scholarly journals Activity of Benomyl for Control of Postbloom Fruit Drop of Citrus Caused by Colletotrichum acutatum

Plant Disease ◽  
2002 ◽  
Vol 86 (6) ◽  
pp. 620-624 ◽  
Author(s):  
N. A. R. Peres ◽  
N. L. Souza ◽  
S. E. Zitko ◽  
L. W. Timmer
Keyword(s):  
Germ Tube ◽  
Good Control ◽  
Colletotrichum Acutatum ◽  
Disease Development ◽  
Mature Leaves ◽  
Fruit Drop ◽  
Fungal Propagules ◽  
Highly Sensitive ◽  
Subsequent Application ◽  
Colony Area

Postbloom fruit drop (PFD) of citrus caused by Colletotrichum acutatum produces orange-brown lesions on petals and induces the abscission of young fruitlets and the retention of the calyces. Despite the fact that C. acutatum is not highly sensitive to benomyl in culture, this fungicide provides good control of the disease under field conditions. This study was undertaken to determine the effect of benomyl on various stages of disease development to understand the basis for its effectiveness in the field. We found that benomyl at 1.0 μg/ml reduced colony area of C. acutatum by about 75% and completely inhibited growth of C. gloeosporioides. Benomyl did not prevent conidial germination even at 100 μg/ml, but reduced germ tube elongation at 10 and 100 μg/ml. When benomyl was applied to flower clusters on screenhouse-grown plants before inoculation, disease severity was greatly reduced. Applications at 24 and 48 h, but not at 72 h, after inoculation reduced PFD severity. Application of benomyl to symptomatic petals not bearing conidia did not prevent or reduce production of inoculum. Application to petals bearing conidia reduced viability of these fungal propagules by only about 50%. The viability of appressoria on mature leaves was not affected by benomyl application. Even when appressoria on mature leaves were stimulated to germinate by treatment with flower extracts, subsequent application of benomyl did not reduce propagule numbers below original levels. Benomyl appears to act by preventing infection and early development of the fungus in petals. However, once symptoms have developed, this fungicide has only minimal effects on further disease development and spread.

scholarly journals Benomyl Sensitivity of Isolates of Colletotrichum acutatum and C. gloeosporioides from Citrus

Plant Disease ◽  
2004 ◽  
Vol 88 (2) ◽  
pp. 125-130 ◽  
Author(s):  
N. A. R. Peres ◽  
N. L. Souza ◽  
T. L. Peever ◽  
L. W. Timmer
Keyword(s):  
Mycelial Growth ◽  
Colletotrichum Acutatum ◽  
Nucleotide Substitutions ◽  
Partial Sequencing ◽  
Research Fields ◽  
Fruit Drop ◽  
Highly Sensitive ◽  
Sensitive Isolate ◽  
Moderately Resistant

Postbloom fruit drop (PFD) of citrus, caused by Colletotrichum acutatum, produces orange-brown lesions on petals and results in premature fruit drop and the retention of calyces. C. gloeosporioides is common in groves and causes postharvest anthracnose on fruit. Both diseases are controlled effectively by the fungicide benomyl in research fields and commercial orchards. Highly sensitive and resistant isolates of C. gloeosporioides were found, whereas all isolates of C. acutatum tested were moderately resistant. In preliminary studies conducted in vitro with three isolates of each, mycelial growth of sensitive isolates of C. gloeosporioides was inhibited completely by benomyl (Benlate 50 WP) at 1.0 μg/ml, whereas resistant isolates grew well at 10 μg/ml. Growth of all isolates of C. acutatum was inhibited by about 55% at 0.1 μg/ml and by 80% at 1.0 μg/ml. Spore germination of C. acutatum was inhibited more at 0.1 μg/ml than at 1.0 μg/ml or higher concentrations. In all, 20 isolates of C. acutatum from 17 groves and 20 isolates of C. gloeosporioides from 7 groves were collected from locations with different histories of benomyl usage in São Paulo, Brazil, and Florida, United States. Benomyl at 1.0 μg/ml completely inhibited growth of 133 isolates of C. gloeosporioides, with the exception of 7 isolates that were highly resistant to the fungicide, whereas all isolates of C. acutatum were only partially inhibited at 0.1 and 1.0 μg/ml. Analysis of variance indicated that the sensitivity of the isolates of C. acutatum was not affected by benomyl usage or grove of origin, and country of origin had only minor effects. No highly resistant or sensitive isolate of C. acutatum was recovered. Partial sequencing of the β-tubulin gene did not reveal nucleotide substitutions in codons 198 or 200 in C. acutatum that usually are associated with benomyl resistance in other fungi.

