Mapping of a broad-spectrum brown planthopper resistance gene, <Emphasis Type="Italic">Bph3</Emphasis>, on rice chromosome 6

The brown planthopper (BPH) is one of the most destructive insect pests of rice in Thailand. We performed a cluster analysis that revealed the existence of four groups corresponding to the variation of virulence against BPH resistance genes in 45 BPH populations collected in Thailand. Rice cultivars Rathu Heenati and PTB33, which carry Bph3, showed a broad-spectrum resistance against all BPH populations used in this study. The resistant gene Bph3 has been extensively studied and used in rice breeding programs against BPH; however, the chromosomal location of Bph3 in the rice genome has not yet been determined. In this study, a simple sequence repeat (SSR) analysis was performed to identify and localize the Bph3 gene derived from cvs. Rathu Heenati and PTB33. For mapping of the Bph3 locus, we developed two backcross populations, BC₁F₂ and BC₃F₂, from crosses of PTB33 × RD6 and Rathu Heenati × KDML105, respectively, and evaluated these for BPH resistance. Thirty-six polymorphic SSR markers on chromosomes 4, 6 and 10 were used to survey 15 resistant (R) and 15 susceptible (S) individuals from the backcross populations. One SSR marker, RM190, on chromosome 6 was associated with resistance and susceptibility in both backcross populations. Additional SSR markers surrounding the RM190 locus were also examined to define the location of Bph3. Based on the linkage analysis of 208 BC₁F₂ and 333 BC₃F₂ individuals, we were able to map the Bph3 locus between two flanking SSR markers, RM589 and RM588, on the short arm of chromosome 6 within 0.9 and 1.4 cM, respectively. This study confirms both the location of Bph3 and the allelic relationship between Bph3 and bph4 on chromosome 6 that have been previously reported. The tightly linked SSR markers will facilitate marker-assisted gene pyramiding and provide the basis for map-based cloning of the resistant gene.     

High-resolution genetic mapping at the <Emphasis Type="Italic">Bph15</Emphasis> locus for brown planthopper resistance in rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.)

Resistance to the brown planthopper (BPH), Nilaparvata lugens Stål, a devastating sucking insect pest of rice, is an important breeding objective in rice improvement programs. Bph15, one of the 17 major BPH resistance genes so far identified in both cultivated and wild rice, has been identified in an introgression line, B5, and mapped on chromosome 4 flanked by restriction fragment length polymorphism markers C820 and S11182. In order to pave the way for positional cloning of this gene, we have developed a high-resolution genetic map of Bph15 by positioning 21 DNA markers in the target chromosomal region. Mapping was based on a PCR-based screening of 9,472 F₂ individuals derived from a cross between RI93, a selected recombinant inbred line of B5 bearing the resistance gene Bph15, and a susceptible variety, Taichung Native 1, in order to identify recombinant plants within the Bph15 region. Recombinant F₂ individuals with the Bph15 genotype were determined by phenotype evaluation. Analysis of recombination events in the Bph15 region delimited the gene locus to an interval between markers RG1 and RG2 that co-segregated with the M1 marker. A genomic library of B5 was screened using these markers, and bacterial artificial chromosome clones spanning the Bph15 chromosome region were obtained. An assay of the recombinants using the sub-clones of these clones in combination with sequence analysis delimited the Bph15 gene to a genomic segment of approximately 47 kb. This result should serve as the basis for eventual isolation of the Bph15 resistance gene.     

High-resolution mapping of a new brown planthopper (BPH) resistance gene, Bph18(t), and marker-assisted selection for BPH resistance in rice (Oryza sativa L.)

