Brown Planthopper Resistance Genes Research Articles

Recent Strategies for Detection and Improvement of Brown Planthopper Resistance Genes in Rice: A Review.

Brown planthopper (BPH; Nilaparvata lugens Stal) is considered the main rice insect pest in Asia. Several BPH-resistant varieties of rice have been bred previously and released for large-scale production in various rice-growing regions. However, the frequent surfacing of new BPH biotypes necessitates the evolution of new rice varieties that have a wide genetic base to overcome BPH attacks. Nowadays, with the introduction of molecular approaches in varietal development, it is possible to combine multiple genes from diverse sources into a single genetic background for durable resistance. At present, above 37 BPH-resistant genes/polygenes have been detected from wild species and indica varieties, which are situated on chromosomes 1, 3, 4, 6, 7, 8, 9, 10, 11 and 12. Five BPH gene clusters have been identified from chromosomes 3, 4, 6, and 12. In addition, eight BPH-resistant genes have been successfully cloned. It is hoped that many more resistance genes will be explored through screening of additional domesticated and undomesticated species in due course.

Improvement of rice blast and brown planthopper resistance of PTGMS line C815S in two-line hybrid rice through marker-assisted selection

Two-line hybrid rice breeding, which plays an important role in ensuring food security in China, is one of important approaches to utilize the heterosis in rice. Breeding of photo-thermo-sensitive genic male sterile (PTGMS) lines of two-line hybrid rice with high resistance to diseases and pests is vital for enhancing rice yield stability, reducing environmental pollution, and increasing rice production efficiency. To breed PTGMS rice with resistance to both rice blast and brown planthopper (BPH), four broad-spectrum blast resistance genes Pi9, Pi47, Pi48, and Pi49 and two BPH resistance genes Bph14 and Bph15 were introgressed into a PTGMS line C815S through backcrossing and gene pyramiding coupled with molecular marker-assisted selection (MAS) in this study. Finally, several improved PTGMS lines of C815S which pyramided 1–3 homozygous rice blast resistance genes and two BPH resistance genes were developed. Evaluation of rice blast resistance showed that the improved PTGMS lines were resistant, while C815S was susceptible or only moderately resistant. Assessment of the BPH resistance showed that C815S was highly susceptible, while the improved lines were resistant. The improved lines had similar major agronomic traits and temperature of fertility transition to C815S, and several traits were even better. The newly developed PTGMS lines can be used for breeding of superior two-line hybrid rice or advanced PTGMS lines.

Fine mapping, candidate genes analysis, and characterization of a brown planthopper (Nilaparvata lugens Stål) resistance gene in the rice variety ARC5984

The brown planthopper (Nilaparvata lugens Stal; BPH) is the most destructive rice pests worldwide. Identification and application of major resistance genes and cultivation of resistant varieties are the most efficient methods to control this insect. In this study, the rice variety, ARC5984, was detected to be highly resistant to BPH due to the presence of a major resistance gene, which has primarily been mapped in a 6-cM region on the long arm of chromosome 4. Fine mapping of the resistance gene was performed using the recombinants derived from BC1F2 individuals; the target gene was described to be a 46-kb region in the Nipponbare genome. Based on the information on the genomic sequences of the varieties Nipponbare, ZS97 and MH63, six, seven and 11 candidate genes were identified in the finally located region, respectively. The relative expression of the candidate genes Os04g35190 and Os04g35210 was significantly different between the resistant and susceptible plants after BPH infestation. The sequencing results indicated the coding domain sequence (CDS) of Os04g35210 from ARC5984 to be identical to that of Bph6. But the CDS of Os04g35190 was different between in ARC5984 and 9311. Moreover, the preliminary-near-isogenic lines (pre-NILs; the lines carrying resistance genes) with genetic background of the 9311 showed significant antixenosis to BPH, and thus, restricted its growth and development when compared with that in the susceptible line of 9311. Finally, a marker-assisted selection (MAS) technique was developed for the markers, RM5635 and BF9; its efficiency has been confirmed by applying it in screening of backcrossed individuals. The development in the fine mapping of the major gene will facilitate efforts of cloning this important resistance gene and to apply it in breeding of BPH-resistance rice varieties.

