Alternative Control of Alternaria Brown Spot in Tangerine

Products that induce disease resistance in plants were evaluated on potted seedlings of rough lemon for citrus scab, caused by Elsinoe fawcettii; grapefruit for melanose, caused by Diaporthe citri; and Dancy tangerine for Alternaria brown spot caused by Alternaria alternata pv. citri. Plants were pruned to a single stem with mature leaves and treated at bud break or various times thereafter. New foliage was inoculated and subsequently evaluated for disease severity. Oxycom, Nutriphite, Messenger, Goemar H11, Serenade, ReZist, ProPhyt, Aliette, Actigard, and KeyPlex were evaluated and compared with benomyl or strobilurin fungicides as standards. Most products reduced disease severity compared with the untreated control, but were less effective than standard fungicides. The most generally effective products were ReZist and Actigard, those that contain or produce phosphorous acid (Aliette and Nutriphite), and a bacterial preparation (Serenade). Oxycom and Messenger controlled scab well in some tests. Products that induce host resistance may be useful for disease control in citrus in an integrated program with standard fungicides.

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Cinnamomun zeylanicum oil and trans-cinnamaldehyde against Alternaria brown spot in tangerine: direct effects and induced resistance

Phytoparasitica ◽

10.1007/s12600-019-00754-x ◽

2019 ◽

Vol 47 (4) ◽

pp. 575-589 ◽

Cited By ~ 1

Author(s):

Fabiano José Perina ◽

Camila Cristina Lage de Andrade ◽

Silvino Intra Moreira ◽

Eduardo Mateus Nery ◽

Claudio Ogoshi ◽

...

Keyword(s):

Induced Resistance ◽

Brown Spot ◽

Direct Effects ◽

Alternaria Brown Spot

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Role of the Host-Selective ACT-Toxin Synthesis Gene ACTTS2 Encoding an Enoyl-Reductase in Pathogenicity of the Tangerine Pathotype of Alternaria alternata

Phytopathology ◽

10.1094/phyto-100-2-0120 ◽

2010 ◽

Vol 100 (2) ◽

pp. 120-126 ◽

Cited By ~ 33

Author(s):

Naoya Ajiro ◽

Yoko Miyamoto ◽

Akira Masunaka ◽

Takashi Tsuge ◽

Mikihiro Yamamoto ◽

...

Keyword(s):

Alternaria Alternata ◽

Essential Gene ◽

Toxin Production ◽

Brown Spot ◽

Gene Encoding ◽

Bac Clone ◽

Biosynthesis Gene Cluster ◽

Enoyl Reductase ◽

Alternaria Brown Spot ◽

Rapid Amplification

The tangerine pathotype of Alternaria alternata produces host-selective ACT-toxin and causes Alternaria brown spot disease of tangerines and tangerine hybrids. Sequence analysis of a genomic BAC clone identified a previously uncharacterized portion of the ACT-toxin biosynthesis gene cluster (ACTT). A 1,034-bp gene encoding a putative enoyl-reductase was identified by using rapid amplification of cDNA ends and polymerase chain reaction and designated ACTTS2. Genomic Southern blots demonstrated that ACTTS2 is present only in ACT-toxin producers and is carried on a 1.9 Mb conditionally dispensable chromosome by the tangerine pathotype. Targeted gene disruption of ACTTS2 led to a reduction in ACT-toxin production and pathogenicity, and transcriptional knockdown of ACTTS2 using RNA silencing resulted in complete loss of ACT-toxin production and pathogenicity. These results indicate that ACTTS2 is an essential gene for ACT-toxin biosynthesis in the tangerine pathotype of A. alternata and is required for pathogenicity of this fungus.