Brown planthopper (BPH) is a destructive insect pest of rice in Asia. Identification and the incorporation of new BPH resistance genes into modern rice cultivars are important breeding strategies to control the damage caused by new biotypes of BPH. In this study, a major resistance gene, Bph18(t), has been identified in an introgression line (IR65482-7-216-1-2) that has inherited the gene from the wild species Oryza australiensis. Genetic analysis revealed the dominant nature of the Bph18(t) gene and identified it as non-allelic to another gene, Bph10 that was earlier introgressed from O. australiensis. After linkage analysis using MapMaker followed by single-locus ANOVA on quantitatively expressed resistance levels of the progenies from an F₂ mapping population identified with marker allele types, the Bph18(t) gene was initially located on the subterminal region of the long arm of chromosome 12 flanked by the SSR marker RM463 and the STS marker S15552. The corresponding physical region was identified in the Nipponbare genome pseudomolecule 3 through electronic chromosome landing (e-landing), in which 15 BAC clones covered 1.612 Mb. Eleven DNA markers tagging the BAC clones were used to construct a high-resolution genetic map of the target region. The Bph18(t) locus was further localized within a 0.843-Mb physical interval that includes three BAC clones between the markers R10289S and RM6869 by means of single-locus ANOVA of resistance levels of mapping population and marker-gene association analysis on 86 susceptible F₂ progenies based on six time-point phenotyping. Using gene annotation information of TIGR, a putative resistance gene was identified in the BAC clone OSJNBa0028L05 and the sequence information was used to generate STS marker 7312.T4A. The marker allele of 1,078 bp completely co-segregated with the BPH resistance phenotype. STS marker 7312.T4A was validated using BC₂F₂ progenies derived from two temperate japonica backgrounds. Some 97 resistant BC₂F₂ individuals out of 433 screened completely co-segregated with the resistance-specific marker allele (1,078 bp) in either homozygous or heterozygous state. This further confirmed a major gene-controlled resistance to the BPH biotype of Korea. Identification of Bph18(t) enlarges the BPH resistance gene pool to help develop improved rice cultivars, and the PCR marker (7312.T4A) for the Bph18(t) gene should be readily applicable for marker-assisted selection (MAS). K. K. Jena and J. U. Jeung contributed equally to this study.     

Pyramiding and evaluation of the brown planthopper resistance genes Bph14 and Bph15 in hybrid rice

The brown planthopper (BPH) is the most devastating insect pest in rice-producing areas. Shanyou 63 has become a widely cultivated hybrid in China over the last two decades; however, this line has become increasingly susceptible to bacterial blight (BB), blast, and BPH, resulting in a rapid decline in its use in rice production. In this study, a molecular marker-assisted selection (MAS) introgression of Bph14 and Bph15 was performed to improve the BPH resistance of Minghui 63 and its derived hybrids such as Shanyou 63. The effect of pyramiding genes was then comprehensively evaluated using three tests that comprised seedbox screening, feeding rate, and antixenosis for settling in the field. The results showed that the improved hybrids containing a single BPH resistance gene showed enhanced resistance (lower resistance score, honeydew weight and number of BPH settling) compared to conventional hybrids, while pyramiding two genes provided even higher resistance. Moreover, both Bph14 and Bph15 are partial dominance genes, and have a strong dosage effect on the resistance to BPH in the hybrid background, which is useful for breeding BPH-resistant hybrids. Field trial data demonstrated that yields of improved hybrid rice were higher than or similar to the control (Shanyou 63) under natural field conditions. These improved versions could be used in breeding programs for “green super rice.”     

High-resolution mapping of the brown planthopper resistance gene Bph6 in rice and characterizing its resistance in the 9311 and Nipponbare near isogenic backgrounds

