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ARS Home » Midwest Area » Urbana, Illinois » Soybean/maize Germplasm, Pathology, and Genetics Research » Research » Publications at this Location » Publication #83068
Title: OCCURRENCE OF SCLEROTINIA SCLEROTIORUM IN SOYBEAN FIELDS IN EAST-CENTRAL ILLINOIS AND ENUMERATION OF INOCULA IN SOYBEAN SEED LOTS

Author
item Hartman, Glen
item KULL, LINDA - UNIV OF ILLINOIS
item HUANG, YI - UNIV OF ILLINOIS

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/8/1997
Publication Date: N/A
Citation: N/A

Interpretive Summary: Sclerotinia sclerotiorum is a fungus which attacks many host plants. On soybean, the disease is referred to as Sclerotinia stem rot (SSR). The disease on soybeans predominates in the northern soybean growing states including Michigan, Minnesota, North Dakota, and Wisconsin. The disease on soybean has been ranked second in yield reduction Illinois in 1994. In 1996, several soybean growers from an area in eastern Illinois contacted plant pathologists about the occurrence of SSR in their fields. Out of 68 fields surveyed, 30 had SSR. Of the fields with SSR, 24 had between 1 and 5% SSR incidence while six fields had over 5% SSR incidence. In addition to the loss of production, the fungus also infects soybean seed, and sclerotia, hard bodies of the fungus that produce mushroom-like structures, are often mixed with the seeds during harvest. Sclerotia were obtained from all but 10 of 81 seed lots obtained from 21 counties in Illinois. Normal-appearing seeds of the 81 seed lots were tested for seeds of the 81 seed lots (100-200 seeds per lot) were tested for germination and incidence of seedborne infection by the fungus. Eight seed lots had at least one infected seed and seed infection rates ranged from 0.07% to 1%. From 10 selected seeds lots, discolored-shriveled seeds had seed infection rates ranging from 0% to 70%. This research shows how widespread this disease can be in localized areas and provides evidence about occurrence of the pathogen in soybean seed lots. These results may have an impact on standardization of seed certification and seed-cleaning equipment, and should be useful to researchers, seedsmen, and extension personnel who are planning management strategies for this disease.

Technical Abstract: Sclerotinia stem rot (SSR) of soybean is an important disease in the northern soybean-production areas of the United States. The occurrence of soybean SSR primarily has been found in the northern most soybean-production areas of Illinois. In this study, the occurrence and distribution of the disease in an area in east-central Illinois was geographically identified. Out of 68 fields surveyed, 30 had SSR. Of the fields with SSR, 24 had between 1 and 5% SSR incidence while six fields had over 5% SSR incidence. The pattern of the disease in one field was mapped and the spatial distribution of SSR was aggregated with a Lloyd's index of 1.4. Sclerotia were obtained from all but 10 of 81 seed lots obtained from 21 counties in Illinois, and one each from Iowa and Wisconsin. Most of the seed lots were from the north and central part of Illinois, but one seed lot was from Madison County in the southwestern part of the state. Sclerotial counts ranged from 0 to 363 per sample. Normal-appearing seeds of the 81 seed lots (100-200 seeds per lot) were tested for germination and incidence of seedborne infection using a seed germination chamber. Eight seed lots had at least one infected seed and seed infection rates ranged from 0.07% to 1%. From 10 selected seeds lots, discolored-shriveled seeds were placed in a seed germination chamber. Seed infection rates ranged from 0% to 70%. Implications about the occurrence of SSR in the state and the importance of seedborne infection are discussed.