aspergillus flavus

Aflatoxins are toxic secondary metabolites produced by speices of Aspergillus including A. flavus and A. parasiticus. Mycotoxins are potential carcinogens and reduce global trade of agricultural products. Soil and peanuts were sampled across fields located in seven important peanut production villages of Astaneh Ashrafieh to investigate the frequency of toxigenic and atoxigenic strains of A. flavus and A. parasiticus. Toxigenicity of the Flavi section strains was evaluated according to change in color of the back of colonies on coconut agar in contact with ammonium hydroxide vapor. 48 isolates of Flavi section were identified, including 20 isolates of A. flavus and 28 isolates of A. parasiticus with nine atoxigenic and 39 toxigenic isolates. Risk maps were developed based on mean toxigenicity where Lakujdeh, Mohsenabad, and Noghredeh respectively with mean toxigenicity of 2.50, 2.25 and 2.10 had the highest risk scores for peanut cultivation while parkaposht, Nubijarmahale and Nabi dehka with mean toxigenicity of 1.00, had the lowest risk scores. Peanut fields located in Dehsar with a mean toxigenicity of 1.50 were classified with moderate risk scores. The outlook of this study was based on identification of atoxigenic isolates of the fungus with potential future application in biological control of toxigenic strains of Flavi section and emphasize on their competitive ability to colonize peanuts as well as developing risk maps to plan for reducing the risk of aflatoxin production on peanuts, an important product of Guilan province, and to pave the way for increased production and export of this product.

Pistachio is an important export product in Iran. This product is constantly threatened by Aspergillus flavus and its aflatoxin. Researchers are now looking to use alternative non-hazardous methods instead of other methods of management of plant diseases, such as the use of chemical pesticides. Plant extracts as an environmentally friendly method can be a good alternative to chemicals. In this study, the effect of plant extracts including lavender (Lavandula stoechas), thyme (Thymus vulgaris), fennel (Foeniculum vulgare) and savory (Satureja hortensis) on the amount of degradation and aflatoxin production in vitro, by paper disk methods and mixing the extract with the culture medium, as well as in the storage conditions and on pistachio were investigated. The results showed that using of 2000 mg/L methanol extract reduced the growth of pathogenic fungus by 65.63%. In the tests of using the extracts on the paper disc as well as mixing the extracts with the culture medium, aqueous extract of lavender with a concentration of 2000 μg/ml prevented the growth of pathogen by 39.31 and 55.96%, respectively, and thyme extract with a concentration of 2000 μg/ml inhibited the fungal growth by 29.33% and 39.54%, respectively. These extracts had the highest effect on the pathogen growth. When the extracts were applied directly to aflatoxin, the results showed that the concentration of 4000 mg/L lavender prevented the aflatoxin production in the culture medium by 91.18%. Finally, aqueous extract of lavender at 4000 mg/L showed the highest effect (76.95% compared to control) in reducing the amount of spores produced by pathogenic fungi on pistachio fruit. The results of aflatoxin content in pistachio showed that both studied plants (lavender and thyme) at concentrations of 2000 and 4000 mg/L significantly reduced the amount of aflatoxin produced. Due to the remarkable and good effect of plant extracts on pistachio fruit under both in vitro and in the storage, the studied extracts, especially lavender and thyme, are natural compounds with high fungicidal effect and environmentally friendly effects.

Contamination to Aspergillus flavus and aflatoxin is a significant and chronic threat of pistachio production, consumption and exportation in the world. The aims of the present study was evaluation of resistance of pistachio cultivars (Shahpasand, Abbasali,Kale-ghouchi, Khanjari, Akbari and Pesteh-garmeh) and relationship between total phenolic content (TPC) and total flavonoid content (TFC) of green hull and kernels, as antioxidant, to A. flavus growth and aflatoxin production. Inoculation of pistachio kernels was done by 2×106 spores of toxigenic A.flavus and aflatoxins (B1 and B2), TPC and TFC of the green hull and kernels were measured by HPLC, Folin-Ciocalteu and aluminum chloride method, respectively. Results showed that Pesteh-garmeh and Akbari cultivars and Shahpasand with the lowest and highest percent colonization of A. flavus and aflatoxin production in kernels were respectively resistant and susceptible and other cultivars were intermediate. TPC and TFC were higher significantly in resistant cultivars than susceptible. A negative correlation was observed between TPC, TFC and aflatoxin content in kernel and green hull of pistachio cultivars, as well as TPC, TFC and A. flavus growth. These findings show the role of TPC and TFC in resistance of pistachio cultivars with contamination to A. flavus growth and aflatoxin production.