Brown planthopper (Nilaparvata lugens Stål, BPH) is one of the most destructive insect pests of rice. Exploring resistance genes from diverse germplasms and incorporating them into cultivated varieties are critical for controlling this insect. The rice variety Swarnalata was reported to carry a resistance gene (designated Bph6), which has not yet been assigned to a chromosome location and the resistance mechanism is still unknown. In this study, we identified and mapped this gene using the F₂ and backcrossing populations and characterized its resistance in indica 9311 and japonica Nipponbare using near isogenic lines (NILs). In analysis of 9311/Swarnalata F₂ population, the Bph6 gene was located on the long arm of chromosome 4 between the SSR markers RM6997 and RM5742. The gene was further mapped precisely to a 25-kb region delimited between the STS markers Y19 and Y9; and the distance between these markers is 25-kb in Nipponbare genome. The Bph6 explained 77.5% of the phenotypic variance of BPH resistance in F₂ population and 84.9% in BC₂F₂ population. Allele from Swarnalata significantly increased resistance to the BPH, resulted in a reduced damage score. In characterization of Bph6-mediated resistance, the BPH insects showed significant preference between NIL-9311 and 9311 in 3 h and between NIL-NIP and Nipponbare in 120 h after release. BPH growth and development were inhibited, and the insect’s survival rates were lower on Bph6-NIL plants, compared with the parents 9311 and Nipponbare. The results indicate that the Bph6 exerted prolonged antixenotic and antibiotic effects in Bph6-NIL plants, and NIL-9311 plants showed a quicker and stronger effect toward BPH than NIL-NIP plants.     

抗褐飞虱水稻品种的培育及其抗性表现

褐飞虱Nilaparvata lugens(Stl)是危害水稻的主要虫害之一,发掘和利用新的抗褐飞虱基因培育抗性品种是目前防治褐飞虱最经济有效的方法之一。抗褐飞虱基因来自药用野生稻的抗虫品种B5,对褐飞虱生物型1和2具有高度抗性,B5携带的抗性基因Bph14被定位在第3染色体上。本研究以B5-10为抗源,以优良杂交稻亲本扬稻6号为受体亲本,通过复交和回交,利用与Bph14紧密连锁的分子标记MRG2329在后代中进行分子标记辅助选择,通过苗期分子标记检测和成株期农艺性状选择,最后育成恢复系R476和杂交组合广两优476。采用苗期群体鉴定技术对R476和广两优476的褐飞虱抗性进行了鉴定,R476和广两优476的抗性水平分别为中抗和中感。广两优476在稻飞虱发生较重的稻田进行试种示范,与对照品种扬两优6号和两优培九相比,广两优476对稻飞虱表现出明显的抗性。研究结果表明在育种过程中利用分子标记辅助选择Bph14基因是培育抗褐飞虱水稻品种的有效途径之一。     

Aspects of brown planthopper adaptation to resistant rice varieties with the Bph3 gene

Despite over 30 years of deployment, varieties with the Bph3 gene for resistance to the brown planthopper (BPH), Nilaparvata lugens (Stål) (Hemiptera: Delphacidae), are still effective in much of the Philippines. In the present study, we determined the effects of adaptation to one resistant variety, IR62 – assumed to possess the Bph3 gene – on (1) resistance against a series of varieties with similar biotypical responses (presumed to contain the same major resistance genes), and (2) a differential variety with the bph4 gene that occurs at the same chromosome position as Bph3. We also examined the effects of high soil nitrogen on the effectiveness of Bph3. Feeding, planthopper biomass, and development times were reduced in a wild BPH population when reared on IR62 compared with the susceptible standard variety TN1. However, nitrogen application increased the susceptibility of IR62. After 13 generations on IR62, BPH had adapted to the plant’s resistance. Virulence of the adapted BPH against the variety ‘Rathu Heenati’ supports the idea that Bph3 is present in IR62. Across similar IR varieties (IR60, IR66, IR68, IR70, IR72, and IR74), feeding, planthopper biomass, and development rates were generally higher for IR62‐adapted than for non‐adapted BPH; however, contrary to expectations, many of these varieties were already susceptible to wild BPH. Fitness was also higher for IR62‐adapted BPH on the variety ‘Babawee’ indicating a close relation between Bph3 and bph4. The results indicate that the conventional understanding of the genetics behind resistance in IR varieties needs to be readdressed to develop and improve deployment strategies for resistance management.     

