Disease Development and Deoxynivalenol Accumulation in Silage Corn

Disease Development and Deoxynivalenol Accumulation in Silage Corn

CPN 5008. Published November 22, 2021. DOI: Forthcoming. 

Richard W. Webster, University of Wisconsin-Madison; Maxwell O. Chibuogwu, University of Wisconsin-Madison; Hannah Reed, University of Wisconsin-Madison; Brian Mueller, University of Wisconsin-Madison; Carol L. Groves, University of Wisconsin-Madison; Albert U. Tenuta, Ontario Ministry of Agriculture, Food and Rural Affairs; Martin I. Chilvers, Michigan State University; Kiersten A. Wise, University of Kentucky; and Damon Smith, University of Wisconsin-Madison.

 

Summary

  • Fusarium graminearum is a fungus that causes the two diseases, Gibberella ear rot and Gibberella stalk rot, which can lower yield and feed quality of silage corn.
  • This fungus produces a secondary metabolite called deoxynivalenol (DON; also known as vomitoxin) during development and colonization of the corn plant, which is toxic to both humans and livestock.
  • Our research found that infection, colonization, and production of DON by F. graminearum in ears and stalks of corn plants can differ, and suggests that the two diseases can occur independently of each other.
  • Foliar fungicides reduced foliar diseases in both years, but the effects of fungicide on DON concentrations across entire plants were inconsistent in 2019.
  • Scouting for Gibberella ear and stalk rot and testing for DON in silage corn is important even if visual ear symptoms are not present as DON may still be accumulating in the stalks.

Introduction

Corn silage is integral for a dairy cow’s diet, often making up more than 50% of total dry matter intake during the winter months (Haerr et al. 2015). Dairy farmers need effective options to protect their corn crop from diseases which may decrease yield and/or decrease feed quality. Two such diseases are Gibberella ear rot and Gibberella stalk rot, both of which, are caused by the fungus Fusarium graminearum. Gibberella ear rot occurs after corn silks, or kernels damaged by insect/bird feeding, are infected by F. graminearum spores. The presence of red to pink fungal growth on the ear are characteristic signs of this disease (Figure 1). Gibberella stalk rot occurs after F. graminearum spores invade root tissue or infect leaf nodes and continue colonization to infect the stalk, causing a disintegration and pink-red coloration in the stalk pith. These diseases are concerning, because  F. graminearum produces toxic secondary metabolites called mycotoxins. Two important mycotoxins produced are deoxynivalenol (DON, also called vomitoxin) and zearalenone (ZEN), with DON being the most commonly found in harvested grain (Wise et al. 2016). DON can cause vomiting, feed refusal, and compromised immune systems in livestock (Pestka 2010; Richard et al. 2003). These induced symptoms lead to decreased dairy cow well-being, lower milk production, and increased risk of DON contamination in milk leading to unacceptable levels for human consumption (>10 ppm; Becker-Algeri et al. 2016; Coffey et al. 2009). Foliar fungicide applications are effective tools to protect silage corn from diseases. The use of fungicides can also increase overall feed quality, and improve the conversion efficiency of feed to milk within dairy cows (Cardoso 2020; Haerr et al. 2015; Hollis et al. 2019).

Figure 1. Ears of corn displaying Gibberella ear rot with visible Fusarium graminearum mycelia.

Research goals

  • Evaluate the effect of foliar fungicide applications on corn foliar diseases and DON levels in silage corn
  • Evaluate brown midrib corn hybrids for their resistance to Gibberella ear and stalk rots and subsequent levels of DON in those plant parts
  • Examine the relationship of F. graminearum presence and DON levels within and between stalks and ears of corn plants 

The research

In 2018 and 2019, field trials using two brown midrib (BMR) silage corn hybrids were conducted at the Arlington Agricultural Research Station in Arlington, Wisconsin. The field trials were conducted to evaluate the effect of different foliar fungicide treatments (13 in 2018 and 11 in 2019; Table 1) and application timings on foliar disease and DON. Diseases such as northern corn leaf blight, tar spot, gray leaf spot, and southern rust were observed across these years and were rated in-season and at harvest. Additionally, freshly chopped silage samples were analyzed for quality, nutritional parameters, and DON levels. 

In both years a subset of field plots from the previously discussed foliar fungicide trials were used to investigate the colonization of F. graminearum and localization of DON within different parts of silage corn. These experiments are referred to as the partitioned sample trials and included fungicide treatments of Headline AMP (pyraclostrobin + metconazole) and Proline 480 SC (prothioconazole) applied at the R1 (silking) growth stage along with a non-treated control. 

Both BMR hybrids were included in these experiments for a total of six treatment combinations. Gibberella ear rot and stalk rot ratings were made in-season and at harvest to examine the impact of the applied fungicides on disease severity. At harvest, stalk samples bearing ears were harvested and partitioned into stalk and ear (husks and shank attached) segments, which were processed and ground separately.  Samples were then analyzed by quantifying F. graminearum DNA quantities (using quantitative polymerase chain reaction i.e. qPCR) and DON concentrations (using enzyme-linked immunosorbent assay i.e. ELISA) in the partitioned segments.

Across the years and hybrids tested, there was little consistency in how fungicide treatments affected the measured yield parameters (dry matter yield, digestibility, moisture, and starch). Fungicide treatments reduced foliar disease levels (Tables 1, 2, 3, 4, 5). In the partitioned sample trials, F. graminearum and DON were detected in all samples. Ear rot and stalk rot severity were relatively high in 2018, with DON concentrations reaching 30 ppm, and lower in 2019, with DON concentrations <5ppm. Concentrations of DON were consistently greater in stalk samples compared to the ear samples in 2019, but in the elevated disease of 2018, there was greater variation of DON accumulation between stalks and ears. Quantities of F. graminearumDNA in ears and stalks were linked to corresponding DON levels in both stalks and ears, but DON levels were not always related. For example, high levels of DON in stalks did not necessarily mean that there were high levels of DON in ears, and vice versa (Figure 2). 

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Disease Development and Deoxynivalenol Accumulation in Silage Corn

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