Near-Infrared Spectroscopic Method for Identification of Fusarium Head Blight Damage and Prediction of Deoxynivalenol in Single Wheat Kernels

Cereal Chem. 87(6):511–517 Fusarium Head Blight (FHB), or scab, can result in significant crop yield losses and contaminated grain in wheat (Triticum aestivum L.). Growing less susceptible cultivars is one of the most effective methods for managing FHB and for reducing deoxynivalenol (DON) levels in grain, but breeding programs lack a rapid and objective method for identifying the fungi and toxins. It is important to estimate proportions of sound kernels and Fusarium-damaged kernels (FDK) in grain and to estimate DON levels of FDK to objectively assess the resistance of a cultivar. An automated single kernel near-infrared (SKNIR) spectroscopic method for identification of FDK and for estimating DON levels was evaluated. The SKNIR system classified visually sound and FDK with an accuracy of 98.8 and 99.9%, respectively. The sound fraction had no or very little accumulation of DON. The FDK fraction was sorted into fractions with high or low DON content. The kernels identified as FDK by the SKNIR system had better correlation with other FHB assessment indices such as FHB severity, FHB incidence and kernels/g than visual FDK%. This technique can be successfully employed to nondestructively sort kernels with Fusarium damage and to estimate DON levels of those kernels. Single kernels could be predicted as having low (<60 ppm) or high (>60 ppm) DON with ≈96% accuracy. Single kernel DON levels of the high DON kernels could be estimated with R = 0.87 and standard error of prediction (SEP) of 60.8 ppm. Because the method is nondestructive, seeds may be saved for generation advancement. The automated method is rapid (1 kernel/sec) and sorting grains into several fractions depending on DON levels will provide breeders with more information than techniques that deliver average DON levels from bulk seed samples. Fusarium Head Blight (FHB), also referred to as scab or Fusarium ear blight, is a fungal disease that affects all classes of wheat, as well as other small grains such as rye, barley, and triticale (Parry et al 1995; McMullen et al 1997). In any growing season, FHB can reach epidemic proportions in the United States and in many other wheat growing regions of the world. The disease has threatened world food supplies due to outbreaks in Asia, Canada, Europe, and South America (Dubin et al 1997). Nganje et al (2004) estimated that from 1993 to 2001, the cumulative direct economic loss from FHB to wheat and barley across nine U.S. states was estimated to be $2.5 billion. Additionally, they estimated the combined direct and secondary economic loss for all cereals to be $7.7 billion. FHB of wheat is caused by several fungal species of the filamentous ascomycetes genus, Fusarium; however, F. graminearum (sexual state: Gibberella zeae) is considered the predominate species causing FHB epidemics in North America (Parry et al 1995; Miedaner 1997; O’Donnell et al 2000). Disease development is favored when high humidity and rainfall occur during wheat flowering and grain-filling stages. Kernels of infected spikes are smaller than normal and often show changes in color and form, which results in a chalky or “tombstone” appearance, especially in cases of more severe infection. Thus, FHB reduces grain yield, but an even more serious threat to food safety is the potential accumulation of secondary fungal metabolites in the grain. Such trichothecene mycotoxins, which are mainly deoxynivalenol (DON) and its derivatives, make the grain unsafe for food or feed (Chelkowski 1991; Parry et al 1995; McMullen et al 1997). Agronomic and chemical control measures are only partly effective in controlling Fusarium in wheat (Stack 1999). Epidemics are often sporadic, with spore production or infection cycles highly influenced by wheat genotypes, crop growth stage, temperature, and moisture; this complexity further confounds the feasibility of chemical control measures. The use of FHB-resistant cultivars, together with appropriate crop management practices, is regarded as perhaps the best method for controlling FHB (Parry et al 1995). Because of this, breeding FHB-resistant cultivars is a primary goal of wheat breeders in affected regions. Resistance to FHB in wheat is quantitatively inherited (Ruckenbauer et al 2001; Miedaner et al 2003). Buerstmayr et al (1999) demonstrated that genes on chromosomes 6D, 6B, 5A, 4D, and 7A are frequently associated with scab resistance in wheat. Furthermore, the most prominent effect out of three identified genomics regions was detected on chromosome 3B, which accounted for ≤60% of phenotypic variance for Type II FHB resistance (Buerstmayr et al 2002). Mesterhazy et al (1999) proposed at least five different resistance reactions to Fusarium: 1) resistance to fungal invasion, 2) resistance to fungal spreading within the spike, 3) resistance to toxin accumulation, 4) resistance to kernel infection, and 5) tolerance. Mesterhazy (2001) extended the list of the components of physiological FHB resistance to include resistance to late blighting and resistance to head death above the infection site. Due to the ease of characterization, the majority of genetic studies and germplasm screening experiments have focused on resistance to spread within the spike. Although resistance to fungal invasion and toxin accumulation may be of equal or arguably greater importance, the difficulty and cost to assess these traits has limited routine applications. Regulation of DON accumulation is a rather complicated process that depends on the host and fungal genotypes as well as ecological conditions (Mesterhazy et al 1999; Bai et al 2001; Miedaner et al 2003). Because of an increasing emphasis on limiting mycotoxins in wheat-based food and feed products, plant breeders and pathologists need precise information to adequately assess Fusarium-damaged kernels (FDK) and the DON content of FDK. Fusarium infection generally affects kernel appearance and can be visually assessed, but insect damage and other fungi can result in similar symptoms and obscure the level of damage due to FHB. Some kernels, possibly those infected at later stages of grainfilling, may have high DON levels but still appear asymptomatic. * The e-Xtra logo stands for “electronic extra” and indicates that Figures 1 and 3 appear in color online. 1 Kansas State University, Biological and Agricultural Engineering Department Manhattan, KS. 2 USDA-ARS CGAHR, Hard Winter Wheat Genetics Research Unit, Manhattan, KS. 3 University of Minnesota, Department of Plant Pathology, St. Paul, MN. 4 USDA ARS CGAHR, EWERU, Manhattan, KS. 5 SDSU, Plant Science, Brookings, SD. 6 USDA ARS CGAHR, EWERU, Manhattan, KS. 7 Corresponding author. E-mail: [email protected] doi:10.1094 / CCHEM-01-10-0006 This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. AACC International, Inc., 2010. e-Xtra*