scholarly journals Recent Introduction and Recombination in Colletotrichum acutatum Populations Associated with Citrus Postbloom Fruit Drop Epidemics in São Paulo, Brazil

2014 ◽  
Vol 104 (7) ◽  
pp. 769-778 ◽  
Author(s):  
Maisa Ciampi-Guillardi ◽  
Cristina Baldauf ◽  
Anete Pereira Souza ◽  
Geraldo José Silva-Junior ◽  
Lilian Amorim
Keyword(s):  
Genetic Structure ◽  
Regional Scale ◽  
Sao Paulo ◽  
Colletotrichum Acutatum ◽  
Common Source ◽  
São Paulo ◽  
Recent Introduction ◽  
Fruit Drop ◽  
Haplotypic Diversity ◽  
Fungal Propagules

Citrus crops in São Paulo State, Brazil, have been severely affected by postbloom fruit drop disease (PFD), which is caused by Colletotrichum acutatum. This disease leads to the drop of up to 100% of young fruits. Previous studies have assumed that this pathogen exhibits a clonal reproductive mode, although no population genetic studies have been conducted so far. Thus, the genetic structure of six C. acutatum populations from sweet orange orchards showing PFD symptoms was determined using nine microsatellite markers, enabling inference on predominant mode of reproduction. C. acutatum populations exhibit a nearly panmictic genetic structure and a high degree of admixture, indicating either ongoing contemporary gene flow at a regional scale or a recent introduction from a common source, since this pathogen was introduced in Brazil only very recently. Sharing haplotypes among orchards separated by 400 km suggests the natural dispersal of fungal propagules, with the possible involvement of pollinators. A significant population expansion was detected, which was consistent with an increase in host density associated with crop expansion toward new areas across the state. Findings of moderate to high levels of haplotypic diversity and gametic equilibrium suggest that recombination might play an important role in these pathogen populations, possibly via parasexual reproduction or a cryptic sexual cycle. This study provides additional tools for epidemiological studies of C. acutatum to improve prevention and management strategies for this disease.

Leaf spot of bananas caused by Mycosphaerella musicola: action of oil on the life cycle of the pathogen

1968 ◽  
Vol 46 (12) ◽  
pp. 1495-1505 ◽  
Author(s):  
R. H. Stover ◽  
J. D. Dickson
Keyword(s):  
Incubation Period ◽  
Leaf Spot ◽  
Germ Tube ◽  
Tube Growth ◽  
Disease Development ◽  
Resistant Varieties ◽  
Mycosphaerella Musicola ◽  
Appressoria Formation ◽  
Ascospore Production ◽  
Germ Tube Growth

Oil spray reduced germination, germ tube growth, and appressoria formation by spores of Mycosphaerella musicola under field conditions for periods varying from 2 days to 2 weeks. Inhibition occurred only when spores were on the same leaf surface to which oil was applied. Appressoria formation and germ tube growth were reduced up to 33% and 25%, respectively. Conidia and ascospore production and dissemination were not adversely affected by oil spray. However, there were fewer sporodochia and perithecia in spots that were slow to develop as a result of oil spray. Oil application up to 2 weeks before or after infection increased the incubation period and the generation time, and reduced the number of spots. Oil is effective in retarding spot development when applied either before streaks appear or at the yellow streak stage of disease development. Oil, when applied during the incubation period or to yellow streaks, causes a variable amount of reduction in spotting and in only a minority of cases is disease development stopped completely. Therefore, leaf spot can build up on oil-sprayed plants when inoculum is abundant and weather favorable. The behavior of the pathogen on oil-sprayed susceptible banana plants is similar to that on partially resistant varieties.

