scholarly journals Apple Scab Disease Severity in the Sais Region of Morocco and its Sensitivity to Three Commercial Fungicides

2019 ◽  
Vol 11 (2) ◽  
pp. 249-257
Author(s):  
Rachid LAHLALI ◽  
Alieu MOININA ◽  
Said EZRARI ◽  
Dustin MACLEAN ◽  
Mohammed BOULIF
Keyword(s):  
Disease Severity ◽  
Venturia Inaequalis ◽  
Apple Scab ◽  
Baseline Sensitivity ◽  
Thiophanate Methyl ◽  
Two Samples ◽  
In Vivo Tests ◽  
Rf Values

Apple scab, Venturia inaequalis (Cooke) G. Winter, results in numerous fungicide applications in the Sais region of Morocco. We conducted the study to determine the susceptibility of cultivars through field survey and to evaluate the sensitivity of V. inaequalis to three fungicides using both in vitro and in vivo methods. We surveyed 100 apple orchards and collected two samples. Disease survey showed that the cultivars were highly susceptible to apple scab (grand mean of leaf scab: Golden Delicious, 40.31%; Starking Delicious, 20.45%; and Gala, 18.92%). Results underlined no significant differences between isolates in term of inhibition rate of mycelial growth and averaged disease severity. However, both treatment and concentration were statistically significant. EC50 values ranged from 2.33 µg/ml to 7.40 µg/ml and resistance factor (RF) values of 0.55, 1.02 and 1.79 were obtained for difenoconazole, trifloxystrobin and thiophanate-methyl, respectively. In vivo tests at a concentration of 10 µg/ml on the isolate ViIF using a curative method showed a high efficacy of trifloxystrobin (96.38%), and low efficacy of thiophanate-methyl (29.65%) and difenoconazole (24.62%). V. inaequalis was most sensitive to trifloxystrobin followed by difenoconazole and thiophanate-methyl, respectively. From this work, it was recommended testing more isolates and contact fungicides in order to develop a baseline sensitivity of the pathogen population against commonly used fungicides to treat the disease, as continued usage over time and the introduction of new fungal races may result in a decrease in fungicide efficacy.

scholarly journals Sensitivity of Venturia inaequalis Isolates to Fungicides Used in Lebanon

Plant Disease ◽  
1997 ◽  
Vol 81 (1) ◽  
pp. 112-112 ◽  
Author(s):  
H. G. Diab Al-Arab ◽  
Y. Abou-Jawdah
Keyword(s):  
Venturia Inaequalis ◽  
Apple Scab ◽  
In Vitro Tests ◽  
In Vitro Activity ◽  
Mountainous Areas ◽  
Single Spore ◽  
The North ◽  
In Vivo Tests

Apple scab, caused by Venturia inaequalis (Cooke) G. Wint. is one of the major apple diseases worldwide. In 1994, the disease caused severe losses particularly in apple orchards of the Akkar mountainous areas of Lebanon, although more than 10 fungicide sprays were applied. A total of 230 isolates of V. inaequalis were collected from 23 orchards and single-spore colonies were prepared. The orchards were selected to represent the major apple-growing areas in Lebanon: Akkar in the north, Kfardibian in northeast Beirut, and Barouk in southeast Beirut. In vitro tests were conducted to evaluate the level of resistance to benzimidazoles and sterol biosynthesis inhibitors (SBI). All isolates tested except one were resistant to benomyl and thiophanate-methyl at 1 μg/ml. The majority of isolates were not inhibited at concentrations as high as 50 μg/ml in mycelial growth. Similarly, the majority of the isolates were not inhibited by benomyl at 1, 5, and 50 μg/ml in spore germination tests. Preliminary in vivo tests with benomyl concerning resistance to benzimidazoles correlated well with in vitro results. All the isolates were inhibited by fenari-mol at 0.25 μg/ml (1) indicating that all the isolates can be considered sensitive to this fungicide. However, the sensitivity levels varied among the various isolates with the ED50 for fenarimol ranging between 0.002 and 0.052 μg/ml. Two new SBIs, bromocunazol and fenbuconazol, not registered for use in Lebanon at the time this study was performed, were also tested. Their ED50 ranged from 0.0089 to 0.025 μg/ml for bromocunazol and from 0.008 to 0.039 μg/ml for fenbuconazol, both indicating a good level of in vitro activity. These results indicate that resistance to benzimidazol is widespread in Lebanon while resistance to SBIs has not yet been detected. Reference: (1) W. Köller et al. Plant Dis. 75:726, 1991.