Genetics of novel brown planthopper Nilaparvata lugens (Stål) resistance genes in derived introgression lines from the interspecific cross O. sativa var. Swarna × O. nivara

The brown planthopper (BPH) Nilaparvata lugens (Stål) (Homoptera: Delphacidae) is considered a threat to rice (Oryza sativa ssp.) crop in many parts of the world including India. Among the BPH-resistance (R) genes so far reported in rice, most of them are ineffective against BPH biotype 4 predominant in the Indian sub-continent. In this study, we show the introgression line RPBio4918-230S was identified as BPH resistant after five years of rigorous screening at seedling stage and two years at tillering and reproductive stages. The inheritance of resistance indicated that two recessive genes are involved at seedling and reproductive stages. The allelic relation with known genes using linked reported markers suggested that the genes present in RPBio4918-230S are different. We report here the genetics of the two newly introgressed BPH resistance genes from O. nivara in the background of Swarna which are effective at all the important growth stages. The genes have been tentatively named as bph39(t) and bph40(t). The honeydew area (feeding rate) and days to wilt parameters observed at 30 days after sowing in BC1F3 indicated that newly introgressed genes have both antibiosis and tolerance mechanisms for resistance. The BPH resistance genes identified in this study would facilitate the breeding of broad spectrum and durable resistance in rice against BPH biotype 4.

Identification of a novel locus, BPH38(t), conferring resistance to brown planthopper (Nilaparvata lugens Stal.) using early backcross population in rice (Oryza sativa L.)

Rice is the most important staple food crop, and it feeds more than half of the world population. Brown planthopper (BPH) is a major insect pest of rice that causes 20–80% yield loss through direct and indirect damage. The identification and use of BPH resistance genes can efficiently manage BPH. A molecular marker-based genetic analysis of BPH resistance was carried out using 101 BC1F5 mapping population derived from a cross between a BPH-resistant indica variety Khazar and an elite BPH-susceptible line Huang–Huan–Zhan. The genetic analysis indicated the existence of Mendelian segregation for BPH resistance. A total of 702 high-quality polymorphic single nucleotide polymorphism (SNP) markers, genotypic data, and precisely estimated BPH scores were used for molecular mapping, which resulted in the identification of the BPH38(t) locus on the long arm of chromosome 1 between SNP markers 693,369 and id 10,112,165 of 496.2 kb in size with LOD of 20.53 and phenotypic variation explained of 35.91%. A total of 71 candidate genes were predicted in the detected locus. Among these candidate genes, LOC_Os01g37260 was found to belong to the FBXL class of F-box protein possessing the LRR domain, which is reported to be involved in biotic stress resistance. Furthermore, background analysis and phenotypic selection resulted in the identification of introgression lines (ILs) possessing at least 90% recurrent parent genome recovery and showing superior performance for several agro-morphological traits. The BPH resistance locus and ILs identified in the present study will be useful in marker-assisted BPH resistance breeding programs.

Phenotypic and transcriptomic responses of two Nilaparvata lugens populations to the Mudgo rice containing Bph1

