Evaluation of Simplicillium lanosoniveum as a Biological Control Agent

View the project final report

• 2009 annual report

Commodities

• Agronomic: soybeans

Practices

• Crop Production: application rate management, biological inoculants
• Pest Management: biological control, chemical control, integrated pest management
• Production Systems: transitioning to organic

Soybean is susceptible to a variety of pathogens, and their control requires large amounts of fungicides, especially in the Southeast and Mid-Gulf regions. Perhaps the most devastating disease is Asian soybean rust (ASR), which was discovered in the US in 2004. With fears of catastrophic yield losses, growers rely on preventative fungicide programs to ward off the disease. Consequently, millions of pounds of fungicides are applied to soybeans every year. In an effort to pursue our recent discovery of an antagonistic fungus that colonizes and parasitizes rust urediniospores, we propose to evaluate Simplicillium lanosoniveum as a biological control agent. Previous work determined the dynamics of the mycoparasite and Phakopsora pachyrhizi, the rust pathogen. In the proposed study, we will develop a real-time PCR assay to detect and quantify the antagonist throughout its emergence, colonization, and parasitism of rust urediniospores under field conditions. Next, we will inoculate field-grown soybeans to assess population dynamics of S. lanosoniveum following inoculation. This project directly addresses three of SARE's priority areas: soil, water, and wildlife conservation; human health and safety; and enhanced quality of life through increased income. Development of a biological control agent will provide safe pesticide alternatives for soybean rust and potentially for other rusts. This research will improve our understanding of the rust-antagonist interface. Furthermore, the ability to monitor S. lanosoniveum will allow us to reach the ultimate goal of developing this novel mycoparasitic fungus into a biological control agent.

We hypothesized that S. lanosoniveum meets the criteria for a successful biological control agent. However, in order to effectively evaluate this antagonist, we examined its life cycle on the soybean leaf surface as it related to the soybean rust disease cycle under field conditions.

The objectives of this study were to:

1. Develop real time quantitative PCR (q-PCR) diagnostic test for S. lanosoniveum. Quantitatively monitor naturally occurring S. lanosoniveum in the field to determine whether it meets the criteria as a biological control agent as it interacts with P. pachyrhizi.
2. Determine the native host range for S. lanosoniveum in Louisiana. Sample and assay other rusts in Louisiana for the presence of S. lanosoniveum to determine the native host range.
3. Evaluate S. lanosoniveum in field plots. Apply S. lanosoniveum to field plots and use q-PCR to evaluate establishment and colonization and compare it to disease incidence and severity.

The evaluation of an organism for potential as a biological control agent appears frequently in recent scientific literature. Our experimental design is based on the criteria discussed by Andrews [1]. However, our approaches are unique in that P. pachyrhizi is an obligate parasite.

In Phase I of the evaluation process, antagonists are selected according to preliminary studies. Our previous research used leaf inoculations to determine the effects of S. lanosoniveum on rust sori development. Additionally, scanning electron microscope studies confirmed the trophic response of the fungus to sori.

Phase II includes the putative mycoparasite in in vivo studies under controlled laboratory conditions. Our previous work included detached leaf assays in which co-inoculations of disease-free leaves with S. lanosoniveum and P. pachyrhizi clearly demonstrated a significant decrease in development of rust sori. Additionally, inoculations of rust-infected soybean leaves revealed that S. lanosoniveum not only decreased additional lesion development, but it also encouraged a significantly higher percentage of red-brown lesions, which have been associated with resistance reactions. Moreover, the antagonist produced a significantly higher number of brown urediniospores that failed to germinate.

Phase III proposes testing of the organism under field conditions. We examined the habitation and epidemiology of S. lanosoniveum by using the q-PCR assay above to monitor the organism in the presence of soybean rust to determine whether it meets the criteria for a biological control agent, i.e. environmental tolerances and rate of establishment. Additionally, we collected rusts from other plant species to evaluate host specificity of S. lanosoniveum. Objectives 1 and 2 addressed these issues.