Fusarium diseases, including corn root rot, sheath rot, stalk rot, and ear rot are frequently occurring in maize producing areas of China. Fusarium stalk rot and ear rot are the most serious diseases and often occur at the same time, but it is unclear whether there is a correlation between Fusarium composition and disease occurrence. This study was conducted to clarify the relationship between the two diseases. A total of 49 corn stalk rot samples were collected from 15 regions of eight provinces in China from 2016 to 2018. The pathogens were isolated and identified separately from stalks, ear stems, and kernels. The contents of the fumonisins (FB₁ and FB₂) were detected in kernels. The results showed that the main Fusarium species were found in corn kernels, ear stems and stalks at the same time. The results showed that 1201 strains of Fusarium verticillioides, 668 strains of Fusarium oxysporum, 574 strains of Fusarium graminearum species complex (FGSC), 318 strains of Fusarium equiseti, 95 strains of Fusarium proliferatum, and 40 strains of Fusarium subglutinans were isolated from 1470 corn kernels, 245 ear stems, and 1225 stalks randomly selected from 49 samples. The contamination rate of fumonisins in the 49 samples was 57.1% with an average content of 1.9 μg/g, of which four samples exhibited higher levels as set by the European Commission (4.0 μg/g). These results provide a certain association between stalk rot and ear rot and lay a foundation to study the relationships among Fusarium maize diseases.

The eukaryotic mRNA surveillance pathway, a pivotal guardian of mRNA fidelity, stands at the nexus of diverse biological processes, including antiviral immunity. Despite the recognized function of splicing factors on mRNA fate, the intricate interplay shaping the mRNA surveillance pathway remains elusive. We illustrate that the conserved splicing factor U2 snRNP auxiliary factor large subunit B (U2AF65B) modulates splicing of mRNA surveillance complex, contributing to transcriptomic homeostasis in maize. The functionality of the mRNA surveillance pathway requires ZmU2AF65B-mediated normal splicing of upstream frameshift 3 ( ZmUPF3 ) pre-mRNA, encoding a core factor in this pathway. Intriguingly, sugarcane mosaic virus (SCMV)–coded nuclear inclusion protein a protease (NIa-Pro) hinders the splicing function of ZmU2AF65B. Furthermore, NIa-Pro disrupts ZmU2AF65B binding to ZmUPF3 pre-mRNA, leading to dysregulated splicing of ZmUPF3 transcripts and, consequently, impairing mRNA surveillance, thus facilitating viral infection. Together, this study establishes that splicing governs the mRNA surveillance pathway and identifies a pathogenic protein capable of disrupting this regulation to compromise RNA immunity.

Viruses often establish their own infection by altering host metabolism. How viruses co-opt plant metabolism to support their successful infection remains an open question. Here, we used untargeted metabolomics to reveal that lactate accumulates immediately before and after robust sugarcane mosaic virus (SCMV) infection. Induction of lactate-involved anaerobic glycolysis is beneficial to SCMV infection. The enzyme activity and transcriptional levels of lactate dehydrogenase (LDH) were up-regulated by SCMV infection, and LDH is essential for robust SCMV infection. Moreover, LDH relocates in viral replicase complexes (VRCs) by interacting with SCMV-encoded 6K2 protein, a key protein responsible for inducing VRCs. Additionally, lactate could promote SCMV infection by suppressing plant defense responses. Taken together, we have revealed a viral strategy to manipulate host metabolism to support replication compartment but also depress the defense response during the process of infection.

