Brown Planthopper Infestation Research Articles

Silencing an ATP-Dependent Caseinolytic Protease Proteolytic Subunit Gene Enhances the Resistance of Rice to Nilaparvata lugens.

The ATP-dependent caseinolytic protease (Clp) system has been reported to play an important role in plant growth, development, and defense against pathogens. However, whether the Clp system is involved in plant defense against herbivores remains largely unclear. We explore the role of the Clp system in rice defenses against brown planthopper (BPH) Nilaparvata lugens by combining chemical analysis, transcriptome, and molecular analyses, as well as insect bioassays. We found the expression of a rice Clp proteolytic subunit gene, OsClpP6, was suppressed by infestation of BPH gravid females and mechanical wounding. Silencing OsClpP6 enhanced the level of BPH-induced jasmonic acid (JA), JA-isoleucine (JA-Ile), and ABA, which in turn promoted the production of BPH-elicited rice volatiles and increased the resistance of rice to BPH. Field trials showed that silencing OsClpP6 decreased the population densities of BPH and WBPH. We also observed that silencing OsClpP6 decreased chlorophyll content in rice leaves at early developmental stages and impaired rice root growth and seed setting rate. These findings demonstrate that an OsClpP6-mediated Clp system in rice was involved in plant growth-defense trade-offs by affecting the biosynthesis of defense-related signaling molecules in chloroplasts. Moreover, rice plants, after recognizing BPH infestation, can enhance rice resistance to BPH by decreasing the Clp system activity. The work might provide a new way to breed rice varieties that are resistant to herbivores.

Combined miRNA and mRNA sequencing reveals the defensive strategies of resistant YHY15 rice against differentially virulent brown planthoppers.

The brown planthopper (BPH) poses a significant threat to rice production in Asia. The use of resistant rice varieties has been effective in managing this pest. However, the adaptability of BPH to resistant rice varieties has led to the emergence of virulent populations, such as biotype Y BPH. YHY15 rice, which carries the BPH resistance gene Bph15, exhibits notable resistance to biotype 1 BPH but is susceptible to biotype Y BPH. Limited information exists regarding how resistant rice plants defend against BPH populations with varying levels of virulence. In this study, we integrated miRNA and mRNA expression profiling analyses to study the differential responses of YHY15 rice to both avirulent (biotype 1) and virulent (biotype Y) BPH. YHY15 rice demonstrated a rapid response to biotype Y BPH infestation, with significant transcriptional changes occurring within 6 hours. The biotype Y-responsive genes were notably enriched in photosynthetic processes. Accordingly, biotype Y BPH infestation induced more intense transcriptional responses, affecting miRNA expression, defenserelated metabolic pathways, phytohormone signaling, and multiple transcription factors. Additionally, callose deposition was enhanced in biotype Y BPH-infested rice seedlings. These findings provide comprehensive insights into the defense mechanisms of resistant rice plants against virulent BPH, and may potentially guide the development of insect-resistant rice varieties.

Brown planthopper infestation on rice reduces plant susceptibility to Meloidogyne graminicola by reducing root sugar allocation.

Plants are simultaneously attacked by different pests that rely on sugars uptake from plants. An understanding of the role of plant sugar allocation in these multipartite interactions is limited. Here, we characterized the expression patterns of sucrose transporter genes and evaluated the impact of targeted transporter gene mutants and brown planthopper (BPH) phloem-feeding and oviposition on root sugar allocation and BPH-reduced rice susceptibility to Meloidogyne graminicola. We found that the sugar transporter genes OsSUT1 and OsSUT2 are induced at BPH oviposition sites. OsSUT2 mutants showed a higher resistance to gravid BPH than to nymph BPH, and this was correlated with callose deposition, as reflected in a different effect on M. graminicola infection. BPH phloem-feeding caused inhibition of callose deposition that was counteracted by BPH oviposition. Meanwhile, this pivotal role of sugar allocation in BPH-reduced rice susceptibility to M. graminicola was validated on rice cultivar RHT harbouring BPH resistance genes Bph3 and Bph17. In conclusion, we demonstrated that rice susceptibility to M. graminicola is regulated by BPH phloem-feeding and oviposition on rice through differences in plant sugar allocation.