High-resolution mapping of two rice brown planthopper resistance genes, Bph20(t) and Bph21(t), originating from Oryza minuta

Brown planthopper (BPH) is one of the most destructive insect pests of rice. Wild species of rice are a valuable source of resistance genes for developing resistant cultivars. A molecular marker-based genetic analysis of BPH resistance was conducted using an F₂ population derived from a cross between an introgression line, ‘IR71033-121-15’, from Oryza minuta (Accession number 101141) and a susceptible Korean japonica variety, ‘Junambyeo’. Resistance to BPH (biotype 1) was evaluated using 190 F₃ families. Two major quantitative trait loci (QTLs) and two significant digenic epistatic interactions between marker intervals were identified for BPH resistance. One QTL was mapped to 193.4-kb region located on the short arm of chromosome 4, and the other QTL was mapped to a 194.0-kb region on the long arm of chromosome 12. The two QTLs additively increased the resistance to BPH. Markers co-segregating with the two resistance QTLs were developed at each locus. Comparing the physical map positions of the two QTLs with previously reported BPH resistance genes, we conclude that these major QTLs are new BPH resistance loci and have designated them as Bph20(t) on chromosome 4 and Bph21(t) on chromosome 12. This is the first report of BPH resistance genes from the wild species O. minuta. These two new genes and markers reported here will be useful to rice breeding programs interested in new sources of BPH resistance.     

水稻OsLecRK1基因介导的抗褐飞虱功能分析

褐飞虱Nilaparvata lugens St(a)l是对水稻最具破坏性的害虫之一,OsLecRK1是水稻Bph3基因簇中对褐飞虱抗性贡献最大的基因.本文对RHTd(含Bph3)等材料进行了褐飞虱抗性评价,克隆并构建了OsLecRK1过量表达突变体水稻,利用该突变体分析了OsLecRK1基因对褐飞虱若虫存活率、若虫发育历期等生物学参数的影响.结果 表明,含Bph3基因水稻RHTd对褐飞虱的抗性明显地强于含Bph1基因水稻Mudgo和bph2基因水稻ASD7,RHTd水稻的褐飞虱受害指数仅为Mudgo和ASD7水稻的53.5％和24.1％.过量表达OsLecRK1基因能显著地增加水稻对褐飞虱的驱避性和抗生性,褐飞虱雌成虫偏好于在野生型水稻上产卵;突变体水稻上的褐飞虱若虫存活率显著地降低,仅为野生型水稻上若虫存活率的75.2％ ～81.8％,且若虫发育历期显著地延长,羽化率和初羽化雌成虫体重均显著地降低;此外,褐飞虱在突变体水稻上取食分泌的蜜露量只有野生型上的40.3％ ～ 60.9％,褐飞虱单雌产卵量只为野生型51％ ～61.2％,卵孵化率只有野生型的52.2％～56.7％,均显著地减少.结果 表明,含Bph3基因水稻RHTd对褐飞虱的抗性明显地高于分别含Bph1、bph2的水稻Mudgo和ASD7;水稻Bph3基因座的OsLecRK1单个基因过量表达即可显著增加水稻对褐飞虱的抗性,OsLecRK1协同影响褐飞虱的多个生物学参数降低褐飞虱的适合度.     

High-resolution mapping of brown planthopper (BPH) resistance gene Bph27(t) in rice (Oryza sativa L.)

Brown planthopper (BPH), Nilaparvata lugens Stål, is a destructive insect pest of rice (Oryza sativa L.). Identification and utilization of resistance genes is an efficient strategy for controlling this insect. BPH-resistant indica cultivars Balamawee, Kaharamana and Pokkali were previously reported to have the same dominant gene Bph9 on chromosome 12. Our studies of BPH feeding performance showed that Balamawee had higher levels of antixenosis and antibiosis against BPH than Kaharamana and Pokkali. In order to identify the BPH resistance gene in Balamawee, an F2 population was derived by crossing Balamawee and susceptible japonica cultivar 02428. A single major resistance gene was identified and mapped to the long arm of chromosome 4. Further recombination analysis showed that the gene was located in an interval of about 63 kb between InDel markers Q52 and Q20. This new BPH resistance locus was designated Bph27(t).     

