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H Scherm
Department of Plant Pathology, University of Georgia, 2105 Miller Plant Sciences, 120 Carlton Street, Athens, GA 30602, USA

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Journal article
Published: 30 September 2020 in Horticulturae
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Blueberry fruit are perishable after harvesting due to fruit softening, water loss and susceptibility to pathogens. Light, especially blue light, increases the accumulation of anthocyanins and reduces postharvest decay in some fruits, but the effect of blue light on postharvest fruit quality attributes in blueberries is unknown. In this study, we evaluated the effect of blue light on fruit quality, anthocyanin accumulation and disease development during postharvest cold storage (2 °C–4 °C) in two experiments with southern highbush blueberry ‘Star’ and rabbiteye blueberry ‘Alapaha’. Overall, diurnal blue light did not affect postharvest fruit quality attributes, such as visual defects, fruit compression, skin puncture, total soluble solid content and titratable acidity, in the two cultivars compared with their respective controls (diurnal white light or continuous darkness). Further, there was no effect of blue light on fruit color and anthocyanin accumulation. Fruit disease incidence in ‘Star’ ranged from 19.0% to 27.3% after 21 days and in ‘Alapaha’ from 44.9% to 56.2% after 24 days in postharvest storage, followed by 4 days at room temperature, but blue light had no consistent effect on postharvest disease incidence for either cultivar. Disease progression following artificial inoculations with Alternaria tenuissima and Colletotrichum acutatum in ‘Star’ was not influenced by light treatment prior to inoculation and during fruit storage. In a separate experiment, we tested the effect of blue light on color development in ‘Farthing’, a southern highbush blueberry cultivar with fruit prone to non-uniform ripening, whereby the stem-end remains green as the rest of the fruit turns blue. Although green stem-end spots turned blue over time, there was no statistically significant effect of the blue light treatment. Overall, these data indicate that blue light does not affect fruit quality attributes or disease development in ripe blueberry fruit during postharvest storage in the conditions investigated here.

ACS Style

Yi-Wen Wang; Helaina Ludwig; Harald Scherm; Marc van Iersel; Savithri Nambeesan. Blue Light Does Not Affect Fruit Quality or Disease Development on Ripe Blueberry Fruit During Postharvest Cold Storage. Horticulturae 2020, 6, 59 .

AMA Style

Yi-Wen Wang, Helaina Ludwig, Harald Scherm, Marc van Iersel, Savithri Nambeesan. Blue Light Does Not Affect Fruit Quality or Disease Development on Ripe Blueberry Fruit During Postharvest Cold Storage. Horticulturae. 2020; 6 (4):59.

Chicago/Turabian Style

Yi-Wen Wang; Helaina Ludwig; Harald Scherm; Marc van Iersel; Savithri Nambeesan. 2020. "Blue Light Does Not Affect Fruit Quality or Disease Development on Ripe Blueberry Fruit During Postharvest Cold Storage." Horticulturae 6, no. 4: 59.

Original article
Published: 02 September 2020 in Plant Pathology
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The North Georgia Mountains are the southernmost region along the United States East Coast where European wine grapes (Vitis vinifera) are grown commercially. Epidemics of downy mildew, caused by Plasmopara viticola, are frequent and severe, but little is known about the epidemiology and the population biology of the pathogen in this region. Disease monitoring in an experimental vineyard from 2015 to 2017 indicated that times of disease onset and progress rates were highly variable across years and cultivars. Oospores were observed microscopically, and simulation with a process‐based model indicated presence of conditions favorable for oospore germination in the spring and early summer each year. A total of 409 P. viticola isolates collected over 3 years were genotyped with seven microsatellite markers, revealing very high genotypic diversity, which when combined with the observation of oospores is indicative of a sexually reproducing population. Among the 409 isolates, 225 multilocus genotypes (MLG) were identified, of which 164 were detected only once and 61 were repeated (clonal). Eight MLG (represented by 28 isolates) were detected across years, suggesting the possibility of asexual overwintering of P. viticola in this region. Across sampling dates, the percentage of isolates belonging to non‐repeated (unique) MLG ranged from 27.3 to 63.2%. Even toward the end of the annual epidemic, the percentage of isolates in non‐repeated MLG was still relatively high around 30%. These MLG may have originated from oospores germinating late during the growing season, although incomplete sampling at earlier dates and contribution by immigration cannot be fully excluded.

ACS Style

Cheng‐Fang Hong; Marin T. Brewer; Phillip M. Brannen; Harald Scherm. Temporal disease dynamics and relative importance of sexual and asexual reproduction of grape downy mildew ( Plasmopara viticola ) in an isolated vineyard in the North Georgia Mountains, USA. Plant Pathology 2020, 69, 1721 -1730.

AMA Style

Cheng‐Fang Hong, Marin T. Brewer, Phillip M. Brannen, Harald Scherm. Temporal disease dynamics and relative importance of sexual and asexual reproduction of grape downy mildew ( Plasmopara viticola ) in an isolated vineyard in the North Georgia Mountains, USA. Plant Pathology. 2020; 69 (9):1721-1730.

Chicago/Turabian Style

Cheng‐Fang Hong; Marin T. Brewer; Phillip M. Brannen; Harald Scherm. 2020. "Temporal disease dynamics and relative importance of sexual and asexual reproduction of grape downy mildew ( Plasmopara viticola ) in an isolated vineyard in the North Georgia Mountains, USA." Plant Pathology 69, no. 9: 1721-1730.