The Bph1 gene was the first reported brown planthopper (BPH, Nilaparvata lugens) resistance gene in Mudgo rice and was widely used as a commercial cultivar for controlling BPH infestations. However, rapid adaptations of BPH on the Mudgo rice resulted in its resistance breakdown and the emergence of virulent BPH populations. Thus, specific BPH populations and rice varieties can serve as good model systems for studying the roles of different bio-compounds and proteins in the insect-plant interactions. Although our understandings have been improved on the complexity of BPH and rice interactions, the underlying molecular mechanisms remain largely unknown. Here we analyzed the feeding performances and the transcriptomic responses of two BPH populations (Mugdo-BPH and TN1-BPH) during compatible (Mudog-BPH feeding on Mudgo rice) and incompatible (TN1-BPH feeding on Mudgo rice) interactions. The electrical penetration graph (EPG) results indicated that the BPH feeding and performances during the incompatible interaction are significantly affected in terms of decreased honeydew, loss of weight, decreased phloem sap ingestion (N4 waveform), but increased non-penetration (NP waveform) phase. Abundance of glucose and trehalose was reduced in BPH during the incompatible interaction. Transcriptomic surveys of insects in both interactions revealed that genes involved in cuticle formation, detoxification, metabolite transport, digestion, RNA processing, lipid or fatty acid metabolism, and proteolysis were significantly down-regulated during the incompatible interaction, whereas genes involved in insulin signaling were significantly upregulated. Knockdown of four genes, including the sugar transporter NlST45, the serine and arginine-rich protein NlSRp54, the cytochrome P450 gene NlCYP6AY1, and the cuticle protein NlCPR70 through RNA-interference revealed thess genes are important for BPH survival. Overall, the results of this study will be helpful for the future researches on BPH virulence shifts.

High-resolution mapping and breeding application of a novel brown planthopper resistance gene derived from wild rice (Oryza. rufipogon Griff)

BackgroundThe brown planthopper (Nilaparvata lugens Stål; BPH), one of the most destructive pests of rice, has proven to be a substantial threat, conferring enormous production losses in Asia and becoming a difficult challenge to manipulate and control under field conditions. The continuous use of insecticides promotes the resurgence of BPH, which results in resistant varieties adapting through the upgrading of new BPH biotypes. To overcome resistance acquired by BPH against resistance varieties, different forms of novel resistant gene fusions act as functional domains for breeding to enhance insect resistance.ResultsThe current study reports on the novel BPH resistance gene Bph36 derived from two introgression lines (RBPH16 and RBPH17) developed from wild rice GX2183 which was previously reported to be resistant to BPH. Using two F2 crossing populations (Kangwenqizhan × RBPH16 and Huanghuazhan × RBPH17) in a bulked segregant analysis (BSA) for identification of resistant genes and QTL analysis, two QTLs for BPH resistance were generated on the long and short arms of chromosome 4, which was further confirmed by developing BC1F2:3 populations by backcrossing via marker assisted selection (MAS) approach. One BPH resistance locus on the short arm of chromosome 4 was mapped to a 38-kb interval flanked by InDel markers S13 and X48, and then was named Bph36, whereas another locus on the long arm of chromosome 4 was also detected in an interval flanked by RM16766 and RM17033, which was the same as that of Bph27. An evaluation analysis based on four parameters (BPH host selection, honeydew weight, BPH survival rate and BPH population growth rate) shows that Bph36 conferred high levels antibiosis and antixenosis to BPH. Moreover, Bph36 pyramided with Bph3, Bph27, and Bph29 through MAS into elite cultivars 9311 and MH511 (harbored Xa23), creating different background breeding lines that also exhibited strong resistance to BPH in the seedling or tillering stage.ConclusionBph36 can be utilized in BPH resistance breeding programs to develop high resistant rice lines and the high-resolution fine mapping will facilitate further map-based cloning and marker-assisted gene pyramiding of resistant gene. MAS exploited to pyramid with Bph3, Bph27, Bph29, and Xa23 was confirmed the effectiveness for BPH resistance breeding in rice and provided insights into the molecular mechanism of defense to control this devastating insect.

Identification of brown planthopper resistance gene Bph32 in the progeny of a rice dominant genic male sterile recurrent population using genome-wide association study and RNA-seq analysis

