Rice production faces new challenges from emerging diseases due to intensive cultivation practices and climate warming in China. A new rice leaf bacterial disease has recently occurred in Northeast China. The symptoms of the disease are similar to those of bacterial leaf blight. Disease lesions spread along leaf edges and are later dried up due to water loss. In this study, 17 bacterial isolates were identified as the causal agents of the new disease following Koch’s postulates. These strains are categorized into two groups based on colony morphology and molecular characterization. Phylogenetic analysis using the five housekeeping genes leuS, gyrB, fusA, pyrG, and rplB reveals that the two groups of the isolates belong to Pantoea ananatis and P. eucalypti, respectively. The new rice disease is caused by P. ananatis, P. eucalypti, or a combination of both bacterial species. A complete genome map has also been assembled for P. eucalypti. Meanwhile, some important virulence factors have been predicted based on gene annotation and determination of extracellular enzymes. Collectively, this study represents the first report of a new rice leaf disease caused by P. eucalypti and the first high-quality genome assembly of P. eucalypti that infects rice leaves.

Frogeye leaf spot (FLS), caused by Cercospora sojina, is a significant disease affecting soybean crops economically. Seed inspection plays a vital role in reducing the incidence of this disease. However, limited research has been conducted on the fast and accurate identification of C. sojina in soybean seeds. In this study, we developed a rapid diagnostic method to detect C. sojina in soybean seeds using loop-mediated isothermal amplification (LAMP) assays. A software application called K-mer Elimination by Cross-reference was utilized to identify specific sequences belonging to C. sojina. The LAMP primer set designed based on the selected specific sequence proved to be highly specific, distinguishing C. sojina from other common soybean pathogens and two maize pathogens of the Cercospora genus. The primer set exhibited remarkable sensitivity, detecting sixteen copies per reaction, which is approximately 1,000 times more sensitive than conventional PCR. The LAMP assays were applied for direct inspection of soybean seeds, revealing that twenty of the thirty tested soybean varieties were contaminated with C. sojina, with contamination rates ranging from 10% to 60%. The seeds of TongNong 943 and JiNong 38 had the highest contamination rate at 60%. Seeds coated with fungicide showed a reduced disease incidence, as demonstrated on PDA medium and in soil pots. In summary, our results indicate that rapid seed diagnosis using LAMP assays can effectively screen out seeds carrying C. sojina, providing a preventive strategy in managing FLS disease.

Northern corn leaf blight (NCLB), caused by Exserohilum turcicum, is one of the most devastating foliar diseases of maize. Rapid and accurate diagnosis for this disease is urgently needed but still limited. Here, we establish a field-deployable diagnostic method to detect E. turcicum based on loop-mediated isothermal amplification (LAMP) assays. A software application called K-mer Elimination by Cross-reference was used to search for the specific sequences belonging to E. turcicum by comparing the whole genome sequence between E. turcicum and other known maize pathogens. Five LAMP primer sets were designed based on specific and single-copy fragments of E. turcicum. Post-LAMP analyses indicated that only the primer set, Et9468_set1, was the most suitable, producing a ladder-like amplification pattern in the agarose gel electrophoresis and a strong fluorescence signal in the presence of SYBR Green I. The LAMP assay using Et9468_set1 primers demonstrated a high level of specificity in distinguishing E. turcicum from six other common fungal pathogens of maize, as well as 12 more fungal and oomycete strains including the epiphytic fungi from maize leaves and other crop pathogens. Moreover, it exhibited remarkable sensitivity by detecting five copies per reaction, which was approximately 10⁴ times more sensitive compared with conventional PCR. The LAMP assay successfully detected E. turcicum in field maize leaves without DNA extraction, demonstrating its suitability for rapid on-spot detection of NCLB. Our study provides a direct LAMP diagnostic method to detect E. turcicum, which enables on-site pathogen detection in the field and the development of preventive strategies for NCLB management.

Trichogramma wasps, egg parasitoids widely used to control lepidopteran pests, have long eluded in-depth molecular mechanistic studies due to their minute size and genetic tool scarcity. While previous RNAi efforts were restricted to T. dendrolimi, we developed the first cross-species RNAi system for both T. dendrolimi and the previously intractable T. ostriniae. Temporal expression profiling identified white and laccase 2 as stage-specific RNAi targets, peaking during prepupal/pupal stages, which were tested across species and developmental stages using microinjection and soaking dsRNA delivery methods. Survival analysis prioritized soaking for T. dendrolimi prepupae/pupae, while microinjection was essential for T. ostriniae to bypass prepupal mortality during soaking. Concentration-dependent RNAi targeting the white gene achieved 85.61% transcript reduction in T. dendrolimi via soaking and 89.36% in T. ostriniae via microinjection at 2000 ng/μL, correlating with 64.06% and 32.09% white-eyed pupae, causing a significant reduction in eye pigments. For the laccase 2 gene, soaking at 2000 ng/μL induced 88.35% transcript reduction in T. dendrolimi and 73.31% in T. ostriniae, leading to incomplete cuticle tanning and sclerotization. This study resolves the long-standing challenge of genetic manipulation in Trichogramma wasps, providing a universally applicable framework to decipher parasitoid–host interactions at the molecular scale, which is useful for sustainable pest management strategies.

Rice false smut caused by Ustilaginoidea virens has become one of the most important rice diseases. U. virens specifically infects rice florets through stamen filaments. However, it is mysterious how U. virens inhibits floral immunity for successful colonization. Here, we show that a small cysteine-rich effector SCRE9 is a key virulence factor in U. virens . Expression of SCRE9 in rice not only suppresses immune responses and false smut resistance, but also significantly increases expression of expansin and gibberellin (GA) biosynthetic genes and GA content in young rice panicles. We further demonstrate that OsSIP1 (SCRE9-interacting protein 1) in rice is targeted by SCRE9 and interacts with the OsMADS63 and OsMADS68 transcription factors that transcriptionally regulate the GA synthesis gene GA3ox1 . Interestingly, the chloroplast-localized OsSIP1 recruits OsMADS63/68 into the chloroplast. SCRE9 causes OsSIP1 to be translocated into the nucleus, thereby releasing OsMADS63/68 from the chloroplast into the nucleus to promote GA3ox1 transcription. Therefore, SCRE9 promotes GA biosynthesis and expression of expansins in rice florets, thus loosening cell walls and overcoming the physical barrier during U. virens infection. The finding uncovers an unidentified floret infection strategy that offsets the deficiency in cell wall degrading ability in the unique floret colonizing fungus.