Soybean Stem Zone Lines: Fact and Fiction
Published: 08/01/2016
DOI: doi.org/10.31274/cpn-20190620-027
CPN-1015
Soybean Stem Zone Lines: Fact and Fiction
FACT: The presence of soybean stem zone lines is associated with stem disease in the Diaporthe-Phomopsis disease complex. This disease complex includes Phomopsis seed decay caused by D. longicolla, pod and stem blight caused by D. sojae, and stem canker caused by D. caulivora and D. aspalathi.
FICTION: Soybean stem zone lines are associated with the stem disease charcoal rot, caused by the fungus Macrophomina phaseolina. However, this association of soybean stem zone lines and charcoal rot is incorrect, and has persisted for several years, resulting in misdiagnosis of the disease.
Zone lines associated with Diaporthe species appear on the inside of lower soybean stems and roots when split longitudinally, or if the outside layer of the stem is scraped away (Figure 1). Lines are thin and dark, appearing in irregular patterns and small circular shapes in mature soybean plants.
Figure 1. Split soybean stem or scrape away outside layer to show “zone lines” caused by Diaporthe fungi
Signs of charcoal rot are tiny, dark survival structures called microsclerotia within and on the surface of the lower stem and taproot. Microsclerotia cause light gray discoloration or a charcoal-like appearance of these plant parts (Figure 2).
Figure 2. Microsclerotia within and on the surface of soybean stem or root tissue
However, signs and symptoms of charcoal rot and zone lines may appear in the same soybean stem, because simultaneous infection by M. phaseolina and Diaporthe species can occur in the same plant (Figure 3).
The bottom line is that zone lines on the interior of soybean stems are associated with Diaporthe fungi and not the fungus that causes charcoal rot, as previously thought. This discovery provides a clearer picture of soybean diseases and the symptoms that result from pathogen infection. Accurate disease identification is the first step to making better disease management decisions, which improves farm profitability and stewardship.
Figure 3. Soybean stem showing symptoms of infection by M. phaseolina and Diaporthe species
Acknowledgments
Authors
Kiersten Wise, Purdue University; Daren Mueller, Iowa State University; Carl Bradley, University of Kentucky; Martin Chilvers, Michigan State University; Anna Freije, Purdue University; Loren Giesler, University of Nebraska-Lincoln; Adam Sisson, Iowa State University; Damon Smith, University of Wisconsin; and Albert Tenuta, Ontario Ministry of Agriculture, Food, and Rural Affairs
All photos were provided by the authors except Figure 3, which is the property of and was provided by Teresa Hughes.
Sponsors
The Soybean Disease Management series is a multi-state and international collaboration sponsored by the United Soybean Board and the North Central Soybean Research Program (NCSRP). This project was funded in part through Growing Forward 2 (GF2), a federal-provincial territorial initiative. The Agricultural Adaption Council assists in the delivery of GF2 in Ontario. The authors thank the United States Department of Agriculture - National Institute of Food and Agriculture and the Grain Farmers of Ontario for their support. Contributors to this series come from land-grant universities in the North Central states and Canada.
This information is provided only as a guide, and the authors assume no liability for practices implemented based on this information.
This publication was developed by the Crop Protection Network, a multi-state and international collaboration of university/provincial extension specialists and public/ private professionals that provides unbiased, research-based information to farmers and agricultural personnel.
This information in this publication is only a guide, and the authors assume no liability for practices implemented based on this information. Reference to products in this publication is not intended to be an endorsement to the exclusion of others that may be similar. Individuals using such products assume responsibility for their use in accordance with current directions of the manufacturer.
The U.S. Department of Agriculture (USDA) prohibits discrimination in all its programs and activities on the basis of race, color, national origin, age, disability, and where applicable, sex, marital status, familial status, parental status, religion, sexual orientation, genetic information, political beliefs, reprisal, or because all or a part of an individual's income is derived from any public assistance program. (Not all prohibited bases apply to all programs.) Persons with disabilities who require alternative means for communication of program information (Braille, large print, audiotape, etc.) should contact USDA's TARGET Center at (202) 720-2600 (voice and TDD). To file a complaint of discrimination write to USDA, Director, Office of Civil Rights, 1400 Independence Avenue, S.W., Washington, D.C. 20250-9410 or call (800) 795-3272 (voice) or (202) 720-6382 (TDD).
USDA is an equal opportunity provider and employer.
©2022 by the Crop Protection Network. All rights reserved.