Brown planthopper (BPH) is one of the most damaging pests of rice. Improving the resistance of rice varieties is considered a safe and effective way to control this pest. Here, a field experiment was conducted to test BPH resistance in a rice population developed by recurrent selection of a variety with dominant genic male sterility. Three high-resistance lines were identified and subjected to a genome-wide association study (GWAS), which mapped the BPH resistance gene to the short arm of chromosome 6. One highly resistant line (14CF2426) was further crossed with Taichuang Native 1 (TN1) to construct an F2 segregating population. Artificial insect infestation identified three quantitative trait loci (QTLs), which were mapped to chromosomes 1, 6, and 10; the QTL on chromosome 6 of 14CF2426 contained a known resistance gene, Bph32. Near-isogenic lines NIL-Bph32 and NIL-bph32 of Bph32 were constructed using molecular marker-assisted selection. RNA sequencing (RNA-seq) detected 1268 differentially expressed genes (DEGs) between the two near-isogenic lines. Compared with NIL-Bph32, 1064 genes were upregulated and 204 were downregulated in NIL-bph32. Gene ontology (GO) enrichment analysis detected 46 significantly enriched terms, and KEGG analysis revealed four significantly enriched metabolic pathways. This robust multi-method strategy showed that combining GWAS analysis with a dominant genic male sterile recurrent rice population can significantly improve the efficiency of gene identification. RNA-seq revealed some candidate genes with a potential regulatory function in BPH resistance, thus providing insights into the transcriptional regulatory network and the molecular mechanisms of resistance.

Identification of spontaneous mutation for broad-spectrum brown planthopper resistance in a large, long-term fast neutron mutagenized rice population

BackgroundThe development of rice varieties with broad-spectrum resistance to insect pests is the most promising approach for controlling a fast evolving insect pest such as the brown planthopper (BPH). To cope with rapid evolution, discovering new sources of broad-spectrum resistance genes is the ultimate goal.ResultsWe used a forward genetics approach to identify BPH resistance genes in rice (Oryza sativa L.) using double digest restriction site-associated DNA sequencing (ddRADseq) for quantitative trait loci (QTL)-seq of the backcross inbred lines (BILs) derived from a cross between the BPH-susceptible cultivar KDML105 and BPH-resistant cultivar Rathu Heenati (RH). Two major genomic regions, located between 5.78–7.78 Mb (QBPH4.1) and 15.22–17.22 Mb (QBPH4.2) on rice chromosome 4, showed association with BPH resistance in both pooled BILs and individual highly resistant and susceptible BILs. The two most significant candidate resistance genes located within the QBPH4.1 and QBPH4.2 windows were lectin receptor kinase 3 (OsLecRK3) and sesquiterpene synthase 2 (OsSTPS2), respectively. Functional markers identified in these two genes were used for reverse screening 9323 lines of the fast neutron (FN)-mutagenized population developed from the BPH-susceptible, purple-pigmented, indica cultivar Jao Hom Nin (JHN). Nineteen FN-mutagenized lines (0.24%) carried mutations in the OsLecRK3 and/or OsSTPS2 gene. Among these mutant lines, only one highly resistant line (JHN4) and three moderately resistant lines (JHN09962, JHN12005, and JHN19525) were identified using three active, local BPH populations. The 19 mutant lines together with three randomly selected mutant lines, which did not harbor mutations in the two target genes, were screened further for mutations in six known BPH resistance genes including BPH9, BPH14, BPH18, BPH26, BPH29, and BPH32. Multiple single nucleotide polymorphisms (SNPs) and insertion-deletion (Indel) mutations were identified, which formed gene-specific haplotype patterns (HPs) essential for broad-spectrum resistance to BPH in both BILs and JHN mutant populations.ConclusionOn the one hand, HPs of OsLekRK2–3, OsSTPS2, and BPH32 determined broad-spectrum resistance to BPH among RH-derived BILs. On the other hand, in the JHN mutant population, BPH9 together with seven significant genes on chromosome 4 played a crucial role in BPH resistance.

