Research and utilization of biological products derived from microbial antagonists for controlling plant pathogenic fungi

Both Rhizoctonia solani Kuhn and Fusarium cause serious harm to productivity in many crops such as cereal crops (rice, maize, potatoes), vegetables (nuts, beans, tomatoes, cabbages, lettuces), fruit and industrial crops (cotton). These pathogenic fungi cause black root rot symptoms, ulcer roots, stem rot, rotting leaves. Annually, fungal diseases damage about of 11.6% agricultural output.

In Vietnam, trillions VND of agricultural output loss due to fungal diseases on a number of important crops such as corn, potato, soybean, beans, etc... So far, in the world, biological products derived from bacterial antagonists are increasingly interested by producers in controlling pathogenic fungi damaging plants. Bacterial antagonists of  Burkholderia, Pseudomonas, Bacillus have been interested because those synthesize some extracellular metabolites with the ability to inhibit the mycelial growth of F. oxysporum and R. solani. Bacterial antagonist of Bacillus, Burkholderia and Pseudomonas isolated from soil and roots are capable of controlling Pythium, R. solani and F.oxysporum.

Currently, main measure is chemical fungicides used to kill pathogenic fungi. The use of many chemical fungicides with high doses for a long time has created an unfavorable environment to beneficial microorganisms, facilitated to fungal diseases and chemical resistant insects as well as  killing beneficial natural enemies. Residues of fungicides, pesticides, chemical on the agricultural products, soil and the ground water which cause serious harm to the health of humans. In some developed countries, chemical fungicides are restricted or prohibited to utilize.

In this paper we introduce the researched results in biological products’ usage from Burkholderia, Pseudomonas and Bacillus to control R. solani and F. oxysporum damaging lettuces and tomatoes.

Control plant pathogenic fungi by extracellular of antagonists

Pseudomonas synthesizes extracellular syringomycin, syringostatin, syringotoxin, cepacin A, cepacin B, phenazine and pyrrolnitrin. Burkholdria synthesizes cepacin and pyrrolnitrin while Bacillus produces surfacin, bacilysin, bacillomycin, mycobacillin. These compounds have antifungal activity against R. solani and F. oxysporum. The fungi have caused serious damage to crop productivity. Currently, the trend to use biological products to kill pathogenic fungi on plant has been increasingly interested by producers.

In vitro, extracellular of strains Pseudomonas, Burkholdria, and Bacillus showed an inhibitory activity of 76, 78 and 74% on the growth of R. solani, while 76, 73, and 75% on the growth of F. oxysporum, respectively. The extracellular of antagonists showed high activity of chitinase, proteinase and β-glucanase but low cellulase activity. In the climate chamber conditions, the fresh biomass of lettuces and tomatoes were not affected negatively by microbial extracellulars. In the greenhouse, the similar results for plant biomass of lettuces and tomatoes were observed. The extracellular of Pseudomonas and Burkholdria inhibited 67% and 75% the growth of R. solani on lettuces but controlled 60% and 75% of F. oxysporum  damaging tomatoes, respectively.




A. Lettuces infected by R.solani in greenhouse
B. Lettuces infected by R.solani, then treatment with extracellular of microbial antagonist in greenhouse
C. Lettuces infected by R.solani, then treatment with cells of microbial antagonist in greenhouse

D. The growth of mycelial R.solani inhibited by microbial antagonist on dual agar plate
E. The growth of mycelial F.oxysporum  inhibited by microbial antagonist on dual agar plate


Control plant pathogenic fungi  by cells of antagonists

Biological products derived from microbial antagonists work well for soils, crops and effectively control plant pathogenic fungi of R.solani, F.oxysporum is the goal of many researchers. In the climate chamber, microbial antagonists of Pseudomonas, Burkholdria, and Bacillus has a positive effect on the growth of lettuces and tomatoes. After treatment with antagonic cells, fresh biomass and dry biomass of shoots, roots of lettuces and tomatoes were significantly increased compared with that of control. Antagonist strains Pseudomonas and Burkholdria were capable of colonizing in the lettuce roots (>106 colonies /cm root), in tomatoes roots (> 2,5x106 colony /cm root). Specially, strains Pseudomonas and Burkholdria did not reduce the number of beneficial microorganisms in the soils.

In the greenhouse, fresh biomass and dried biomass of lettuces treated with antagonists were higher than those of control. Also, Burkholdria and Pseudomonas controlled 50-75% R.solani growth. The same results were observed on tomatoes in which Pseudomonas and Burkholdria killed 75% and 66% F. oxysporum, respectively. The results exhibited that Pseudomonas and Burkholdria had a positive effect on roots and plant growth.  On the other hands, benefical microbial communities surrounding rhizosphere of treated tomatoes, and treated lettuces were not damaged by antagonists.

Undoubtedly, using biological products derived from bacterial antagonists to control pathogenic fungi damaging crops will bring lasting benefits to producers such as increased crop yields, friendly environment. Also, it reduced investment costs and barren soil. These contribute an important role in the development of organic agriculture and sustainable environment. Producers are assured to use bacterial antagonists to control R.solani and F. oxysporum.

Source: Enzyme Biotechnology Laboratory, Institute of Biotechnology
Link to Vietnamese Version

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