Physoderma Brown Spot and Stalk Rot of Corn Caused by Physoderma maydis in Iowa

(1)

Plant Pathology and Microbiology Publications

Plant Pathology and Microbiology

5-4-2015

Physoderma Brown Spot and Stalk Rot of Corn

Caused by Physoderma maydis in Iowa

Alison E. Robertson

Iowa State University, [email protected]

Laura Jesse

Gary Munkvold

Ericka Salaau Rojas

University of Massachusetts, East Wareham

Daren S. Mueller

Follow this and additional works at:

https://lib.dr.iastate.edu/plantpath_pubs

Part of the

Agricultural Science Commons

,

Agriculture Commons

,

Agronomy and Crop

Sciences Commons

, and the

Plant Pathology Commons

The complete bibliographic information for this item can be found at

https://lib.dr.iastate.edu/

plantpath_pubs/240

. For information on how to cite this item, please visit

http://lib.dr.iastate.edu/

howtocite.html

.

This Article is brought to you for free and open access by the Plant Pathology and Microbiology at Iowa State University Digital Repository. It has been accepted for inclusion in Plant Pathology and Microbiology Publications by an authorized administrator of Iowa State University Digital Repository. For more information, please [email protected].

(2)

Physoderma Brown Spot and Stalk Rot of Corn Caused by Physoderma

maydis in Iowa

Abstract

Physoderma brown spot (PBS) and stalk rot (PSR) of corn is caused by the fungus Physoderma maydis and

was first described in 1910 in India and then in 1911 in Illinois, U.S. (Tisdale 1919). In the 1930s, PBS caused

5–10% yield losses in the southeastern United States (Eddins 1933). The pathogen is now found in most

corn-producing areas in the world. PBS is not usually considered an economically important disease in the

Midwest, but incidence of the disease has increased within the past decade in Iowa. In 2013, the estimated

yield loss from this disease was over 13 million bushels (ranked 6 of 14 foliar diseases) in the United States

and Ontario, Canada (Mueller et al. 2014).

Disciplines

Agricultural Science | Agriculture | Agronomy and Crop Sciences | Plant Pathology

Comments

This article is published as Robertson, A. E., Jesse, L., Munkvold, G., Salaau Rojas, E., and Mueller, D. S. 2015.

Physoderma brown spot and stalk rot of corn caused by Physoderma maydis in Iowa. Plant Health Progress

16: 90-92. doi:

10.1094/PHP-BR-15-0003

. Posted with permission

(3)

PLANT HEALTH PROGRESS  Vol. 16, No. 2, 2015  Page 90

Plant Health Brief

Physoderma Brown Spot and Stalk Rot of Corn

Caused by Physoderma maydis in Iowa

Alison E. Robertson, Laura Jesse, and Gary Munkvold, Department of Plant Pathology and Microbiology, Iowa State University, Ames

50011; Erika Salaau Rojas, UMass Cranberry Station, University of Massachusetts, East Wareham 02538; and Daren S. Mueller, Department of Plant Pathology and Microbiology, Iowa State University, Ames 50011

Accepted for publication 2 April 2015. Published 4 May 2015.

Robertson, A. E., Jesse, L., Munkvold, G., Salaau Rojas, E., and Mueller, D. S. 2015. Physoderma brown spot and stalk rot of corn caused by Physoderma maydis in Iowa. Plant Health Progress doi:10.1094/PHP-BR-15-0003.

Physoderma brown spot (PBS) and stalk rot (PSR) of corn is caused by the fungus Physoderma maydis and was first described in 1910 in India and then in 1911 in Illinois, U.S. (Tisdale 1919). In the 1930s, PBS caused 5–10% yield losses in the southeastern United States (Eddins 1933). The pathogen is now found in most corn-producing areas in the world. PBS is not usually considered an economically important disease in the Midwest, but incidence of the disease has increased within the past decade in Iowa. In 2013, the estimated yield loss from this disease was over 13 million bushels (ranked 6 of 14 foliar diseases) in the United States and Ontario, Canada (Mueller et al. 2014).

All parts of the corn plant can be infected by P. maydis but infections are most common on leaves. Symptoms of PBS are numerous small (approximately ¼-inch diameter), yellowish to brown, round or oval spots that usually occur in broad bands across the leaf (Fig. 1). Dark purplish to black oval spots can also occur on the leaf midrib, stalk, leaf sheath, and husks. Foliar symptoms of PBS can be confused with eyespot (Aureobasidium zeae) (Fig. 2, left), southern rust (Puccinia polysora) (Fig. 2, center), or genetic flecking. None of the aforementioned diseases cause purple-black spots on the leaf midrib. Oval spots on the leaf sheaths can be mistaken for purple leaf sheath, which is usually characterized by larger, dark, irregular blotches (Fig. 2, right). In addition, plants exhibiting symptoms of PBS are often stunted with thin stalks and are typically found in localized, low-lying areas of fields.

Stalk rot symptoms are usually not as apparent. Most

agronomists reporting PSR infections notice it when stalks easily and audibly snap at a lower node when plants are pushed aside to walk across rows (see Supplemental Material sidebar). Nodes at

which breakage occurs are black and rotted (Fig. 3, left), and pith rotting may be evident (Fig. 3, right). Microscopic examination of rotted tissue reveals thousands of light brown, round sporangia (Fig. 4).