Gapless Genome Assembly of Rice ZH8015 and Preliminary Multi-omics Analysis to Investigate ZH8015 Responses against Brown Planthopper Infestation

Accurate genomic information is essential for advancing genetic breeding research in specific rice varieties. This study presents a gapless genome assembly of indica rice cultivar ZhongHui 8015 (ZH8015) using PacBio HiFi, Hi-C, and ONT (Oxford Nanopore Technologies) ultra-long sequencing technologies, annotating 43 037 gene structures. Subsequently, utilizing this genome along with transcriptomic and metabolomic techniques, we explored the response of ZH8015 to brown planthopper (BPH) infestation. Continuous transcriptomic sampling indicated significant changes in gene expression levels around 48 h after BPH feeding. Enrichment analysis revealed particularly significant alterations in genes related to reactive oxygen species scavenging and cell wall formation. Metabolomic results demonstrated marked increases in levels of several monosaccharides as cell wall components and dramatic changes in flavonoid contents. Omics association analysis identified differentially expressed genes associated with key metabolites, shedding light on ZH8015’s response to BPH infestation. In summary, our study constructed a reliable genome sequence resource for ZH8015, and the preliminary multi-omics results will guide future insect-resistant breeding research.

Defense Regulatory Network Associated with circRNA in Rice in Response to Brown Planthopper Infestation

The brown planthopper (BPH), Nilaparvata lugens (Stål), a rice-specific pest, has risen to the top of the list of significant pathogens and insects in recent years. Host plant-mediated resistance is an efficient strategy for BPH control. Nonetheless, BPH resistance in rice cultivars has succumbed to the emergence of distinct virulent BPH populations. Circular RNAs (circRNAs) play a pivotal role in regulating plant–environment interactions; however, the mechanisms underlying their insect-resistant functions remain largely unexplored. In this study, we conducted an extensive genome-wide analysis using high-throughput sequencing to explore the response of rice circRNAs to BPH infestations. We identified a total of 186 circRNAs in IR56 rice across two distinct virulence groups: IR-IR56-BPH (referring to IR rice infested by IR56-BPH) and IR-TN1-BPH, along with a control group (IR-CK) without BPH infestation. Among them, 39 circRNAs were upregulated, and 43 circRNAs were downregulated in the comparison between IR-IR56-BPH and IR-CK. Furthermore, in comparison with IR-CK, 42 circRNAs exhibited upregulation in IR-TN1-BPH, while 42 circRNAs showed downregulation. The Gene Ontology and Kyoto Encyclopedia of Genes and Genomes enrichment analysis revealed that the targets of differentially expressed circRNAs were considerably enriched in a multitude of biological processes closely linked to the response to BPH infestations. Furthermore, we assessed a total of 20 randomly selected circRNAs along with their corresponding expression levels. Moreover, we validated the regulatory impact of circRNAs on miRNAs and mRNAs. These findings have led us to construct a conceptual model that circRNA is associated with the defense regulatory network in rice, which is likely facilitated by the mediation of their parental genes and competing endogenous RNA (ceRNA) networks. This model contributes to the understanding of several extensively studied processes in rice-BPH interactions.

Identification and Functional Characterization of Two Major Loci Associated with Resistance against Brown Planthoppers (Nilaparvata lugens (Stål)) Derived from Oryza nivara.