scholarly journals Pre- and Post-Infection Activity of Pyraclostrobin for Control of Anthracnose Fruit Rot of Strawberry Caused by Colletotrichum acutatum

Plant Disease ◽  
2006 ◽  
Vol 90 (7) ◽  
pp. 862-868 ◽  
Author(s):  
William W. Turechek ◽  
Natália A. Peres ◽  
Nicole A. Werner
Keyword(s):  
New York ◽  
Post Infection ◽  
Field Studies ◽  
Fruit Rot ◽  
Colletotrichum Acutatum ◽  
Disease Development ◽  
Infection Period ◽  
Significant Control ◽  
Infection Treatment ◽  
Control Equivalent

The effect of pre- and post-infection-period applications of pyraclostrobin (Cabrio EG) on the development of anthracnose fruit rot was characterized in a controlled-climate study and validated in field studies in New York and Florida. Plants of the day-neutral cv. Tristar were inoculated with C. acutatum and placed into mist chambers at 14, 22, or 30°C. The plants were removed from the chambers after 3, 6, 12, or 24 h of misting and placed on greenhouse benches to allow disease development. The fungicide pyraclostrobin was applied to the berries at a concentration equivalent to 168 g a.i./ha at 3, 8, 24, and 48 h prior to inoculation and exposure to their wetting period, or 3, 8, 24, and 48 h following inoculation and exposure to their wetting period. All pyraclostrobin treatments suppressed disease compared with the corresponding untreated control treatments. The highest incidence of disease occurred on plants exposed to the longest wetness durations (12 and 24 h) or highest temperature treatments (22 and 30°C). Post-infection applications of pyraclostrobin provided significant control when applications were made within 3 and often up to 8 h after wetting, but generally were less effective than protective sprays. We further tested the ability of pyraclostrobin to control anthracnose when applied as a protectant or as an after-infection application in inoculated field plots exposed to a short (8 h) or long (24 h) wetting period in Florida and in New York. In three of the four experimental plots, disease control equivalent to or better than the protective spray was achieved when pyraclostrobin was applied up to 24 h after infection for long and short wetting periods. In the remaining plot, conditions for disease development were exceptionally favorable. The protective treatment provided approximately 75% control, whereas the best post-infection treatment provided only 50% control. Our study indicates that for short wetting events, such as those associated with seasonal thunderstorms, growers can wait until after such an infection event before applying pyraclos-trobin and achieve control equivalent to a protective application.

scholarly journals Transformative tools for tackling tuberculosis

2015 ◽  
Vol 212 (11) ◽  
pp. 1759-1769 ◽  
Author(s):  
Jennifer L. Gardiner ◽  
Christopher L. Karp
Keyword(s):  
Mycobacterium Tuberculosis ◽  
Host Response ◽  
Control Strategies ◽  
Disease Development ◽  
Diagnostic Biomarkers ◽  
Human Host ◽  
Current State ◽  
Highly Sensitive ◽  
The World ◽  
Total Body

The world is in need of more effective approaches to controlling tuberculosis. The development of improved control strategies has been hampered by deficiencies in the tools available for detecting Mycobacterium tuberculosis and defining the dynamic consequences of the interaction of M. tuberculosis with its human host. Key needs include a highly sensitive, specific nonsputum diagnostic; biomarkers predictive of responses to therapy; correlates of risk for disease development; and host response–independent markers of M. tuberculosis infection. Tools able to sensitively detect and quantify total body M. tuberculosis burden might well be transformative across many needed use cases. Here, we review the current state of the field, paying particular attention to needed changes in experimental paradigms that would facilitate the discovery, validation, and development of such tools.

