Deoxynivalenol Contamination For Different Wheat Grain Handling Conditions

Kentucky wheat (Triticum aestivum L.) producers have anecdotal observations of higher grain quality when wheat was harvested at greater than 15% grain moisture. This has led producers with grain drying systems to frequently harvest at 18 to 20% grain moisture to preserve test weight, reduce deoxynivalenol (DON) contamination, and allow earlier planting of double-crop soybean [Glycine max (L.) Merr.]. Wheat harvested with greater than 14% grain moisture should be dried shortly after harvest to 12.5% to allow long-term storage without risk of spoilage (McNeill, Overhults, & Montros, 2009). Another concern for grain harvested between 18 and 20% grain moisture is DON contamination. Deoxynivalenol is a mycotoxin byproduct of Fusarium graminearum infection (Cowger & Arellano, 2013). Fusarium graminearum infection can occur during anthesis through to the soft dough stage and can continue to grow at a grain moisture content as low as 15% (Cowger & Arellano, 2013, Sherwood & Peberdy, 1974). This can lead to the potential of additional DON accumulating in harvested grain. There has been little work done to determine if DON contamination increases in stored wheat grain that has greater than 15% grain moisture. The specific objectives of the study were to determine the effect of grain storage conditions of soft red winter wheat harvested at greater than 15% grain moisture on DON contamination, grain moisture before drying, and test weight before and after grain drying. Soft red winter wheat trials were established at the University of Kentucky Research and Education Center in Princeton, KY, (37°6′N, 87°52′W) with a no-till drill (Plotseed XL, Wintersteiger Inc., Salt Lake City, UT) into corn (Zea mays L.) stubble in 7-in rows. Trials were established on a Crider silt loam (fine-silty, mixed, active, mesic Typic Paledalfs) and Zanesville silt loam (fine-silty, mixed, active, mesic Oxyaquic Fraguidalf) on 11 Oct. and 28 Nov. 2018. Plots were approximately 4 ft wide and 15 ft long. Plots were managed according to University of Kentucky Cooperative Extension Service recommendations (Lee et al., 2009). Four replications were evaluated; each replicate consisted of eight grain samples from eight environments (Table 1). Although the target harvest moisture was 20 to 22% w.b. (wet basis), grain moisture content at harvest ranged from 14.3 to 21.2% (Table 1) due to of environmental factors. Wheat was harvested with a small plot combine (Delta, Wintersteiger Inc.) equipped with a weigh system (Harvest Master, Juniper Systems Inc., Logan, UT). Approximately 3 lbs of grain were collected from each plot. A 1-lb subsample was placed on a table in a metal equipment shed in unsealed plastic bags (Ziploc, SC Johnson, Racine, WI) for 1 wk for the October-planted wheat and 2 wk for the November-planted wheat. Digital hygrometers (Amazon, Seattle, WA) with confirmed accuracy were used to monitor the temperature and relative humidity in each grain sample at least twice a day. The remaining 2 lb of grain were stored in sealed plastic bags in a walk-in cooler (37 °F; Forma-Kool, Chesterfield, MI) for 1 to 2 wk to maintain the harvest grain moisture and hinder F. graminearum growth prior to drying. Wheat was dried to 12.5% moisture with a laboratory-scale thin layer drying system (White, Bridges, McNeill, & Overhults, 1985). Grain moisture and test weight were determined with a Dickey–John Grain Analysis Computer (Model 2500-UGMA, Dickey–John, Auburn, IL) immediately after harvest and drying. Deoxynivalenol contamination was determined with EnivroLogix Mycotoxin Test Strips (Portland, ME). Data were analyzed as a randomized complete block design (PROC GLIMMIX; SAS version 9.4; SAS Institute Inc., Cary, NC). The LSmeans statement and the Tukey–Kramer method was used to determine differences in DON contamination, grain moisture before drying, and test weight before and after drying occurred. Wheat was held in unsealed plastic bags in the metal equipment shed to simulate conditions in the top layer of a grain bin prior to drying. Observations revealed that grain temperature was generally greater than the ambient air temperature and both followed the daily pattern as expected (Figure 1 and Figure 2). Although the relative humidity of the air fluctuated, the relative humidity of the simulated top layer of a grain bin remained fairly constant (as influenced by grain moisture) (Figure 1 and Figure 2). Despite fluctuations in air temperature and relative humidity (KY Mesonet, http://www.kymesonet.org, accessed 6 Apr. 2020), the estimated wheat equilibrium moisture content across the 7- and 15-d holding periods remained constant (P < .05) at about 15 and 14%, respectively (Table 2). When wheat was stored in an environment that simulated conditions in the top layer of a bin dryer, there was no difference (P = .4463) in DON contamination compared with grain that was stored in the walk-in cooler to retain grain moisture and hinder F. graminearum growth until drying (Table 3). The lack of difference in DON contamination was not surprising, given that the mean estimated moisture content during handling (Table 2) was less than 15%, which is the minimum needed for satisfactory F. graminearum growth and the potential for additional DON accumulation (Sherwood & Peberdy, 1974). Although every effort was made to harvest at the targeted 20 to 22% grain moisture, environmental conditions prevented harvest for most environments until 14 to 16% grain moisture (Table 1). In addition to holding environment, the impact of DON contamination was also examined to determine whether the two different holding times (7 d for the October-planted crop and 15 d for the November-planted crop) resulted in different levels of DON contamination. It was found that DON contamination was similar (P = .7967) for both the 1- and 2-wk holding periods. The goal of this project was to determine whether DON contamination increased during the holding period for grain harvested between 20 and 22% moisture. Despite enduring harvest challenges that prevented the entire study to be harvested at between 20 and 22% grain moisture, there was one environment (eight samples) that was harvested at approximately 21% moisture. These eight samples were from an October-planted crop and therefore the holding period for these samples was 7 d. The mean DON contamination of these eight samples was 0.5 ppm when placed into conditions that would simulate the top layer of bin conditions prior to drying. This was similar (P = .1358) to the samples that were stored in the cooler (0.6 ppm) prior to drying to prevent additional fungal growth and mycotoxin accumulation (data not shown). Overall, the findings of this project were that DON contamination did not increase when wheat was stored in environments that simulated conditions in the top layer of a bin dryer for 1 to 2 wk prior to drying the grain to 12.5% moisture for long-term storage. Unfortunately, this may be caused by harvest challenges that forced harvest to occur later than the 20 to 22% grain moisture targeted. In general, the mean estimated equilibrium moisture content was less than the minimum 15% moisture content that is needed for satisfactory F. graminearum growth and potential DON accumulation for most of the samples examined. However, there were eight samples that were within the targeted range (21%). For these samples, DON contamination did not increase after one week in conditions that simulated the top layer of a bin dryer compared with grain that was stored in a cooler to prevent additional DON contamination. This suggests that there may be potential for wheat harvested at up to 21% grain moisture to be held for 1 to 2 wk before drying to 12.5% grain moisture without elevating DON contamination. However, it is important to dry wheat grain as soon as possible to 12.5% grain moisture for long-term storage and to keep the storage environment at less than 65% relative humidity to prevent problems with spoilage and additional DON accumulation (McNeill et al., 2009). The authors declare no conflict of interest. Funding was provided by the Kentucky Small Grain Growers Promotion Council and was greatly appreciated. The authors thank Connor Raymond, Curtis Bradley, Hunter Adams, Jacob Foote, and Gracie Harper for their help with this project. Special thanks to Kiersten Wise and Nolan Anderson for the use of their Enivrologix scanner and equipment.