, CA 94710
| | - Douglas M Light
- Plant Mycotoxin Research Unit, Western Regional Research Center, United States Department of Agriculture-Agricultural Research Service (USDA-ARS) Albany, CA 94710
| | - Joel Siegel
- USDA-ARS, San Joaquin Valley Agricultural Sciences Center, Parlier CA 93648-9757
| | - Ryan D Puckett
- University of California-Davis, Kearney Agricultural Research and Extension Center, Parlier 93648
| | - Themis J Michailides
- University of California-Davis, Kearney Agricultural Research and Extension Center, Parlier 93648
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