The distribution frequency of pathogenic fungi associated with root and crown rot of winter wheat (Triticum aestivum) from 104 fields in the North China Plain was determined during the period from 2013 to 2016. The four most important species identified were Bipolaris sorokiniana (24.0% from roots; 33.7% from stems), Fusarium pseudograminearum (14.9% from roots; 27.8% from stems), Rhizoctonia cerealis (1.7% from roots; 4.4% from stems), and Gaeumannomyces graminis var. tritici (9.8% from roots; 4.4% from stems). We observed that the recovered species varied with the agronomic zone. Fusarium pseudograminearum was predominant in regions 1 and 3, whereas F. graminearum, F. acuminatum, and R. cerealis were predominant in regions 2 and 4. The incidence of F. pseudograminearum and R. cerealis was significantly different between regions 1 and 4, while no significant association was found in the distribution of the other species and the agronomic zones. A negative correlation between the frequency of occurrence of F. pseudograminearum and mean annual precipitation during 2013–2016 (r = −0.71; P < 0.01) in the North China Plain and a positive correlation between the mean annual precipitation during 2013–2016 and the frequency of occurrence of F. asiaticum (r = 0.74; P < 0.01) were observed. Several Fusarium species were also found with low frequencies of ~2.1%−3.4 % (F. graminearum, F. acuminatum, and F. sinensis) and ~0.1%−1.3% (F. equiseti, F. oxysporum, F. proliferatum, F. culmorum, F. avenaceum, and F. asiaticum). In more than 93% of the fields, from the root and crown tissues of wheat, two or more root and crown rot species were isolated. The coexistence of Fusarium spp. and B. sorokiniana in one field (65.4%) or in individual plants (11.6%) was more common than for the other species combinations. Moreover, this is the first report on the association between F. sinensis and root and crown rot of wheat. Our results would be useful in the framing guidelines for the management of root and crown rot fungi in wheat in different agronomic zones of the North China Plain.

Chaetomium globosum is a common plant endophytic fungi that exhibits great biocontrol potential in plant disease. Fusarium crown rot (FCR) is an important disease in wheat that seriously threatens wheat production worldwide. The control effect of C. globosum against wheat FCR remains unclear. In this study, we introduced an identified C. globosum 12XP1-2-3 and tested its biological control potential against wheat FCR. The hypha and fermentation broth exhibited an antagonistic effect against Fusarium pseudograminearum. Results from indoor experiments showed that C. globosum 12XP1-2-3 might delay the onset of symptoms of brown stem base and significantly reduced the disease index (37.3%). Field trials showed that wheat seeds coated with a spore suspension of 12XP1-2-3 grew better than the control seeds, had control effects of 25.9–73.1% on FCR disease, and increased wheat yield by 3.2–11.9%. Analysis of rhizosphere microorganisms revealed that seeds coated with C. globosum (‘Cg’ treatment) had a greater effect on fungal rather than on bacterial alpha diversity and may improve the health state of rhizosphere microorganisms, as reflected by the significantly increased fungal Shannon index at Feekes 11 and the increased complexity of the bacterial co-occurrence network but decreased complexity of the fungal network. Moreover, the accumulation of beneficial bacteria such as Bacillus and Rhizobium at Feekes 3, and Sphingomonas at Feekes 7 in the ‘Cg’ treatment may be the important contributions to healthier wheat growth state, significantly reduced relative abundance of Fusarium at Feekes 11, and reduced occurrence of FCR disease. These results provide a basis for further research on the mechanism of action of C. globosum and its application in the biological control of FCR in the field.

