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Control of Stemphylium Leaf Blight Disease of Onion and Elevation of Seed Production Using Certain Bioagents

Kamal A.M. Abo-Elyousr, Sobhy I.I. Abdel-Hafez and Ismail R. Abdel-Rahim
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Objective: This present study aimed to study the effect of some bioagents against Stemphylium vesicarium in vitro and under greenhouse conditions. Materials and Methods: The isolate of Stemphylium vesicarium used in this study was recovered from a diseased onion in Assiut Governorate (Egypt) and the experiments of biocontrol of the disease were carried out under greenhouse condition at Assiut University. Data were analyzed using one-way ANOVA with the SPSS 10.0 software program. Means were compared by the Duncan’s multiple tests and statistical significance was determined at 5% level. Results: After preliminary screening on antagonistic activity of 20 fungal isolates recovered from onion plants, two isolates to control the disease under greenhouse conditions were selected namely, Trichoderma harzianum isolate 3013 and Stachybotrys chartarum isolate 2031. Application of T. harzianum isolate 3013 and Stachybotrys chartarum isolate 2031 showed, when applied before pathogen infection, a reduction in disease by 67.9 and 71.3%, respectively. As well as after pathogen infection they caused a reduction in the disease by 72.8 and 73.2%. In comparison, the applied fungicide Ridomil gold plus reduced the disease by 84.4 and 95.7% before and after pathogen inoculation, respectively. Spore suspension of Trichoderma harzianum isolate 3013 and Stachybotrys chartarum isolate 2031 and Ridomil gold plus improved number of seeded fruits, number of seeds per inflorescence and weight of seeds per inflorescence compared to infected control. Conclusion: It could be control of SLB under greenhouse condition with this bioagents. The use of T. harzianum isolate 3013 and Stachybotrys chartarum isolate 2031 could be used to control onion Stemphylium blight disease and elevate the seed production.

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Kamal A.M. Abo-Elyousr, Sobhy I.I. Abdel-Hafez and Ismail R. Abdel-Rahim, 2017. Control of Stemphylium Leaf Blight Disease of Onion and Elevation of Seed Production Using Certain Bioagents. International Journal of Plant Pathology, 8: 1-7.

DOI: 10.3923/ijpp.2017.1.7

Received: September 01, 2016; Accepted: November 17, 2016; Published: December 15, 2016


In Egypt (Assiut governorate) the first report of Stemphylium leaf blight (SLB) of onion caused by Stemphylium vesicarium (Wall.) Simmons was reported by Hassan et al.1. The disease was reported by Shishkoff and Lorbeer2 in the main production areas of the world. It is more severe on seed crop compared to bulb crop3 causing sometimes 100% loose of the seed production4,5. Although chemical control of SLB had been practiced, its success depends largely on high number of spraying6. Today there are strict regulations on chemical fungicide use, due to residual toxicity problems and environmental pollution7. As well as, using of synthetic fungicides can cause development of fungicide-resistant strains of the pathogen. Therefore, there are a large number of studies have been devoted to searching for alternative control strategies to plant pathogens8-11. Trichoderma spp. are considered most popular and environmentally friendly bio-control agents against numerous phytopathogenic fungi12, they successfully suppress leaf fungal pathogens13 and many others soil-borne pathogens14. According our information there no study has been done on use of Stachybotrys chartarum against SLB under greenhouse condition.

In Egypt, Stemphylium blight is one of the most important disease attacked onion plant especially in seed production. It cause considerable losses in seed crops of onion and sometimes causes 100% loss. For this problem of Stemphylium blight the present study is undertaken to evaluate new strains of local bioagents for the management of Stemphylium blight of onion.


Source of Stemphylium vesicarium and inoculum preparation: The isolate of Stemphylium vesicarium used in this study was recovered from a diseased onion in Assiut governorate (Egypt), identified and deposited in Assiut University Mycological center under accession number AUMC10512. The pathogenicity of this isolate was previously tested showing 37.25% disease severity15. The inoculums were prepared from stock cultures on PDA media stored at 4°C. A piece of culture medium containing mycelium (approximately 2 mm) of fungi was placed centrally on 9 cm diameter petri dish with PDA medium and incubated at 25±1°C for 15 days under a 12 h photoperiod using a near-ultraviolet light suspended approximately 20 cm above the cultures. Ten milliliters of sterile distilled water was then added to each plate and colonies were scraped with a sterile needle. The resulting conidial suspension (5×104 conidia mL–1) inoculated onto leaves and seed-stalks of onion plants (110 days old cv., ‘Giza 6’) using an atomizer.