scholarly journals Baseline Sensitivities of Venturia inaequalis Populations to the Strobilurin Fungicide Kresoxim-methyl

Plant Disease ◽  
1999 ◽  
Vol 83 (3) ◽  
pp. 274-278 ◽  
Author(s):  
Gilberto Olaya ◽  
Wolfram Köller
Keyword(s):  
Venturia Inaequalis ◽  
Resistance Development ◽  
Additional Tool ◽  
Apple Leaves ◽  
Scab Control ◽  
In Vivo Tests ◽  
Strobilurin Fungicide ◽  
The Mean

The efficacies of the new strobilurin fungicide kresoxim-methyl for the protection of apple leaves from infection by baseline populations of Venturia inaequalis were uniform across five major apple growing regions in North America. The mean ED50 value determined for 25 populations was 0.35 μg ml-1, with values ranging from 0.11 μg ml-1 to 0.75 μg ml-1. The mean level of scab control achieved at the kresoxim-methyl dose of 4 μg ml-1 was 93%. For one of the five orchards sampled in each region, kresoxim-methyl sensitivities of germinating conidia were determined. Sensitivities of 250 isolates were broadly distributed, with ED50 values ranging from 0.003 μg ml-1 to 0.14 μg ml-1 and a mean of 0.02 μg ml-1. This broad range of in vitro sensitivities was not reflected for the in vivo efficacy of kresoxim-methyl in the protection of apple leaves from scab infections. The discrepancy between in vivo and in vitro sensitivities implies that in vivo tests are more useful for the monitoring of kresoxim-methyl sensitivities of orchard populations. Because it can be expected that only isolates resistant under both test conditions will be prone to future selection, such isolates will contribute to increased frequencies of the least sensitive isolates described in this baseline study. Testing of in vitro isolate sensitivities will, therefore, provide an additional tool in the monitoring of kresoxim-methyl resistance development.

scholarly journals Detection and Characterization of Benzimidazole Resistance in California Populations of Colletotrichum cereale

Plant Disease ◽  
2008 ◽  
Vol 92 (2) ◽  
pp. 239-246 ◽  
Author(s):  
Francis P. Wong ◽  
Karla A. de la Cerda ◽  
Rufina Hernandez-Martinez ◽  
Sharon L. Midland
Keyword(s):  
Creeping Bentgrass ◽  
Baseline Sensitivity ◽  
Putting Greens ◽  
Thiophanate Methyl ◽  
Annual Bluegrass ◽  
Sensitivity Distribution ◽  
Exposed Population ◽  
Colletotrichum Cereale

Colletotrichum cereale is the causal agent of turfgrass anthracnose, which has become a serious problem on annual bluegrass (Poa annua) and creeping bentgrass (Agrostis palustris) golf course putting greens. Thiophanate-methyl is a benzimidazole (methyl benzimidazole carbamate [MBC]) fungicide used for the management of anthracnose. In this study, we examined 481 isolates from 10 California populations to determine the presence and frequency of MBC resistance. An in vitro methodology was developed to construct a baseline sensitivity distribution using 60 isolates from an unexposed population (TCGC). The 50% effective dose (ED50) values for the baseline sensitivity distribution for thiophanate-methyl ranged from 0.14 to 2.3 μg/ml with a mean of 0.75 μg/ml. For 60 isolates assayed from an exposed population (AHCC), 57 isolates were not responsive to in vitro concentrations of thiophanate-methyl of up to 30 μg/ml. Isolates nonresponsive to thiophanate-methyl were not responsive to benomyl in vitro. Two isolates nonresponsive in vitro to thiophanate-methyl or benomyl were not controlled in vivo on annual bluegrass plants treated preventively with either fungicide at 11 mg/ml, confirming the results of the in vitro testing. The remaining 361 isolates from eight populations were tested using the single discriminatory dose of thiophanate-methyl at 10 μg/ml. A high proportion (>90%) of isolates from six of the populations were resistant to thiophanate-methyl, indicating the presence of practical resistance at these locations. To determine the molecular mechanism of MBC resistance, the two β-tubulin genes, TUB1 and TUB2, of 12 resistant and 6 sensitive isolates were amplified and sequenced, revealing a glutamic acid to lysine substitution at position 198 of TUB2 that was present in all resistant isolates. This work confirms the presence of MBC resistance in C. cereale populations from California and presents methods and information that can be used to manage resistance to the MBC fungicides and improve anthracnose management programs.

