Fusarium Head Blight Severity Research Articles

Characterizing Winter Wheat Germplasm for Fusarium Head Blight Resistance Under Accelerated Growth Conditions.

Fusarium head blight (FHB) is one of the economically important diseases of wheat as it causes severe yield loss and reduces grain quality. In winter wheat, due to its vernalization requirement, it takes an exceptionally long time for plants to reach the heading stage, thereby prolonging the time it takes for characterizing germplasm for FHB resistance. Therefore, in this work, we developed a protocol to evaluate winter wheat germplasm for FHB resistance under accelerated growth conditions. The protocol reduces the time required for plants to begin heading while avoiding any visible symptoms of stress on plants. The protocol was tested on 432 genotypes obtained from a breeding program and a genebank. The mean area under disease progress curve for FHB was 225.13 in the breeding set and 195.53 in the genebank set, indicating that the germplasm from the genebank set had higher resistance to FHB. In total, 10 quantitative trait loci (QTL) for FHB severity were identified by association mapping. Of these, nine QTL were identified in the combined set comprising both genebank and breeding sets, while two QTL each were identified in the breeding set and genebank set, respectively, when analyzed separately. Some QTLs overlapped between the three datasets. The results reveal that the protocol for FHB evaluation integrating accelerated growth conditions is an efficient approach for FHB resistance breeding in winter wheat and can be even applied to spring wheat after minor modifications.

Efficacy of Fungicides against Fusarium Head Blight Depends on the Timing Relative to Infection Rather than on Wheat Growth Stage

Fungicides used to control Fusarium head blight (FHB) are commonly applied at the wheat growth stage considered to be most susceptible, i.e., anthesis. We compared the efficacy of the most commonly used fungicide groups that were applied following two strategies: (i) at pre-defined growth stages, from the first half of heading to the end of flowering (experiment 1, in 2013 to 2015), or (ii) based on timing of infection by F. graminearum, specifically at 10, 7, 4, or 1 day before, or 3 or 5 days after artificial inoculation of the fungus (experiment 2, in 2017 and 2018). Fungicide efficacy was evaluated in terms of FHB incidence, FHB severity, and DON contamination by using generalised mixed models. In experiment 1, all fungicide groups reduced FHB severity and DON but only by <50% compared to an untreated control, with no differences among fungicides or growth stages at time of application. In experiment 2, the efficacy of fungicides was higher for applications at 1 or 4 days before inoculation than at 7 or 10 days before or 3 or 5 days after inoculation, with differences among fungicide groups. Based on our results, the timing of fungicide application for FHB control should be based on the time of F. graminearum infection rather than on wheat phenology.

Wheat Fusarium Head Blight Detection Using UAV-Based Spectral and Texture Features in Optimal Window Size

By combining the spectral and texture features of images captured by unmanned aerial vehicles (UAVs), the accurate and timely detection of wheat Fusarium head blight (FHB) can be realized. This study presents a methodology to select the optimal window size of the gray-level co-occurrence matrix (GLCM) to extract texture features from UAV images for FHB detection. Host conditions and the disease distribution were combined to construct the model, and its overall accuracy, sensitivity, and generalization ability were evaluated. First, the sensitive spectral features and bands of the UAV-derived hyperspectral images were obtained, and then texture features were selected. Subsequently, spectral features and texture features extracted from windows of different sizes were input to classify the area of severe FHB. According to the model comparison, the optimal window size was obtained. With the collinearity between features eliminated, the best performance of the logistic model reached, with an accuracy, F1 score, and area under the receiver operating characteristic curve of 0.90, 0.79, and 0.79, respectively, when the window size of the GLCM was 5 × 5 pixels on May 3, and of 0.90, 0.83, and 0.82, respectively, when the size was 17 × 17 pixels on May 8. The results showed that the selection of an appropriate GLCM window size for texture feature extraction enabled more accurate disease detection.

