Greenhouse Evaluation of Products That Induce Host Resistance for Control of Scab, Melanose, and Alternaria Brown Spot of Citrus

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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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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Diagrammatic scale for assessing foliar symptoms of alternaria brown spot in citrus

Agronomy Science and Biotechnology ◽

10.33158/asb.2016v2i2p57 ◽

2017 ◽

Vol 2 (2) ◽

pp. 57 ◽

Cited By ~ 1

Author(s):

Ivan Bortolato Martelli ◽

Camilla de Andrade Pacheco ◽

Marinês Bastianel ◽

Evandro Henrique Schinor ◽

Patrícia Marluci da Conceição ◽

...

Keyword(s):

Disease Severity ◽

Fungal Disease ◽

Brown Spot ◽

Foliar Symptoms ◽

Alternaria Brown Spot ◽

Precision And Accuracy ◽

Diagrammatic Scale

Alternaria brown spot (ABS) is the main fungal disease of mandarins. Cause damage to fruits, branches and leaves. For determinations of disease severity in fruit, there is a specific diagrammatic scale, which does not occur for foliar lesions. In order to standardize leaf reviews of ABS in citrus, a diagrammatic scale was developed from the collection of symptomatic Dancy tangerine and Murcott tangor leaves, with ten levels, from zero to 97% of the area damaged by the pathogen. They were tested by five evaluators who analyzed 100 pictures of symptomatic leaves with and without the use of the proposed scale. To validate the scale, precision and accuracy of assessors in rating the images were compared. Results showed that the use of the scale improved the accuracy of the evaluators, with increased accuracy. This shows that the leaf scale can be used to determine the severity of alternaria brown spot in citrus.

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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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Environmental Factors Affecting the Severity of Alternaria Brown Spot of Citrus and Their Potential Use in Timing Fungicide Applications

Plant Disease ◽

10.1094/pdis.2000.84.6.638 ◽

2000 ◽

Vol 84 (6) ◽

pp. 638-643 ◽

Cited By ~ 29

Author(s):

L. W. Timmer ◽

H. M. Darhower ◽

S. E. Zitko ◽

T. L. Peever ◽

A. M. Ibáñez ◽

...

Keyword(s):

Environmental Factors ◽

Disease Severity ◽

Environmental Data ◽

Brown Spot ◽

Weather Data ◽

Leaf Wetness ◽

Point System ◽

Leaf Wetness Duration ◽

Alternaria Brown Spot ◽

Trap Plants

Alternaria brown spot affects many tangerines and their hybrids, causing lesions on leaves, twigs, and fruit resulting in reduced yield and fruit quality. Field studies were conducted in a severely affected Minneola tangelo grove in central Florida from 1996 to 1998 to determine the environmental factors associated with infection of field trees and potted trap plants. Conidial production peaked following large flushes of new leaves, which were heavily infected. Most infections occurred during the summer rainy season, but trap plants became infected nearly every week of the year. When plants were exposed for 1-week periods, linear regression analysis indicated that disease severity on trap plants was positively related to the amount of rainfall, duration of leaf wetness, and average daily temperatures, and negatively related to the number of conidia trapped. Similar relationships occurred with trap plants exposed for 24-h periods on 141 different dates, except that temperature was not a significant factor. Nevertheless, these factors individually or combined in stepwise multiple regressions explained only a low percentage of the variability in disease severity with both weekly and daily trap plant sampling. When daily environmental data were categorized as: (i) rain versus no rain, (ii) <10 h or >10 h leaf wetness duration, and (iii) average temperature <20°C, 20 to 28°C, and >28°C, relationships to disease severity on trap plants were clearer. Disease severity on days with rain was nearly double that of days without rain, but considerable infection occurred on days with >10 h leaf wetness duration and no rain. Infection was greatest on days with temperatures of 20 to 28°C and slightly less at lower or higher temperatures. A point system, called the ALTER-RATER, was designed whereby each day would be assigned a severity value according to the prevailing environmental conditions. A fungicide application would be made after a predetermined number of points had accumulated. Simulated spray programs based on accumulation of 50, 75, 100, and 150 points from historical weather data at several locations indicated that from 8 to 15, 6 to 8, 5 to 6, or 3 to 4 sprays, respectively, would be needed depending on year and location in Florida. Such a weather-based control system could reduce the number of fungicide applications and improve control of Alternaria brown spot of tangerine.