In vitro, preliminary determination of antagonistic capability of non-pathogenic fungal against Stemphylium vesicarium: Twenty fungal isolates were recovered from onion plants and identified by Abdel-Hafez et al.16 and antagonistic capability of it were carried out using Dual culture method described by Li et al.17.

Petri dishes (9 cm diameter) containing 15 mL PDA medium were seeded with inoculum of the SLB (approximately 5 mm) pathogen on one plate edge, then after 48 h. Incubation at 25±1°C the tested fungal isolates were seeded on opposite position edge. Plates inoculated with Stemphylium vesicarium only as well as tested fungi only were used as a control. The observations were recorded when the growth of the pathogen completely covered the plate surface in the control treatment. Three replicates of both control and treated plates were used. An arbitrary scale index was used to show the mechanism of antagonism plus inhibition zone diameter. N: No antagonism (Inhibition zone 0 mm), L: Low antagonism (Inhibition zone less than 3 mm), M: Moderate antagonism (Inhibition zone 3-7 mm), H: High antagonism (Inhibition zone>7 mm) and OG: Over growth (Mycoparastism).

Chitinase activity: Conidia from 4 days old Potato Dextrose Agar (PDA) cultures of the fungal isolate that showed overgrowth on Stemphylium vesicarium AUMC10512 were grown on 250 mL Erlenmeyer flasks containing 50 mL liquid culture medium. These medium contains the following components (g L–1), 1.4 (NH4)2SO4, 2.0 KH2PO4, 6.9 NaH2PO4, 0.3 MgSO4.7H2O, 1.0 colloidal chitin and 10 peptone18.

Colloidal (acid swollen) chitin was prepared as follows: One gram of chitin (crab shell) was added to 10 mL of 85% orthophosphoric acid. The mixture was stirred to make a gelatinous paste and stored at 0°C for 24 h. The gelatinous mixture was re-precipitated into an excess of cold (15°C) distilled water. It was made to a paste using a pestle and mortar and then re-suspended in Na-acetate buffer (50 mM, pH 4.75). The suspension was stored in a sterile container at 10°C.

Chitinase activity was assayed as follows: a tube containing reaction mixture [0.55 mL of acid swollen chitin (5 gL–1, suspended in 50 mM Na-acetate buffer, pH 4.75), 0.30 mL of acetate buffer (50 mM, pH 4.75) and 0.15 mL of culture filtrate] was incubated at 47°C for 1 h in un-stirred condition. The reaction was terminated by adding 1 mL of potassium sodium-tartrate reagent to the reaction mixture19. A control was taken where the enzyme was deactivated by adding 1 mL of potassium sodium-tartrate reagent before the commencement of incubation. The alkaline tartrate reagent was prepared by mixing 270 g potassium sodium-tartrate dissolved in 400 mL distilled water and a solution of 6.25 g of phenol in 10% sodium hydroxide solution (17.5 g NaOH in 175 mL distilled water). The reagent was stored in a dark bottle. One milliliter of dinitrosalicylic acid (DNS) reagent was added to the tubes and the tubes were kept in a boiling water bath for 5 min. The DNS reagent was prepared by dissolving 1.5 g of 3, 5-dinitrosalicylic acid in 100 mL of distilled water. The reaction mixture was cooled to 30°C. Seven milliliters of distilled water were added to each tube to make up the final volume to 10 mL. The mixture was centrifuged at 5000 rpm for 5 min and the intensity of colour (formed due to the reaction of N-acetyl-D-glucosamine released with dinitrosalicylic acid) was measured at 540 nm by a spectrophotometer20.

One unit of enzyme activity was defined as the amount of enzyme required for the formation of 1 μg of the product per minute of the reaction, under the standard assay conditions.

Biological control of Stemphylium blight in vivo: Two antagonistic fungal isolates Trichoderma harzianum isolate 3013 (6×108 conidia mL–1) and Stachybotrys chartarum isolate 2031 were selected to application for controlling onion SLB disease under greenhouse condition. All treatments were applied by two methods, the first was applied bioagents before 48 h of pathogen’s inoculation, while the second was applied after 48 h of pathogen’s inoculation. Disease assessment of each treatment was recorded 15 days after inoculation as a percentage disease severity previously described by Hussein et al.21. The foliar fungicide Ridomil gold plus (2 g L–1) was used as a positive control for the comparison purpose with the biocontrol agents in controlling the disease incidence. Each pot was sprayed with 100 mL of each treatment (conidia of bioagents or fungicide) and three replicates were used to each treatment. Negative control were used and treated with sterile water. The chemical composition of Ridomil gold plus (w/w): Mefenoxam 2.5%, dicopper chloride trihydroxide 69%, adhesive components 6% and carrier 22.5%. Mefenoxam is the common name of methyl N-(methoxy acetyl)-N-(2.6-xylyl)-D-lalaninate; methyl (R)-2-[(2, 6-dimethylphenyl) methoxyacetyl] amino-propionate.