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Sensitivity of Alternaria alternata from Citrus to Boscalid and Polymorphism in Iron-Sulfur and in Anchored Membrane Subunits of Succinate Dehydrogenase

Plant Disease ◽

10.1094/pdis-04-14-0374-re ◽

2015 ◽

Vol 99 (2) ◽

pp. 231-239 ◽

Cited By ~ 5

Author(s):

Byron Vega ◽

Megan M. Dewdney

Keyword(s):

Succinate Dehydrogenase ◽

Alternaria Alternata ◽

Mycelial Growth ◽

Conidial Germination ◽

Brown Spot ◽

Sequence Comparisons ◽

Sensitivity Tests ◽

Alternaria Brown Spot ◽

Succinate Dehydrogenase Inhibitor

Boscalid, a succinate dehydrogenase inhibitor (SDHI), was registered in 2011 to control Alternaria brown spot (ABS) of citrus, caused by Alternaria alternata. In this study, the effect of boscalid on mycelial growth, conidial germination, and resazurin reduction was established in a subset of 16 sensitive isolates using three different media. Conidial germination and mycelial growth inhibition were not suppressed even at higher concentrations of boscalid, although effective concentration to inhibit 50% growth (EC50) values were established with each method. Resazurin reduction produced the lowest EC50 values and was selected for further sensitivity tests. In total, 419 isolates, never exposed to boscalid and collected from Florida tangerine orchards between 1996 to 2012, were tested for boscalid sensitivity. The sensitivity distribution was a unimodal curve with a mean EC50 value of 0.60 μg/ml and a range of 0.07 to 5.84 μg/ml. The molecular characterization of the succinate dehydrogenase (SDH) genes were also determined in a subset of 15 isolates, exhibiting great variability in boscalid sensitivity, by cloning and sequencing the sdhB, sdhC, and sdhD genes. Sequence comparisons of the SDH complex revealed the presence of mutations in 14 of 15 isolates. In total, 21 mutations were identified. Double and multiple mutations were observed in SDHC and SDHD, respectively. In SDHB, 4 mutations were observed while, in SDHC and SDHD, 5 and 12 mutations were detected, respectively. No mutations were found in the highly conserved histidine residues at positions 277 in SDHB, 134 in SDHC, and 133 in SDHD, typically observed in SDHI-resistant isolates. Our findings suggest that A. alternata populations from Florida are sensitive to boscalid and it could be used in ABS spray programs. Boscalid resistance is currently not a problem, although further monitoring for resistance is advisable.

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Temperature, Leaf Wetness, and Isolate Effects on Infection of Minneola Tangelo Leaves by Alternaria sp.

Plant Disease ◽

10.1094/pdis.1999.83.5.429 ◽

1999 ◽

Vol 83 (5) ◽

pp. 429-433 ◽

Cited By ~ 35

Author(s):

Y. Canihos ◽

T. L. Peever ◽

L. W. Timmer

Keyword(s):

Polynomial Equation ◽

Brown Spot ◽

Effect Of Temperature ◽

Leaf Wetness ◽

Significant Difference ◽

Alternaria Brown Spot ◽

Detached Leaves ◽

Alternaria Sp ◽

Response To Temperature

Alternaria brown spot causes necrotic lesions on immature leaves, twigs, and fruit of tangerines and their hybrids, reducing yield and fruit quality. The effect of temperature, leaf wetness, and isolate was evaluated in an in vitro system using immature detached leaves of Minneola tangelo Infection was greatest at 27°C, decreased gradually as the temperature declined to 24, 20, and 17°C, and dropped sharply at 32°C. Levels of infection were low at 4 and 8 h of leaf wetness and continued to increase with longer wetting periods up to 36 h. A polynomial equation was developed that provided a good fit for the data (adjusted R2 = 0.93). Isolates differed in aggressiveness, but there was no significant difference among isolates in their response to temperature and leaf wetness duration.