The brown planthopper (BPH) is a highly destructive pest of rice, causing significant economic losses in various regions of South and Southeast Asia. Researchers have made promising strides in developing resistance against BPH in rice. Introgression line RPBio4918-230S, derived from Oryza nivara, has shown consistent resistance to BPH at both the seedling and adult stages of rice plants. Segregation analysis has revealed that this resistance is governed by two recessive loci, known as bph39(t) and bph40(t), contributing to 21% and 22% of the phenotypic variance, respectively. We later mapped the genes using a backcross population derived from a cross between Swarna and RPBio4918-230S. We identified specific marker loci, namely RM8213, RM5953, and R4M17, on chromosome 4, flanking the bph39(t) and bph40(t) loci. Furthermore, quantitative expression analysis of candidate genes situated between the RM8213 and R4M17 markers was conducted. It was observed that eight genes exhibited up-regulation in RPBio4918-230S and down-regulation in Swarna after BPH infestation. One gene of particular interest, a serine/threonine-protein kinase receptor (STPKR), showed significant up-regulation in RPBio4918-230S. In-depth sequencing of the susceptible and resistant alleles of STPKR from Swarna and RPBio4918-230S, respectively, revealed numerous single nucleotide polymorphisms (SNPs) and insertion-deletion (InDel) mutations, both in the coding and regulatory regions of the gene. Notably, six of these mutations resulted in amino acid substitutions in the coding region of STPKR (R5K, I38L, S120N, T319A, T320S, and F348S) when compared to Swarna and the reference sequence of Nipponbare. Further validation of these mutations in a set of highly resistant and susceptible backcross inbred lines confirmed the candidacy of the STPKR gene with respect to BPH resistance controlled by bph39(t) and bph40(t). Functional markers specific for STPKR have been developed and validated and can be used for accelerated transfer of the resistant locus to elite rice cultivars.

Comprehensive transcriptomic analysis of three varieties with different brown planthopper-resistance identifies leaf sheath lncRNAs in rice

BackgroundLong non-coding RNAs (lncRNAs) have been brought great attention for their crucial roles in diverse biological processes. However, systematic identification of lncRNAs associated with specialized rice pest, brown planthopper (BPH), defense in rice remains unexplored.ResultsIn this study, a genome-wide high throughput sequencing analysis was performed using leaf sheaths of susceptible rice Taichung Native 1 (TN1) and resistant rice IR36 and R476 with and without BPH feeding. A total of 2283 lncRNAs were identified, of which 649 lncRNAs were differentially expressed. During BPH infestation, 84 (120 in total), 52 (70 in total) and 63 (94 in total) of differentially expressed lncRNAs were found only in TN1, IR36 and R476, respectively. Through analyzing their cis-, trans-, and target mimic-activities, not only the lncRNAs targeting resistance genes (NBS-LRR and RLKs) and transcription factors, but also the lncRNAs acting as the targets of the well-studied stress-related miRNAs (miR2118, miR528, and miR1320) in each variety were identified. Before the BPH feeding, 238 and 312 lncRNAs were found to be differentially expressed in TN1 vs. IR36 and TN1 vs. R476, respectively. Among their putative targets, the plant-pathogen interaction pathway was significantly enriched. It is speculated that the resistant rice was in a priming state by the regulation of lncRNAs. Furthermore, the lncRNAs extensively involved in response to BPH feeding were identified by Weighted Gene Co-expression Network Analysis (WGCNA), and the possible regulation networks of the key lncRNAs were constructed. These lncRNAs regulate different pathways that contribute to the basal defense and specific resistance of rice to the BPH.ConclusionIn summary, we identified the specific lncRNAs targeting the well-studied stress-related miRNAs, resistance genes, and transcription factors in each variety during BPH infestation. Additionally, the possible regulating network of the lncRNAs extensively responding to BPH feeding revealed by WGCNA were constructed. These findings will provide further understanding of the regulatory roles of lncRNAs in BPH defense, and lay a foundation for functional research on the candidate lncRNAs.