Effect of various treatments on seed production: At the end of experiments, some parameters were determined such as, number of flowers per inflorescence, number of seeded fruits per inflorescence, number of seed per inflorescence and weight of seeds (g) per inflorescence after completion of flowering/harvest season as described by Asaduzzaman et al.22.

Statistical analysis: The data were analysed using an one-way ANOVA with the SPSS 10.0 software program. Mean and standard errors were calculated for three replicate values. Means were compared by the Duncan's multiple tests and statistical significance was determined at 5% level.


Antagonistic effect of some recovered fungal isolates against growth of Stemphylium vesicarium in vitro: Data in Table 1 indicated that, seven isolates exhibited antibiosis effect to suppress mycelial growth of pathogen producing an inhibition zones. These isolates included three categories according to diameter of inhibition zone: Low inhibition zone (less than 3 mm), it was shown by Chaetomium specifer (No. 2027), moderate inhibition zone (3-7 mm), it was represented by five fungal isolates namely, Chaetomium globosum (No. 3003, 3038 and 3045) and Stachybotrys chartarum (No. 2032 and 2033) and high inhibition zone (more than 7 mm), it was produced by S. chartarum (No. 2031). According to the ability of tested isolates to compete on n utrient and space against S. vesicarium, 9 isolates of Trichoderma showed more than 50% of inhibition growth of the pathogen. Four isolates of T. harzianum exhibited the highest rate of pathogen inhibition contributing 73.1, while five isolates of T. longibrachiatum showed inhibition rate equaling 70.3%. Isolate of Stachybotrys chartarum isolate 2031 showed inhibition of mycelial growth rate contributing 52.2%. The other remained isolates exhibited inhibition against the pathogen growth ranging between 8.6-43.7% (Table 1).

Chitinase activity: Chitinase activity was tested for antagonistic fungal isolates that showed overgrowth on S. vesicarium AUMC10512. These isolates (12 isolates) showed different significant degrees of chitinase activity (Table 2). Isolates of T. harzianum (4 isolates) exhibited the highest values of chitinase activity ranging 1.98-2.7 U min–1. Of these isolates, T. harzianum isolate 3013 showed the maximum chitinase activity contributing 2.7 U min–1. The remaining isolates were exhibited chitinase activity as the following: T. longibrachiatum (5 isolates) showed chitinase activity contributing 1.42-1.73 U min–1 and Gliocladium roseum (3 isolates) comprising 1.06-1.37 U min–1, showed no chitinase activity.

Table 1:
In vitro, antagonistic effect of some recovered fungal isolates against growth of Stemphylium vesicarium
AMGI: Percentage of average of mycelial growth inhibition, Arbitrary antagonistic scale, N: No antagonistic effect, OG: Over growth on pathogen mycelia, L: Low inhibition zone (less than 3mm), M: Moderate inhibition zone (3-7 mm) and H: High inhibition zone (more than 7 mm)

Table 2:
Chitinase activity of antagonistic fungal isolates that showed overgrowth on Stemphylium vesicarium AUMC10512
Numbers within column of chitinase activity are means of three replicates. Different letters within column indicate significant differences (p≤0.05) based on one-way ANOVA analysis

Biological control of Stemphylium blight disease in vivo: Data in Table 3 showed that all treatments caused more than 50% disease reduction either before or after inoculation. While, Ridomil gold plus showed the highest percentage of disease reduction either before or after pathogen inoculation comprising 84.4 and 95.8%, respectively followed by T. harzianum isolate 3013 Stachybotrys chartarum isolate 2031 in both experiments. The best treatment after Ridomil gold plus is T. harzianum isolate 3013 since it reduced the disease severity in both experiments to 73% compared to infected control.