Aggressiveness of Fusarium culmorum isolates for head blight symptoms is highly stable across four cereal crops

AbstractFusarium culmorum is an important component of Fusarium head blight (FHB) in Northern Europe in all cereals. We analysed the stability of six isolates differing in origin by inoculating them on four winter cereal crops (bread wheat, durum wheat, triticale and rye) with two cultivars each across three years and used disease symptoms as aggressiveness trait. Isolates significantly differed in their aggressiveness, measured as mean FHB severity, as well as the resistance of the cereals (p ≤ .01). Within the crops, bread and durum wheat were the most susceptible and showed significant differences between cultivars, triticale and rye were much less affected. Isolate × cereal and isolate × cultivar interactions were not significant. Accordingly, the isolates showed a similar ranking for all cereals and cultivars. The nivalenol‐producing isolate FC60 was the least aggressive isolate. Despite large differences on the host side, aggressiveness was a stable, highly heritable trait in F. culmorum.

Molecular Mapping of Quantitative Trait Loci for Fusarium Head Blight Resistance in a Doubled Haploid Population of Chinese Bread Wheat.

Fusarium head blight (FHB) is a destructive disease of wheat worldwide, particularly in China. To map genetic loci underlying FHB resistance, a doubled haploid (DH) population consisting of 174 lines was developed from a cross between widely grown Chinese cultivars Yangmai 16 and Zhongmai 895. The DH population and parents were evaluated in field nurseries at Wuhan in 2016 to 2017 and 2017 to 2018 crop seasons with both spray inoculation and natural infection, and at Jingzhou in 2017 to 2018 crop season with grain-spawn inoculation. The DH lines were genotyped with a wheat 660K SNP array. The FHB index, plant height, anther extrusion, and days to anthesis were recorded and used for quantitative trait loci (QTL) analysis. Seven QTL for FHB resistance were mapped to chromosome arms 3BL, 4AS, 4BS, 4DS, 5AL, 6AL, and 6BS in at least two environments. QFhb.caas-4BS and QFhb.caas-4DS co-located with semi-dwarfing alleles Rht-B1b and Rht-D1b, respectively, and were associated with anther extrusion. The other five QTL were genetically independent of the agronomic traits, indicating their potential value when breeding for FHB resistance. Based on correlations between FHB indices and agronomic traits in this population, we concluded that increasing plant height to some extent would enhance FHB resistance, that anther extrusion had a more important role in environments with less severe FHB, and that days to anthesis were independent of the FHB response when viewed across years. PCR-based markers were developed for the 3BL and 5AL QTL, which were detected in more than three environments. The InDel marker InDel_AX-89588684 for QFhb.caas-5AL was also validated on a wheat panel, confirming its effectiveness for marker-assisted breeding for improvements in FHB resistance.

Silicon soil amendment as a complement to manage tan spot and fusarium head blight in wheat

Tan spot, caused by Pyrenophora tritici-repentis, and fusarium head blight (FHB), caused by the Fusarium graminearum species complex, are among the main wheat diseases worldwide. This 3-year field study evaluated the effect of soil incorporation of calcium silicate, a source of silicon (Si), to manage tan spot and FHB and improve grain yield and quality. The effect of Si was compared on two cultivars contrasting in disease resistance and associated with one or two fungicide sprays. Calcium silicate fertilization increased the Si concentration in the soil and wheat leaf and spike tissues. The increase of Si concentration in wheat tissues was associated with reduction in the severity of both tan spot and FHB, consequently increased the quality and grain yield of wheat. The reduction of disease severity conferred by Si was greater for tan spot than FHB. The greatest control of tan spot and FHB was obtained with the moderately resistant cultivar grown in soil amended with calcium silicate (+Si) and treated with two fungicide sprayings. On the other hand, the highest grain yield, under high disease pressure, was obtained in +Si plants, regardless of the cultivar, treated with two fungicide sprays. The results of this study show for the first time that the incorporation of Si in the soil complemented the effect of genetic resistance and fungicide treatments in controlling both tan spot and FHB. Furthermore, results indicate that calcium silicate fertilization is useful as part of integrated management of these wheat diseases.