Study on Hyperspectral Reflectance of Brown Planthopper (Nilaparvata lugens) Infestation in Rice

Background: Pest management plays crucial role in yield prediction in all crops. In Rice, Brown Planthopper (BPH) plays major role in yield reduction. Pest forewarning in agriculture is the important tool and popularly used in various countries to avoid huge fertilizer and pesticide application. In this regard, Hyperspectral remote sensing gives various information about the spectral characteristics of BPH infected plants. Methods: Investigations were carried out to assess the damage of BPH infestation at the field level using a portable Hyper spectral radiometer. The farmers field at the BPH prone area of Kuttalam block, Nagapattinam district, Tamil Nadu was chosen to analyze the spectral reflectance of BPH -infected and uninfected plants and derive certain vegetation indices for accurate forewarning. The specific spectral bands from visible to infra-red (445 nm, 550 nm, 670 nm, 760 nm, 800 nm) were utilized to detect of BPH-infested plants over the field area. Result: Among various vegetation indices, the index MCARI (Modified Chlorophyll Absorption Reflectance Index) was performed well with high accuracy from early to late infestation at the field level and considered as the most effective tool in Precision Agriculture. As a result, The specific indices were analysed over BPH infected area to prevent greater spreading of pest damage and to minimize pesticides in the field.

Effect of Paclobutrazol Application on Enhancing the Efficacy of Nitenpyram against the Brown Planthopper, Nilaparvata lugens.

The brown planthopper (BPH), Nilaparvata lugens, is one of the most destructive rice pests in Asia. It has already developed a high level of resistance to many commonly used insecticides including nitenpyram (NIT), which is a main synthetic insecticide that is used to control BPH with a much shorter persistence compared to other neonicotinoid insecticides. Recently, we found that an exogenous supplement of paclobutrazol (PZ) could significantly enhance the efficacy of NIT against BPH, and the molecular mechanism underlying this synergistic effect was explored. The results showed that the addition of a range of 150-300 mg/L PZ increased the toxicity of NIT against BPH with the highest mortalities of 78.0-87.0% on the 16th day after treatments, and PZ could also significantly prolong the persistence of the NIT efficacies. Further investigation suggested that PZ directly increased the content of flavonoids and H2O2 in rice and increased the activity of polyphenol oxidase, which might be involved in the constitutive defense of rice in advance. Additionally, there was an interaction between PZ and BPH infestation, indicating that PZ might activate the host defense responses. Therefore, PZ increased the efficacy of NIT against the brown planthoppers by enhancing the constitutive and inducible defense responses of rice. Our study showed for the first time that PZ could contribute to improving the control effects of insecticides via inducing the defense responses in rice plants against BPH, which provided an important theoretical basis for developing novel pest management strategies in the field.

Infestation by the Piercing-Sucking Herbivore Nilaparvata lugens Systemically Triggers JA- and SA-Dependent Defense Responses in Rice.

It has been well documented that an infestation of the piercing-sucking herbivore, brown planthopper (BPH), Nilaparvata lugens, activates strong local defenses in rice. However, whether a BPH infestation elicits systemic responses in rice remains largely unknown. In this study, we investigated BPH-induced systemic defenses by detecting the change in expression levels of 12 JA- and/or SA-signaling-responsive marker genes in different rice tissues upon a BPH attack. We found that an infestation of gravid BPH females on rice leaf sheaths significantly increased the local transcript level of all 12 marker genes tested except OsVSP, whose expression was induced only weakly at a later stage of the BPH infestation. Moreover, an infestation of gravid BPH females also systemically up-regulated the transcription levels of three JA-signaling-responsive genes (OsJAZ8, OsJAMyb, and OsPR3), one SA-signaling-responsive gene (OsWRKY62), and two JA- and SA- signaling-responsive genes (OsPR1a and OsPR10a). Our results demonstrate that an infestation of gravid BPH females systemically activates JA- and SA-dependent defenses in rice, which may in turn influence the composition and structure of the community in the rice ecosystem.

The Bph45 Gene Confers Resistance against Brown Planthopper in Rice by Reducing the Production of Limonene.