Genetic mapping of the rice resistance-breaking gene of the brown planthopper Nilaparvata lugens

Host plant resistance has been widely used for controlling the major rice pest brown planthopper (BPH, Nilaparvata lugens). However, adaptation of the wild BPH population to resistance limits the effective use of resistant rice varieties. Quantitative trait locus (QTL) analysis was conducted to identify resistance-breaking genes against the anti-feeding mechanism mediated by the rice resistance gene Bph1. QTL analysis in iso-female BPH lines with single-nucleotide polymorphism (SNP) markers detected a single region on the 10th linkage group responsible for the virulence. The QTL explained from 57 to 84% of the total phenotypic variation. Bulked segregant analysis with next-generation sequencing in F₂ progenies identified five SNPs genetically linked to the virulence. These analyses showed that virulence to Bph1 was controlled by a single recessive gene. In contrast to previous studies, the gene-for-gene relationship between the major resistance gene Bph1 and virulence gene of BPH was confirmed. Identified markers are available for map-based cloning of the major gene controlling BPH virulence to rice resistance.     

Candidate genes and molecular markers associated with brown planthopper (<Emphasis Type="Italic">Nilaparvata lugens</Emphasis> Stål) resistance in rice cultivar Rathu Heenati

Brown planthopper (BPH) is a destructive insect pest of rice and causes severe yield loss. In attempts to develop a BPH-resistant rice variety, Rathu Heenati (RH), a rice cultivar with a strong BPH resistance, has been used as the donor in breeding programs. Quantitative trait loci analysis was conducted for the area under the curve of BPH damage scores of a backcross (BC₃F₅) population infested by six different BPH populations. Single nucleotide polymorphism (SNP) markers on chromosome 4, i.e., LecRK2-SNP and LecRK3-SNP, and markers on chromosome 6, i.e., Bph32-SNP and SSR23, were identified to be associated with resistance against five BPH populations. To identify genes on chromosome 6 that are involved in BPH resistance, expression analysis was conducted for genes located in the genomic region of Bph32-SNP and SSR23. Genes that showed differential expression ofRH at 24 h after BPH infestation, when compared to an RH control, were identified. Those that encode proteins putatively involved in the BPH resistance mechanism are LOC_Os06g03240, LOC_Os06g03380, LOC_Os06g03486, LOC_Os06g03514, LOC_Os06g03520, LOC_Os06g03610, LOC_Os06g03676, and LOC_Os06g03890. SNP markers were developed from several differentially expressed genes and were validated by genotyping in the backcross population. The SNP marker developed from LOC_Os06g03514 showed the highest association with BPH resistance and the gene may be involved in the BPH resistance mechanism. This SNP marker will be useful in breeding programs for BPH resistance.     

云南野生稻抗褐飞虱评价及其抗性基因鉴定

褐飞虱是水稻生产中最严重的害虫之一,从野生稻中发掘抗虫基因,有利于培育具有抗虫能力强的水稻新品种。该研究通过对云南野生稻进行温室和大田抗虫鉴定以及9个已知抗褐飞虱基因的PCR鉴定,发现云南野生稻对褐飞虱表现出不同程度的抗性,尤其疣粒野生稻和药用野生稻对褐飞虱表现出高抗,可作为抗虫基因发掘的优良抗源材料;不同褐飞虱抗性的云南野生稻中含有的抗褐飞虱基因差异很大,3种野生稻中均不含Bph1和Bph18(t)抗病基因,景洪普通野生稻和元江普通野生稻可能含bph2基因,东乡普通野生稻可能含bph2、Bph15和Bph27(t)基因,疣粒野生稻中可能含bph2和bph19(t)基因,药用野生稻和药用野生稻(宽叶型)中可能含bph2和Bph6基因,药用野生稻F1中可能含bph2、Bph14和bph20(t)基因,药用野生稻F2中可能含bph2和Bph27(t)基因或者其同源基因。该研究为快速发掘利用云南野生稻中的抗虫基因奠定了理论基础。     

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.     