scholarly journals Shift in Sensitivity of Alternaria solani in Response to QoI Fungicides

Plant Disease ◽  
2004 ◽  
Vol 88 (2) ◽  
pp. 181-187 ◽  
Author(s):  
J. S. Pasche ◽  
C. M. Wharam ◽  
N. C. Gudmestad
Keyword(s):  
Disease Severity ◽  
Spore Germination ◽  
Early Blight ◽  
Alternaria Solani ◽  
Baseline Sensitivity ◽  
Qoi Fungicides ◽  
Cross Sensitivity ◽  
Significant Difference

Isolates of Alternaria solani, cause of potato early blight, collected in 1998 through 2001 from various potato growing areas across the midwestern United States, were tested for sensitivity to azoxystrobin. Isolates collected in 1998, prior to the introduction of azoxystrobin, were tested to establish the baseline sensitivity of the fungus to this fungicide. Isolates collected in subsequent years, not necessarily from the same sites as baseline isolates, were tested to determine if populations of A. solani had become less sensitive to azoxystrobin. Azoxystrobin sensitivity was determined utilizing an in vitro spore germination assay. The effective fungicide concentration that inhibited spore germination by 50% (EC50) was determined for each isolate. There was no significant difference in mean EC50 values between baseline isolates and all other isolates collected through 1999. Mean azoxystrobin EC50 values of A. solani isolates collected in 2000 and 2001 were significantly higher compared with means from previous years, and mean azoxystrobin EC50 values from 2001 were significantly higher than means from isolates collected in 2000. A subset of 54 A. solani isolates was evaluated in vitro for cross-sensitivity to pyraclostrobin and trifloxystrobin. A highly significant and strong correlation among the isolates tested for fungicide cross-sensitivity was detected between azoxystrobin and pyraclostrobin; however, the correlation between azoxystrobin and trifloxystrobin, and between trifloxystrobin and pyraclostrobin, was significant but weak. A second subset of five isolates was chosen for in vivo assessment of azoxystrobin, pyraclostrobin, and trifloxystrobin sensitivity. Disease severity on plants treated with azoxystrobin and pyraclostrobin was significantly greater with reduced-sensitive A. solani isolates compared with sensitive isolates. Disease severity was not statistically different between azoxystrobin reduced-sensitive and sensitive A. solani isolates on plants treated with trifloxystrobin. This is the first report of a shift in sensitivity to QoI fungicides in a fungus possessing only an anamorphic stage.

scholarly journals Improving the Biocontrol Potential of Bacterial Antagonists with Salicylic Acid against Brown Rot Disease and Impact on Nectarine Fruits Quality

Agronomy ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 209
Author(s):  
Nadia Lyousfi ◽  
Rachid Lahlali ◽  
Chaimaa Letrib ◽  
Zineb Belabess ◽  
Rachida Ouaabou ◽  
...  
Keyword(s):  
Salicylic Acid ◽  
Disease Severity ◽  
Mycelial Growth ◽  
Brown Rot ◽  
Antagonistic Bacteria ◽  
Biological Treatments ◽  
Rot Disease ◽  
The Impact

The main objective of this study was to evaluate the ability of both antagonistic bacteria Bacillus amyloliquefaciens (SF14) and Alcaligenes faecalis (ACBC1) used in combination with salicylic acid (SA) to effectively control brown rot disease caused by Monilinia fructigena. Four concentrations of salicylic acid (0.5%, 2%, 3.5%, and 5%) were tested under in vitro and in vivo conditions. Furthermore, the impact of biological treatments on nectarine fruit parameters’ quality, in particular, weight loss, titratable acidity, and soluble solids content, was evaluated. Regardless of the bacterium, the results indicated that all combined treatments displayed a strong inhibitory effect on the mycelial growth of M. fructigena and disease severity. Interestingly, all SA concentrations significantly improved the biocontrol activity of each antagonist. The mycelial growth inhibition rate ranged from 9.79% to 88.02% with the highest reduction rate recorded for bacterial antagonists in combination with SA at both concentrations of 0.5% and 3.5%. The in vivo results confirmed the in vitro results with a disease severity varying from 0.00% to 51.91%. A significant biocontrol improvement was obtained with both antagonistic bacteria when used in combination with SA at concentrations of 0.5% and 2%. The lowest disease severity observed with ACBC1 compared with SF14 is likely due to a rapid adaptation and increase of antagonistic bacteria population in wounded sites. The impact of all biological treatments revealed moderate significant changes in the fruit quality parameters with weight loss for several treatments. These results suggest that the improved disease control of both antagonistic bacteria was more likely directly linked to both the inhibitory effects of SA on pathogen growth and induced fruit resistance.