Abelmoschus manihot (Linn. ) Medicus (A. manihot) is an annual to perennial herb of the Malvaceae okra, mainly distributed in Guangdong, Guangxi, Fujian, Hunan, Hubei provinces. It can not only be used as an ornamental flower, but also has important economic and medicinal value. Last year, 10% A. manihot in 1,000 acres were observed with stalk rot in the Zhongshang Agricultural Industrial Park, 50 meters east of Provincial Highway 235 in Gaoyang County of Hebei province. Internal discoloration of the stem began brown to black discoloration of the vascular system and became hollow, with the mycelium growing on the surface. Stems from symptomatic plants (approximately 5 mm2) were dissected, washed free of soil, then soaked in 75% ethanol for 16 s to surface-sterilize, and 40 s in HgCl2, then rinsed three times in sterile water. After being dried with blotting paper, five pieces were placed on potato dextrose agar (PDA). After cultured 2 or 3 days, five isolates were purified and re-cultured on PDA in the dark at 25°C. The color of the colony was white. The hyphae were radial in PDA, and the aerial hyphae were flocculent, well-developed with luxuriant branches. The colonies were white and floccus, and the aerial hyphae were well developed, branched and without septum on corn meal agar (CMA). The sporangia were large or petal shaped, composed of irregular hyphae, terminal or intermediate , with the size of (31.6-88.4) μm ×(12.7- 14.6) μm. Vesicles were spherical, terminal or intermediate, ranging from 14.6 to 18.5μm. Oogonia were globose, terminal and smooth which stipe was straight. Antheridia were clavate or baggy and mostly intercalary, sometimes terminal. Oospores were aplerotic, 21.5 to 30.0 μm in diameter, 1.6 to 3.1 μm in wall thickness. The isolates morphological characteristics were consistent with P. aphanidermatum (van der Plaats-Niterink 1981, Wu et al. 2021 ). To identify the isolates, universal primers ITS1/ITS4 (White et al. 1993) were used for polymerase chain reaction–based molecular identification. The amplification region was sequenced by Sangon Biotech (Shanghai, China) and submitted to GenBank (MW819983). BLAST analysis showed that the sequence was 100% identical to Pythium aphanidermatum. Pathogenicity tests were conducted 3 times, with 4 treatments and 2 controls each time. The plants treated were 6 months old. Then the hyphae growing on PDA for 7 days were cut into four pieces. Next, they were inoculated into the soil of the A. manihot. Negative control was inoculated only with PDA for 7 days ( Zhang et al. 2000). The plants were then placed in a greenhouse under 28°C, 90% relative humidity. After inoculated 20 to 30 days, the infected plants showed stalk rot, the same symptoms as observed on the original plants. The control plants didn’t display symptoms. Pythium aphanidermatum was re-isolated from infected stems and showed the same characteristics as described above and was identical in appearance to the isolates used to inoculate the plants. To our knowledge, this is the first report of Pythium aphanidermatum infecting A. manihot stem and causing stalk rot in China. It may become a significant problem for A. manihot. Preliminary management practices are needed for reducing the cost and losses of production.

Salicylic acid (SA) plays a crucial role in the defence strategies of plants against fungal pathogens. To circumvent plant immunity, pathogens use metabolic enzymes such as salicylate hydroxylase to degrade SA, thereby facilitating successful pathogenicity after infection. This phenomenon has not been previously reported in Cochliobolus heterostrophus . Our study demonstrates that high concentrations of SA can inhibit both growth and spore germination; however, at concentrations below 1 mM, SA does not significantly impact the growth and spore germination of C . heterostrophus , which is capable of metabolising exogenously supplied SA. Transcriptome and LC–MS analyses indicated that C . heterostrophus metabolises exogenous SA via the gentisic acid (GA) pathway, involving genes such as 5‐salicylate hydroxylase ( ChnagG ). Prokaryotic expression of ChnagG confirmed its ability to convert SA into GA. Additionally, we created ChnagG gene deletion and complementation mutants, revealing that ChnagG influences melanin synthesis and the pathogenicity of C . heterostrophus . Analysis of the SA signalling pathway in plants during fungal infection indicated that the ChnagG knockout mutant did not alter the synthesis of SA in its host maize; however, it led to the upregulation of the downstream signalling pathway ZmPR1 gene compared to the wild type. These findings suggest that C . heterostrophus obstructs the immune signalling pathway of maize through SA metabolism, thereby enhancing its infection and pathogenicity. This study lays the groundwork for further elucidating the mechanisms underlying the interaction between maize and C . heterostrophus .