Effects of nitrogen deficiency induced by straw decomposition after incorporation into soil on the autophagy and pathogenicity of Fusarium graminearum based on an off‐line simulation

AbstractThe high severity of plant diseases has hampered the implementation of straw incorporation technology in practice. To clarify the relationship between the nitrogen deficiency caused by wheat straw decomposition and Fusarium head blight (FHB) occurrence, five nitrogen levels as 0%, 25%, 50%, 75% and 100% were set to simulate the nitrogen changing after straw incorporated into soil and its effects on the pathogenicity of Fusarium graminearum. Nitrogen starvation degree was characterized by autophagy. Seedling infection and toxin production were used to test pathogenicity. The results showed that biomass of F. graminearum cultured in 25% nitrogen level medium for 72 hr and 120 hr were 0.39 g/ml and 0.29 g/ml, respectively, and were greater than those of other treatments at the same time (p < .05). The spore germination in 0%, 25%, 50% and 75% nitrogen level media were greater than those in 100% nitrogen level medium, in which the total nitrogen deficiency was the greatest (p < .05), reaching 64.5%. Total nitrogen deficiency would lead to F. graminearum autophagic death, while other treatments displayed different starvation responses in F. graminearum. F. graminearum cultured in 25% and 50% nitrogen levels media for 48 and 72 hr or in 75% nitrogen level medium for 168 hr produced more deoxynivalenol (DON). The lesion lengths caused by F. graminearum treated with 25%, 50% and 75% nitrogen levels for 72 hr were 18.33 mm, 15.78 mm and 14.96 mm, respectively, which were significantly longer than the lesions at the 0% (10.57 mm) and 100% (12.18 mm) nitrogen levels. The results indicated that the pathogenicity of F. graminearum was affected by nitrogen levels significantly and partial nitrogen deficiency could prompt the severity of FHB.

Fusion of Deep Convolution and Shallow Features to Recognize the Severity of Wheat Fusarium Head Blight.

A fast and nondestructive method for recognizing the severity of wheat Fusarium head blight (FHB) can effectively reduce fungicide use and associated costs in wheat production. This study proposed a feature fusion method based on deep convolution and shallow features derived from the high-resolution digital Red-green-blue (RGB) images of wheat FHB at different disease severity levels. To test the robustness of the proposed method, the RGB images were taken under different influence factors including light condition, camera shooting angle, image resolution, and crop growth period. All images were preprocessed to eliminate background noises to improve recognition accuracy. The AlexNet model parameters trained by the ImageNet 2012 dataset were transferred to the test dataset to extract the deep convolution feature of wheat FHB. Next, the color and texture features of wheat ears were extracted as shallow features. Then, the Relief-F algorithm was used to fuse the deep convolution feature and shallow features as the final FHB features. Finally, the random forest was used to classify and identify the features of different FHB severity levels. Results show that the recognition accuracy of the proposed fusion feature model was higher than those of models using other features in all conditions. The highest recognition accuracy of severity levels was obtained when images were taken under indoor conditions, with high resolution (12 MB pixels), at 90° shooting angle during the crop filling period. The Relief-F algorithm assigned different weights to the features under different influence factors; it made the fused feature model more robust and improved the ability to recognize wheat FHB severity levels using RGB images.

