The root-knot nematode Meloidogyne graminicola is an important pathogen in rice, causing huge yield losses annually worldwide. Details of the interaction between rice and M. graminicola and the resistance genes in rice still remain unclear. In this study, proteome-wide analyses of the compatible interaction of the japonica rice cultivar “Nipponbare” (NPB) with M. graminicola were performed. In total, 6072 proteins were identified in NPB roots with and without infection of M. graminicola by label-free quantitative mass spectrometry. Of these, 513 specifically or significantly differentially expressed proteins were identified to be uniquely caused by nematode infection. Among these unique proteins, 99 proteins were enriched on seven Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. By comparison of protein expression and gene transcription, LOC_Os01g06600 (ACX, a glutaryl-CoA dehydrogenase), LOC_Os09g23560 (CAD, a cinnamyl-alcohol dehydrogenase), LOC_Os03g39850 (GST, a glutathione S-transferase) and LOC_Os11g11960 (RPM1, a disease resistance protein) on the alpha-linolenic acid metabolism, phenylpropanoid biosynthesis, glutathione metabolism and plant–pathogen interaction pathways, respectively, were all associated with disease defense and identified to be significantly down-regulated in the compatible interaction of NPB with nematodes, while the corresponding genes were remarkably up-regulated in the roots of a resistant rice accession “Khao Pahk Maw” with infection of nematodes. These four genes likely played important roles in the compatible interaction of rice with M. graminicola. Conversely, these disease defense-related genes were hypothesized to be likely involved in the resistance of resistant rice lines to this nematode. The proteome-wide analyses provided many new insights into the interaction of rice with M. graminicola.

The distribution range of root-knot nematode Meloidogyne graminicola is rapidly expanding, posing a severe threat to rice production. In this study, the sequences of cytochrome oxidase subunit I (COI) genes of rice M. graminicola populations from all reported provinces in China were amplified and sequenced by PCR. The distribution pattern and phylogenetic tree showed that all 54 M. graminicola populations in China have distinct geographical distribution characteristics; specifically, cluster 1 (southern China), cluster 2 (central south and southwest China), and cluster 3 (central and eastern China). The high haplotype diversity (Hd = 0.646) and low nucleotide diversity (π = 0.00682), combined with the negative value of Tajima’s D (−1.252) and Fu’s Fs (−3.06764), suggested that all nematode populations were expanding. The existence of high genetic differentiation (Fst = 0.5933) and low gene flow (Nm = 0.3333) indicated that there was a block of gene exchange between most populations. Mutation accumulation with population expansion might be directly responsible for the high genetic differentiation; therefore, the tested nematode population showed high within-group genetic variation (96.30%). The haplotype Hap8 was located at the bottom of the network topology, with the widest distribution and the highest frequency (59.26%), indicating that it was the ancestral haplotype. The populations in cluster 3 were newly invasive according to the lowest frequency of occurrence of Hap8, the highest number of endemic haplotypes, and the highest total haplotype frequency (60%). In contrast, cluster 1 having the highest genetic diversity (Hd = 0.772, π = 0.01127) indicated that it was the most primitive. Interestingly, the highest gene flow (Nm > 1), lowest genetic differentiation (Fst ≤ 0.33), and closest genetic distance (0.000) only occurred between the Guangdong/Hainan population and others, which suggested that there might be channels for gene exchange between them and that long-distance dispersal occurred. This suggestion is further confirmed by the weak correlation between genetic distance and geographical distance. Based on these data, a hypothesis can be drawn that M. graminicola populations in China were spreading from south to north, specifically from Guangdong and Hainan Provinces to other regions. Natural selection (including anthropogenic) and genetic drift were the main drivers of their evolution. Coincidentally, this hypothesis was consistent with the gradual warming trend and the chronological order of reporting these populations. The main factors influencing current M. graminicola population expansion and distribution patterns might be geography, climate, long-distance seedling transport, interregional operations of agricultural machinery, and rotation mode. It reminds human beings of the necessity to be vigilant about preventing nematode disease according to local conditions all year round.

