بادام زمینی

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.

White stem rot caused by Sclerotium rolfsii is a soilborne disease which is extensively common across the groundnut farms of Guilan province, especially during the harvest period. Using the beneficial microbial agents is an alternative method for applying the chemical fungicides.

To find the appropriate fungal antagonistic isolates for the biological control of peanut white stem rot, the effect of three isolates of Trichoderma spp., three isolates of Penicillium spp., two isolates of Aspergillus spp. and one isolate of Cladosporium cladosporioides were studied on S. rolfsii in vitro using dual culture, slide culture, volatile metabolites and non-volatile metabolites. Peanut plants were inoculated with these fungal isolates as well as S. rolfsii in greenhouse experiments, and parameters including disease severity, height, fresh weight, and dry weight of the plant were measured.

The results showed that in the dual culture method, T. harzianum and T. virens were most capable of suppressing the mycelial growth of S. rolfsii with a suppression capability of 93.58% and 92.94%, respectively. In the slide culture method, all isolates turned out to be effective in suppressing the mycelia growth of S. rolfsii, except for T. virens and T. viride. In the volatile metabolite assay, P. glabrum and A. flavus with 81.25% and 75%, respectively and in the non-volatile metabolite method, T. harzianum and T. viride with 93.75% and 97.5% respectively showed the greatest ability to inhibit S. rolfsii mycelial growth. Moreover, the effects of these fungi on the control of S. rolfsii pathogen were explored in greenhouse trials. The results revealed that P. glabrum was 39.4% effective and T. viride was 38.8% effective in reducing the extent and intensity of the disease. Under the presence of the pathogen, the treatment of these antagonistic fungi in greenhouse conditions enhanced plant height, shoot and root fresh and dry weight. In the in vitro and greenhouse approaches, an analysis of variance and a comparison of means of the attributes using the least significant difference (LSD) indicated significant differences (P ≤0.01 and P≤ 0.05) among the examined fungi.

The results of the in vitro and greenhouse trials showed that T. viride, T. harzianum, P. glabrum, A. flavus, and C. cladosporioides, which are present in the natural flora of groundnuts, have the potential capability of the biological control of S. rolfsii as the pathogen of groundnut stem white rot.