Original article
Published: 22 March 2020 in Journal of Phytopathology
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A spectrophotometric method for determining the viability of sporangia and zoospores of the oomycete Plasmopara viticola (causal agent of grapevine downy mildew) is described and evaluated to overcome the limitations of currently available methods for assessing propagule viability. Sporangia produced on leaf discs in the laboratory were harvested at different days after the initiation of sporulation (DAS) to yield differences in sporangium viability. Sporangia were suspended in sterile water, the suspensions were placed in a cuvette, and sporangium germination was monitored in a spectrophotometer (λ = 600 nm) at 2‐ to 3‐min intervals for 5 hr. Absorbance started to increase after sporangia were suspended in water for ~30–60 min followed by major peak(s) for younger sporangia (1–3 DAS), whereas low to no increase in absorbance was observed for senescent sporangia (>7 DAS). Microscopic observation confirmed that the increase in absorbance corresponded to the release and active swimming of zoospores, whereas absorbance decreased when zoospores encysted and settled. A positive correlation (r = .839, p = .0365) was observed when the time to the initial increase in absorbance was plotted against the age of sporangia. The time to the absorbance peak (marking the time of maximum zoospore movement) was shortest for immature sporangia (0 DAS), longest for young sporangia (2 DAS) and decreased for mature and senescent sporangia. A similar pattern was observed for the standardized area under the absorbance curve (indicating the overall quantity of zoospores released), for which values were lowest for immature and senescent sporangia, highest for young sporangia and intermediate for mature sporangia. Consistent patterns obtained across two independent experiments suggest that the method is reproducible and may be further developed for other zoospore‐releasing pathogens.

ACS Style

Cheng‐Fang Hong; Harald Scherm. A spectrophotometric approach for determining sporangium and zoospore viability of Plasmopara viticola. Journal of Phytopathology 2020, 168, 297 -302.

AMA Style

Cheng‐Fang Hong, Harald Scherm. A spectrophotometric approach for determining sporangium and zoospore viability of Plasmopara viticola. Journal of Phytopathology. 2020; 168 (5):297-302.

Chicago/Turabian Style

Cheng‐Fang Hong; Harald Scherm. 2020. "A spectrophotometric approach for determining sporangium and zoospore viability of Plasmopara viticola." Journal of Phytopathology 168, no. 5: 297-302.

Research article
Published: 01 January 2020 in Plant Disease
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Orange cane blotch (OCB), an algal disease on commercial blackberry plants in the southeastern United States, has been an increasing concern among producers. The causal agent, Cephaleuros virescens, produces brightly colored green to orange lesions on blackberry stems, but proof of actual damage and impact on crop yield has not been documented. Naturally infected stem sections were viewed using transmission and scanning electron microscopy to evaluate cane damage. Surface abrasions, intercellular growth, and occasional intracellular growth were observed on the surface and epidermal layers. Field studies at four commercial sites over 2 years were conducted to assess the impact of OCB on yield in ‘Ouachita’ blackberry plants not treated with algicidal chemicals. Neither cane diameter nor berry size was impacted by severity of OCB; however, berry number decreased with increasing OCB intensity in a nonlinear manner, thereby resulting in reduced yields.

ACS Style

Frances B. Browne; Phillip M. Brannen; Harald Scherm; Elizabeth A. Richardson; Jeremy R. Taylor. Yield Response to Orange Cane Blotch of Blackberry Grown in the Georgia Coastal Plain. Plant Disease 2020, 104, 161 -167.

AMA Style

Frances B. Browne, Phillip M. Brannen, Harald Scherm, Elizabeth A. Richardson, Jeremy R. Taylor. Yield Response to Orange Cane Blotch of Blackberry Grown in the Georgia Coastal Plain. Plant Disease. 2020; 104 (1):161-167.

Chicago/Turabian Style

Frances B. Browne; Phillip M. Brannen; Harald Scherm; Elizabeth A. Richardson; Jeremy R. Taylor. 2020. "Yield Response to Orange Cane Blotch of Blackberry Grown in the Georgia Coastal Plain." Plant Disease 104, no. 1: 161-167.

Journal article
Published: 01 June 2019 in Plant Disease
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Epidemiological field studies utilizing disease monitoring, spore trapping, and trap plants were conducted on rabbiteye blueberry (Vaccinium virgatum) between 2014 and 2017 to shed light on the epidemiology of Exobasidium leaf and fruit spot, an emerging disease in the southeastern United States caused by the fungus Exobasidium maculosum. Wash plating of field-collected blueberry tissue from the late dormant season through bud expansion showed that the pathogen overwintered epiphytically on blueberry plants in the field, most likely in its yeast-like conidial stage. Agrichemical applications during the dormant season altered epiphytic populations of the pathogen, which correlated directly with leaf spot incidence later in the spring. Disease monitoring of field plants and weekly exposure of potted trap plants revealed that young leaves at the mouse-ear stage were most susceptible to infection, that disease incidence on leaves progressed monocyclically, and that infection periods were associated with rainfall variables such as the number of days per week with ≥1.0 mm of rain or cumulative weekly rainfall. Weekly spore trapping with an Andersen sampler showed that airborne inoculum was detected only after sporulating leaf lesions producing basidiospores were present in the field, suggesting that the primary inoculum is not airborne. The first symptoms on young, green fruit were observed soon after petal fall (requiring removal of the waxy fruit layer to visualize lesions), and visible disease progress on fruit was delayed by 1 to 3 weeks relative to that on leaves. Fruit infection of field plants and trap plants occurred before airborne propagules were detected by spore trapping and before sporulating leaf lesions were present in the field. Hence, this study showed that fruit infections are initiated by the same initial inoculum as leaf infections but it was not possible to conclusively exclude the possibility of a contribution of basidiospore inoculum from leaf lesions to disease progress on later developing fruit. This is one of only a few studies addressing the epidemiology and disease cycle of an Exobasidium sp. in a pathosystem where artificial inoculation has not been possible to date.