Brown planthopper (BPH), a monophagous phloem feeder, consumes a large amount of photoassimilates in rice and causes wilting. A near-isogenic line 'TNG71-Bph45' was developed from the Oryza sativa japonica variety 'Tainung 71 (TNG71) carrying a dominant BPH-resistance locus derived from Oryza nivara (IRGC 102165) near the centromere of chromosome 4. We compared the NIL (TNG71-Bph45) and the recurrent parent to explore how the Bph45 gene confers BPH resistance. We found that TNG71-Bph45 is less attractive to BPH at least partially because it produces less limonene. Chiral analysis revealed that the major form of limonene in both rice lines was the L-form. However, both L- and D-limonene attracted BPH when applied exogenously to TNG71-Bph45 rice. The transcript amounts of limonene synthase were significantly higher in TNG71 than in TNG71-Bph45 and were induced by BPH infestation only in the former. Introgression of the Bph45 gene into another japonica variety, Tainan 11, also resulted in a low limonene content. Moreover, several dominantly acting BPH resistance genes introduced into the BPH-sensitive IR24 line compromised its limonene-producing ability and concurrently decreased its attractiveness to BPH. These observations suggest that reducing limonene production may be a common resistance strategy against BPH in rice.

Combined Physio-Biochemical and Transcriptome Analyses Illuminate the Resistance Response of Rice Priming with Decoyinine against Nilaparvata lugens

The brown planthopper (BPH), Nilaparvata lugens (Stål) (Hemiptera: Delphacidae), is a notorious pest in rice production. The microbial secondary metabolite, decoyinine (DCY), is produced by Streptomyces hygroscopicus. Recent studies found that seed priming with DCY could enhance rice resistance to BPH and Laodelphax striatellus; however, the mechanism of enhancing insect resistance in rice remains unclear. Here, an integrated physio-biochemical and transcriptome analysis was performed on rice priming with DCY after BPH infestation. Defense-related enzymes activities such as catalase (CAT), superoxide dismutase (SOD), peroxidase (POD), glutathione S transferase (GST), and polyphenol oxidase (PPO), concentrations of hydrogen peroxide (H2O2), callose, and free amino acids in rice priming with DCY were significantly increased than in control plants after BPH infestation. Concentrations of soluble sugars, sucrose, and glucose were higher in rice treated with DCY than in the control after BPH infestation; however, the concentration of malondialdehyde (MDA) was significantly decreased in rice treated with DCY after BPH infestation. In the transcriptome analysis, GO functional annotation and KEGG pathway analysis were enriched in defense response, transcription factors, secondary metabolites, reactive oxygen species, and cell wall organization and these data also support physio-biochemical results. The qRT-PCR results further verified the differential expressed genes related to DCY-treated rice responding to BPH. Meanwhile, it indicated that DCY might enhance the resistance of rice to BPH by regulating the rice WRKY transcription factor genes. Our results provide a basis for further exploring the molecular mechanism of the defense response of rice priming with DCY against BPH infestation and could provide valuable resources to control insect pests.

The Role of Biopesticide in Increasing Rice Farmer's Profit

Rice farmers' excessive use of chemical pesticides has increased the brown planthopper infestation. The Integrated Pest Management - Farmer Field School (SLPHT) conducted efforts to replace pesticides with environmentally friendly materials. Cost savings arise because the farmers of the "IPM community" apply IPM principles such as using self-made bio-pesticides, hence, the quality of the grain produced is rated higher. Therefore, this study aims to determine the characteristics of farmers using production factors and to analyze the effect of biological pesticides on the profits of rice cultivars in the Indramayu Regency. The analysis tool consists of descriptive qualitative and multiple linear regression using pesticides as the independent variable. The highest cost of rice farming is the labor of 52% - 67%. Furthermore, approximately 61.8% of farmers own paddy fields measuring between ​​0.5 ha - 2 ha. The proportion of cultivars that uses biological and chemical pesticides are only 24.4% and 75.6%, respectively. The test shows that labor is a burden on farmers. This was observed from its negative effect, while the land area has a positive and significant impact on their profit levels. The results of this study are essential. This is shown by the negative relationship between profits and biological pesticides, indicating that the use of these pesticides did not provide better benefits than the chemical counterpart.