In Vitro Methods as a Tool in Neurotoxicity Studies

1995 ◽  
Vol 23 (4) ◽  
pp. 491-496
Author(s):  
Hanna Tähti ◽  
Leila Vaalavirta ◽  
Tarja Toimela
Keyword(s):  
Risk Evaluation ◽  
Toxicity Testing ◽  
In Vitro Models ◽  
In Vitro Tests ◽  
Industrial Chemicals ◽  
Mercury Compounds ◽  
Toxicological Data ◽  
In Vivo Tests

— There are several hundred industrial chemicals with neurotoxic potential. The neurotoxic risks of most of these chemicals are unknown. Additional methods are needed to assess the risks more effectively and to elucidate the mechanisms of neurotoxicity more accurately than is possible with the conventional methods. This paper deals with general tasks concerning the use of in vitro models in the evaluation of neurotoxic risks. It is based on our previous studies with various in vitro models and on recent literature. The induction of glial fibrillary acidic protein in astrocyte cultures after treatment with known neurotoxicants (mercury compounds and aluminium) is discussed in more detail as an important response which can be detected in vitro. When used appropriately with in vivo tests and with previous toxicological data, in vitro neurotoxicity testing considerably improves risk assessment. The incorporation of in vitro tests into the early stages of risk evaluation can reduce the number of animals used in routine toxicity testing, by identifying chemicals with high neurotoxic potential.

scholarly journals Role of in vitro and in vivo tests of hypersensitivity in beryllium workers.

1977 ◽  
Vol 30 (1) ◽  
pp. 24-28 ◽  
Author(s):  
C D Price ◽  
W J Williams ◽  
A Pugh ◽  
D H Joynson
Keyword(s):  
In Vivo Tests

scholarly journals Effect of Timing of Application of the Biological Control Agent Microsphaeropsis ochracea on the Production and Ejection Pattern of Ascospores by Venturia inaequalis

2004 ◽  
Vol 94 (12) ◽  
pp. 1305-1314 ◽  
Author(s):  
O. Carisse ◽  
D. Rolland
Keyword(s):  
Biological Control ◽  
Biological Control Agent ◽  
Venturia Inaequalis ◽  
Apple Scab ◽  
Control Agent ◽  
Sterile Leaf ◽  
Ascospore Production ◽  
Fall Application ◽  
Leaf Disks

Field and in vitro trials were conducted to establish the influence of the biological control agent Microsphaeropsis ochracea on the ejection pattern of ascospores by Venturia inaequalis and on apple scab development, and to establish the best timing of application. The ejection pattern of ascospores was similar on leaves sprayed with M. ochracea and on untreated leaves. Fall application of M. ochracea combined with a delayed-fungicide program was evaluated in orchards with intermediate and high scab risk. For both orchards, it was possible to delay the first three and two infection periods in 1998 and 1999, respectively, without causing significant increase or unacceptable leaf and fruit scab incidence. To evaluate the best timing of application, sterile leaf disks were inoculated with V. inaequalis and then with M. ochracea 0, 2, 4, 6, 8, 10, 12, 14, and 16 weeks later. After incubation under optimal conditions for pseudothecia development, the number of ascospores was counted. Similarly, M. ochracea was sprayed on scabbed leaves on seven occasions from August to November 1999 and 2000. Leaves were overwintered on the orchard floor and ascospore production was evaluated the following spring. Ascospore production was reduced by 97 to 100% on leaf disks inoculated with M. ochracea less than 6 weeks after inoculation with V. inaequalis, but ascospore production increased with increasing period of time when M. ochracea was applied 8 to 16 weeks after the inoculation with V. inaequalis. In the orchard, the greatest reduction in production of ascospores (94 to 96% in 2000 and 99% in 2001) occurred on leaves sprayed with M. ochracea in August. The production of ascospores was reduced by 61 to 84% in 2000 and 93% in 2001 on leaves sprayed with M. ochracea in September, reduced by 64 to 86% in 2000 and 74 to 89% in 2001 on leaves sprayed in October, and reduced by 54 and 67% in 2000 and 2001, respectively, on leaves sprayed in November. It was concluded that M. ochracea should be applied in August or September and that ascospore maturation models and delayed-fungicide program could be used in orchards treated with this biological control agent.

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