ACS Style

R. J. Ingram; H. D. Ludwig; H. Scherm. Epidemiology of Exobasidium Leaf and Fruit Spot of Rabbiteye Blueberry: Pathogen Overwintering, Primary Infection, and Disease Progression on Leaves and Fruit. Plant Disease 2019, 103, 1293 -1301.

AMA Style

R. J. Ingram, H. D. Ludwig, H. Scherm. Epidemiology of Exobasidium Leaf and Fruit Spot of Rabbiteye Blueberry: Pathogen Overwintering, Primary Infection, and Disease Progression on Leaves and Fruit. Plant Disease. 2019; 103 (6):1293-1301.

Chicago/Turabian Style

R. J. Ingram; H. D. Ludwig; H. Scherm. 2019. "Epidemiology of Exobasidium Leaf and Fruit Spot of Rabbiteye Blueberry: Pathogen Overwintering, Primary Infection, and Disease Progression on Leaves and Fruit." Plant Disease 103, no. 6: 1293-1301.

Original article
Published: 24 April 2019 in Journal of Phytopathology
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Previous phylogenetic studies of the grape downy mildew pathogen, Plasmopara viticola, revealed five cryptic species in eastern North America that differed in their host range and geographic distribution. Preliminary comparative studies also documented differences in temperature responses during infection between certain cryptic species, indicating the biological relevance of knowing which cryptic species of the pathogen are present in a given region. However, limited information is available regarding the presence, prevalence and dynamics of cryptic species of P. viticola in the southeastern United States. Here, 301 P. viticola isolates obtained from cultivated grape species in five distinct grape‐growing regions of Georgia and Florida were subjected to cleaved amplified polymorphic sequence analysis and multilocus sequencing (internal transcribed spacer region of the rDNA, actin and β‐tubulin) to identify cryptic species and infer phylogenetic relationships. Three cryptic species, P. viticola clade aestivalis (Pva), clade vinifera (Pvv) and clade vulpina (Pvu), were identified in Georgia, whereas two, Pva and Pvv, were found in Florida; all three cryptic species are reported here for the first time in Georgia, whereas Pva is reported for the first time in Florida. Pva was the most prevalent cryptic species (72.1% of isolates) and was distributed widely from the North Georgia Mountains to Mid‐Florida, whereas Pvv (27.2%) and Pvu (0.7%) were found only in the Coastal Plain region of the two states. Interestingly, Pvu was obtained from French American hybrid Blanc du Bois and could be subcultured on Vitis vinifera Chardonnay, suggesting a broader host range than only the wild species Vitis vulpina reported previously.

ACS Style

Cheng‐Fang Hong; Marin T. Brewer; Phillip M. Brannen; Harald Scherm. Prevalence, geographic distribution and phylogenetic relationships among cryptic species of Plasmopara viticola in grape‐producing regions of Georgia and Florida, USA. Journal of Phytopathology 2019, 167, 422 -429.

AMA Style

Cheng‐Fang Hong, Marin T. Brewer, Phillip M. Brannen, Harald Scherm. Prevalence, geographic distribution and phylogenetic relationships among cryptic species of Plasmopara viticola in grape‐producing regions of Georgia and Florida, USA. Journal of Phytopathology. 2019; 167 (7-8):422-429.

Chicago/Turabian Style

Cheng‐Fang Hong; Marin T. Brewer; Phillip M. Brannen; Harald Scherm. 2019. "Prevalence, geographic distribution and phylogenetic relationships among cryptic species of Plasmopara viticola in grape‐producing regions of Georgia and Florida, USA." Journal of Phytopathology 167, no. 7-8: 422-429.

Original article
Published: 25 January 2019 in Plant Pathology
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Downy mildew (Plasmopara viticola) is one of the most important diseases in grape‐growing areas worldwide, including Brazil. To examine pathogen population biology and structure, 516 single lesions colonized by P. viticola were sampled during 2015/16 growing season from 9 grape cultivars in 11 locations in subtropical areas of São Paulo State, Brazil. For identification of cryptic species, a subsample of 130 isolates was subjected to cleaved amplified polymorphic sequence analysis, and for 91 of these isolates the ITS1 region was sequenced. These analyses suggest that the population of P. viticola in São Paulo State consists of a single cryptic species, P. viticola clade aestivalis. Seven microsatellite markers were used to determine the genetic structure of all 516 P. viticola isolates, whereby 23 alleles and 55 multilocus genotypes (MLG) were observed. Among these MLG, 34.5% were clonal and represented 93% of the isolates sampled. Four dominant genotypes were present in at least 5 different locations, corresponding to 65.7% of the sampled isolates. Genotypic diversity (Ĝ = 0.21 to 0.89) and clonal fraction (0.58 to 0.96) varied among locations (populations). Most populations showed significant deviation from Hardy‐Weinberg expectations; in addition, excess of heterozygosity was verified for many loci. However, principal coordinate analysis revealed no clusters among locations, and no significant isolation by distance was found, suggesting high levels of migration. The results indicate that downy mildew epidemics result from multiple clonal infections caused by a few genotypes of P. viticola, and reproduction of P. viticola in São Paulo State is predominantly asexual. This article is protected by copyright. All rights reserved.

ACS Style

M. P. Camargo; C. F. Hong; L. Amorim; H. Scherm. Cryptic species and population genetic structure ofPlasmopara viticolain São Paulo State, Brazil. Plant Pathology 2019, 68, 719 -726.

AMA Style

M. P. Camargo, C. F. Hong, L. Amorim, H. Scherm. Cryptic species and population genetic structure ofPlasmopara viticolain São Paulo State, Brazil. Plant Pathology. 2019; 68 (4):719-726.

Chicago/Turabian Style

M. P. Camargo; C. F. Hong; L. Amorim; H. Scherm. 2019. "Cryptic species and population genetic structure ofPlasmopara viticolain São Paulo State, Brazil." Plant Pathology 68, no. 4: 719-726.

