A diagnostic guide for red crown rot of soybean

Authors: KLECZEWSKI, NATHAN - Growmark; BRADLEY, CARL - University Of Kentucky; Hartman, Glen; KANDEL, Y - Iowa State University; MUELLER, DAREN - Iowa State University; RODRIGUEZ-SALAMANCA, LINA - Iowa State University

Submitted to: Plant Health Progress
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/6/2022
Publication Date: 11/15/2022
Citation: Kleczewski, N.M., Bradley, C.A., Hartman, G.L., Kandel, Y., Mueller, D., Rodriguez-Salamanca, L. 2022. A diagnostic guide for red crown rot of soybean. Plant Health Progress. 24(1):123-129. https://doi.org/10.1094/PHP-04-22-0041-DG.
DOI: https://doi.org/10.1094/PHP-04-22-0041-DG

Interpretive Summary: The official common name of the disease on soybean is red crown rot (RCR). On peanut, the common disease name is Cylindrocladium black rot. On soybean, RCR and its causal fungal pathogen (Calonectria ilicicola) were first reported in 1973. This diagnostic guide provides information on disease distribution, disease diagnosis through symptomatology, use of molecular tools for identifying the fungus, and a review of methods for screening soybean germplasm for resistance. This guide will be useful for disease diagnosticians, extension agents, and soybean growers.

Technical Abstract: The official common name of the disease on soybean is red crown rot (RCR). Other names such Cylindrocladium root rot, black root rot, and Calonectria root rot also have been used especially for other hosts. On peanut, the common disease name is Cylindrocladium black rot and was first recorded on peanut in Georgia in 1965. On soybean, the fungal pathogen Calonectria ilicicola Boedijn & Reitsma (anamorph Cylindrocladium parasiticum Crous, Wingfield, and Alfennas) was reported in 1973. The ß-tubulin gene provides the greatest resolution of the species using molecular techniques. Foliar symptoms of RCR are often first observed between R3-R5 developmental stages of growth. Stem symptoms begin as a darkened, maroon/brick red discoloration of the lower stem that typically begin at the soil line and extend up the stem several centimeters. Roots can be extensively colonized during the seedling stage, resulting in stand reduction and pre- and post-emergent damping off. Within the United States, RCR has been observed on soybean in Delaware, Georgia, Illinois, Kentucky, Louisiana, Maryland, Mississippi, North Carolina, South Carolina, and Virginia. Additional research on soybean resistance and methods to evaluate soybean resistance are discussed.