An Evaluation of Hydrophilic Polymers for Formulating the Bioherbicide AgentsAlternaria cassiaeandA. eichhorniae

1997 ◽  
Vol 11 (2) ◽  
pp. 212-220 ◽  
Author(s):  
Yasser M. Shabana ◽  
R. Charudattan ◽  
James T. Devalerio ◽  
Mohamed A. Elwakil
Keyword(s):  
Spore Germination ◽  
Xanthan Gum ◽  
Water Concentration ◽  
Hydrophilic Polymers ◽  
Disease Development ◽  
Fungal Propagules ◽  
Aqueous Gels ◽  
Two Parameters ◽  
Over Time ◽  
Better Than

Eight polymers capable of forming aqueous gels were compared for their capacity to retain hydration over time, to promote spore germination, and to prolong the viability of germinated spores (= germlings) ofAlternaria cassiae, a bioherbicide agent for sicklepod. When compared at a standard 0.1% w/w (gel/water) concentration, the eight gels retained hydration for 6 d with no significant differences among them in the rate of dehydration. The best concentration of each gel that yielded 95 to 100% spore germination within 6 h after hydration was then chosen, and the gels were compared at these concentrations to determine the duration of effectiveness of the gels. The effectiveness was rated on the basis of the proportions of alive germlings versus germinated spores and alive germlings versus total spores, determined with the aid of a fluorescent vital stain. Based on these two parameters, the most effective gel was Kelzan® xanthan gum. However, all gels supported > 50% alive germlings over a period of 1 wk, suggesting that the addition of any of these polymers to the inoculum suspension should enable the fungal propagules to remain moist for a prolonged period, benefit from the high ambient moisture to improve germination, and promote disease development. Accordingly, seven of these gels were tested for their ability to enhance pathogenicity of a mycelial inoculum ofA. eichhorniae, a bioherbicide agent for waterhyacinth. Gellan gum and Kelgin®-HV were most effective in promoting disease, followed by Evergreen® 500 polyacrylamide, and Kelgin®-LV, Metamucil®, Kelzan® xanthan gum, and N-Gel™ were no better than the control inoculum without any gel. Thus, the gels may have differential effects on different fungi and inoculum types. Nonetheless, the results confirm the utility and feasibility of hydrophilic gels as formulating materials for bioherbicides.

scholarly journals Baseline Sensitivities of Fungal Pathogens of Fruit and Foliage of Citrus to Azoxystrobin, Pyraclostrobin, and Fenbuconazole

Plant Disease ◽  
2005 ◽  
Vol 89 (11) ◽  
pp. 1186-1194 ◽  
Author(s):  
S. N. Mondal ◽  
Alka Bhatia ◽  
Turksen Shilts ◽  
L. W. Timmer
Keyword(s):  
Mycelial Growth ◽  
Fungal Pathogens ◽  
Fungal Species ◽  
Brown Spot ◽  
Colletotrichum Acutatum ◽  
Fungicide Sensitivity ◽  
Fruit Drop ◽  
Coefficients Of Variation ◽  
Foliar Pathogens