Journal article
Published: 05 September 2018 in Horticulturae
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With the growing popularity of blueberries and the associated increase in blueberry imports and exports worldwide, delivering fruit with high quality, longer shelf-life, and meeting phytosanitary requirements has become increasingly important. The objective of this study was to determine the effects of electron beam irradiation using a new Electronic Cold-PasteurizationTM (ECPTM) technology on fruit quality, microbial safety, and postharvest disease development in two southern highbush blueberry cultivars, ‘Farthing’ and ‘Rebel’. Fruit packed in clamshells were subjected to four levels of ECPTM irradiation (0, 0.15, 0.5, and 1.0 kGy) and evaluated for fruit quality attributes, surface microbial load, and postharvest disease incidence during various storage times after treatment and cold storage. Overall, there was no effect of irradiation on visual fruit quality in either cultivar. Fruit firmness and skin toughness in ‘Farthing’ was reduced following irradiation at 1.0 kGy, but no such effect was observed in ‘Rebel’. Other fruit quality characteristics such as fruit weight, total soluble solids content, or titratable acidity were not affected. Irradiation at 1.0 kGy significantly reduced total aerobic bacteria and yeast on the fruit surface, and in the case of ‘Rebel’, also levels of total coliform bacteria. There was no significant effect of irradiation on postharvest disease incidence in these trials. Overall, data from this study suggests that an irradiation dose lower than 1.0 kGy using ECPTM can be useful for phytosanitary treatment in blueberry fruit while avoiding undesirable effects on fruit quality in a cultivar-dependent manner.

ACS Style

Savithri U. Nambeesan; John W. Doyle; Helaina D. Capps; Chip Starns; Harald Scherm. Effect of Electronic Cold-PasteurizationTM (ECPTM) on Fruit Quality and Postharvest Diseases during Blueberry Storage. Horticulturae 2018, 4, 25 .

AMA Style

Savithri U. Nambeesan, John W. Doyle, Helaina D. Capps, Chip Starns, Harald Scherm. Effect of Electronic Cold-PasteurizationTM (ECPTM) on Fruit Quality and Postharvest Diseases during Blueberry Storage. Horticulturae. 2018; 4 (3):25.

Chicago/Turabian Style

Savithri U. Nambeesan; John W. Doyle; Helaina D. Capps; Chip Starns; Harald Scherm. 2018. "Effect of Electronic Cold-PasteurizationTM (ECPTM) on Fruit Quality and Postharvest Diseases during Blueberry Storage." Horticulturae 4, no. 3: 25.

Journal article
Published: 01 September 2018 in Horticulturae
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Ripening in blueberry fruit is irregular and occurs over an extended period requiring multiple harvests, thereby increasing the cost of production. Several phytohormones contribute to the regulation of fruit ripening. Certain plant growth regulators (PGRs) can alter the content, perception, or action of these phytohormones, potentially accelerating fruit ripening and concentrating the ripening period. The effects of three such PGRs—ethephon, abscisic acid, and methyl jasmonate—on fruit ripening were evaluated in the rabbiteye blueberry (Vaccinium virgatum) cultivars ‘Premier’ and ‘Powderblue’. Application of ethephon, an ethylene-releasing PGR, at 250 mg L−1 when 30–40% of fruit on the plant were ripe, accelerated ripening by increasing the proportion of blue (ripe) fruit by 1.5–1.8-fold within 4 to 7 days after treatment in both cultivars. Ethephon applications did not generally alter fruit quality characteristics at harvest or during postharvest storage, except for a slight decrease in juice pH at 1 day of postharvest storage and an increase in fruit firmness and titratable acidity after 15 days of postharvest storage in Powderblue. In Premier, ethephon applications decreased the proportion of defective fruit at 29 days of postharvest storage. Abscisic acid (600–1000 mg L−1) and methyl jasmonate (0.5–1 mM) applications did not alter the proportion of ripe fruit in either cultivar. These applications also had little effect on fruit quality characteristics at harvest and during postharvest storage. None of the above PGR applications affected the development of naturally occurring postharvest pathogens during storage. Together, data from this study indicated that ethephon has the potential to accelerate ripening in rabbiteye blueberry fruit, allowing for a potential decrease in the number of fruit harvests.

ACS Style

Yi-Wen Wang; Anish Malladi; John W. Doyle; Harald Scherm; Savithri U. Nambeesan. The Effect of Ethephon, Abscisic Acid, and Methyl Jasmonate on Fruit Ripening in Rabbiteye Blueberry (Vaccinium virgatum). Horticulturae 2018, 4, 24 .

AMA Style

Yi-Wen Wang, Anish Malladi, John W. Doyle, Harald Scherm, Savithri U. Nambeesan. The Effect of Ethephon, Abscisic Acid, and Methyl Jasmonate on Fruit Ripening in Rabbiteye Blueberry (Vaccinium virgatum). Horticulturae. 2018; 4 (3):24.

Chicago/Turabian Style

Yi-Wen Wang; Anish Malladi; John W. Doyle; Harald Scherm; Savithri U. Nambeesan. 2018. "The Effect of Ethephon, Abscisic Acid, and Methyl Jasmonate on Fruit Ripening in Rabbiteye Blueberry (Vaccinium virgatum)." Horticulturae 4, no. 3: 24.

Journal article
Published: 01 June 2017 in Crop Protection
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ACS Style

Sara Thomas-Sharma; Harald Scherm. Pre- and post-anthesis activity of fenbuconazole and triforine against blueberry flower infection by Monilinia vaccinii-corymbosi. Crop Protection 2017, 96, 180 -187.