Triticum varieties grown as ‘ancient grains’ in New York differ in susceptibility to Fusarium head blight and harbor diverse Fusarium flora

Fusarium head blight (FHB) of Triticum spp. is caused by diverse, mycotoxigenic members of the genus Fusarium. In New York, United States, Fusarium graminearum is considered the primary FHB incitant on common wheat (Triticum aestivum), but there is no record of the Fusarium spp. colonizing wheat crops marketed as high value ‘ancient grains’ (T. dicoccum, T. spelta, and T. monococcum). The incidence and severity of FHB on these crops was recorded at variety trials in 2017 and 2018, and a brief survey of the Fusarium flora associated with symptomatic spikes was conducted at these trials and an additional research site in 2018. A significant difference in mean incidence and severity was observed between crop varieties in 2017, suggesting that partial varietal resistance will contribute to successful FHB management in New York ‘ancient grain’ crops. The survey of Fusarium flora associated with symptomatic tissue recorded seven species or species complexes, based on colony morphology and DNA sequence homology. Fusarium acuminatum, F. avenaceum, the F. graminearum species complex, the F. incarnatum-equiseti species complex, F. poae and F. sporotrichioides have been linked previously to FHB in wheat, while F. armeniacum had not been associated with FHB symptomatic wheat spikes prior to this study. The diversity of Fusarium species recovered raises the concern that mycotoxins which are not routinely tested for may be found in high-value Triticum crops grown in New York.

Evaluation of Application Timing of Miravis Ace for Control of Fusarium Head Blight in Wheat

Fusarium head blight (FHB) is a serious disease of wheat and barley that not only lowers yield but also contaminates the grain with associated mycotoxins such as deoxynivalenol (DON). Chemical control options for FHB and DON include application of triazole fungicides at the anthesis or flowering stage. This presents practical challenges for growers in managing FHB, as the appropriate timing window typically lasts only 3 to 4 days. If this small window is missed, due to weather conditions or technical problems, fungicide application is less effective in controlling FHB and DON. The present work was conducted over 2 years (2019 and 2020) to test the efficacy of a new fungicide (pydiflumetofen + propiconazole) from Syngenta labeled as Miravis Ace in controlling FHB and DON content at 50% head emergence (Feekes 10.3), anthesis (Feekes 10.5.1), and end of flowering (Feekes 10.5.3) stages. Prosaro 421 SC, a standard FHB control triazole fungicide, was used at all three stages for comparison with the test fungicide. Miravis Ace application at 50% head emergence provided significant control over the nontreated check for FHB incidence (2020), FHB severity (2019), and DON content (2019) with control efficacies as high as 51, 69, and 52%, respectively. However, mean control percentages relative to the check were highest with Miravis Ace at anthesis in both 2019 and 2020 for all the FHB parameters. In conclusion, 50% head emergence provides statistically significant control on FHB and DON, but anthesis was the most effective application stage for Miravis Ace.

Multifaceted Insights on Fusarium Head Blight in Small Grains in Pennsylvania

Fusarium head blight (FHB) is a serious disease of small-grain cereals that causes economic losses due to both yield reduction and mycotoxin contamination worldwide. To optimize the regional management of the disease, knowledge of risk factors associated with FHB outbreaks and mycotoxin accumulation are essential steps. Therefore, a 2-year survey was conducted during the summers of 2018 and 2019, in which naturally FHB-affected spikes from different hosts were collected across the major cereal-producing regions of Pennsylvania (South, Central, and North). FHB severity (%) data were recorded from each field. Furthermore, a collection of 307 Fusarium graminearum isolates was used to investigate specific components of the pathogen biology, such as the composition of the trichothecene genotype, saprophytic and pathogenic fitness, and sensitivity to triazole-based fungicides. Our results confirm that FHB is an important disease in Pennsylvania, and the risk of disease epidemics may be impacted by both the year and the location. Overall, the regional population of F. graminearum causing FHB in Pennsylvania is the 15ADON genotype. Based on in vitro and in vivo experiments, F. graminearum populations obtained from three distinct small-grain management regions could not be differentiated for the majority of fitness traits examined. All isolates were sensitive to tebuconazole and metconazole fungicides in vitro. Overall, this new knowledge can help shed light on the relative importance of FHB epidemics in Pennsylvania and provide directions for monitoring the sustainability of the integrated strategies used to manage FHB and mycotoxin accumulation.