Development of rice introgression lines with brown planthopper resistance and low amylose content for germplasm sources through marker-assisted selection

The brown planthopper (BPH) is one of the most serious problems affecting rice production. This study incorporated the BPH resistance gene, Bph3, derived from a Rathu Heenati × Pathumthani 1 variety, which is susceptible to BHP and has low amylose content in the endosperm and both of these traits are closely linked on chromosome 6. The objective of this study was to develop introgression lines as germplasm sources with BPH resistance and low amylose content with other removed linkage drag traits and photoperiod insensitivity using marker-assisted selection. The newly developed multiplex simple sequence repeat markers specific to both genes were utilized for screening of the F2 progeny possessing genotypes with breaking linkage drag and selected photoperiod insensitive lines. Then, evaluation of the selected lines for BPH resistance was conducted in the seedling stage of the F4 progeny and the resistant character was segregated. Selection was made for BPH-resistant plants and their genotype controlling resistance on chromosome 4 was additionally determined using marker RM 16355. The results revealed that all the selected plants had the same genotype as the Rathu Heenati variety. Finally, the elite rice lines could be used as a germplasm source in rice breeding for BPH resistance and low amylose content. Moreover, unfavorable traits were removed by phenotypic selection from the Rathu Heenati variety such as photoperiod sensitivity, non-fragrance and tall plant type. Thus, these rice lines can be used as a germplasm resource for a rice breeding program in the future.

Development of molecular marker and introgression of Bph3 into elite rice cultivars by marker-assisted selection.

The brown planthopper (BPH) is a serious insect pest of rice and a substantial threat to rice production. Identification of new BPH resistance genes and their transfer into modern rice cultivars are effective breeding approaches to reduce the damage caused by BPH. In this study, we mapped a BPH resistance gene to a 50-kb genomic interval between two InDel markers 4M03980 and 4M04041 on the short arm of chromosome 4 in indica rice cultivar BP60, where the BPH resistance gene was mapped in Rathu Heenati by Liu et al. (2015) and named “Bph3”. This region contains two annotated genes Os04g0201900 and Os04g0202300, which encode lectin receptor kinases responsible for BPH resistance. We also developed a molecular marker “MM28T” for Bph3, and introgression Bph3 into susceptible rice restorer lines Guihui582 and Gui7571 by the marker-assisted selection (MAS) approach. The BPH resistance level is significantly enhanced in the Bph3-introgression lines, the resistance scores decrease from 8.2 to 3.6 for Guihui582 and decrease from 8.7 to around 3.8 for Gui7571. Therefore, developing molecular markers for the BPH resistance gene Bph3 and using them for molecular breeding will facilitate the creation of BPH-resistance rice cultivars to reduce damage caused by BPH.

Mapping of Resistance Genes to Brown Planthopper in Untup Rajab, an Indonesian Local Rice Variety

<p>Brown planthopper (BPH) is a major rice pest in Indonesia. The most economical and effective approach to control the insect pest is by using resistant varieties. Exploring for resistance genes is, therefore, a prerequisite for effective breeding program for BPH resistance. This study aimed to map BPH resistance genes in Untup Rajab, an Indonesian local rice variety. Genetic map was constructed using an F2 population from a cross between TN-1 and Untup Rajab, and SNP markers from RiceLD SNP Chip. Phenotyping was performed using bulk seedling test on F2:3 seedlings against two BPH populations, i.e. X1 and S1. Four QTLs<br />were identified on chromosomes 5, 6, 8, and 11 with PVE values of 7.63%, 9.40%, 17.66%, and 3.05%, respectively. Relatively normal distribution of resistance phenotype and the relatively low PVE values indicate that Untup Rajab has a quantitative resistance to BPH with two different resistance loci identified for each BPH test population. The QTL on chromosome 8 overlaps with OsHI-LOX gene, which is associated with resistance to BPH, and adjacent to another QTL for resistance to green leafhopper. The QTL on chromosome 6 was found near OsPLDα4 and OsPLDα5 genes which are related to BPH resistance. Meanwhile, the QTL intervals on chromosome 5 and 11 did not overlap with any known BPH QTLs or genes, which make them attractive candidates for novel BPH resistance gene discovery.</p>

Identification and fine mapping of Bph33, a new brown planthopper resistance gene in rice (Oryza sativa L.)