The baseline sensitivities for mycelial growth of foliar fungal pathogens of citrus, Colletotrichum acutatum, Alternaria alternata, Elsinoe fawcettii, Diaporthe citri, and Mycosphaerella citri, the causal agents of postbloom fruit drop, brown spot of tangerine, citrus scab, melanose, and greasy spot, respectively, were determined in vitro for azoxystrobin, pyraclostrobin, and fenbuconazole. The effective dose to reduce growth by 50% (ED50 values) was determined for each pathogen-fungicide combination using five isolates from different citrus areas of Florida and eight fungicide concentrations. A discriminatory dose for each combination was selected near the ED50, and the range of sensitivity of 50 to 62 isolates of each fungal species was determined. The effect of salicylhydroxamic acid (SHAM) on the sensitivity of the five fungal species to azoxystrobin and pyraclostrobin was determined. Since mycelial growth of A. alternata was insensitive to azoxystrobin, the effect of that fungicide with and without SHAM on spore germination was assessed. The ED50 values for most fungal pathogens of citrus were relatively high compared with foliar pathogens of other tree crops. Values for azoxystrobin ranged from a low of 0.06 μg/ml with E. fawcettii to a high of >100 μg/ml with A. alternata. With pyraclostrobin, the values ranged from a low of 0.019 μg/ml with D. citri to a high of 0.87 μg/ml with A. alternata. With fenbuconazole, the lowest ED50 value was 0.21 μg/ml with M. citri and the highest was 1.01 μg/ml with C. acutatum, but A. alternata and D. citri were not tested. SHAM was inhibitory to all species and reduced growth of D. citri greatly. Inclusion of SHAM in the medium did not greatly affect the sensitivity of mycelial growth of these fungi to azoxystrobin or pyraclostrobin, nor did it affect the ED50 values for conidial germination of A. alternata. The coefficients of variation for the sensitivity of 50 to 62 isolates of each species to these fungi ranged from 7.3% with the pyraclostrobin-C. acutatum combination to a high of 55.0% with the fenbuconazole- M. citri combination. Discriminatory doses have been established for these pathogen- fungicide combinations that should be useful for detecting major shifts in fungicide sensitivity.

scholarly journals Evaluation of Growth Regulator Inhibitors for Controlling Postbloom Fruit Drop (PFD) of Citrus Induced by the Fungus Colletotrichum acutatum

HortScience ◽  
2006 ◽  
Vol 41 (5) ◽  
pp. 1317-1321 ◽  
Author(s):  
Hui-Qin Chen ◽  
Katherine L. Dekkers ◽  
Lihua Cao ◽  
Jacqueline K. Burns ◽  
L. W. Timmer ◽  
...  
Keyword(s):  
Systemic Acquired Resistance ◽  
Auxin Transport ◽  
Sweet Orange ◽  
Acquired Resistance ◽  
Colletotrichum Acutatum ◽  
Yield Losses ◽  
Commercial Products ◽  
Young Fruit ◽  
Factors Associated ◽  
Fruit Drop

Postbloom fruit drop (PFD) of citrus is incited by the fungus Colletotrichum acutatum J. H. Simmonds and may result in young fruit drop and severe yield losses. Previous studies suggested that imbalance of growth regulators such as auxin, ethylene, and jasmonic acid (JA) plays an essential role in young fruit abscission. In this work, we determined the factors associated with fungal-induced fruit drop by testing compounds inhibitory to hormonal transport or biosynthesis. As assessed on sweet orange (Citrus sinensis Osbeck) and grapefruit (C. paradisi Macf.) for 4 years, we found that many auxin transport and action inhibitors such as 2,3,5-triiodobenzolic acid (TIBA), 2-(4-chlorophenoxy)-2-methyl-propionic acid (clofibrate), or quercetin and JA biosynthesis inhibitors such as salicylic acid (SA) and aspirin (methyl-SA) applied 7 d after C. acutatum infection resulted in higher percentages of young fruit retention compared with the water controls. The commercial products ReZist and Actigard, widely used as systemic acquired resistance (SAR) agents, also improved fruit retention. Furthermore, application of gibberellic acid (GA3) on sweet orange, regardless of C. acutatum infection, significantly increased fruit retention. These commercial products may be very useful in managing this destructive disease of citrus in the field.

Evaluation of fungicide applications to sweet orange at different flowering stages for control of postbloom fruit drop caused by Colletotrichum acutatum

2008 ◽  
Vol 27 (1) ◽  
pp. 71-76 ◽  
Author(s):  
A. de Goes ◽  
R.B.O. Garrido ◽  
R.F. Reis ◽  
R.B. Baldassari ◽  
M.A. Soares
Keyword(s):  
Sweet Orange ◽  
Colletotrichum Acutatum ◽  
Fruit Drop
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