Transcriptome and metabolome analyses reveal the responses of brown planthoppers to RH resistant rice cultivar.

The brown planthopper (BPH) Nilaparvata lugens (Stål) (Hemiptera: Delphacidae) is one of the most destructive rice pests in Asia. The application of insect-resistant rice cultivars is currently one of the principal means of controlling BPH. Understanding the physiological response mechanisms of BPH feeding on insect-resistant rice is the key for maintaining rice yield. Here, we measured the ecological fitness and analyzed the whole-body transcriptome and metabolome of BPH reared on susceptible cultivar Taichung Native 1 (TN1) and resistant cultivar Rathu Heenati (RH). Our results showed that RH significantly decreased the survival rate, female adult weight, honeydew secretion, the number of eggs laid per female and fat content of BPH. We identified 333 upregulated and 486 downregulated genes in BPH feeding on RH. These genes were mainly involved in energy metabolism, amino acid metabolism, hormone synthesis and vitamin metabolism pathways. We also detected 145 differentially accumulated metabolites in BPH reared on RH plants compared to BPH reared on TN1 plants, including multiple carbohydrates, amino acids, lipids, and some nucleosides. Combined analyses of transcriptome and metabolome showed that five pathways, including starch, sucrose, and galactose metabolism, were altered. The network for these pathways was subsequently visualized. Our results provide insights into the mechanisms of metabolite accumulation in BPH feeding on the RH rice variety. The results could help us better understand how insect-resistant rice cultivars combat BPH infestation, which is important for the comprehensive management of BPH.

Damage of brown planthopper (BPH) Nilaparvata lugens and rice leaf folder (LF) Cnaphalocrocis medinalis in parent plants lead to distinct resistance in ratoon rice

ABSTRACT Herbivore-induced defense responses are often specific, whereas plants could induce distinct defense responses corresponding to infestation by different herbivorous insects. Brown plant hopper (BPH) Nilaparvata lugens, a phloem-feeding insect, and rice leaf folder (LF) Cnaphalocrocis medinalis, a chewing insect, are both specialist herbivores on rice. To characterize the distinct resistance primed by prior damage to these two specialist herbivores, we challenged rice plants with two herbivores during vegetative growth of parent plants and assessed plant resistance in subsequent ratoons. Here, we show that LF and BPH induce different suites of defense responses in parent rice plants, LF induced higher level of JA accumulation and OsAOS, OsCOI1 transcripts, while BPH induced higher accumulation of SA and OsPAL1 transcripts. Moreover, an apparent loss of LF resistance was observed in OsAOS, OsCOI1 RNAi lines. Ratoon plants generated from parents receiving prior LF infestation exhibited higher jasmonic acid (JA) levels and elevated levels of transcripts of defense-related genes associated with JA signaling, while ratoon generated from parents receiving prior BPH infestation exhibited higher salicylic acid (SA) levels and elevated levels of transcripts of defense-related genes associated with SA signaling. Moreover, previous LF infestation obviously elevated ratoons resistance to LF, while previous infestation by BPH led to enhanced resistance in ratoons to BPH. Pre-priming of ratoons defense to LF was significantly reduced in OsAOS and OsCOI1 RNAi plant, but silencing OsAOS and OsCOI1 did not attenuate ratoons resistance to BPH. These results suggest that infestation of two specialist herbivores with different feeding styles in parent crop led to distinct defense responses in subsequent rations, and the acquired resistance to LF in ratoons is associated with priming of jasmonic acid-dependent defense responses.

Molecular mapping and transfer of a novel brown planthopper resistance gene bph42 from Oryza rufipogon (Griff.) To cultivated rice (Oryza sativa L.).