BackgroundHost-plant resistance is the most desirable and economic way to overcome BPH damage to rice. As single-gene resistance is easily lost due to the evolution of new BPH biotypes, it is urgent to explore and identify new BPH resistance genes.ResultsIn this study, using F2:3 populations and near-isogenic lines (NILs) derived from crosses between two BPH-resistant Sri Lankan rice cultivars (KOLAYAL and POLIYAL) and a BPH-susceptible cultivar 9311, a new resistance gene Bph33 was fine mapped to a 60-kb region ranging 0.91–0.97 Mb on the short arm of chromosome 4 (4S), which was at least 4 Mb distant from those genes/QTLs (Bph12, Bph15, Bph3, Bph20, QBph4 and QBph4.2) reported before. Seven genes were predicted in this region. Based on sequence and expression analyses, a Leucine Rich Repeat (LRR) family gene (LOC_Os04g02520) was identified as the most possible candidate of Bph33. The gene exhibited continuous and stable resistance from seedling stage to tillering stage, showing both antixenosis and antibiosis effects on BPH.ConclusionThe results of this study will facilitate map-based cloning and marker-assisted selection of the gene.

Pyramiding Xa21, Bph14, and Bph15 genes into the elite restorer line Yuehui9113 increases resistance to bacterial blight and the brown planthopper in rice

Utilization of resistant varieties is the most economical and effective strategy to control bacterial blight (BB) and brown planthopper (BPH) in rice. Yuehui9113 is a widely used elite restorer line with high combining ability, and one of its hybrids, C815S/Yuehui9113, has been designated as a check variety for late season single-cropping rice; however, both of the parental lines are susceptible to BB and BPH. To simultaneously improve resistance to both BB and BPH in Yuehui9113 and F1 hybrids derived from it, one BB resistance gene (Xa21) and two BPH resistance genes (Bph14 and Bph15) were pyramided in Yuehui9113 using a marker-assisted backcrossing (MABC) strategy coupled with phenotypic selection in this study. Evaluation of BB and BPH resistance showed that all improved restorer lines that were homozygous for the resistance genes, and their derived F1 hybrids crossed with C815S, were at least moderately resistant to fourteen Xanthomonas oryzae pv. oryzae (Xoo) strains except for strain FuJ. They were also resistant or highly resistant to BPH, except for the improved line BX9113-06 and its hybrid C815S/BX9113-06, suggesting that BB and BPH resistances were significantly improved compared with the parent Yuehui9113 and the original hybrid C815S/Yuehui9113. Evaluation of agronomic traits and plot yields in 2014 and 2016 suggested that the improved lines BX9113-01 and BX9113-12 and their hybrids with C815S are superior or similar to the original parental line Yuehui9113 and the original hybrid C815S/Yuehui9113 with respect to important agronomic traits, and the two hybrids showed higher yield potential than the control hybrid C815S/Yuehui9113. The results of this study show that introgression of the Xa21, Bph14, and Bph15 genes can significantly improve resistance to BB and BPH in Yuehui9113 and its hybrids. Thus, the improved restorer lines BX9113-01 and BX9113-12 will play an important role in breeding hybrid rice with high levels of resistance to BB and BPH in the Yangtze River valley of China.

Insights into the structure–function relationship of brown plant hopper resistance protein, Bph14 of rice plant: a computational structural biology approach

Brown plant hopper (BPH) is one of the major destructive insect pests of rice, causing severe yield loss. Thirty-two BPH resistance genes have been identified in cultivated and wild species of rice Although, molecular mechanism of rice plant resistance against BPH studied through map-based cloning, due to non-existence of NMR/crystal structures of Bph14 protein, recognition of leucine-rich repeat (LRR) domain and its interaction with different ligands are poorly understood. Thus, in the present study, in silico approach was adopted to predict three-dimensional structure of LRR domain of Bph14 using comparative modelling approach followed by interaction study with jasmonic and salicylic acids. LRR domain along with LRR-jasmonic and salicylic acid complexes were subjected to dynamic simulation using GROMACS, individually, for energy minimisation and refinement of the structure. Final binding energy of jasmonic and salicylic acid with LRR domain was calculated using MM/PBSA. Free-energy landscape analysis revealed that overall stability of LRR domain of Bph14 is not much affected after forming complex with jasmonic and salicylic acid. MM/PBSA analysis revealed that binding affinities of LRR domain towards salicylic acid is higher as compared to jasmonic acid. Interaction study of LRR domain with salicylic acid and jasmonic acid reveals that THR987 of LRR form hydrogen bond with both complexes. Thus, THR987 plays active role in the Bph14 and phytochemical interaction for inducing resistance in rice plant against BPH. In future, Bph14 gene and phytochemicals could be used in BPH management and development of novel resistant varieties for increasing rice yield.