In the main wheat production area of China (the Huang Huai Plain [HHP]), both Fusarium graminearum and Fusarium asiaticum, the causal agents of Fusarium head blight (FHB), are present. We investigated whether the relative prevalence of F. graminearum and F. asiaticum is related to cropping systems and/or climate factors. A total of 1,844 Fusarium isolates were obtained from 103 fields of two cropping systems: maize–wheat and rice–wheat rotations. To maximize the differences in climatic conditions, isolates were sampled from the north and south HHP regions. Based on the phylogenetic analysis of EF-1α and Tri101 sequences, 1,207 of the 1,844 isolates belonged to F. graminearum, and the remaining 637 isolates belonged to F. asiaticum. The former was predominant in the northern region: 1,022 of the 1,078 Fusarium isolates in the north were F. graminearum. The latter was predominant in the southern region: 581 of the 766 Fusarium isolates belonged to F. asiaticum. Using an analysis based on generalized linear modeling, the relative prevalence of the two species was associated more with climatic conditions than with the cropping system. F. graminearum was associated with drier conditions and cooler conditions during the winter but also with warmer conditions in the infection and grain-colonization period as well as with maize–wheat rotation. The opposite was true for F. asiaticum. Except for the 15-acetyldeoxynvalenol genotype, the trichothecene chemotype composition of F. asiaticum differed between the two cropping systems. The 3-acetyldeoxynivalenol genotype was more prevalent in the maize–wheat rotation, whereas the nivalenol genotype was more prevalent in the rice–wheat rotation. The results also suggested that environmental conditions in the overwintering period appeared to be more important than those in the infection, grain-colonization, and preanthesis sporulation periods in affecting the relative prevalence of F. graminearum and F. asiaticum. More research is needed to study the effect of overwintering conditions on subsequent epidemic in the following spring.

Fusarium crown rot (FCR) is an important and devastating disease of wheat (Triticum aestivum) caused by the fungus Fusarium pseudograminearum and related pathogens. Using two distinct susceptible cultivars, we investigated the isolation frequencies of F. pseudograminearum and quantified its biomass accumulation and the levels of the associated toxins deoxynivalenol (DON) and DON-3-glucoside (D3G) in inoculated field-grown wheat plants. We detected F. pseudograminearum in stem, peduncle, rachis, and husk tissues, but not in grains, whereas DON and D3G accumulated in stem, rachis, husk, and grain tissues. Disease severity was positively correlated with the frequency of pathogen isolation, F. pseudograminearum biomass, and mycotoxin levels. The amount of F. pseudograminearum biomass and mycotoxin contents in asymptomatic tissue of diseased plants were associated with the distance of the tissue from the diseased internode and the disease severity of the plant. Thus, apparently healthy tissue may harbor F. pseudograminearum and contain associated mycotoxins. This research helps clarify the relationship between F. pseudograminearum occurrence, F. pseudograminearum biomass, and mycotoxin accumulation in tissues of susceptible wheat cultivars with or without disease symptoms, providing information that can lead to more effective control measures.