AMA Style

Sara Thomas-Sharma, Harald Scherm. Pre- and post-anthesis activity of fenbuconazole and triforine against blueberry flower infection by Monilinia vaccinii-corymbosi. Crop Protection. 2017; 96 ():180-187.

Chicago/Turabian Style

Sara Thomas-Sharma; Harald Scherm. 2017. "Pre- and post-anthesis activity of fenbuconazole and triforine against blueberry flower infection by Monilinia vaccinii-corymbosi." Crop Protection 96, no. : 180-187.

Journal article
Published: 21 December 2016 in Journal of Phytopathology
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Flowers can serve as infection courts for specialized and unspecialized plant pathogens, but little is known about the ability of floral tissues to undergo induced resistance (IR) responses against these pathogens. We studied the expression of IR marker genes in tomato and blueberry flowers treated with the inducers methyl jasmonate (MeJA), benzothiadiazole-S-methyl ester (BTH) and 2,6-dichloroisonicotinic acid (INA). In tomato, spray application of MeJA and BTH (but not INA) to entire plants (leaves, stems and flowers) resulted in a significant (P < 0.05) overexpression of Pin2 (5.2-fold) and PR-4 (5.6-fold) in pistil tissues, respectively. A statistically similar expression was obtained in pistils when flowers were protected from direct spray, indicating a systemic response. In blueberry, where information about IR marker genes is limited, PR-3 and PR-4 orthologs were first identified and characterized using in silico and wet-laboratory techniques. In subsequent induction experiments, INA and BTH induced overexpression of PR-4 in blueberry pistils by 3.2- and 1.8-fold, respectively, when entire plants were treated. In blueberry flowers protected from spray applications, all chemicals applied to vegetative tissues led to significant overexpression of PR-4 (MeJA: 1.4-fold, BTH: 2.9-fold and INA: 1.6-fold), with BTH also inducing PR-3 (1.7-fold). The effect of these responses in protecting flowers was studied by inoculating treated tomato flowers with the necrotroph Botrytis cinerea and blueberry flowers with the hemi-biotroph Monilinia vaccinii-corymbosi. In both pathosystems, no significant disease suppression associated with resistance inducer application was observed under the conditions studied. Thus, although IR marker genes were shown to be inducible in floral tissue, the magnitude of this response was insufficient to suppress pathogen ingress.

ACS Style

Sara Thomas-Sharma; James H. Leebens-Mack; Harald Scherm. Marker Gene Overexpression in Flowers Treated with Resistance Inducers does not Correlate with Protection Against Flower-Infecting Fungi in Tomato and Blueberry. Journal of Phytopathology 2016, 165, 53 -63.

AMA Style

Sara Thomas-Sharma, James H. Leebens-Mack, Harald Scherm. Marker Gene Overexpression in Flowers Treated with Resistance Inducers does not Correlate with Protection Against Flower-Infecting Fungi in Tomato and Blueberry. Journal of Phytopathology. 2016; 165 (1):53-63.

Chicago/Turabian Style

Sara Thomas-Sharma; James H. Leebens-Mack; Harald Scherm. 2016. "Marker Gene Overexpression in Flowers Treated with Resistance Inducers does not Correlate with Protection Against Flower-Infecting Fungi in Tomato and Blueberry." Journal of Phytopathology 165, no. 1: 53-63.

Research article
Published: 01 January 2016 in Plant Disease
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Blueberry red ringspot virus (BRRV) has become prevalent in southern highbush blueberry in the southeastern United States but information about the yield effects associated with the disease is limited and conflicting. A 3-year study was conducted on mature, container-grown plants of ‘Star’ and ‘Jewel’ blueberry that were either systemically infected or not infected with BRRV to determine the effect of the disease on flower bud numbers and fruit yield and on advances or delays in fruit ripening. On Star, flower bud counts were lower for BRRV-positive plants (P = 0.0137 in one year and P = 0.1085 in another) but no such effect was observed for Jewel. When fruit were harvested over time during the ripening period in the spring, no consistent yield or berry weight reductions were observed due to BRRV infection for either cultivar. On Star, fruit maturity tended to be slightly advanced in BRRV-positive plants in all years. Specifically, the weight of unripe fruit remaining after the last harvest was consistently lower for BRRV-positive plants than for BRRV-negative plants, suggesting that BRRV infection in Star may lead to a shorter fruit ripening period. No such effect on fruit ripening was observed for Jewel. It is concluded that—for the cultivars examined in this study—BRRV causes a relatively benign infection with no negative yield implications.

ACS Style

L. A. Williford; A. T. Savelle; Harald Scherm. Effects of Blueberry red ringspot virus on Yield and Fruit Maturation in Southern Highbush Blueberry. Plant Disease 2016, 100, 171 -174.

AMA Style

L. A. Williford, A. T. Savelle, Harald Scherm. Effects of Blueberry red ringspot virus on Yield and Fruit Maturation in Southern Highbush Blueberry. Plant Disease. 2016; 100 (1):171-174.

Chicago/Turabian Style

L. A. Williford; A. T. Savelle; Harald Scherm. 2016. "Effects of Blueberry red ringspot virus on Yield and Fruit Maturation in Southern Highbush Blueberry." Plant Disease 100, no. 1: 171-174.