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Fine Mapping for Identification of Citrus Alternaria Brown Spot Candidate Resistance Genes and Development of New SNP Markers for Marker-Assisted Selection

Frontiers in Plant Science ◽

10.3389/fpls.2016.01948 ◽

2016 ◽

Vol 7 ◽

Cited By ~ 11

Author(s):

Jose Cuenca ◽

Pablo Aleza ◽

Andres Garcia-Lor ◽

Patrick Ollitrault ◽

Luis Navarro

Keyword(s):

Resistance Genes ◽

Fine Mapping ◽

Marker Assisted Selection ◽

Snp Markers ◽

Brown Spot ◽

Alternaria Brown Spot

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Brown spot disease severity, yield and yield loss relationships in pigmented upland rice cultivars from East Nusa Tenggara, Indonesia

Biodiversitas Journal of Biological Diversity ◽

10.13057/biodiv/d210443 ◽

2020 ◽

Vol 21 (4) ◽

Author(s):

Yosep S. Mau ◽

Antonius Ndiwa ◽

Shirly Oematan

Keyword(s):

Disease Severity ◽

Yield Loss ◽

Upland Rice ◽

Brown Spot ◽

Yield Reduction ◽

Rice Cultivars ◽

Rice Varieties ◽

Resistance Level ◽

Spot Disease ◽

Brown Spot Disease

Abstract. Mau YS, Ndiwa ASS, Oematan SS. 2020. Brown spot disease severity, yield and yield loss relationships in pigmented upland rice cultivars from East Nusa Tenggara, Indonesia. Biodiversitas 21: 1625-1634. Brown spot is one of the most devastating diseases of rice, which could lead to total yield loss. The disease has a worldwide distribution, more specifically in areas where water supply is scarce, most specifically in the dry upland areas. Almost all stages of rice are affected by the disease, where leaves and grains are mostly affected. Considerable differences exist in susceptibility to brown spot among rice varieties, which may cause a large variation in yield loss caused by the disease. Therefore, the resistance level of rice varieties and their yield reduction has to be regularly evaluated and updated. There are only a few reports on the relationship between brown spot severity with yield and yield loss of upland rice, and is even lacking in pigmented upland rice. The objectives of the present study were to assess the brown spot severity and resistance level in pigmented upland rice cultivars from East Nusa Tenggara Province, Indonesia, and to elucidate their relationships with yield and yield reduction. Twenty four pigmented upland rice genotypes were evaluated in the field during May to October 2019, and their disease responses and yields were recorded. Disease severity was observed weekly and used to calculate Area Under the Disease Progress Curve (AUDPC) for comparison among the genotypes. The relationships between disease severity and AUDPC with yield and yield loss were also examined. The results showed significant variation in brown spot severity and AUDPC, ranging from, respectively, 11.11% to 40.70% and 398.42%-days to 1081.30%-days. Yields and yield losses of test genotypes also varied substantially. Yields under diseased-free and diseased plots ranged from, respectively, 2.34 t ha-1 to 6.13 t ha-1 and 1.68 t ha-1 to 3.74 t ha-1 while yield loss was between 10.46% and 56.15%. Six genotypes were moderately resistant, four genotypes were moderately susceptible and 14 genotypes were susceptible to brown spot. Neither disease severity nor AUDPC had a linear relationship with yield but both exhibited positive and linear relationships with yield loss.

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Purification and characterization of an endopolygalacturonase from the rough lemon pathotype ofAlternaria alternata,the cause of citrus brown spot disease

Physiological and Molecular Plant Pathology ◽

10.1006/pmpp.1997.0106 ◽

1997 ◽

Vol 51 (3) ◽

pp. 155-167 ◽

Cited By ~ 22

Author(s):

A. Isshiki ◽

K. Akimitsu ◽

K. Nishio ◽

M. Tsukamoto ◽

H. Yamamoto

Keyword(s):

Brown Spot ◽

Purification And Characterization ◽

Spot Disease ◽

Rough Lemon ◽

Brown Spot Disease

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Evaluation of Foliar Diseases for Soybean Entries in the Pan-African Trials in Malawi and Zambia

Plant Disease ◽

10.1094/pdis-12-19-2617-sr ◽

2020 ◽

Vol 104 (8) ◽

pp. 2068-2073

Author(s):

Christabell Nachilima ◽

Godfree Chigeza ◽

Mwila Chibanda ◽

Hapson Mushoriwa ◽

Brian D. Diers ◽

...

Keyword(s):

Disease Severity ◽

The United States ◽

Sub Saharan Africa ◽

Brown Spot ◽

Soybean Rust ◽

Growth Stages ◽

Foliar Diseases ◽

Pan African ◽

Private And Public ◽

Sub Saharan

Soybean production has expanded worldwide including countries in sub-Saharan Africa. Several national and international agencies and research groups have partnered to improve overall performance of soybean breeding stocks and have introduced new germplasm from Brazil and the United States with the goal of developing new high-yielding cultivars. Part of this effort has been to test improved soybean lines/cultivars accumulated from private and public sources in multilocational trials in sub-Saharan Africa. These trials are known as the Pan-African Soybean Variety Trials, and the entries come from both private and public breeding programs. The objective of this research was to evaluate entries in the trials that include commercial cultivars or advanced experimental lines for the incidence and severity of foliar diseases. All trials were planted in December 2018 with six located in Zambia and one in Malawi. Plants were evaluated during the reproductive growth stages using a visual pretransformed severity rating scale. Foliar disease ratings were recorded for three bacterial diseases, six fungal diseases, one oomycete, and viruses. The overall occurrence of most of the diseases was high except for soybean rust and target spot, which were only found at two and one location, respectively. However, disease severity was generally low, although there were differences in disease severity ratings among the entries at some of the locations for brown spot, downy mildew, frogeye leaf spot, red leaf blotch, and soybean rust.

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