Rice (Oryza sativa) is an important food crop in China and root-knot nematode Meloidogyne graminicola has been one of the most important diseases on rice in recently five years (Ju et al. 2020). In August 2020, rice plants were found to be maldeveloped, yellow leaves and hooked root tips in an irrigated paddy field of Yuanyang County, Xinxiang City, Henan Province. Fifty rice plants were randomly collected and 84.0 percent plants were infected with root-knot nematodes, with root-gall index of 56.0. Then nematodes from rice roots were isolated with 100-μm and 25-μm sieves. A large number of females, some third-stage juveniles (J3s), and a small number of males of Meloidogyne spp. were found in root galls of all samples after dissected, and then were identified and measured under the microscope. In females (n = 20), the perineal pattern was dorsoventrally oval with low and round dorsal arch, and the lateral field was not obvious or absent, striae are usually smooth, with occasional short and irregular striatal fragmentation. The morphological data of females are as follows: body length (BL) = 516.9 ± 72.5 μm (424.2 to 611.6 μm), body width (BW)= 328.4 ± 80.7 μm (232.1 to 437.4 μm), stylet length = 11.2 ± 1.3 μm (7.7 to 13.9 μm), dorsal pharyngeal gland orifice to stylet base (DGO) = 3.9 ± 0.5 μm (3.2 to 4.5 μm), vulval slit length = 24.3 ± 4.6 μm (15.2 to 31.4 μm), vulval slit to anus distance = 16.2 ± 2.5 μm (10.1 to 20.2 μm). Males are long cylindrical, wormlike, with a short round tail. Morphological measurements of males (n = 20) were BL = 1,218.0 ± 150.7μm (1,085.7 to 1,692.2 μm), BW = 34.2 ± 4.6 μm (28.5 to 39.7 μm), stylet = 17.4 ± 0.7 μm (15.9 to 19.3 μm), DGO = 3.6 ± 0.7 μm (2.5 to 4.5 μm), tail = 10.8 ± 2.1 μm (8.0 to 14.8 μm), spicule = 30.3 ± 2.6 μm (24.7 to 36.3 μm). The egg masses from the females were incubated at 28℃ for 48 hours. Measurements of J2s (n = 20) were BL = 444.2 ± 37.8 μm (315.7 to 547.5 μm), BW = 21.2 ± 2.7 μm (16.7 to 26.4 μm), stylet = 14.2 ± 0.3 μm (13.6 to 14.8 μm), DGO = 3.5 ± 0.5 μm (2.7 to 4.5 μm), tail = 70.8 ± 5.1 μm (61.3 to 80.8 μm), hyaline tail length = 21.0 ± 2.5 μm (16.3 to 26.1 μm). These morphological features are consistent with the original description by Golden and Birchfield (1965). DNA of a single female from each sample was extracted for molecular identification. Primer pairs D2A/D3B (5´-ACAAGTACCGTGAGGGAAAGTTG-3´/ 5´-TCGGAAGGAACCAGCTACTA-3´) (De Ley et al. 1999) and the species-specific primers Mg-F3/Mg-R2 (5'-TTATCGCATCATTTTATTTG-3'/ 5'-CGCTTTGTTAGAAAATGACCCT-3') (Htay et al. 2016) were used to amplify D2/D3 region of 28S RNA and the internal transcribed spacer (ITS) region, respectively. The amplified sequences of D2/D3 region (GenBank MW490724, 766 bp) shared 99.9% and 99.7% homology with the sequences of M. graminicola (MN647592, MT576694) isolated from Guangxi and Anhui Province (Ju et al. 2020), respectively, while ITS region sequences (MW487239, 369 bp) shared 100% and 99.7% homology to M. graminicola isolate GXL3 (MN636702) and FQJJ01 (MT159690), respectively. In order to verify the pathogenicity of nematodes, about 300 J2s were inoculated on ten 14-week-old rice (Oryza sativa cv. Nipponbare) planted in pots with sterilized sandy soil, respcectively, and maintained in a greenhouse at 28°C/26°C with a 16h/8h light/dark photoperiod and 75% relative humidity. At 14 days post inoculation, obvious symptoms of hook galls were observed on roots in all inoculated rice plants, and females and males in the same shape as the collected samples were found in the root galls under the stereoscopic microscope. No symptoms were observed on non-inoculated rice plants. After 28 days, the growth of the inoculated rice plants was significantly worse than that of uninoculated ones, with yellow leaves and short plants. These results confirmed the pathogenicity of M. graminicola on rice and it indicated that M. graminicola was already spread from the main rice-producing areas to the wheat and rice rotation areas. To our knowledge, this is the first report of M. graminicola in the Henan Province of China.