Automatic Evaluation of Wheat Resistance to Fusarium Head Blight Using Dual Mask-RCNN Deep Learning Frameworks in Computer Vision

In many regions of the world, wheat is vulnerable to severe yield and quality losses from the fungus disease of Fusarium head blight (FHB). The development of resistant cultivars is one means of ameliorating the devastating effects of this disease, but the breeding process requires the evaluation of hundreds of lines each year for reaction to the disease. These field evaluations are laborious, expensive, time-consuming, and are prone to rater error. A phenotyping cart that can quickly capture images of the spikes of wheat lines and their level of FHB infection would greatly benefit wheat breeding programs. In this study, mask region convolutional neural network (Mask-RCNN) allowed for reliable identification of the symptom location and the disease severity of wheat spikes. Within a wheat line planted in the field, color images of individual wheat spikes and their corresponding diseased areas were labeled and segmented into sub-images. Images with annotated spikes and sub-images of individual spikes with labeled diseased areas were used as ground truth data to train Mask-RCNN models for automatic image segmentation of wheat spikes and FHB diseased areas, respectively. The feature pyramid network (FPN) based on ResNet-101 network was used as the backbone of Mask-RCNN for constructing the feature pyramid and extracting features. After generating mask images of wheat spikes from full-size images, Mask-RCNN was performed to predict diseased areas on each individual spike. This protocol enabled the rapid recognition of wheat spikes and diseased areas with the detection rates of 77.76% and 98.81%, respectively. The prediction accuracy of 77.19% was achieved by calculating the ratio of the wheat FHB severity value of prediction over ground truth. This study demonstrates the feasibility of rapidly determining levels of FHB in wheat spikes, which will greatly facilitate the breeding of resistant cultivars.

Using anthesis date as a covariate to accurately assessing type II resistance to Fusarium head blight in field-grown bread wheat

The identification of sources of resistance to Fusarium head blight (FHB) in bread wheat is key to the sustainable management of the disease. An accurate characterization of resistance is critical; however, the experimental designs commonly used disregard germplasm variability in anthesis date (moment of highest disease susceptibility). Here, an accurate methodology for assessing type II resistance to FHB in the field was developed. Individual spikes of 126 RILs were point-inoculated at their optimum moment. The effect of anthesis date and environmental conditions on the prediction of bread wheat lines' performance was established. Anthesis date explained 26% of the total phenotypic variation for Severity at 21 days post-inoculation (dpi). Including this factor in the model increased the accuracy of the best linear unbiased predictors through a reduction of the residual and genotype by environment interaction variances. In addition, the genotypic variance and heritability of FHB severity at 21 dpi were increased. In summary, including the anthesis date effect in the model lead to a more precise and objective characterization of the level of genetic type II resistance to FHB under field conditions.

In Vitro Wheat Immature Spike Culture Screening Identified Fusarium Head Blight Resistance in Wheat Spike Cultured Derived Variants and in the Progeny of Their Crosses with an Elite Cultivar.

Fusarium head blight (FHB) is a devastating fungal disease of wheat (Triticum aestivum L.). The lack of genetic resources with stable FHB resistance combined with a reliable and rapid screening method to evaluate FHB resistance is a major limitation to the development of FHB resistant wheat germplasm. The present study utilized an immature wheat spike culture method to screen wheat spike culture derived variants (SCDV) for FHB resistance. Mycotoxin concentrations determined by liquid chromatography-tandem mass spectrometry (LC-MS/MS) correlated significantly (P < 0.01) with FHB severity and disease progression during in vitro spike culture. Selected SCDV lines assessed for FHB resistance in a Fusarium field disease nursery in Carman, Manitoba, Canada in 2016 showed significant (P < 0.01) correlation of disease severity to the in vitro spike culture screening method. Selected resistant SCDV lines were also crossed with an elite cv. CDC Hughes and the progeny of F2 and BC1F2 were screened by high resolution melt curve (HRM) analyses for the wheat UDPglucosyl transferase gene (TaUGT-3B) single nucleotide polymorphism to identify resistant (T-allele) and susceptible (G-allele) markers. The progeny from the crosses were also screened for FHB severity using the immature spike culture method and identified resistant progeny grouped according to the HRM genotyping data. The results demonstrate a reliable approach using the immature spike culture to screen for FHB resistance in progeny of crosses in early stage of breeding programs.

