First report of Sclerotinia sclerotiorum causing stem rot on soybeans in Ethiopia

Authors: PAWLOWSKI, MICHELLE - University Of Illinois; MURITHI, HARUN - International Institute Of Tropical Agriculture (IITA); HAILEMARIAM, MESFIN - Jimma University; TESFAY, ABUSH - International Institute Of Tropical Agriculture (IITA); Hartman, Glen

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/4/2019
Publication Date: 6/5/2019
Citation: Pawlowski, M.L., Murithi, H., Hailemariam, M., Tesfaye, A.A., Hartman, G.L. 2019. First report of Sclerotinia sclerotiorum causing stem rot on soybeans in Ethiopia. Plant Disease. https://doi.org/10.1094/PDIS-05-19-0929-PDN.
DOI: https://doi.org/10.1094/PDIS-05-19-0929-PDN

Interpretive Summary: Sclerotinia stem rot (SSR) is a devastating disease of soybean and many other hosts that is caused by a fungal pathogen named Sclerotinia sclerotiorum. The disease has not been reported in Ethiopia but is known to occur in Nigeria and South Africa. In this study, 100 randomly selected soybean plants were evaluated for SSR in Ethiopia. All but 16 stems had stem rot symptoms indicating a high degree of occurrence. The fungus was cultured on media to confirm its identification morphologically. The fungus was inoculated on plants, which confirmed it could cause SSR on soybean. Further confirmation was completed by molecular testing, which showed that one part of the genome was 99% identical to S. sclerotiorum. To our knowledge this is the first report of Sclerotinia stem rot on soybean in Ethiopia. This information is important to researchers interested in geographical distribution of pathogens as well as breeders interested in developing tolerance to this disease in Ethiopia.

Technical Abstract: Sclerotinia stem rot (SSR) is a devastating disease of soybean and over 500 other host plant species that is caused by the fungal pathogen Sclerotinia sclerotiorum. This disease on soybean has not been reported in Ethiopia. A sample of 100 randomly selected plants were evaluated for SSR. All but 16 stems had stem rot symptoms. Sclerotia from infected plants were placed on potato dextrose agar in 9.8-cm diameter Petri plates. White mycelia grew from the sclerotia and covered the entire plate after 48 hours with sclerotia forming on the edge of the plate by 4 days. To confirm pathogenicity, a mycelial plug was removed from the margin of a 2 day-old-colony by pressing the large end of a 200 µl pipette tip into the culture and placing it on top of a cut stem above the second trifoliolate of four 3-week-old plants of soybean cultivar Williams 82. Plants were then incubated in a moist chamber for 48 hours prior to being placed in a greenhouse held at 22°C with a 16-hour photoperiod. Necrotic lesions and white mycelia appeared on the stems four days post-inoculation. The pathogen was re-isolated and confirmed morphologically to be S. sclerotiorum. Further confirmation was completed by extracting DNA, using ITS (ITS4: 5’-TCCTCCGCTTATTGATATGC-3'; ITS1: 5’- TCCGTAGGTGAACCTGCGG-3') primers, which produced 477 bp amplicons that were purified and sequenced. The top BLAST hit for the ITS region had 99% identity to S. sclerotiorum. In Africa, S. sclerotiorum has been found on soybean in Nigeria and South Africa. To our knowledge this is the first report of Sclerotinia stem rot on soybean in Ethiopia.