Introduction: Tomato bacterial wilt (TBW) is a destructive soil-borne bacterial infection caused by Ralstonia solanacearum. Various nanoparticles have been employed as antibacterial agents to manage TBW via soil application. However, research on the effects of nanoparticles on plant endophytes remains limited.Methods: Here, an analysis of the endophytic bacterial community was performed on healthy and infected tomatoes that were treated with Cu-Ag nanoparticles and thiodiazole-copper via high-throughput 16S rRNA gene amplicon sequencing.Results: The relative abundance levels of beneficial bacteria, including Acidobacteriota, Firmicutes, Actinobacteriota, and Myxococcota, were higher in infected tomato roots treated with Cu-Ag nanoparticles compared with thiodiazole-copper. Functional predictions show that Cu-Ag nanoparticles may affect pyruvate metabolism, oxidative phosphorylation, purine metabolism, carbon metabolism, secondary metabolite production, and the metabolic pathways associated with microbial communities.Discussion: These results could reveal the mechanism by which nanoparticles influence the endophytic microbiomes of plant roots and direct the rational application of nanoparticlesin sustainable agriculture.

Bacterial leaf blight (BLB) is a destructive disease caused by Xanthomonas oryzae pv. oryzae (Xoo). It has been proven that BLB adversely influences the growth and production of rice, resulting in substantial losses in yield. Nanoparticle–antimicrobial compounds possess excellent physicochemical properties, which have generated groundbreaking applications in protecting rice against BLB attacks. However, there is less research focused on the interaction between nanoparticles and the microbiome of BLB rice leaves, particularly the structure and function of endophytic bacteria, which are essential to plant health and pathogenesis. Therefore, the study explored how Cu-Ag nanoparticles influenced the endophytic bacteria’s composition and functions in healthy and BLB rice leaves. The data demonstrated that the relative abundance of beneficial bacteria, Burkholderiales, Micrococcales, and Rhizobiales, increased after the introduction of Cu-Ag nanoparticles on the leaves of BLB rice. The examination of PAL activity demonstrated that nanoparticles limited the spread of Xoo in rice leaves. Furthermore, endophytic community functional prediction demonstrated that nanoparticles may regulate the physiological process associated with potential stress resistance and growth-promoting function in the endophytic communities. This investigation may enhance the understanding of interactions between nanoparticles and the composition of rice endophytic microbiome, which can contribute to the exploration and application of nanomaterials in crop pathogen management.

Background Potassium (K), an important nutrient element, can improve the stress resistance/tolerance of crops. The application of K in resisting plant parasitic nematodes shows that the K treatment can effectively reduce the occurrence of nematode diseases and increase crop yield. However, data on K₂SO₄ induced rice resistance to Meloidogyne graminicola are still lacking. To evaluate rice resistance against M. graminicola induced by K2SO4 and to further clarify its mechanism is essential for the rational use of K fertilizer to ensure the safety of rice production.Results In this work, K₂SO₄ treatment effectively reduced the numbers of both galls and nematodes in rice roots, and delayed the development of nematodes to the adult stage. Rather than by affecting the attractiveness of roots to nematodes and the morphological phenotype of giant cells at feeding sites, such effect was achieved by rapidly stimulating hydrogen peroxide (H₂O₂) accumulation, increasing callose deposition. Meanwhile, such induced resistance required the active participation of the potassium channel OsAKT1 and the potassium transporter OsHAK5. The numbers of both galls and nematodes were higher in both gene deficient plants than that in the wild-type plants, and the K₂SO₄-induced resistance showed weaker in the defective plants than in the wild-type plants.Conclusions K₂SO₄ treatment effectively induces rice resistance to root-knot nematode M. graminicola. The mechanism of inducing resistance is to prime the basic defense of rice, up-regulating the expression of resistance-related genes and with the involvement of K⁺ channel and transporter. These laid a foundation for further study on the mechanism of rice to defense against root-knot nematodes and the effective use of potassium fertilizer to improve rice resistance against nematodes in the field.