Evaluation of the Alter-Rater Model for Timing of Fungicide Applications for Control of Alternaria Brown Spot of Citrus

Alternaria brown spot, caused by Alternaria alternata, results in serious yield losses of tangerines and their hybrids in Florida. The Alter-Rater model predicts the need for fungicide applications based on daily cumulative points that are assigned on the basis of rainfall, leaf wetness, and temperature. Previously, Alter-Rater threshold or trigger values of 50, 75, 100, and 150 points for application of copper fungicides were suggested for groves with different cultivars and disease histories. In this study, we evaluated thresholds of 50, 100, and 150 points in four Minneola tangelo and Murcott tangor groves in 2000 and 2001. For comparison, copper fungicides were applied according to the DISC Copper Model in 2000 and according to calendar sprays in 2001. Use of the Alter-Rater model resulted in fewer sprays in three of the four groves in 2000 and better fruit quality in the other grove than the Copper Model. Compared to a calendar spray schedule in 2001, use of the Alter-Rater model resulted in fewer sprays in two of the four groves but more sprays in one grove. The results confirmed that the Alter-Rater is a valuable tool for timing fungicide applications and that its use results in better disease control or fewer sprays.

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An Isolate of Alternaria alternata That Is Pathogenic to Both Tangerines and Rough Lemon and Produces Two Host-Selective Toxins, ACT- and ACR-Toxins

Phytopathology ◽

10.1094/phyto-95-0241 ◽

2005 ◽

Vol 95 (3) ◽

pp. 241-247 ◽

Cited By ~ 67

Author(s):

A. Masunaka ◽

K. Ohtani ◽

T. L. Peever ◽

L. W. Timmer ◽

T. Tsuge ◽

...

Keyword(s):

Alternaria Alternata ◽

Leaf Spot ◽

The Other ◽

Brown Spot ◽

Parasexual Cycle ◽

Rough Lemon ◽

Alternaria Brown Spot ◽

Alternaria Species ◽

Genomic Regions ◽

Toxin Producers

Two different pathotypes of Alternaria alternata cause Alternaria brown spot of tangerines and Alternaria leaf spot of rough lemon. The former produces the host-selective ACT-toxin and the latter produces ACR-toxin. Both pathogens induce similar symptoms on leaves or young fruits of their respective hosts, but the host ranges of these pathogens are distinct and one pathogen can be easily distinguished from another by comparing host ranges. We isolated strain BC3-5-1-OS2A from a leaf spot on rough lemon in Florida, and this isolate is pathogenic on both cv. Iyokan tangor and rough lemon and also produces both ACT-toxin and ACR-toxin. Isolate BC3-5-1-OS2A carries both genomic regions, one of which was known only to be present in ACT-toxin producers and the other was known to exist only in ACR-toxin producers. Each of the genomic regions is present on distinct small chromosomes, one of 1.05 Mb and the other of 2.0 Mb. Alternaria species have no known sexual or parasexual cycle in nature and populations of A. alternata on citrus are clonal. Therefore, the ability to produce both toxins was not likely acquired through meiotic or mitotic recombination. We hypothesize that a dispensable chromosome carrying the gene cluster controlling biosynthesis of one of the host-selective toxins was transferred horizontally and rearranged by duplication or translocation in another isolate of the fungus carrying genes for biosynthesis of the other host-selective toxin.

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Effect of Lesion Age, Humidity, and Fungicide Application on Sporulation of Alternaria alternata, the Cause of Brown Spot of Tangerine

Plant Disease ◽

10.1094/pd-90-1051 ◽

2006 ◽

Vol 90 (8) ◽

pp. 1051-1054 ◽

Cited By ~ 18

Author(s):

R. F. Reis ◽

A. de Goes ◽

S. N. Mondal ◽

T. Shilts ◽

F. C. Brentu ◽

...

Keyword(s):

Alternaria Alternata ◽

Unit Area ◽

Spore Production ◽

Brown Spot ◽

Yield Losses ◽

Conidial Production ◽

Leaf Lesion ◽

Inoculum Production ◽

The World ◽

Alternaria Brown Spot

Alternaria brown spot, caused by Alternaria alternata, causes yield losses and fruit blemishes on many tangerines and their hybrids in most citrus areas of the world where susceptible cultivars are grown. Although the conditions affecting infection and disease severity are known, little information is available on inoculum production on infected tissue. We found that sporulation on leaves began about 10 days after symptoms developed, was abundant from 20 to 40 days, and declined thereafter. Conidial production was far greater on leaf than on fruit or twig lesions. Spore production per unit area of leaf lesion was greater on the more susceptible hybrids, Minneola and Orlando tangelos, than on the less susceptible Murcott tangor. At 74% relative humidity, conidial production on leaf lesions was low, but it was abundant at 85, 92.5, 96, and 100%. Application of QoI or copper fungicides, but not ferbam, suppressed sporulation on leaf lesions for about 14 to 21 days after application. Additional applications did not appear to be more effective than a single spray in reducing inoculum production.