Aspergillus flavus grows on a wide range of agricultural and food products and causes contamination with aflatoxin. One of the suitable methods for controlling aflatoxin is the use of biological agents, which is possible by the application of effective bacterial antagonists. The objectives of the present study were to isolate and characterize a superior biocontrol agent against the above-mentioned fungus on pistachio, to develop an industrial culture medium and to optimize its growth conditions for enhancing maximum biomass production for Bacillus amyloliquefaciens UTB96. According to the results, this strain was capable of significant growth inhibition of A. flavus and reducing aflatoxin concentration in the pistachio up to 98.38%. Moreover, its VOCs showed growth inhibition as well. The most effective environmental factors were screened using the Bremenplacket design, in terms of their effects on the biomass production of the antagonistic bacterium and optimizing the production of bacterial biomass in culture medium designed using the screened factors. The results showed that sugarcane molasses and corn steep could be used as the industrial sources of carbon (C) and nitrogen (N) in production at 10 and 2 g/l respectively. Optimum conditions for maximum production of biomass in this culture medium included pH=7, 30°C and C/N ratio 1:23. Using the optimized culture medium and conditions in a semi-industrial method, the amount of biomass was reached up to 0.17 g/l, and the antagonistic effects increased by 8%. Bacillus species used in this work shows some similarities with B. velezensis that needs to be validated by further molecular analysis.

Aflatoxin contamination of pistachio nut is a health challenge that can affect the economic value of the largest Iranian non-oil exports. This potent hepatocarcinogen mycotoxin is produced by some species of Aspergillus, particularly by A. flavus, under certain conditions during fruiting, harvesting, transportation and storage. Infection of pistachio to the fungus in the orchard is the key factor in its contamination with aflatoxin. This situation occurs with the formation of early splited pistachios and mechanical damages that caused by biotic and abiotic factors. The environmental temperature and relative humidity and the moisture content of pistachio, during the different stages of pistachio production and processing, have significant roles in the incidence and distribution of fungal contamination as well as the increasing of aflatoxin production. The inhibition of these factors is possible with applying of some agronomic, mechanical, physical and biological methods. Orchard establishment based on principles of gardening like optimal plant spacing, uniformity of cultivars, good pruning, proper irrigation method and nutrition along with on time harvesting, proper processing and storage, can guarantee the production of a healthy and valuable product. Biological controls using nontoxinogenic strains of A. flavus and yeasts are also recorded as successful strategies for reducing the pistachio aflatoxin.

In this investigation the effect of Trichoderma isolates in inhibition of Aspergillus flavus growth and reducing of aflatoxin B1 (AFB1) was studied in culture media and pistachio nuts. Among Trichoderma isolates, T1, T3, T4 and T17 isolates showed significant impact on inhibiting of A. flavus R5growth. T3 and T4 isolates were the most effective isolates, which caused 84.40% and 77.88% reduction of aflatoxin produced by A. flavus R5on pistachio and 88.03% and 79.73% reduction of aflatoxin B1 which was added to the medium respectively. In order to study the way the Trichoderma isolates affected the pathogen, the influence of volatile compounds and filtrate culture extract of Trichoderma isolates on A. flavus R5 growth were investigated. Study on volatile compounds effect showed that T1, T3, T4 and T17 isolates with 60.66%, 68.88%, 63.33% and 59% reduction of fungal growth, respectively. The results showed that T1, T3, T4 and T17 isolates could inhibit the mycelia growth of A. flavus in PDB liquid medium. Isolates of T3 and T4 caused 58.88% and 50.01% reduction of fungal biomass, followed by 90.76% and 86.25% reduction of aflatoxin B1 (AFB1), respectively. Results of the most experiments that was done in this study showed that T3 and T4 isolates are the most effective isolates in biological control of A. flavus R5. According to ITS1- 5.8s- ITS2 Gene Sequence analysis, T1, T3 and T4 isolates belonged to T. harzianum, T. longibrachiatum and T. harzianum, respectively.