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Figure 1. States with reported incidences of Goss’s wilt since first identification in 1969 (white star).
Goss’s wilt, a persistent and economically significant disease of corn in the Midwest and the Western Great Plains, is caused by the bacterium Clavibacter michiganensis subsp. nebraskensis (Cmn). The disease was first observed in Dawson County, Nebraska in 1969. By the end of the 1970s, the disease had spread to most of Nebraska and to a few areas in Colorado, Kansas, Iowa, and South Dakota. Throughout the decades, the bacterial pathogen Cmn continued to spread throughout corn-growing regions of North America. To date, Goss’s wilt has been found in 18 states and in Alberta, Manitoba, and Ontario, Canada (Figure 1).1,2
In Texas, Goss’s wilt was first found in 2009 in Dallam county, followed by occurrences of the disease in separate locations in the High Plains as well as in Jackson county in 2014.3
Infection commonly occurs following severe weather systems with abundant rain and conditions that result in wounded plant tissues, similar to weather events seen in Southeast Texas in 2015 and 2016. Corn residue is a source of primary inoculum for Cmn under naturally occurring field conditions. University of Nebraska plant pathologists demonstrated that Cmn could be recovered eight months after harvest from 80% of infected leaf tissue left on the soil surface; however, the bacterium could not be recovered from infected leaf debris that was buried four or eight inches in the soil.4 Thus, as the bacterium was spread to new areas (via movement with weather fronts, or on infected corn debris) it failed to become established because infected debris was buried with adequate fall tillage. The increase in the practices of conservation tillage and continuous corn production throughout the Corn Belt are a contributing factor to the resurgence of Goss’s wilt. Because corn residue at the soil surface has the potential to harbor a substantial amount of Cmn inocula, once introduced into a field, the bacteria can survive on surface debris and gradually increase to levels that are likely to cause a significant problem when favorable weather conditions occur.
Figure 2. Identifying characteristics for Goss’s wilt.
(A) leaf “freckles�? on a plant symptomatic for Goss’s wilt (right) appear similar to saprophytic fungal growth (left).
(B) bacterial ooze.
(C) freckles appear luminous when held up to block the sun.
The disease occurs as either a vascular wilt or leaf blight. Systemic infection that occurs early in the season results in a vascular wilt. Leaf blight symptoms (Figure 2) usually appear mid-season as long, gray-green to black, water-soaked streaks extending along leaf veins. Small, dark, water-soaked flecks, referred to as “freckles�?, often occur inside larger lesions and at the edges of lesions where symptoms are advancing. Leaf freckles are luminous when lighted from behind, such as when the sun is used as backlighting. Bacterial cells may ooze from infected leaves and dry on leaf surfaces forming a shellac-like sheen. As lesions mature, large areas of tan to brown dead leaf tissues are apparent.
Figure 3. Symptoms of Goss’s wilt can be confused with other causes of leaf necrosis.
Goss’s wilt symptoms can be confused with other causes of leaf necrosis such as: northern corn leaf blight, heat stress, Stewart’s wilt, drought and nutrient deficiency. (Figure 3). Growth of saprophytic fungi on dead leaf tissue may appear similar to the freckles associated with Goss’s wilt (Figure 2).
Symptomatic leaf tissue should be examined by a plant disease clinic for diagnosis in order to ensure proper management of Goss’s wilt in future plantings. In a plant diagnostic laboratory, samples may be evaluated for typical symptoms: long, chlorotic to necrotic lesions with dark leaf freckles often found at margins of symptomatic tissues, bacterial streaming or ooze when viewed with a compound microscope, the presence of bacterial exudates appearing shellac-like on leaf surfaces (may or may not be present depending on prevailing weather), and results from plating of bacteria on selective media and/or immunological tests (i.e. ImmunoStrip® by Agdia®). ImmunoStrip® is a lateral flow strip that can quickly detect presence of Cmn by a related Clavibacter species that cross-reacts with Cmn.3
Samples may be sent to the Texas Plant Disease Diagnostic Lab in College Station for disease identification and confirmation. For more information about sample submission, contact the lab directly.
Texas A&M University Research Park
College Station, Texas 77845
Samples should be collected from fresh leaves displaying all stages of infection if possible and, if available, a generous amount of material should be sent. Leaves can be placed between newspaper or paper towels, but DO NOT WRAP LEAF TISSUE IN WET PAPER TOWELS. Excessive moisture can cause decay of plant tissues and encourage fungal growth, making diagnosis difficult. Ship samples in a crush-proof container (sturdy box) immediately after collecting and if possible, ship packages early in the week to avoid weekend holdovers. Include a completed Plant Disease Diagnostic Form (found at the following website: http://plantclinic.tamu.edu/forms/d1178/), and the required fees for the service. Provide any other information that may be useful for diagnosis, including any other factors that may have caused symptoms similar to Goss’s wilt.
Severe occurrences of Goss’s wilt are now seen over a wider geographic area than in previous decades. This is likely due to pockets of the pathogen becoming established in individual fields. Although often initially undetected, the bacterium may survive and cause small pockets of infection where conservation tillage and continuous corn production are practiced. The probability of Goss’s wilt increases when severe weather conditions conducive to infection occur and a susceptible corn product is grown in that particular field. Small areas of severe occurrences of Goss’s wilt may continue until commercial products with increased resistance become available in these regions, or agricultural practices that reduce the source of inocula are practiced.
Management practices to help reduce Goss’s wilt include:
Product selection and field management are the most effective options for managing Goss’s Wilt as there are no commercially available crop protection products on the market today that are effective against the disease during the growing season.
In response to the increased prevalence of Goss’s wilt, Monsanto has committed special efforts to develop new corn products with increased tolerance to the disease in all geographies. Large screening nurseries have been established in many areas that provide corn breeders an opportunity to assess the response of an individual corn product to Goss’s wilt under different environments and differing levels of disease severity. Monsanto corn products are assigned a tolerance rating based upon their response to the disease across all geographies. Disease tolerance ratings range from 1 to 9, with 1 being excellent resistance and 9 being poor resistance. Monsanto breeders are using genetic markers to enhance traditional phenotypic selection for increased resistance to Goss’s wilt. Phenotypic selection and marker-assisted breeding are important tools in the development of Goss’s wilt resistant corn products which have helped to speed up the development process for new products. The result has been an increased number of new corn products with improved resistance to Goss’s wilt.
1 Jackson, T.A., Harveson, R.M., and Vidaver, A.K. 2007. Goss’s bacterial wilt and leaf blight of corn. NebGuide G1675. University of Nebraska-Lincoln Extension. http://extensionpublications.unl.edu/. 2 Distribution map of Clavibacter michiganensis subsp. nebraskensis. April 2000. Map No. 549. CAB International. 3 Isakeit, T. 2015. Goss’s wilt of corn in Texas. Texas A&M AgriLife Extension. http://agrilife.org/. 4 Schuster, M.L. 1975. Leaf freckles and wilt of corn incited by Corynebacterium nebraskense. 5 Freije, A., Ikley, J., Wise, K., and Johnson, B. 2015. Goss’s wilt on grass hosts. Purdue Extension. BP-88-W. https://extension.purdue.edu/. Schuster, Hoff, Mandel, Lazar, 1972. Research Bulletin 270. University of Nebraska-Lincoln. Jackson, T. 2007. Goss’s bacterial wilt and leaf blight. Plant Disease Central. University of Nebraska. http://pdc.unl.edu. Corn disease management. 2002. Illinois Agronomy Handbook, 23rd edition. University of Illinois Extension. Web sources verified 06/22/16. 160621093240