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Environmental Factors Affecting Production, Release, and Field Populations of Conidia of Alternaria alternata, the Cause of Brown Spot of Citrus

Phytopathology ◽

10.1094/phyto.1998.88.11.1218 ◽

1998 ◽

Vol 88 (11) ◽

pp. 1218-1223 ◽

Cited By ~ 40

Author(s):

L. W. Timmer ◽

Z. Solel ◽

T. R. Gottwald ◽

A. M. Ibañez ◽

S. E. Zitko

Keyword(s):

Alternaria Alternata ◽

Field Studies ◽

Brown Spot ◽

Leaf Wetness ◽

Average Wind Speed ◽

Susceptible Host ◽

Spore Trap ◽

Factors Affecting ◽

Average Wind ◽

Alternaria Brown Spot

Alternaria brown spot, caused by Alternaria alternata pv. citri, affects many tangerines and their hybrids, causing loss of immature leaves and fruit and reducing the marketability of the remaining fruit. Conidial production of A. alternata was greatest on mature leaves moistened and maintained at near 100% relative humidity (RH) for 24 h, whereas leaves that had been soaked or maintained at moderate RH produced few conidia. Conidial release from filter paper cultures and infected leaves was studied in a computer-controlled environmental chamber. Release of large numbers of conidia was triggered from both substrates by sudden drops in RH or by simulated rainfall events. Vibration induced release of low numbers of conidia, but red/infrared irradiation had no effect. In field studies from 1994 to 1996, air sampling with a 7-day recording volumetric spore trap indicated that conidia were present throughout the year with periodic large peaks. The number of conidia captured was not closely related to rainfall amounts or average wind speed, but was weakly related to the duration of leaf wetness. Likewise, disease severity on trap plants placed in the field weekly during 1995 to 1996 was not closely related to conidial numbers or rainfall amounts, but was weakly related to leaf wetness duration. Sufficient inoculum appears to be available to allow infection to occur throughout the year whenever susceptible host tissue and moisture are available.

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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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Chromosome-scale genome sequence of Alternaria alternata causing Alternaria brown spot of citrus

Molecular Plant-Microbe Interactions ◽

10.1094/mpmi-10-20-0278-sc ◽

2021 ◽

Author(s):

Yunpeng Gai ◽

Haijie Ma ◽

Yanan Chen ◽

Lei Li ◽

Yingze Cao ◽

...

Keyword(s):

Genome Sequence ◽

Genome Assembly ◽

Alternaria Alternata ◽

Draft Genome ◽

Gc Content ◽

Brown Spot ◽

Toxin Gene ◽

Alternaria Brown Spot ◽

Alternaria Species ◽

Chromosome Level

Alternaria brown spot (ABS) caused by Alternaria alternata is an economically important fungal disease of citrus worldwide. The ABS pathogen A. alternata tangerine pathotype can produce a host-specific ACT toxin, which is regulated by ACT toxin gene cluster located in the conditionally dispensable chromosome (CDC). Previously, we have assembled a draft genome of A. alternata tangerine pathotype strain Z7, which comprises 165 contigs. In this study, we report a chromosome-level genome assembly of A. alternata Z7 through the combination of Oxford nanopore sequencing and Illumina sequencing technologies. The assembly of A. alternata Z7 had a total size of 34.28 Mb, with a GC content of 51.01% and contig N50 of Mb. The genome is encompassed 12067 protein-coding genes, 34 rRNAs, and 107 tRNAs. Interestingly, A. alternata Z7 is composed of 10 essential chromosomes (ECs) and 2 conditionally dispensable chromosomes (CDCs), which is consistent with the experimental evidences of pulsed-field gel electrophoresis (PFGE). To our best knowledge, this is the first chromosome-level genome assembly of A. alternata. In addition, a database for citrus-related Alternaria genomes has been established to provide public resources for the sequences, annotation and comparative genomics data of Alternaria species. The improved genome sequence and annotation at the chromosome level is a significant step toward a better understanding of the pathogenicity of A. alternata. The database will be updated regularly whenever the genomes of newly isolated Alternaria species are available. The citrus-related Alternaria genomes database is open accessible through http://www.zjudata.com/alternaria/blast.php.