Maize yellow mosaic virus (MaYMV), a new species in the genus Polerovirus (family Solemoviridae), was reported in maize for the first time in China in 2016 (Chen et al., 2016). Later, MaYMV was found in other gramineous species including sugarcane (Saccharum spp.), itch grass (Rottboellia cochinchinensis), millet (Panicum miliaceum) and sorghum (Sorghum bicolor) in several countries in Asia, Africa, and South America (Yahaya et al. 2017; Lim et al. 2018; Sun et al. 2019; Nithya et al. 2021). Here, we report its presence in cultivated wheat (Triticum aestivum), detected using high-throughput sequencing (HTS). In 2021 in Henan Province, China, wheat plants with virus-like symptoms such as yellowing, stunting, and vein clearing were collected from fields in Luoyang (three plants, cv. Luohan 6), Nanyang (two plants, cv. Xinong 979), and Anyang (one plant, cv. Bainong 207). RNA was extracted from symptomatic leaves of each plant sample using TRIzol reagent (Invitrogen, Carlsbad, CA, USA). From each sample, 1 μg of RNA was mixed into a single pool to construct an rRNA-depleted RNA-seq library using a TruSeq RNA Sample Prep Kit for sequencing on the HiSeq X-Ten platform as 150-bp paired-end reads. A total of 88,892,804 clean reads were obtained after removing adaptor sequences and low-quality reads. Reads were mapped against the wheat genome database (IWGSC RefSeq v2.1) using the hisat2 v2.0.5 program. Remaining sequences were de novo assembled into contigs with Trinity program. Contigs from barley yellow dwarf virus PAV (BYDV-PAV), and BYDV-GAV were identified using a Blast search of the NCBI nr/nt database, all previously reported in wheat in China. Interestingly, four contigs with high similarity (>95%, at the nucleotide level) to MaYMV were also identified. Using the sequence of MaYMV isolate Yunnan 9 (KU291105) as reference, a total of 1,260 reads from HTS mapped to the virus genome with a coverage of 75.5% (average coverage: 33.5×). For verifying the presence of MaYMV in the source samples, MaYMV-specific primers MV-fw/MV-rev were designed to amplify the 513-bp fragment of the RdRp gene by a reverse transcription-polymerase chain reaction (RT-PCR) using the original total RNA. RT-PCR assay revealed that only 1 of the 6 samples tested positive for MaYMV, while the remaining plants were positive for other viruses (BYDV-PAV and BYDV-GAV that produce similar symptoms; viral-specific primers as previously described [Liu et al., 2020]). A subsequent survey of 17 winter wheat fields in 2021 confirmed that 6 of 286 wheat samples with virus symptoms were infected with MaYMV; 4 positives were from Linfen, Shanxi Province and 1 each from Yuanyang and Anyang, Henan Province. The full genome of wheat-infecting MaYMV isolate Anyang1 was then sequenced using RT-PCR with Sanger sequencing technology; the genomic sequence (5,642 nt) was deposited in GenBank as accession OK331995. BLASTn search showed that the complete genome sequence of this virus is 99.0%, 98.9% and 98.7% identical to isolate SC1 (MK652148), Guizhou1 (KU291107) and Yunnan 11 (KU248489), respectively. Also, the MaYMV isolate Anyang1 obtained in this study clustered with other MaYMV isolates in a phylogenetic analysis based on MaYMV full genomes. To the best of our knowledge, this is the first report of MaYMV in wheat worldwide. The presence of MaYMV in wheat is important because winter wheat could serve as an overwintering reservoir of MaYMV and perpetuate the virus in wheat-maize rotation systems in northern China.

Both wheat powdery mildew severities and nitrogen input levels can lead to changes in spectral reflectance, but they have been rarely studied simultaneously for their effect on spectral reflectance. To determine the effects and influences of different nitrogen input levels on monitoring wheat powdery mildew and estimating yield by near-ground hyperspectral remote sensing, Canopy hyperspectral reflectance data acquired at Feekes growth stage (GS) 10.5.3, 10.5.4, and 11.1 were used to monitor wheat powdery mildew and estimate grain yield under different nitrogen input levels during the 2016–2017, 2017–2018, 2018–2019 and 2019–2020 seasons. The relationships of powdery mildew and grain yield with vegetation indices (VIs) derived from spectral reflectance data across the visible (VIS) and near-infrared (NIR) regions of the spectrum were studied. The relationships of canopy spectral reflectance or first derivative spectral reflectance with powdery mildew did not differ under different nitrogen input levels. However, the dynamics of VIs differed in their sensitivities to nitrogen input levels, disease severity, grain yield, The area of the red edge peak (Σdr_{680–760 nm}) was a better overall predictor for both disease severity and grain yield through linear regression models. The slope parameter estimates did not differ between the two nitrogen input levels at each GSs. Hyperspectral indices can be used to monitor wheat powdery mildew and estimate grain yield under different nitrogen input levels, but such models are dependent on GS and year, further research is needed to consider how to incorporate the growth stage and year-to-year variation into future applications.