Updated October 9, 2018:
Full report attached.
Different pathogens consistently cause substantial yield losses in soybean. The control of these plant pathogens requires the adoption of integrated management practices. Our ultimate goal is to reduce yield losses caused by seedling diseases of soybean by exploiting native bio-control agents (BCAs) already present in the soil and by refining management strategies to enhance and optimize the activity of these beneficial organisms against pathogens detrimental to soybean production.
Throughout this project we identified BCAs that were effective against Pythium species, Rhizoctonia solani, Fusarium virguliforme, and Macrophomina phaseolina. The activity of the BCAs was confirmed in laboratory, growth chamber, and greenhouse studies. Field studies were conducted in 2016 and 2017 against F. virguliforme, M. phaseolina, R. solani, and 6 different Pythium species. The tested BCAs did not show a significant effect on Pythium, F. virguliforme, or R. solani under the tested conditions. With M. phaseolina, select BCAs decreased the incidence of the disease in the field. A series of experiments revealed that in addition to their antibiotic activity against plant pathogens, tested BCAs also induced resistance mechanisms in soybean, thus providing an additional layer of protection against seedling pathogens. Finally, variation in the sensitivity of the BCAs to the different fungicides was observed. Some of these BCAs could therefore be added with a fungicide to the seed.
Our data shows that BCAs can be successfully used to manage several diseases of soybean. Additional work is needed to optimize the delivery of the BCAs in the field and to develop methodologies to integrate their use with fungicides. Another area that needs to be expanded upon is the use of emerging techniques to characterize the incidence and activity of the BCAs in different soils and with different management practices. The ultimate goal would be to develop recommendations to enrich soils with native BCAs.
We are collaborating with SIU’s Office of Technology Transfer (OTT) to assess the commercial potential of the performed work and to protect some of the findings through patenting and/or trademarking.
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Different pathogens consistently cause substantial yield losses in soybean, thus affecting soybean production worldwide. The control of these plant pathogens requires the adoption of integrated management practices incorporating diverse strategies including cultural practices, genetic resistance, and the use of chemicals. Recently, the use of bio-control agents (BCAs) has emerged as an efficient, safe, and environmentally friendly choice that could be adopted as a component for the integrated management of diseases. BCAs combat plant pathogens through a variety of mechanisms including competition, antibiosis, and parasitism. Some BCAs have even been reported to promote plant growth and induce systemic resistance (ISR) in treated plants. In fact, these BCAs were found to activate different signal transduction pathways in susceptible cultivars thereby rendering them more tolerant to fungal, bacterial, and viral pathogens. Exploiting the ability of BCAs to induce ISR in plants is highly desirable, especially since ISR is not specific, meaning that plants exhibiting ISR usually become more tolerant to pathogens belonging to different species, genera, and even kingdoms.
Several fungal species belonging to the genus Trichoderma have been reported to exhibit anti-microbial activity against plant pathogens. Some isolates have also been reported to induce ISR in plants. Species of the Trichoderma genus occur all over the world. Members of this genus have several characteristics that make them formidable competitors against fungi and oomycetes, thus rendering them potential BCAs; members in this genus usually reproduce quickly and profusely. They can also endure adverse conditions that many other fungal pathogens cannot usually tolerate. Remarkably, different Trichoderma spp. have been reported to be active as BCAs against a wide range of pathogens. Interestingly, isolates from the same species may vary significantly in their aggressiveness against the same fungal pathogens. As such, they can be specific as BCAs against a particular plant pathogen.
Possible limitations to the use of BCAs include their sensitivity to prevailing abiotic factors that affect their activity, such as soil physical and chemical characteristics. There are several commercially available biological control products based on fungal or bacterial BCAs for use with different crops. There are very limited options of BCAs to be used in soybean, especially fungal BCAs targeting pathogens that cause seedling diseases of soybean. A significant impediment against the large-scale use of fungal BCAs is the difficulty in integrating their use with the use of fungicides.
