Plant Pathogen Rusts in Precipitation

Beginning in the Spring of 2005, scientists at the Illinois State Water Survey and the USDA Agricultural Research Service (ARS) scientists in St. Paul, Minnesota have collaborated to screen precipitation samples for the presence of soybean rust since the spring of 2005. This study uses samples from the National Atmospheric Deposition Program’s National Trends Network (NADP/NTN). This study continues today.

The objective of this cooperative research is to isolate, detect and monitor spores of Asian Soybean Rust (ASR, Phakopsora pachyrhizi) across the eastern United States. ASR (Figure 1) is a fungal plant disease that spreads by producing millions of spores in infected fields over the growing season. These spores are carried by the atmosphere to other locations. As with other atmospheric contaminants, the spores are removed as rain washes particles out of the atmosphere.

During the first sampling year 2005, the NADP developed a method to filter and preserve solids within our precipitation samples that were collected over a 16- week period during the spring. Sample filters were shipped weekly to the USDA-Cereal Disease Laboratory (USDA-CDL). Scientists at the USDA-CDL laboratory use the NTN filters to identify the genetic makeup of ASR using real-time polymerase chain reaction (PCR) methods. See this page for more information.

Combined with the week of precipitation occurrence and the site location, we can track the movement of ASR spores over North American soybean growing regions. This tracking ability is the real advantage of USDA teaming up with the NADP, and is in part why we continue this research collaboration today. This tracking information is also being presented at the U.S. Department of Agriculture Soybean Rust web page.

USDA-CDL scientists are expanding the scope of the original study to also test NADP/NTN sample filters for other plant pathogens. Several wheat rusts have been tested, including stripe rust (Puccinia striiformis), leaf rust (Puccinia triticina) and stem rust (Puccinia graminis). Select corn rusts (Figure 2) and sugar cane rusts (brown and orange) have also been tested. Testing for these pathogen species occurs during the winter wheat growing season, across sites in the southeastern United States. Sampling is ongoing.

The information obtained in this study can be expanded through the use of meteorological models to evaluate the source regions of the plant pathogens. The precipitation, time and location provided by the NADP network sample, can be combined and analyzed using a back trajectory model to determine the source location of the pathogens (see Figure 3, and Krupa et al., 2006).

Over the summer and early fall, 2009, U of I scientists developed several geographic databases for mapping purposes. These were designed to correlate agricultural rust disease information with meteorological information. These maps allow researchers to investigate the interrelationship between meteorology and the transport of rust spores through the atmosphere. An evaluation of weekly occurrence of ASR deposition over four years shows when and where deposition occurred during the growing seasons, and how this related to precipitation intensity, hurricane-induced precipitation, etc. Two one-week examples Figure 4 and Figure 5 are shown here. Preliminary results indicate that there is some correlation between hurricane tracks and the spread of plant pathogens.

Papers Using These Data:

Barnes, C.W., Szabo, L.J., and Bowersox, V.C. 2009. Identifying and quantifying Phakopsora pachyrhizi spores in rain. Phytopathology 99:328–338.

Krupa, S., Bowersox, V., Claybrooke, R., Barnes, C. W., Szabo, L., Harlin, K., and Kurle, J., 2006. Introduction of Asian soybean rust urediniospores into the midwestern United States—a case study. Plant Dis. 90:1254-1259.

Tao, Z, D. Malvick, R. Claybrooke, C. Floyd, C. Bernacchi, G. Spoden, J. Kurle, D. Gay, V. Bowersox, and S. Krupa, 2009.“Predicting the Risk of Soybean Rust in Minnesota,” International Journal of Biometeorology 53(6): 509-421, DOI 10.1007/s00484-009-0239-y.

Soybean Rust

Figure 1 (Click to enlarge)

Corn Rust

Figure 2 (Click to enlarge)

Back Trajectory

Figure 3 (Click to enlarge)

ASR in NADP Samples

Figure 4 (Click to enlarge)

ASR in NADP Samples

Figure 5 (Click to enlarge)