Journal article
Published: 01 April 2015 in Phytopathology®
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The purpose of this study was to determine the fine-scale genetic structure of populations of the brown rot pathogen Monilinia fructicola within individual peach tree canopies to better understand within-tree plant pathogen diversity and to complement previous work on spatiotemporal development of brown rot disease at the canopy level. Across 3 years in a total of six trees, we monitored disease development, collected isolates from every M. fructicola symptom during the course of the season, and created high-resolution three-dimensional maps of all symptom and isolate locations within individual canopies using an electromagnetic digitizer. Each canopy population (65 to 173 isolates per tree) was characterized using a set of 13 microsatellite markers and analyzed for evidence of spatial genetic autocorrelation among isolates during the epidemic phase of the disease. Results showed high genetic diversity (average uh = 0.529) and high genotypic diversity (average D = 0.928) within canopies. The percentage of unique multilocus genotypes within trees was greater for blossom blight isolates (78.2%) than for fruit rot isolates (51.3%), indicating a greater contribution of clonal reproduction during the preharvest epidemic. For fruit rot isolates, between 54.2 and 81.7% of isolates were contained in one to four dominant clonal genotypes per tree having at least 10 members. All six fruit rot populations showed positive and significant spatial genetic autocorrelation for distance classes between 0.37 and 1.48 m. Despite high levels of within-tree pathogen diversity, the contribution of locally available inoculum combined with short-distance dispersal is likely the main factor generating clonal population foci and associated spatial genetic clustering within trees.

ACS Style

S. E. Everhart; Harald Scherm. Fine-Scale Genetic Structure of Monilinia fructicola During Brown Rot Epidemics Within Individual Peach Tree Canopies. Phytopathology® 2015, 105, 542 -549.

AMA Style

S. E. Everhart, Harald Scherm. Fine-Scale Genetic Structure of Monilinia fructicola During Brown Rot Epidemics Within Individual Peach Tree Canopies. Phytopathology®. 2015; 105 (4):542-549.

Chicago/Turabian Style

S. E. Everhart; Harald Scherm. 2015. "Fine-Scale Genetic Structure of Monilinia fructicola During Brown Rot Epidemics Within Individual Peach Tree Canopies." Phytopathology® 105, no. 4: 542-549.

Journal article
Published: 01 December 2014 in Journal of Nematology
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Greenhouse tests were conducted to evaluate (i) the effect of Meloidogyne incognita infection in cotton on plant growth and physiology including the height-to-node ratio, chlorophyll content, dark-adapted quantum yield of photosystem II, and leaf area; and (ii) the extent to which moderate or high levels of resistance to M. incognita influenced these effects. Cultivars FiberMax 960 BR (susceptible to M. incognita) and Stoneville 5599 BR (moderately resistant) were tested together in three trials, and PD94042 (germplasm, susceptible) and 120R1B1 (breeding line genetically similar to PD94042, but highly resistant) were paired in two additional trials. Inoculation with M. incognita generally resulted in increases in root gall ratings and egg counts per gram of root compared with the noninoculated control, as well as reductions in plant dry weight, root weight, leaf area, boll number, and boll dry weight, thereby confirming that growth of our greenhouse-grown plants was reduced in the same ways that would be expected in field-grown plants. In all trials, M. incognita caused reductions in height-to-node ratios. Nematode infection consistently reduced the area under the height-to-node ratio curves for all genotypes, and these reductions were similar for resistant and susceptible genotypes (no significant genotype × inoculation interaction). Our study is the first to show that infection by M. incognita is associated with reduced chlorophyll content in cotton leaves, and the reduction in the resistant genotypes was similar to that in the susceptible genotypes (no interaction). The susceptible PD94042 tended to have increased leaf temperature compared with the genetically similar but highly resistant 120R1B1 (P < 0.08), likely attributable to increased water stress associated with M. incognita infection.

ACS Style

Ping Lu; Richard F. Davis; Robert C. Kemerait; Marc W. Van Iersel; Harald Scherm. Physiological Effects of Meloidogyne incognita Infection on Cotton Genotypes with Differing Levels of Resistance in the Greenhouse. Journal of Nematology 2014, 46, 352 -359.

AMA Style

Ping Lu, Richard F. Davis, Robert C. Kemerait, Marc W. Van Iersel, Harald Scherm. Physiological Effects of Meloidogyne incognita Infection on Cotton Genotypes with Differing Levels of Resistance in the Greenhouse. Journal of Nematology. 2014; 46 (4):352-359.

Chicago/Turabian Style

Ping Lu; Richard F. Davis; Robert C. Kemerait; Marc W. Van Iersel; Harald Scherm. 2014. "Physiological Effects of Meloidogyne incognita Infection on Cotton Genotypes with Differing Levels of Resistance in the Greenhouse." Journal of Nematology 46, no. 4: 352-359.

Meta analysis
Published: 04 August 2014 in Annual Review of Phytopathology
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The term data deluge is used widely to describe the rapidly accelerating growth of information in the technical literature, in scientific databases, and in informal sources such as the Internet and social media. The massive volume and increased complexity of information challenge traditional methods of data analysis but at the same time provide unprecedented opportunities to test hypotheses or uncover new relationships via mining of existing databases and literature. In this review, we discuss analytical approaches that are beginning to be applied to help synthesize the vast amount of information generated by the data deluge and thus accelerate the pace of discovery in plant pathology. We begin with a review of meta-analysis as an established approach for summarizing standardized (structured) data across the literature. We then turn to examples of synthesizing more complex, unstructured data sets through a range of data-mining approaches, including the incorporation of 'omics data in epidemiological analyses. We conclude with a discussion of methodologies for leveraging information contained in novel, open-source data sets through web crawling, text mining, and social media analytics, primarily in the context of digital disease surveillance. Rapidly evolving computational resources provide platforms for integrating large and complex data sets, motivating research that will draw on new types and scales of information to address big questions.

ACS Style

H. Scherm; C.S. Thomas; K.A. Garrett; J.M. Olsen. Meta-Analysis and Other Approaches for Synthesizing Structured and Unstructured Data in Plant Pathology. Annual Review of Phytopathology 2014, 52, 453 -476.

AMA Style

H. Scherm, C.S. Thomas, K.A. Garrett, J.M. Olsen. Meta-Analysis and Other Approaches for Synthesizing Structured and Unstructured Data in Plant Pathology. Annual Review of Phytopathology. 2014; 52 (1):453-476.

