Phakopsora pachyrhizi, the causal organism of soybean rust, was first found in the continental United States in 2004 and has been found on soybean, kudzu, Florida beggarweed, and three Phaseolus species in the field. The pathogen has been reported to occur on more than 90 legume species worldwide and it is likely to infect native and introduced legume species in the United States. The objective of this study was to determine if 176 species representing 57 genera of legumes, the majority of which are either native or naturalized to soybean-growing areas of the United States, could be hosts of P. pachyrhizi. Between one and three accessions of each species, a total of 264 accessions, were inoculated with a mixture of four isolates of P. pachyrhizi. Severity and sporulation were rated on a 1-to-5 scale at 14 and 28 days after inoculation. P. pachyrhizi was confirmed by the presence of sporulating uredinia and/or immunological assay on 65 new species in 25 genera; 12 of these genera have not been reported previously as hosts. Many of the newly identified hosts grow in the southern United States, and like kudzu, could serve as overwintering hosts for P. pachyrhizi.

Phytophthora sojae causes damping-off, root rot, and stem rot of soybean, particularly in poorly drained soils. Soybean cultivar resistance is one of the primary methods to control this disease, with Rps1c, Rps1k, and Rps1a being the most commonly used genes. The Varietal Information Program for Soybeans (VIPS) at the University of Illinois evaluates soybean cultivars for resistance to a number of diseases including Phytophthora root rot (PRR). The objectives of this research were to evaluate PRR resistance among commercial cultivars or advanced lines, and to compare these results with the information on PRR resistance provided by the company that entered the cultivar in VIPS. Each year from 2004 to 2008, between 600 and 900 cultivars were evaluated for resistance to either race 17 or 26 of P. sojae using the hypocotyl inoculation method. P. sojae single resistance genes were reported in 1,808 or 51% of the entries based on company information. Of these, the most commonly reported resistance genes were Rps1c (50%), Rps1k (40%), and Rps1a (10%). To a much smaller degree, companies reported using Rps3a (0.3%), Rps1b (0.2%), and Rps7 (0.2%). For the duration of the 5-year testing period, almost half of the cultivars (46%) were entered in VIPS with no reported resistance genes, and only nine out of a total of 3,533 entries (less than 0.3%) reported a stacked combination of resistance genes. Agreement between company-reported genes and any resistance found in the VIPS PRR evaluation was highest for those cultivars claiming to have Rps1c (90%) and Rps1k (83%), followed by Rps1a (70%). On average, 54% of the cultivars submitted to VIPS each year were new, reflecting the rapid development and turnover of soybean cultivars provided by the soybean seed companies.

The soybean crop is one of the most important crops worldwide, as the seeds are used for both protein meal and vegetable oil. Soybean acreage covers an estimated 6% of the arable land in the world, and since the 1970s, soybean has had the highest percent increase of hectares in production compared to any other major crop. As demand for soybean continues to rise, the production area and worldwide trade are likely to increase. Biotic constraints, such as pathogens, pests, and weeds, can be detrimental to soybean production, causing significant negative impacts to yield. To successfully reduce losses caused by pathogens and pests, various practices such as cultural and seed sanitation techniques, pesticide applications, and deployment of resistance are used. For many years, public institutions have conducted regional yield trials on both private and public sector soybean cultivars. In Illinois, the University of Illinois Variety Testing Program created a public database for growers. Prompted in part by disease reports on cultivars entered into the Variety Testing Program, the Illinois Soybean Association began providing funds in 1998 to obtain additional information from regional trials to benefit growers in the state. The researchers in the Soybean Variety Testing Program conduct replicated field trials and evaluate these plots for agronomic characteristics such as height, lodging, maturity, and yield. In addition to standard yield trial data, protein and oil content are analyzed.

After soybean rust was confirmed in soybean in the USA, sentinel plots were established in 26 states to monitor its spread. Funding for establishing, sampling, and monitoring the plots came from the USDA, national, regional, and state soybean commodity boards, and state departments of agriculture, extension services, and universities. The presence of sentinel plots for soybean rust monitoring provided the potential for reducing the time and expense of extensive statewide travel for collection of soybean leaf samples for monitoring the incidence of other foliar diseases of soybean in Illinois. Accepted for publication 27 July 2010. Published 27 August 2010.

Phakopsora pachyrhizi, the causal organism of soybean rust, was first found on Glycine max in the continental United States in 2004, and subsequently on Pueraria lobata, Desmodium tortuosum, three Phaseolus species, and Erythrina herbacea in the field. The pathogen has been reported to occur on over 150 legume species worldwide, and it is likely to infect native and introduced legume species in the USA. The objective of this study was to determine if USA-native or -naturalized legume species could become infected with P. pachyrhizi in field conditions. A total of 80 accessions representing 52 species in 29 genera were infected in the field trials. Crotalaria retusa, Lathyrus latifolius, Phaseolus angustissimus, P. polystachios, and Robinia hispida are new hosts. This is the first report showing the broad host range of P. pachyrhizi based on field infections in the USA. Some of these hosts grow in the southern USA, and could, like kudzu, overwinter P. pachyrhizi. Accepted for publication 18 August 2008. Published 3 November 2008.