Evaluation and breeding application of six brown planthopper resistance genes in rice maintainer line Jin 23B

BackgroundThe brown planthopper (BPH), an insect species that feeds on rice plants (Oryza sativa L.), is one of the most destructive insect pests of rice. BPH can be controlled with chemical pesticides, but they are expensive in terms of the cost and environmental hazards. Hence, utilization of resistance genes in resistant varieties is considered as a more economical and eco-friendly effective method for control.ResultsIn this study, six dominant BPH-resistance genes (Bph3, Bph14, Bph15, Bph18, Bph20 and Bph21) were introduced into an elite indica rice cultivar Jin 23B using the marker-assisted selection (MAS) method of breeding. One line combining Bph14 and Bph15 and six single gene introgression lines were used to evaluate the gene effects based on three parameters: seedling and tillering resistance of the rice genotypes, honeydew weight, and BPH survival rate. Among all improved lines, combination of Bph14 and Bph15 had the largest effect in conferring resistance to BPH. Bioassays showed that the order of the gene effects was Bph14/Bph15 > Bph15 ≥ Bph14 ≥ Bph20 ≥ Bph21 ≥ Bph3 > Bph18 > none at the rice seedling stage. The pyramided or single-gene introgression lines showed enhanced resistance relative to the control. Furthermore, field trial data demonstrated that yields of improved Jin 23B lines were similar to the control under BPH-free field conditions.ConclusionsEach of the BPH resistance genes reduced BPH growth and development, and was effective at both the seedling and tillering growth stages. These lines can be used in rice hybrid and production in China.

Development of 25 near-isogenic lines (NILs) with ten BPH resistance genes in rice (Oryza sativa L.): production, resistance spectrum, and molecular analysis

A first set of 25 NILs carrying ten BPH resistance genes and their pyramids was developed in the background of indica variety IR24 for insect resistance breeding in rice. Brown planthopper (Nilaparvata lugens Stal.) is one of the most destructive insect pests in rice. Development of near-isogenic lines (NILs) is an important strategy for genetic analysis of brown planthopper (BPH) resistance (R) genes and their deployment against diverse BPH populations. A set of 25 NILs with 9 single R genes and 16 multiple R gene combinations consisting of 11 two-gene pyramids and 5 three-gene pyramids in the genetic background of the susceptible indica rice cultivar IR24 was developed through marker-assisted selection. The linked DNA markers for each of the R genes were used for foreground selection and confirming the introgressed regions of the BPH R genes. Modified seed box screening and feeding rate of BPH were used to evaluate the spectrum of resistance. BPH reaction of each of the NILs carrying different single genes was variable at the antibiosis level with the four BPH populations of the Philippines. The NILs with two- to three-pyramided genes showed a stronger level of antibiosis (49.3-99.0%) against BPH populations compared with NILs with a single R gene NILs (42.0-83.5%) and IR24 (10.0%). Background genotyping by high-density SNPs markers revealed that most of the chromosome regions of the NILs (BC3F5) had IR24 genome recovery of 82.0-94.2%. Six major agronomic data of the NILs showed a phenotypically comparable agronomic performance with IR24. These newly developed NILs will be useful as new genetic resources for BPH resistance breeding and are valuable sources of genes in monitoring against the emerging BPH biotypes in different rice-growing countries.