Onion seed production: Most of treatments used in this study to control Stemphylium blight disease spore suspension of Trichoderma harzianum isolate 3013 and Stachybotrys chartarum isolate 2031 and Ridomil gold plus improved number of seeded fruits, number of seeds per inflorescence and weight of seeds per inflorescence (Table 4) the seed production decreased to 0.5 g inflorescence–1 in negative control (Fig. 1) compared with healthy floral stalks (2.8 g inflorescence–1). Treatments of floral stalks by Ridomil gold plus either before or after the infection by S. vesicarium improved the seed production to 2.5 and 2.7 g of seed inflorescence–1, respectively. Also application of spore suspension of T. harzianum isolate 3013 either before or after the infection by S. vesicarium improved the seed production to 2.2-2.4 g of seed inflorescence–1. The lowest seed production (1.4 g seed inflorescence–1) was recorded by using spore suspension of Stachybotrys chartarum isolate 2031 after the infection by S. vesicarium (Table 4).

Fig. 1(a-d):
Onion Stemphylium blight and seed losses attributed to the infection by Stemphylium vesicarium AUMC10512, (a) Healthy onion floral stalks after completion of flowering/harvest season, (b) Infected onion floral stalks by S. vesicarium AUMC10512, (c) Healthy Inflorescence containing fruited flowers and (d) Inflorescence showing the huge losses of seed production

Table 3:
Effect of application of certain treatments on disease severity of Stemphylium blight under greenhouse condition
Number within columns are means of three replicates. Values within columns that associated with different letters indicate significant differences (p≤0.05) based on one-way ANOVA analysis


Many studies have been carried out to find alternative control strategies of plant pathogens instead of fungicide application as the fungicide has environmental pollution and can lead to development of fungicide resistant strains23. In the present study the antagonistic capability of 20 fungal isolates was tested in vitro against S. vesicarium AUMC10512 among them T. harzianum showed highest degree of competition as well as mycoparastism against the pathogen.

Table 4:
Effect of application of some treatments on seed production by onion plants infected by Stemphylium vesicariumi AUMC10512 under greenhouse condition

Also, Stachybotrys chartarum isolate 2031, as a new bioagents used for foliar diseases, exhibited good antibiosis effect producing highest inhibition zone against S. vesicarium AUMC10512. These results were in agreement with laboratory experiment carried out by Rossi and Pattori24, whereas they reported that production of S. vesicarium conidia was significantly reduced by T. harzianum. In recent years, Trichoderma harzianum (at 1%) exhibited a strong reducing effect on the disease development of Stemphylium blight of onion13. The results of this investigation indicated that the mechanism of antagonistic capability of T. harzianum depends on competition on nutrient and space (causing inhibition rate up to 73.1%) and mycoparastism (overgrowth and chitinase activity up to 2.7 U min–1). The general mechanism of biological control by Trichoderma spp. can be divided into direct and indirect effects on the plant pathogen. Direct effects include competition for nutrients or space, production of antibiotic and lytic enzymes, inactivation of the pathogen’s enzymes and parasitism. Indirect effects include all aspects that produce morphological and biochemical changes in the host plant producing induced resistance25,26.

The results of management of Stemphylium blight disease under greenhouse condition showed that Ridomil gold plus showed the highest disease reduction percentage either before or after inoculation up to 84.4 and 95.8%, respectively and T. harzianum isolate 3013 caused disease reductions reached to more than 71.3 and 73.2% before and after pathogen inoculation, respectively. The same results were reported by Prakasam and Sharma27, mentioned that among 17 fungal isolates and 6 bacterial isolates, T. harzianum (Th-3) expressed high level of disease reduction under glasshouse and field conditions. Also, Hussein et al.21 selected several bioagents to control S. vesicarium under greenhouse condition, out of them T. harzianum showed reduction in diseases severity up to 36.22%. Shahnaz et al.28 studied the management of onion foliar diseased caused by Alternaria porri and S. vesicarium and other fungal pathogens in vivo. They reported that application of T. harzianum resulted in significantly reduction of disease intensity as compared to control. Trichoderma spp., as a biocontrol agent has gained more importance. These antagonistic organisms act on the pathogen by different mechanisms via competition lysis, antibiosis, siderophore production and hyperparasitism29. Trichoderma harzianum and its products induce systemic resistance against several plant pathogens30,31. Different elicitors, including xylanase, have been isolated from Trichoderma and they trigger the synthesis of various defense compounds, including phytoalexins32 and defense related enzymes viz., phenylalanine ammonia lyase, peroxidase, polyphenol oxidase and β-1-3-glucanase33.


The current study proved that the use of T. harzianum isolate 3013 and Stachybotrys chartarum isolate 2031 have fungicidal impact to control onion Stemphylium blight disease and elevate the seed production as alternatives to fungicides.

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