Brown planthopper (BPH), Nilaparvata lugens (Stål), is one of the most destructive pests of rice accounting for 52% of annual yield loss. The breakdown of resistance against known BPH biotypes necessitates the identification and deployment of new genes from diverse sources. The current study aimed at mapping and transfer of a novel BPH resistance gene from the wild species of rice O. rufipogon accession CR100441 to the elite rice cultivar against BPH biotype 4. The phenotypic screening against BPH biotype 4 was conducted using the standard seedbox screening technique (SSST). Inheritance study using damage score caused by BPH infestation at the seedling stage indicated the presence of a single major recessive gene with the segregation ratio of susceptible to resistant plants in 3:1 (210:66, χ2c = 0.17 ≤ χ20.05,1 = 3.84). The genotyping of the mapping population was done using polymorphic microsatellite markers between PR122 and O.rufipogon acc.CR100441 spanning all the 12 chromosomes of rice. A total of 537 SSR markers were used to map a BPH resistance gene (designated as bph42) on the short arm of chromosome 4 between RM16282 and RM6659. QTL analysis identified a peak marker RM16335 contributing 29% of the phenotypic variance at 40.76 LOD. The identified marker co-segregates with the bph42 and hence could be efficiently used for marker-assisted selection (MAS) for the transfer of resistance into elite rice cultivars. The introgression lines with higher yield and BPH resistance were identified and are under advanced yield trails for further varietal release.

Transcriptome Analysis Reveals Crosstalk between the Abscisic Acid and Jasmonic Acid Signaling Pathways in Rice-Mediated Defense against Nilaparvata lugens.

The brown planthopper (BPH) impacts both rice yield and quality. The exogenous application of abscisic acid (ABA) and jasmonic acid (JA) has been previously shown to induce rice resistance to BPH; however, the regulation of rice-mediated defense by these plant growth regulators is unclear. We applied exogenous JA and ABA to rice and analyzed molecular responses to BPH infestation. Nine RNA libraries were sequenced, and 6218 differentially expressed genes (DEGs) were generated and annotated. After ABA + BPH and JA + BPH treatments, 3491 and 2727 DEGs, respectively, were identified when compared with the control (BPH alone). GO enrichment and KEGG pathway analysis showed that the expression of several JA pathway genes (OsAOS2, encoding allene oxide synthase; OsOPR, 12-oxo-phytodienoic acid reductase; and OsACOX, acy1-CoA oxidase) were significantly up-regulated after ABA + BPH treatment. Furthermore, exogenous JA increased the expression of genes involved in ABA synthesis. Meanwhile, the expression levels of genes encoding WRKY transcription factors, myelocytomatosis protein 2 (MYC2) and basic leucine zippers (bZIPs) were up-regulated significantly, indicating that ABA and JA might function together to increase the expression of transcription factors during the rice defense response. The DEGs identified in this study provide vital insights into the synergism between ABA and JA and further contribute to the mechanistic basis of rice resistance to BPH.

Seed Coating with Triflumezopyrim Induces the Rice Plant’s Defense and Inhibits the Brown Planthopper’s Feeding Behavior

Triflumezopyrim (TFM), a novel mesoionic insecticide, has been effective in controlling sucking insect pests such as the brown planthopper (BPH). However, the mechanism of TFM as a seed coating agent in paddy fields remains unclear. Here, we investigate the seed germination rates (>80%) and seedling emergence rates (>85%) of rice treated with TFM at 0, 22.5, 45.0, 67.5, and 90.0 g a.i. ha−1 with no significant effect on germination rates. In addition, the low TFM residue concentration (0.04 mg. kg−1) is maintained in the rice stem. Meanwhile, the TFM seeds’ treatments lead to increased oxalic acid, flavonoids, total phenol, callose contents, and elevated C/N ratio in rice plants at 60 and 90 days after sowing (DAS). The electrical penetration graph (EPG) results indicate that TFM as a seed coating treatment prolongs the non-probing period and inhibits phloem sap ingestion at 90 DAS. Furthermore, the mechanically transplanted rice treated with TFM provides long-term prevention against the BPH infestation. This study demonstrates that seeds treated with TFM play a vital role in controlling the BPH population up to >90%. These results provide a novel valuable control strategy for BPH in the rice fields.