Identification and validation of Fusarium head blight resistance QTL in the U.S. soft red winter wheat cultivar ‘Jamestown’

AbstractUse of genetic resistance is one of the most important strategies to manage the devastating disease Fusarium head blight (FHB) in wheat. Numerous quantitative trait loci (QTL) having varying effects on reducing FHB and the mycotoxin deoxynivalenol (DON) accumulation have been reported from Asian, European, or distant sources such as wild relatives of wheat (Triticum aestivum L.). However, coming from nonadapted backgrounds, the incorporation of such QTL into regional breeding programs has often resulted in the simultaneous transfer of other undesirable traits. Therefore, it is important to identify, characterize, and deploy sources of genetic resistance that do not suffer from poor adaptability and/or linkage drag. In the present work, QTL associated with FHB resistance in a high‐yielding, moderately resistant soft red winter wheat cultivar ‘Jamestown’ were mapped and validated. The QTL mapping was done using a recombinant inbred line (RIL) population of Pioneer ‘25R47’ × Jamestown having 186 individuals. Phenotyping over 2 yr at three locations, and genotyping using the 90K single nucleotide polymorphism (SNP) platform identified two new QTL, named QFHB.vt‐1B.1 and QFHB.vt‐1B.2, on the chromosome 1B long arm. The QTL contributed to FHB incidence, FHB severity, Fusarium‐damaged kernels, and DON content. Independent mapping of these QTL using two additional RIL populations of FG95195 × Jamestown (170 RILs) and Jamestown × LA97113UC‐124 (77 RILs) validated their stability and effectiveness in different genetic backgrounds. Kompetitive allele specific polymerase chain reaction (KASP) assays were developed using linked SNPs for marker‐assisted selection of the QTL. These QTL are being used in breeding programs to develop FHB‐resistant, high‐yielding varieties.

Characterization of a novel antifungal protein produced by Paenibacillus polymyxa isolated from the wheat rhizosphere.

Fusarium head blight (FHB) is one of the disasters that seriously harm wheat and other small grain crops. It causes spoilage and mildew of the grain leading to a significant decline in the yield and quality of the grain. This research aimed to isolate antagonistic bacteria to purify antifungal proteins. A strain was isolated from the rhizosphere of healthy wheat in a wheat field affected by a severe FHB epidemic. This isolated strain was tentatively identified as Paenibacillus polymyxa 7F1, which displayed a strong inhibitory effect against several other pathogens. One novel antifungal protein was purified from the P. polymyxa 7F1 and successfully expressed. A crude culture of P. polymyxa 7F1 demonstrated antifungal activity that was stable at a temperature range of 60-90 °C and a pH range of 2.6-9.0. However, the antifungal activity of the P. polymyxa 7F1 was inhibited with proteinase K, trypsin, and neutral protease treatment. A 36 kDa protein with broad-spectrum antifungal activity was purified from the P. polymyxa 7F1. A glycosyl hydrolase domain was identified from this protein through liquid chromatography-mass spectrometry (LC-MS) analysis. A recombinant plasmid pET32a(+)/36kd for prokaryotic expression was constructed, and the renatured p36kd protein demonstrated similar antifungal activity to the 36 kDa protein purified from the P. polymyxa 7F1. A novel antifungal protein produced by P. polymyxa 7F1 was purified and expressed. The recombinant protein showed good antifungal activity as the novel purified protein. The novel antifungal protein provides an effective way to control the Fusarium head blight. © 2020 Society of Chemical Industry.