There are few published reports of PSR and associated stalk breakage caused by this pathogen. In Illinois, severe outbreaks with up to 80% lodging in some fields were reported in the early 1970s (Burns and Shurtleff 1973). PSR with stalk breakage was observed for the first time in fields in southwest and western Iowa in 2013. The following year, numerous reports of PSR and stalk breakage were received from northwest and north central Iowa, with a few reports from southern and southwest Iowa. Disease incidence ranged from a few plants to 80% across entire fields. Plants with PSR were often vigorous with large ears and well-developed kernels; the characteristic foliar symptoms were rarely present.

FIGURE 1

Characteristic leaf symptoms of Physoderma brown spot.

Supplemental Material: download at Plant Health Progress

▪ MOV file (27 MB) showing a stalk infected with Physoderma brown spot easily and audibly snapping at a lower node.

http://dx.doi.org/10.1094/PHP-BR-15-0003ex

Corresponding author: A. E. Robertson. Email: [email protected]

(4)

ROLE OF WEATHER IN THE OUTBREAK OF PHYSODERMA STALK BREAKAGE AND ROT IN IOWA

The increase of PBS and PSR in Iowa is likely related to hybrid genetics, current crop production practices, and/or wet springs. Conditions early in the growing season in Iowa may become more conducive for this disease if average precipitation increases across the Corn Belt, which is anticipated by global climate change predictions (Hatfield et al. 2011). Further research to understand the biology and management of PSR is needed. Iowa weather data from 2013 and 2014 support earlier reports that PBS and PSR are more severe when excessive rain occurs (Burns and Shurtleff 1973; Tisdale 1919). Above normal precipitation (8.7 inches

versus 4.8 inches (30-year mean) in May 2013 delayed planting in Iowa by two to three weeks (mid-May) compared to the previous five years. The 2014 season was more typical with 50% of the crop planted by the end of the first week of May. Areas of Iowa where PSR was reported experienced significant rainfall (3.9-5.2 inches within a one week period) when corn was between V5 and V9 growth stages. This was typically the last two weeks of June. Additional rainfall (5 or more inches) was reported the following 7–10 days in these regions in 2014. Parts of Iowa with no PSR reports, such as northwest Iowa in 2013, experienced dry conditions (less than 1 inch of rain) during V5-V9 growth stages (Abendroth et al. 2011).

FIGURE 2

Characteristics of diseases similar to Physoderma leaf spot: (left) eyespot, caused by Aureobasidium zeae; (center) Southern rust, caused by Puccinia

polysora; and (right) purple leaf sheath, caused by saprophytic fungi and bacteria developing on pollen and dust that collect behind the leaf

sheath.

FIGURE 3

Symptoms of Physoderma stalk rot: (left) the nodes at which breakage occurs are black and rotted; (right) rotting of the pith at the affected nodes.

(5)

PLANT HEALTH PROGRESS  Vol. 16, No. 2, 2015  Page 92

Management of diseases caused by P. maydis are complicated since it is difficult to predict locations that might receive abundant rainfall with warm temperatures during susceptible crop stages. Nevertheless, standard disease management practices can be considered. No resistance to P. maydis is commercially available in the United States, but preliminary observations from recent outbreaks suggest that current hybrids vary in susceptibility (A. Robertson, unpublished data). Rotation and tillage practices may

reduce inoculum. Although no efficacy data is publically

available, most fungicides registered for use on corn in the United States are labeled for PBS (www.cdms.net). A report from China indicates that application of the fungicide tebuconazole at crop development stage V8 reduced disease severity considerably and yields were greater (Li et al. 2010). The increased prevalence of PSR in Iowa is a concern to seed companies and farmers because of the potential for lodging and yield loss. Since the biology of disease caused by P. maydis is poorly understood, further research is needed to enable effective management practices to be

identified and implemented; for example, inoculation methods to screen germplasm for resistance to P. maydis, as well as evaluate fungicide efficacy.

LITERATURE CITED

Abendroth, L. J., Elmore, R. W., Boyer, M. J., and Marlay, S. K. 2011. Corn growth and development. Ext. Pub. PMR 1009. Iowa State University Ames.

Burns, E. E., and Shurtleff, M. C. 1973. Observations of Physoderma maydis in Illinois: Effects of tillage practices in field corn. Plant Dis. Rep. 27:630-633.

Eddins, A. H. 1933. Infection of corn plants by Physoderma zeae-maydis Shaw. J. Agric. Res. 46:241-252.

Hatfield, J. L., Boote, K. J., Kimball, B. A., Ziska, L. H., Izaurralde, R. C., Ort, D., Thomson, A. M., and Wolfe, D. I. 2011. Climate impacts on agriculture: Implications for crop production. Agron. J. 103:351-370. Li, J., Jiang, X., Wang, Y., Ge, D., Nie, L., and Wu, S. 2010. Effect of

tebuconazole on the spatial distribution of corn brown spot and the yield to summer maize. Agrochemicals 2010-07.

Mueller, D. 2014. Corn disease loss estimates from the United States and Ontario, Canada—2013. Ext. Pub. BP-96-13-W. Purdue University, West Lafayette, IN.

Tisdale, W. H. 1919. Physoderma disease of corn. J. Agric. Res. 16:137-154.

FIGURE 4

Light brown, round sporangia of Physoderma maydis recovered from diseased tissues.