Chicago/Turabian Style

H. Scherm; C.S. Thomas; K.A. Garrett; J.M. Olsen. 2014. "Meta-Analysis and Other Approaches for Synthesizing Structured and Unstructured Data in Plant Pathology." Annual Review of Phytopathology 52, no. 1: 453-476.

Journal article
Published: 01 April 2014 in Plant Disease
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Xylella fastidiosa causes bacterial leaf scorch, a new disease of southern highbush blueberry in the southeastern United States. Infections occlude the xylem of affected plants, causing drought-like symptoms and, eventually, plant death. To assess the likelihood of mitigation of bacterial leaf scorch through cultural practices such as pruning or hedging of affected plants, we determined the localization and population density of X. fastidiosa in naturally infected blueberry plants with varying levels of bacterial leaf scorch severity. Stem segments were sampled from the current season's growth down to the base of the plant, as were root segments on plants that were either asymptomatic or had light, moderate, or severe symptoms in three plantings affected by the disease. Stem sap was extracted from each segment and population densities of X. fastidiosa were determined using real-time polymerase chain reaction with species-specific primers. Detection frequencies were lowest (but non-zero) in sap from asymptomatic plants and highest in plants with severe symptoms. In asymptomatic plants, detection was generally least frequent (0 to 20.0%) in top and root sections and highest (4.6 to 55.6%) in middle and base stem sections. As disease severity increased, detection frequencies in roots increased to >80% in two plantings and to 60% in the third planting. Overall, detection frequencies were highest (>80%) in middle and base stem sections of plants from the moderate and severe disease classes. The lowest bacterial titers (averaging 0 to 2.1 × 101 CFU per 50 μl of sap) were observed in top and root sections of asymptomatic plants, whereas the highest titers (generally between 104 and 105 CFU per 50 μl of sap) were obtained from middle, base, and root sections of plants from the moderate and severe classes. The presence of the bacterium in middle and base stem sections at low disease severity indicates rapid distribution of X. fastidiosa in affected plants. Because the pathogen accumulates in the roots at moderate and high disease severity levels, management strategies such as pruning and mowing are unlikely to be effective in curing affected plants from bacterial leaf scorch.

ACS Style

R. M. Holland; R. S. C. Christiano; E. Gamliel-Atinsky; Harald Scherm. Distribution of Xylella fastidiosa in Blueberry Stem and Root Sections in Relation to Disease Severity in the Field. Plant Disease 2014, 98, 443 -447.

AMA Style

R. M. Holland, R. S. C. Christiano, E. Gamliel-Atinsky, Harald Scherm. Distribution of Xylella fastidiosa in Blueberry Stem and Root Sections in Relation to Disease Severity in the Field. Plant Disease. 2014; 98 (4):443-447.

Chicago/Turabian Style

R. M. Holland; R. S. C. Christiano; E. Gamliel-Atinsky; Harald Scherm. 2014. "Distribution of Xylella fastidiosa in Blueberry Stem and Root Sections in Relation to Disease Severity in the Field." Plant Disease 98, no. 4: 443-447.

Journal article
Published: 30 November 2013 in Postharvest Biology and Technology
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Postharvest decay, caused by various fungal pathogens, is an important concern in commercial blueberry production, but current options for managing postharvest diseases are limited for this crop. Four plant essential oils (cinnamon oil, linalool, p-cymene, and peppermint leaf oil) and the plant oil-derived biofungicides Sporan (rosemary and wintergreen oils) and Sporatec (rosemary, clove, and thyme oils) were evaluated as postharvest biofumigants to manage fungal decay under refrigerated holding conditions. Hand-harvested Tifblue rabbiteye blueberry fruit were inoculated at the stem end with conidial suspensions of Alternaria alternata, Botrytis cinerea, Colletotrichum acutatum, or sterile deionized water (check inoculation) and subjected to biofumigation treatments under refrigeration (7 °C) for 1 wk. Sporatec volatiles reduced disease incidence significantly (P < 0.05) in most cases, whereas other treatments had no consistent effect on postharvest decay. Sensory analysis of uninoculated, biofumigated berries was performed utilizing a trained sensory panel, and biofumigation was found to have significant negative impacts on several sensory attributes such as sourness, astringency, juiciness, bitterness, and blueberry-like flavor. Biofumigated fruit were also analyzed for antioxidant capacity and individual anthocyanins, and no consistent effects on these antioxidant-related variables were found in treated berries. Because of limited efficacy in reducing postharvest decay, negative impacts on sensory qualities, and failure to increase antioxidant levels, the potential for postharvest biofumigation of blueberries under refrigerated holding conditions appears limited.

ACS Style

L.K. Mehra; D.D. MacLean; R.L. Shewfelt; K.C. Smith; H. Scherm. Effect of postharvest biofumigation on fungal decay, sensory quality, and antioxidant levels of blueberry fruit. Postharvest Biology and Technology 2013, 85, 109 -115.

AMA Style

L.K. Mehra, D.D. MacLean, R.L. Shewfelt, K.C. Smith, H. Scherm. Effect of postharvest biofumigation on fungal decay, sensory quality, and antioxidant levels of blueberry fruit. Postharvest Biology and Technology. 2013; 85 ():109-115.

Chicago/Turabian Style

L.K. Mehra; D.D. MacLean; R.L. Shewfelt; K.C. Smith; H. Scherm. 2013. "Effect of postharvest biofumigation on fungal decay, sensory quality, and antioxidant levels of blueberry fruit." Postharvest Biology and Technology 85, no. : 109-115.