Identification of novel quantitative trait loci associated with brown planthopper resistance in the rice landrace Salkathi

The brown planthopper (BPH) is a potent pest of rice in Asia and Southeast Asia. Host resistance has been found to be the most suitable alternative to manage the insect. But varietal resistance has been found to be short-lived. There has been a constant search for alternate resistance genes. We developed an F8 recombinant inbred population for the BPH resistance gene in Salkathi, an indica landrace from Odisha, India. Phenotyping of RILs against the BPH population at Cuttack, Odisha showed continuous skewed variation with four peaks at 2.1–3.0, 4.1–5.0, 6.1–7.0 and 8.1–9.0 SES score, suggesting the involvement of quantitative loci for resistance to BPH in Salkathi. Mapping showed the presence of two QTLs on the short arm of chromosome 4. One QTL, with phenotype variance of 37.02% is located between the markers RM551 and RM335. The other QTL, with phenotype variance of 7.1% is located between markers RM335 and RM5633. The two QTLs have been designated as qBph4.3 and qBph4.4. QBph4.3 seems to be a novel QTL associated with BPH resistance. We have successfully transferred qBph4.3 and qBph4.4 into two elite rice cultivars, Pusa 44 and Samba Mahsuri. Fine mapping of the identified QTLs may lead to a successful transfer of QTLs into other elite germplasm backgrounds.

Development and evaluation of near-isogenic lines for brown planthopper resistance in rice cv. 9311.

Brown planthopper (BPH) is the most destructive pest of rice in Asia. To date 29 BPH resistance genes have been identified, but only a few genes are being used in breeding due to inefficient markers for marker-assisted selection (MAS) and little knowledge of the real effects of the genes. In this study we individually transferred 13 genes or QTLs (Bph14, QBph3, QBph4, Bph17, Bph15, Bph20, Bph24, Bph6, Bph3, Bph9, Bph10, Bph18 and Bph21) into cultivar 9311 by marker assisted backcross breeding (MABB). Through positive and negative selection we narrowed the segments from donors containing Bph14, Bph15, Bph6 and Bph9 to 100–400 kb. Whole-genome background selection based on a high resolution SNP array was performed to maximize reconstitution of the recurrent parent genome (RPG 99.2–99.9%). All genes reduced BPH growth and development and showed antibiotic responses in seedlings. Based on genetic effects and amino acid sequences of genes in three clusters we inferred that Bph10 and Bph21 might be identical to Bph26, whereas Bph9 and Bph18 were different. Bph15 might be same with Bph17, but QBph4, Bph20 and Bph24 might be different. We believe that these NILs will be useful in rice BPH resistance research and breeding.

Bph32, a novel gene encoding an unknown SCR domain-containing protein, confers resistance against the brown planthopper in rice.

An urgent need exists to identify more brown planthopper (Nilaparvata lugens Stål, BPH) resistance genes, which will allow the development of rice varieties with resistance to BPH to counteract the increased incidence of this pest species. Here, using bioinformatics and DNA sequencing approaches, we identified a novel BPH resistance gene, LOC_Os06g03240 (MSU LOCUS ID), from the rice variety Ptb33 in the interval between the markers RM19291 and RM8072 on the short arm of chromosome 6, where a gene for resistance to BPH was mapped by Jirapong Jairin et al. and renamed as “Bph32”. This gene encodes a unique short consensus repeat (SCR) domain protein. Sequence comparison revealed that the Bph32 gene shares 100% sequence identity with its allele in Oryza latifolia. The transgenic introgression of Bph32 into a susceptible rice variety significantly improved resistance to BPH. Expression analysis revealed that Bph32 was highly expressed in the leaf sheaths, where BPH primarily settles and feeds, at 2 and 24 h after BPH infestation, suggesting that Bph32 may inhibit feeding in BPH. Western blotting revealed the presence of Pph (Ptb33) and Tph (TN1) proteins using a Penta-His antibody, and both proteins were insoluble. This study provides information regarding a valuable gene for rice defence against insect pests.