Chitosan Hydrochloride Decreases Fusarium graminearum Growth and Virulence and Boosts Growth, Development and Systemic Acquired Resistance in Two Durum Wheat Genotypes.

Fusarium head blight (FHB) is a devastating disease for cereals. FHB is managed by fungicides at anthesis, but their efficacy is variable. Conventional fungicides accumulate in the soil and are dangerous for animal and human health. This study assayed the antifungal ability of chitosan hydrochloride against Fusarium graminearum. Chitosan reduced F. graminearum growth and downregulated the transcript of the major genes involved in the cell growth, respiration, virulence, and trichothecenes biosynthesis. Chitosan promoted the germination rate, the root and coleoptile development, and the nitrogen balance index in two durum wheat genotypes, Marco Aurelio (FHB-susceptible) and DBC480 (FHB-resistant). Chitosan reduced FHB severity when applied on spikes or on the flag leaves. FHB severity in DBC480 was of 6% at 21 dpi after chitosan treatments compared to F. graminearum inoculated control (20%). The elicitor-like property of chitosan was confirmed by the up-regulation of TaPAL, TaPR1 and TaPR2 (around 3-fold). Chitosan decreased the fungal spread and mycotoxins accumulation. This study demonstrated that the non-toxic chitosan is a powerful molecule with the potential to replace the conventional fungicides. The combination of a moderately resistant genotype (DBC480) with a sustainable compound (chitosan) will open new frontiers for the reduction of conventional compounds in agriculture.

First Report of Fusarium poae Causing Fusarium Head Blight of Wheat in Georgia, USA.

Fusarium head blight (FHB) is one of the most troublesome fungal diseases challenging US wheat (Triticum aestivum L.) production (Savary et al. 2019). Harmful mycotoxin contamination, primarily due to deoxynivalenol (DON) in the Fusarium-damaged kernels (FDK), can negatively impact human and livestock health (McMullen et al. 1997). Although Fusarium graminearum is the primary causal agent of FHB, several other species including F. poae could pose a risk by producing dangerous mycotoxins such as nivalenol, DON, HT-2, and T-2 (Stenglein 2009). Severe FHB epidemics on wheat have occurred in recent years along with increased corn acreage across the southeast US specifically in Georgia (Ghimire et al. 2020). Five symptomatic wheat heads displaying bleaching symptoms were randomly collected from 19 different fields across 13 counties of Georgia in late spring of 2018. Infected kernels were dipped in 6% sodium hypochlorite for 10 min and rinsed three times with sterilized water. Blot dried kernels were placed on potato dextrose agar (PDA) and incubated for 7 days at 25°C under 12-h photoperiod. Three isolates (GA18W-2.1.6, GA18W-6.1.4, and GA18W-10.2.3) from Terrell, Peach, and Sumter counties exhibited dense, whitish mycelium colony typical of F. poae (Leslie and Summerell 2006). When grown in carboxymethylcellulose broth, isolates produced globose to piriform microconidia (5.1 to 12.4 µm by 4.4 to 11.2 µm) that were aseptate or had a single septation. The morphological identification was further confirmed by DNA sequencing. Single hyphal tip isolates were grown on cellophane overlain on PDA for 10 days. Fungal DNA was extracted using a Qiagen DNeasy Plant Mini Kit. Genomic DNA was sequenced using TEF1 and TEF2 primer pairs that target the translation elongation factor 1-α (EF1-α) locus (O'Donnell et al. 1998). BLASTn query of the obtained sequences of GA18W-2.1.6 (accession no. MT856907) and GA18W-10.2.3 (accession no. MT856909) were identified as F. poae with a 99% sequence homology with GenBank reference accession MK629641, while GA18W-6.1.4 (accession no. MT856908) displayed 100% similarity with F. poae accession KJ947343. Koch's postulates were performed under greenhouse conditions. Three seeds of the FHB susceptible wheat cultivar 'SS8641' were planted in individual cone-tainers with three replications (two cone-tainers/replicate). Wheat plants were vernalized for six weeks and then moved back to the greenhouse. Each F. poae isolate was spray inoculated (50,000 spores/ml) at the flowering stage onto 18-24 wheat heads. A field isolate of F. graminearum was included as a positive control whereas heads mock-inoculated with water were used as a negative control. Inoculated wheat heads were incubated in black plastic bags for 48 hours. Disease severity and FDK were recorded three weeks post inoculation. Disease severities were 6.7% (GA18W-2.1.6), 8.3% (GA18W-10.2.3), and 15.2% (GA18W-6.1.4) compared to 90.0% in the positive control similar to Arrúa et al (2019). No symptoms were observed in the negative control. FDK was 18% (GA18W-2.1.6), 28% (GA18W-10.2.3) and 44% (GA18W-6.1.4). F. poae was re-isolated from the infected heads and found to be morphologically identical to the isolates used for inoculation. To our knowledge, this is the first report of F. poae associated with FHB of wheat in the state of Georgia, USA. F. poae isolates from Georgia might produce mycotoxins in addition to reducing grain yield which needs further study.