Journal article
Published: 01 February 2013 in Plant Disease
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Postharvest decay, incited by various fungal pathogens, is a major concern in most blueberry production areas of the United States. Because the risk of infection is increased by fruit bruising, which in turn is increased by machine-harvesting, it has been difficult to harvest fruit from the early-maturing but soft-textured southern highbush blueberries (SHB) mechanically for the fresh market. This could change fundamentally with the recent development of SHB genotypes with crisp-textured (“crispy”) berries, i.e., fruit with qualitatively firmer flesh and/or more resistant skin. Four replicate row sections of two or three SHB genotypes having crispy fruit and three with conventional fruit were either hand- or machine-harvested at a commercial blueberry farm in northern Florida in April 2009 and May 2010. Harvested fruit were sorted, packed, and placed in cold storage (2°C) for up to 3 weeks. Average counts of aerobic bacteria, total yeasts and molds, coliforms, and Escherichia coli on fruit samples before the cold storage period were below commercial tolerance levels in most cases. In both years, natural disease incidence after cold storage was lowest for hand-harvested crispy fruit and highest for machine-harvested conventional fruit. Interestingly, machine-harvested crispy fruit had the same or lower disease incidence as hand-harvested conventional fruit. Across all treatments, natural postharvest disease incidence was inversely related to fruit firmness, with firmness values >220 g/mm associated with low disease. In separate experiments, samples from the 0-day cold storage period were inoculated at the stem end with Alternaria alternata, Botrytis cinerea, or Colletotrichum acutatum, and disease incidence was assessed after 7 days in a cold room followed by 60 to 72 h at room temperature. In response to artificial inoculation, less disease developed on crispy berries. No significant effect of harvest method was observed, except for A. alternata inoculation in 2009, when hand-harvested fruit developed a lower level of disease than machine-harvested fruit. Taken together, this study suggests that mechanical harvesting of SHB cultivars with crisp-textured berries is feasible from a postharvest pathology perspective.

ACS Style

Lucky Mehra; D. D. MacLean; A. T. Savelle; Harald Scherm. Postharvest Disease Development on Southern Highbush Blueberry Fruit in Relation to Berry Flesh Type and Harvest Method. Plant Disease 2013, 97, 213 -221.

AMA Style

Lucky Mehra, D. D. MacLean, A. T. Savelle, Harald Scherm. Postharvest Disease Development on Southern Highbush Blueberry Fruit in Relation to Berry Flesh Type and Harvest Method. Plant Disease. 2013; 97 (2):213-221.

Chicago/Turabian Style

Lucky Mehra; D. D. MacLean; A. T. Savelle; Harald Scherm. 2013. "Postharvest Disease Development on Southern Highbush Blueberry Fruit in Relation to Berry Flesh Type and Harvest Method." Plant Disease 97, no. 2: 213-221.

Journal article
Published: 01 February 2013 in Crop Protection
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ACS Style

J.C. Haralson; P.M. Brannen; D.S. Nesmith; H. Scherm. Chemical control of Cylindrocladium and Rhizoctonia root rots in blueberry propagation. Crop Protection 2013, 44, 1 -5.

AMA Style

J.C. Haralson, P.M. Brannen, D.S. Nesmith, H. Scherm. Chemical control of Cylindrocladium and Rhizoctonia root rots in blueberry propagation. Crop Protection. 2013; 44 ():1-5.

Chicago/Turabian Style

J.C. Haralson; P.M. Brannen; D.S. Nesmith; H. Scherm. 2013. "Chemical control of Cylindrocladium and Rhizoctonia root rots in blueberry propagation." Crop Protection 44, no. : 1-5.

Journal article
Published: 24 October 2012 in European Journal of Plant Pathology
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Tree canopies are architecturally complex and pose several challenges for measuring and characterizing spatial patterns of disease. Recently developed methods for fine-scale canopy mapping and three-dimensional spatial pattern analysis were applied in a 3-year study to characterize spatio-temporal development of pre-harvest brown rot of peach, caused by Monilinia fructicola, in 13 trees of different maturity classes. We observed a negative correlation between an index of disease aggregation and disease incidence in the same tree (r = −0.653, P < 0.0001), showing that trees with higher brown rot incidence had lower aggregation of affected fruit in their canopies. Significant (P ≤ 0.05) within-canopy aggregation among symptomatic fruit was most pronounced for early-maturing cultivars and/or early in the epidemic. This is consistent with the notion of a greater importance of localized, within-tree sources of inoculum at the beginning of the epidemic. Four of five trees having >10 blossom blight symptoms per tree showed a significant positive spatial association of pre-harvest fruit rot to blossom blight within the same canopy. Spatial association analyses further revealed one of two outcomes for the association of new fruit rot symptoms with previous fruit rot symptoms in the same tree, whereby the relationship was either not significant or exhibited a significant negative association. In the latter scenario, the newly diseased fruit were farther apart from previously symptomatic fruit than expected by random chance. This unexpected result could have been due to uneven fruit ripening in different sectors of the canopy, which could have affected the timing of symptom development and thus led to negative spatial associations among symptoms developing over time in a tree.

ACS Style

S. E. Everhart; A. Askew; Lynne Seymour; H. Scherm. Spatio-temporal patterns of pre-harvest brown rot epidemics within individual peach tree canopies. European Journal of Plant Pathology 2012, 135, 499 -508.

AMA Style

S. E. Everhart, A. Askew, Lynne Seymour, H. Scherm. Spatio-temporal patterns of pre-harvest brown rot epidemics within individual peach tree canopies. European Journal of Plant Pathology. 2012; 135 (3):499-508.

Chicago/Turabian Style

S. E. Everhart; A. Askew; Lynne Seymour; H. Scherm. 2012. "Spatio-temporal patterns of pre-harvest brown rot epidemics within individual peach tree canopies." European Journal of Plant Pathology 135, no. 3: 499-508.