Acquired resistance to benomyl and some other systemic fungicides in a strain of Botrytis cinerea in cyclamen
A benomyl-resistant strain (R) ofBotrytis cinerea was isolated from cyclamen that had been sprayed with relatively high doses of Benlate two weeks before. In vitro mycelial growth of this strain was less inhibited on PDA containing 1000 μg/ml benomyl (Benlate, 50% W.P.) than that of another, wild isolate ofB. cinerea from cyclamen on PDA with 0.5 μg/ml of the fungicide.
The R-strain was also resistant to methyl-thiophanate, furidazol and to a lesser extent to thiabendazole. Mycelial growth of 5 other isolates was much more inhibited by benomyl than by thiabendazole.
Resistance was retained for at least 20 weeks after repeated subculturing on fungicide-free agar.
Effects of the fungicides benomyl, captan and chlorothalonil on soil microbial activity and nitrogen dynamics in laboratory incubations
The use of fungicides in agriculture, to protect plants from soil-borne pathogens, is a common practice. However, there is a dearth of information on the side-effects of fungicides on key soil ecological processes. We investigated the effects of three fungicides, benomyl, captan and chlorothalonil, on soil microbial activity (substrate-induced respiration and dehydrogenase activity), and nitrogen dynamics (NH4–N and NO3–N) in two laboratory experiments, one with captan and chlorothalonil and another with captan. In each laboratory batch incubation, soil was treated with a fungicide at approximately recommended field application rates (benomyl, 51 mg a.i. kg−1, captan,125 mg a.i. kg−1 and chlorothalonil, 37 mg a.i. kg−1) and incubated at 30°C for 8 weeks. Some soils were amended with either ground alfalfa leaves or ground wheat straw to provide additional substrates for soil microorganisms and to alter rates of nitrogen mineralization/immobilization. All three fungicides suppressed the peak soil respiration in unamended soil by 30–50%, but the three fungicides had different effects in the amended soils. Soil dehydrogenase activity was stimulated by benomyl (18–21%) and chlorothalonil (8–15%) except in the alfalfa amended soil, but was decreased by captan (40–58%) in both the straw-amended and unamended soils. The fungicide-treated soils in general had less microbial biomass N concentrations than the untreated soils. Captan-treated soils had much higher NH4 N concentrations than the control soils, with or without the organic amendments. Benomyl and chlorothalonil had little influence on soil NH4 N concentrations. Net N mineralization and nitrification rates were influenced by all fungicide treatments as well as by the addition of organic materials. N mineralization rates were significantly higher in captan-treated soils than in untreated soils. N dynamics were influenced by chlorothalonil in a similar pattern to captan but reached peak nitrification rates earlier (day 7), in the alfalfa-amended soil. The effects of the three fungicides on soil microbial activity and nitrogen dynamics depended on the quality of the organic materials added to the soil. The patterns of effects of the fungicides on soil nutrient cycling processes were not large and were specific to each fungicide. Captan appeared to have more pronounced overall effects on soil microbial activity and nitrogen dynamics than either benomyl or chlorothalonil.
On the specificity of the in vitro and in vivo antifungal activity of benomyl
With respect to sensitivity to benomyl in vitro four categories of fungi were distinguished; taxonomically related fungi usually proved to belong to the same category. Within the form-class Deuteromycetes a correlation appeared to exist between sensitivity to this fungicide and morphogenesis of conidia.Phoma betae, in contrast to all otherPhoma spp., was shown to be highly resistant to benomyl. This, however, may be expected on account of its perfect state.
The data on the in vitro antifungal activity of benomyl conformed to those on the effectiveness of benomyl against plant diseases.
The Influence of Benomyl on Penicillin Production and Rhizosphere Organisms
Aims: To evaluate the antimicrobial effects of benomyl (a systemic fungicide) on penicillin production and rhizosphere organisms of cowpea plant.
Study Design: 3 factor factorial experiment.
Place and Duration of Study: Department of Microbiology, Federal University of Technology, Akure, Nigeria, 2006.
Methodology: Complementary plate and pot experiments were designed to achieve these objectives. Bioassay methods such as the agar cup plate and the agar plug techniques were used to examine the metabolic fitness of Penicillium italicum and Penicillium oxalicum for penicillin production when cultured in agar medium with varying concentrations of benomyl. The pot experiment was also carried out to determine the effect of 0.8g of benomyl on the microbial load of 1.5kg of rhizosphere soil of cowpea.
Results: Biological assay predominantly shows that benomyl at different concentration has the ability to impair the metabolic and mitotic activity of Penicillium species mentioned above. This development resulted in the inhibition of penicillin and other allied metabolites. It was discovered that there was a reduction in the microbial load of rhizosphere soil containing benomyl and the fungicide was incriminated to be responsible for it. Conclusion: Certain species of bacteria and fungi that predominated in the rhizosphere soil sample without benomyl were either few or absent in the sample with benomyl.
Isolation and 16S rRNA-Based Identification of Benomyl-Degrading Bacteria
Laboratory experiments were conducted to isolate and identify Benlate- (Benomyl) degrading microorganisms from two soil types collected from different locations in Khartoum State, Sudan. Benomyl degradation was studied at two temperatures (28 and 40ºC) in soil treated with three Benomyl concentrations (0.032, 3.2 and 8.0mg Benomyl/g soil) and incubated for 360 days. Potential degraders were also tested in mineral salt liquid medium using Benomyl as a sole carbon source. Degradation percentages were then determined and the most efficient Benomyl degraders were identified by amplification with 16S rRNA gene, sequencing and alignment with deposited sequences in the international gene bank. A total of 64 isolates were recovered from the two soil types, with 59 (92.2%) isolates recovered from the clay soil. Thirty four isolates were recovered from clay soil treated with 8.0mg Benomyl/g soil and incubated at 28ºC. The most efficient Benomyl degraders, with degradation percentages in the range of 44-59, were identified as Pseudomonas stutzeri (Two different isolates), Pseudomonas putida, Acinetobacter johnsonii, Brevibacillus invocatus, Bacillus clausii, Lysinibacillus sp. and Agrobacterium radiobacter.
 Bollen, G.J. and Scholten, G., 1971. Acquired resistance to benomyl and some other systemic fungicides in a strain of Botrytis cinerea in cyclamen. Netherlands Journal of Plant Pathology, 77(3), pp.83-90.
 Chen, S.K., Edwards, C.A. and Subler, S., 2001. Effects of the fungicides benomyl, captan and chlorothalonil on soil microbial activity and nitrogen dynamics in laboratory incubations. Soil Biology and Biochemistry, 33(14), pp.1971-1980.
 Bollen, G.J. and Fuchs, A., 1970. On the specificity of the in vitro and in vivo antifungal activity of benomyl. Netherlands journal of plant pathology, 76(6), pp.299-312.
 Ekundayo, F.O., Oladunmoye, M.K., Fagbola, O. and Osonubi, O., 2012. The Influence of Benomyl on Penicillin Production and Rhizosphere Organisms. Journal of Experimental Agriculture International, pp.477-484.
 El-Hussein, A.A., Elsalahi, R.H., Osman, A.G., Sherif, A.M. and Marmar, A., 2014. Isolation and 16s rrna-based identification of benomyl-degrading bacteria. Biotechnology Journal International, pp.670-683.