Dynamic Remote Sensing Prediction for Wheat Fusarium Head Blight by Combining Host and Habitat Conditions

Remote sensing technology provides a feasible option for early prediction for wheat Fusarium head blight (FHB). This study presents a methodology for the dynamic prediction of this classic meteorological crop disease. Host and habitat conditions were comprehensively considered as inputs of the FHB prediction model, and the advantages, accuracy, and generalization ability of the model were evaluated. Firstly, multi-source satellite images were used to predict growth stages and to obtain remote sensing features, then weather features around the predicted stages were extracted. Then, with changes in the inputting features, the severity of FHB was dynamically predicted on February 18, March 6, April 23, and May 9, 2017. Compared to the results obtained by the Logistic model, the prediction with the Relevance Vector Machine performed better, with the overall accuracy on these four dates as 0.71, 0.78, 0.85, and 0.93, and with the area under the receiver operating characteristic curve as 0.66, 0.67, 0.72, and 0.75. Additionally, compared with the prediction with only one factor, the integration of multiple factors was more accurate. The results showed that when the date of the remote sensing features was closer to the heading or flowering stage, the prediction was more accurate, especially in severe areas. Though the habitat conditions were suitable for FHB, the infection can be inhibited when the host’s growth meets certain requirements.

Is Disease Intensity a Good Surrogate for Yield Loss or Toxin Contamination? A Case Study with Fusarium Head Blight of Wheat.

Sometimes plant pathologists assess disease intensity when they are primarily interested in other response variables, such as yield loss or toxin concentration in harvested products. In these situations, disease intensity potentially could be considered a surrogate of yield or toxin. A surrogate is a variable which can be used instead of the variable of interest in the evaluation of experimental treatments or in making predictions. Surrogates can be measured earlier, more conveniently, or more cheaply than the variable of primary interest, but the reliability or validity of the surrogate must be shown. We demonstrate ways of quantifying two facets of surrogacy by using a protocol originally developed by Buyse and colleagues for medical research. Coefficient-of-determination type statistics can be used to conveniently assess the strength of surrogacy on a unitless scale. As a case study, we evaluated whether field severity of Fusarium head blight (i.e., FHB index) can be used as a surrogate for yield loss and deoxynivalenol (DON) toxin concentration in harvested wheat grain. Bivariate mixed models and corresponding approximations were fitted to data from 82 uniform fungicide trials conducted from 2008 to 2013. Individual-level surrogacy-for predicting the variable of interest (yield or DON) from the surrogate (index) in plots with the same treatment-was very low. Trial-level surrogacy-for predicting the effect of treatment (e.g., mean difference) for the variable of interest based on the effect of the treatment on the surrogate (index)-was moderate for yield, and only low for DON. Challenges in using disease severity as a surrogate for yield and toxin are discussed.