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First Report of Alternaria Brown Spot of Citrus Caused by Alternaria alternata in Yunnan Province, China

Plant Disease ◽

10.1094/pdis-94-3-0375c ◽

2010 ◽

Vol 94 (3) ◽

pp. 375-375 ◽

Cited By ~ 7

Author(s):

X. F. Wang ◽

Z. A. Li ◽

K. Z. Tang ◽

C. Y. Zhou ◽

L. Yi

Keyword(s):

Alternaria Alternata ◽

Yunnan Province ◽

Morphological Characteristics ◽

Control Measures ◽

Brown Spot ◽

Control Treatment ◽

Infected Leaf ◽

Conidial Suspension ◽

First Report ◽

Alternaria Brown Spot

Brown spot of citrus is considered a major problem on the fruit of many citrus cultivars grown for fresh markets including tangerines (Citrus reticulata) and their hybrids. It causes lesions on leaves, stems, and fruit and reduces yield and fruit quality (2). In 2003 in southern Wenshan Municipality, Yunnan Province in China, sporadic occurrence of Alternaria brown spot was observed on Tangfang mandarin, a local citrus cultivar identified preliminarily as a kind of mandarin hybrid. From 2006 to 2008, nearly 80% of local orchards were infected with the disease. Fruit symptoms typical of Alternaria brown spot ranging from light brown, slightly depressed spots to circular and dark brown areas were observed. Leaves showed small, brown, circular spots and irregular blighted areas with characteristic yellow halos. Tissues from the margin of fruit spots or infected leaf parts of eight different trees were surface sterilized in 1.5% sodium hypochlorite for 1 min, plated on potato dextrose agar (PDA), and then incubated at 27°C in the dark for 1 week. Dark brown mycelia and pigmented septate conidia with lengths of 10 to 35 μm and widths of 5 to 13 μm were produced. On the basis of conidial morphological characteristics, the pathogen was identified as Alternaria alternata (Fr.:Fr.) Keissl (1). Detached young healthy leaves of ‘Minneola’ tangelo (C. reticulata × C. paradisi) were sprayed with a conidial suspension of 105 conidia per ml and incubated in a moist chamber at 27°C. A control treatment with an equal number of leaves was sprayed with distilled water only. After 48 h, seven of these isolates caused necrotic lesions on detached leaves, characteristic of the disease, whereas there were no symptoms on leaves of the water control. Pure cultures were recovered on PDA from symptomatic tissues and the morphological characteristics of the conidia closely fit the description of A. alternata, confirming Koch's postulates. Currently, the distribution of Alternaria brown spot of citrus is confined to southern Wenshan Municipality in Yunnan Province where it is a serious disease problem on the most important commercial cultivar in this region. The identification of the pathogen now allows for appropriate field management and control measures. To our knowledge, this is the first report of Alternaria brown spot of citrus in China. References: (1) Z. Solel. Plant Pathol. 40:145, 1991. (2) J. O. Whiteside. Plant Dis. Rep. 60:326, 1976.

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Function of Genes Encoding Acyl-CoA Synthetase and Enoyl-CoA Hydratase for Host-Selective ACT-Toxin Biosynthesis in the Tangerine Pathotype of Alternaria alternata

Phytopathology ◽

10.1094/phyto-99-4-0369 ◽

2009 ◽

Vol 99 (4) ◽

pp. 369-377 ◽

Cited By ~ 27

Author(s):

Y. Miyamoto ◽

Y. Ishii ◽

A. Honda ◽

A. Masunaka ◽

T. Tsuge ◽

...

Keyword(s):

Alternaria Alternata ◽

Gene Disruption ◽

Toxin Production ◽

Brown Spot ◽

Acid Moiety ◽

Targeted Gene Disruption ◽

Brown Spot Disease ◽

Alternaria Brown Spot ◽

Genes Encoding ◽

Enoyl Coa Hydratase

The tangerine pathotype of Alternaria alternata produces host-selective ACT-toxin and causes Alternaria brown spot disease. Sequence analysis of a genomic cosmid clone identified a part of the ACTT gene cluster and implicated two genes, ACTT5 encoding an acyl-CoA synthetase and ACTT6 encoding an enoyl-CoA hydratase, in the biosynthesis of ACT-toxin. Genomic Southern blots demonstrated that both genes were present in tangerine pathotype isolates producing ACT-toxin and also in Japanese pear pathotype isolates producing AK-toxin and strawberry pathotype isolates producing AF-toxin. ACT-, AK-, and AF-toxins from these three pathotypes share a common 9,10-epoxy-8-hydroxy-9-methyl-decatrienoic acid moiety. Targeted gene disruption of two copies of ACTT5 significantly reduced ACT-toxin production and virulence. Targeted gene disruption of two copies of ACTT6 led to complete loss of ACT-toxin production and pathogenicity and a putative decatrienoic acid intermediate in ACT-toxin biosynthesis accumulated in mycelial mats. These results indicate that ACTT5 and ACTT6 are essential genes in ACT-toxin biosynthesis in the tangerine pathotype of A. alternata and both are required for full virulence of this fungus.

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