In the past two years we have screened a collection of potential fungal BCAs isolated from soybean production fields in IL, IA, MI, IN, AR, and NE. A subset of these BCA isolates was found to be very effective at antagonizing several soybean pathogens in lab and greenhouse studies while also protecting treated plants. These BCA isolates were effective when used alone or when used in combination with other BCAs. Tools were developed to identify and quantify these organisms.
The long-term objective behind the proposed research was to develop and optimize the use of BCA-based tools to manage diseases of soybean, especially those caused by soil-born pathogens such as Fusarium spp., Rhizoctonia solani, Macrophomina phaseolina, Phytophthora sojae, and Pythium spp. Bullet points summarizing our findings over the three years of this project follow:
? Fifty-eight potential bio-control agents (BCA) were tested against 7 fungal pathogens. Several specific BCAs showed activity against Fusarium graminearum, Fusarium virguliforme, Rhizoctonia solani, and Macrophomina phaseolina.
? Fourteen BCAs were tested against 12 oomycete species. Some of the BCAs demonstrated trends of plant protection against several Pythium species.
? Eleven BCAs were evaluated for their sensitivity to different fungicide belonging to different groups (pyraclostrobin, prothioconazole, sedaxane, fludioxonil, thiabendazole, metalaxyl, and sedaxane). Preliminary results indicated that some of the BCAs could be added with a fungicide seed treatment with minimum inhibition occurring.
? Preliminary data indicates that, in addition to their antibiotic activity against plant pathogens, some BCAs also seem to induce resistance mechanisms in soybean, thus providing an additional layer of protection against seedling pathogens. BCAs can affect plant pathogens by directly affecting their growth or indirectly by inducing defense mechanisms in the plants, thus enhancing their tolerance to potential plant pathogens. Two greenhouse experiments were carried out at SIUC to monitor the expression of nine soybean defense-related genes upon exposure to F. virguliforme and R. solani in the presence of the BCAs. Our data indicate that the presence of some of the BCAs resulted in the induction of some of the soybean defense-related genes by as much as 16 fold. In addition to their antibiotic activity against plant pathogens, some of the BCAs appear to induce resistance mechanisms in soybean, thus providing an additional layer of protection against seedling pathogens.
? QPCR probes specific to the fungal BCAs species were developed, and their specificity and sensitivity confirmed. Two approaches can be used to integrate the use of BCAs in pest management strategies: introducing new BCAs to production fields and ensuring their survivability under prevailing conditions and/or adjusting management practices to ensure that the activity of BCAs native to production fields is preserved and enhanced. We have developed several tools, including specific QPCR probes, that allow for the detection and quantification of fungal BCAs. The developed tools could be used to monitor the presence of BCAs in soils collected from soybean production fields with different soil physical and chemical characteristics, different cropping histories, and different soil management practices. This will permit us to ultimately provide recommendations to producers to enhance the activity of BCAs native to production fields. The developed tools could also be used to monitor the survivability of “introduced” BCAs and the effect of these BCAs on the presence of select fungal pathogens that cause seedling diseases of soybean in the rhizosphere of soybean seedlings treated with BCAs.
? Initiated the development of a strategy to commercialize the developed tools. We are collaborating with SIU’s Office of Technology Transfer (OTT) “http://siusystem.edu/tech-transfer/” to assess the commercial potential of the performed work. A preliminary technology domain search shows considerable patenting activity encompassing biocontrol agents for plant disease mitigation, indicating strong commercial interest. Since 2010, more than 750 non-provisional US patent applications have been filed related to biocontrol agent seed coatings, most by Syngenta, BASF, Pioneer, Bayer, and other agricultural companies. Issued patents typically claim one or more bacteria species coupled with a complementary pesticide, fungicide, or delivery agent. A smaller subset of issued applications claim strains of isolated bacteria that are combined with other strains to produce synergistic effects.
Future work should focus on optimizing the delivery of the BCAs in the field, developing methodologies to integrate their use with the use of fungicides, and expanding performance testing of a set of characterized BCAs under different field conditions and with various disease pressures. Finally, another to area that needs to be expanded on would be to use emerging techniques to characterize the incidence and activity of the BCAs under the influence of different soil conditions and management practices. The ultimate goal would be to develop recommendations to enrich soils with native BCAs.