Mechanisms of Trichomes and Terpene Compounds in Indigenous and Commercial Thai Rice Varieties against Brown Planthopper.

Simple SummaryHerbivorous insects and their host plants have a long history of co-evolution. Plants produce specialized morphological structures known as trichomes, which may be involved in the antibiosis and antixenosis traits of the host plant when interacting with insect herbivores. The host plant also produces chemicals that may act as a repellent or antifeedant to reduce infestation by herbivores. Several studies over the last few decades have revealed that trichomes perform an important role in plants’ defense against herbivores. However, little information is available on the physical and chemical defense of indigenous and commercial Thai rice varieties against major pests such as the brown planthopper (BPH). In this study, we found a negative relationship between the density of prickle trichomes and the BPH infestation level. The volatile organic compound (VOC) emission profiles from rice plants indicated that β-Sesquiphellandrene induced by BPH possibly repelled BPH.Plant trichomes generally act as a physical defense against herbivore attacks and are present in a variety of plants, including rice plants. This research examined the physical and chemical defenses of rice plants against the brown planthopper (BPH), Nilaparvata lugens (Stål) (Hemiptera: Delphacidae). A total of 10 rice varieties were used in this study. An electron microscope was used to observe trichomes. Constitutive and induced volatile compound profiles were assessed using GC-MS analyses. The preference of BPH for volatiles from the 10 rice plants was tested using a two-choice arena olfactometer system. The density of prickle trichomes had a negative relationship with the BPH injury level. Without BPH infestation, the volatile of the most resistant rice variety (Rathu Heenati (RH)) was preferred by BPH than those of the other varieties, with the exception of Gled Plah Chawn. However, the relative BPH preference for volatiles from the RH variety decreased during BPH infestation. When rice plants were infested by BPH, the numbers of VOCs and these quantities decreased. In the RH variety, the emission of essentities found without BPH infestation ceased during infestation by BPH. During the BPH infestation, rice plants started to emit new VOCs that were not detected before the BPH infestation started. In conclusion, we discovered that rice plants defended against BPH by changing VOC components during BPH infestation and β-Sesquiphellandrene was likely the most effective component.

Metabolite profiles of brown planthopper-susceptible and resistant rice (Oryza sativa) varieties associated with infestation and mechanical stimuli

Understanding brown planthopper (BPH) resistance mechanism will expedite selective breeding of better BPH resistant lines of rice (Oryza sativa). Metabolic responses during BPH infestation derived from wound stress imposed by insect feeding, comparing with mechanical piercing will provide an insight into resistance mechanism in rice. Therefore, this study aimed to compare the metabolic responses of needle piercing treatment and BPH feeding treatment in BPH-susceptible (KD) and BPH-resistant (RH) varieties at four different time points (0, 6, 24 and 96 h) using liquid chromatography-high resolution mass spectrometry (LC-HRMS). Phenotypes of RH were not different among the treatments, whereas KD exhibited hopperburn symptom at 96 h post-BPH infestation. Principal component and cluster analyses revealed that metabolite profiles between KD and RH were different in response to both insect and mechanical stimuli. Metabolite profiles of RH under BPH and mechanical treatments at 24 and 96 h were different from the untreated, whereas metabolite profiles of KD after BPH infestation at 24 and 96 h were distinct from needle piercing and no treatment, suggesting that the resistant variety has an ability to adapt and defend both mechanical and insect stimuli. Metabolomics result showed that BPH infestation perturbed purine salvage biosynthesis (e.g., inosine, hypoxanthine) in both varieties, amino acid biosynthesis (e.g., phenylalanine, tryptophan) in KD, while the infestation perturbed lysine metabolism (pipecolic acid) and phenylpropanoid pathway (2-anisic acid) only in RH. BPH and mechanical stimuli perturbed phenylamide only in RH, but not in KD. These findings revealed that different rice varieties utilize different metabolites in response to insect and mechanical stimuli, resulting in different degrees of resistance.