Evaluation of soybean entries in the Pan-African trials for response to Coniothyrium glycines, the cause of red leaf blotch

Authors: MURITHI, HARUN - Oak Ridge Institute For Science And Education (ORISE); PAWLOWSKI, MICHELLE - University Of Illinois; DEGU, TIZAZU - Ethiopian Institute Of Agricultural Research; HUNDE, DERESSE - Ethiopian Institute Of Agricultural Research; MALEDE, MOLLA - Ethiopian Institute Of Agricultural Research; OBUA, TONNY - Makerere University; MUSHORIWA, HAPSON - International Crops Research Institute For Semi-Arid Tropics (ICRISAT) - Nigeria; COYNE, DANNY - International Institute For Tropical Agriculture; TUKAMUHABWA, PHINEHAS - Makerere University; Hartman, Glen

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/12/2021
Publication Date: 2/5/2022
Citation: Murithi, H.M., Pawlowski, M.L., Degu, T., Hunde, D., Malede, M., Obua, T., Mushoriwa, H., Coyne, D., Tukamuhabwa, P., Hartman, G.L. 2022. Evaluation of soybean entries in the Pan-African trials for response to Coniothyrium glycines, the cause of red leaf blotch. Plant Disease. 106:535-540. https://doi.org/10.1094/PDIS-05-21-1017-RE.
DOI: https://doi.org/10.1094/PDIS-05-21-1017-RE

Interpretive Summary: Red leaf blotch, caused by a fungus, is an important disease of soybean known to cause yield losses across soybean growing regions in Africa. Fungicides are one option to manage this disease, but utilization of host resistance may be a better option suited for smallholder soybean farmers in Africa. Fifty-nine soybean entries were evaluated for red leaf blotch severity in nine field locations in Ethiopia, Kenya, Uganda, and Zambia. Disease incidence was 100% and disease severity differed among entries at eight of the nine locations. Mean severity rating ranged from 1.4 to 3.2 based on 0 to 5 scale with higher disease severities recorded in Ethiopia followed by Zambia. The cultivar SC Signal had the lowest red leaf blotch severity ratings in the combined analysis. This is the first extensive report evaluating soybean genotypes for resistance against red leaf blotch under multiple environments. This work is important to the seed industry, scientists, seed technologists and growers that may need to know more about soybean resistance to red leaf blotch.

Technical Abstract: Red leaf blotch, caused by the fungus Coniothyrium glycines, is an important disease of soybean known to cause yield losses across soybean growing regions in Africa. Fungicides are one option to manage this disease, but utilization of host resistance may be a better option suited for smallholder soybean farmers in Africa. Fifty-nine soybean entries were evaluated for red leaf blotch severity in nine field locations in Ethiopia, Kenya, Uganda, and Zambia. Disease incidence was 100% and disease severity differed (P < 0.01) among entries at eight of the nine locations. Mean severity rating ranged from 1.4 to 3.2 based on 0 to 5 scale with higher disease severities recorded in Ethiopia followed by Zambia. Seven of the 59 entries were common to all nine locations and had severity ranging from 1.7 to 2.9. The cultivar SC Signal had the lowest red leaf blotch severity ratings in the combined analysis. Based on correlations of weather variables to red leaf blotch severity, mean rainfall from planting to assessment date had a positive correlation (r = 0.90; P = 0.010) as did wind speed (r = 0.74; P = 0.0235). Other variables, such as temperature and relative humidity, did not correlate to red leaf blotch severity. This is the most comprehensive report to date on the disease incidence in the region, which for the first time demonstrates an association between rainfall and wind speed with red leaf blotch severity. It also represents the first extensive report evaluating soybean genotypes for resistance against red leaf blotch under multiple environments.