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Efficacy of Pre- and Postinoculation Application of Fungicides to Expanding Young Citrus Leaves for Control of Melanose, Scab, and Alternaria Brown Spot

Plant Disease ◽

10.1094/pdis-91-12-1600 ◽

2007 ◽

Vol 91 (12) ◽

pp. 1600-1606 ◽

Cited By ~ 11

Author(s):

S. N. Mondal ◽

A. Vicent ◽

R. F. Reis ◽

L. W. Timmer

Keyword(s):

Disease Control ◽

Leaf Area ◽

Quadratic Equation ◽

Brown Spot ◽

Copper Hydroxide ◽

Fungicide Application ◽

Potted Plants ◽

Rough Lemon ◽

Alternaria Brown Spot ◽

Young Leaves

In greenhouse trials, copper hydroxide, pyraclostrobin, and famoxadone were applied to actively growing young citrus seedlings to determine the duration of protection of young leaves provided by these fungicides against melanose, caused by Diaporthe citri, citrus scab, caused by Elsinoe fawcettii, and Alternaria brown spot, caused by Alternaria alternata. Fungicides were applied to different sets of potted plants of grapefruit for control of melanose, of rough lemon for control of scab, and of Dancy tangerine for control of Alternaria brown spot 1 to 6 days prior to inoculation, as well as on the day of inoculation. Leaf area of treated shoots was estimated on the day of fungicide application and the day of inoculation and disease severity evaluated subsequently. In most cases, copper hydroxide and famoxadone provided at least 50% control of all three diseases for only about 2 days after application. Generally, there was little or no disease control when the products were applied 4 or more days before inoculation. In contrast, pyraclostrobin usually provided a high level of control of all three diseases when applied up to 5 days prior to inoculation. The level of disease control decreased as the interval between a fungicide application and inoculation increased and the relationship between disease control and leaf expansion best fit a quadratic equation. Effective disease control was observed with copper hydroxide and famoxadone until leaf area had increased by 100 to 200%, whereas control with pyraclostrobin was observed up to 400 to 500% increase in leaf area. In postinoculation tests with scab and melanose, pyraclostrobin provided high levels of disease control (>75%) when applied up to 2 days after inoculation, whereas copper hydroxide and famoxadone had minimal postinoculation activity. Applications of pyraclostrobin to the spring flush growth of citrus trees are much more likely to provide control of melanose, scab, and Alternaria brown spot than those of famoxadone or copper hydroxide.

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Inoculum Sources, Infection Periods, and Effects of Environmental Factors on Alternaria Brown Spot of Mandarin in Mediterranean Climate Conditions

Plant Disease ◽

10.1094/pdis-09-13-0956-re ◽

2014 ◽

Vol 98 (3) ◽

pp. 409-417 ◽

Cited By ~ 9

Author(s):

D. D. M. Bassimba ◽

J. L. Mira ◽

A. Vicent

Keyword(s):

Classification Tree ◽

Disease Onset ◽

Epidemiological Studies ◽

Brown Spot ◽

Morphological Identification ◽

Weather Factors ◽

Climate Conditions ◽

Airborne Inoculum ◽

Alternaria Brown Spot ◽

Serious Disease

Alternaria brown spot (ABS), caused by Alternaria alternata, is a serious disease affecting mandarin in humid and in semi-arid regions. The information available from Florida cannot be easily extrapolated to Mediterranean regions; thus, epidemiological studies were conducted during two consecutive years in Spain. Pathogenic isolates were found in the canopy and leaf litter and on weeds of the genus Sonchus. The pathogen survived in fallen immature leaves for up to 76 days, until complete leaf decay. Conidia of Alternaria spp. were captured continuously and pathogenic isolates were detected in all sampling dates. However, the number of pathogenic isolates was not correlated with the total captured, indicating that morphological identification is not sufficient for airborne inoculum monitoring. In contrast to humid areas, infections occurred mainly in spring and autumn. Classification tree analysis indicated that virtually all infections occurred on weeks with rainfall ≥2.5 mm and average temperature ≥12.5°C. Based on regression quantiles, the amount of rainfall, number of rain days, and total wetness duration were considered important factors increasing ABS incidence during infection periods. The development of decision support systems for ABS control in Mediterranean conditions may benefit from the restricted periods of infection and the strong influence of weather factors in disease onset.

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