Microarray analysis of the interaction between the aphid <Emphasis Type="Italic">Rhopalosiphum padi</Emphasis> and host plants reveals both differences and similarities between susceptible and partially resistant barley lines

The bird cherry-oat aphid (Rhopalosiphum padi L.) is an important pest on cereals causing plant growth reduction without specific leaf symptoms. Breeding of barley (Hordeum vulgare L.) for R. padi resistance shows that there are several resistance genes, reducing aphid growth. To identify candidate sequences for resistance-related genes, we performed microarray analysis of gene expression after aphid infestation in two susceptible and two partially resistant barley genotypes. One of the four lines is a descendant of two of the other genotypes. There were large differences in gene induction between the four lines, indicating substantial variation in response even between closely related genotypes. Genes induced in aphid-infested tissue were mainly related to defence, primary metabolism and signalling. Only 24 genes were induced in all lines, none of them related to oxidative stress or secondary metabolism. Few genes were down-regulated, with none being common to all four lines. There were differences in aphid-induced gene regulation between resistant and susceptible lines. Results from control plants without aphids also revealed differences in constitutive gene expression between the two types of lines. Candidate sequences for induced and constitutive resistance factors have been identified, among them a proteinase inhibitor, a serine/threonine kinase and several thionins. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Marker-assisted pyramiding of brown planthopper (Nilaparvata lugens Stål) resistance genes Bph1 and Bph2 on rice chromosome 12

Brown planthopper (BPH) (Nilaparvata lugens St?l) is a significant insect pest of rice (Oryza sativa L.). We constructed a gene-pyramided japonica line, in which two BPH resistance genes Bph1 and Bph2 on the long arm of chromosome 12 independently derived from two indica resistance lines were combined through the recombinant selection. The gene-pyramiding was achieved based on the previously constructed high-resolution linkage maps of the two genes. Two co-dominant and four dominant PCR-based markers flanking the loci were used to select for a homozygous recombinant line in a segregating population that was derived from a cross between the parental homozygous single-gene introgression lines. BPH bioassay showed that the resistance level of the pyramided line was equivalent to that of the Bph1-single introgression line, which showed a higher level of resistance than the Bph2-single introgression line. The pyramid line should provide a useful experimental means for studying the fine structure of the chromosomal region covering these two major BPH resistance genes.     

Fine mapping of brown planthopper (Nilaparvata lugens Stål) resistance gene Bph28(t) in rice (Oryza sativa L.)

The brown planthopper (BPH; Nilaparvata lugens Stål) is one of the most destructive insect pests of rice (Oryza sativa L.) throughout the Asian rice-growing countries. DV85 is a BPH-resistant indica variety. A single dominance gene conferring resistance in DV85 was previously mapped on the long arm of chromosome 11. The objectives of this study were to investigate feeding behaviors of BPH on DV85 plants and fine-map the BPH resistance gene, here designated Bph28(t). A seedling bulk test was conducted to identify resistant plant reactionsvg to BPH feeding. The results showed that the resistance of DV85 functions by means of tolerance during BPH attack, rather than non-preference and antibiosis. For fine mapping, two F2 populations were developed by crossing DV85 with the susceptible japonica variety Kinmaze and indica 9311. A high-resolution genetic map harboring Bph28(t) was constructed and Bph28(t) was finally physically defined to an interval of 64.8 kb between markers Indel55 and Indel66. The fine-mapped Bph28(t) gene will facilitate marker-assisted gene pyramiding for BPH resistance.     

Genetic and biochemical mechanisms of rice resistance to planthopper

Key message

This article presents a comprehensive review on the genetic and biochemicalmechanisms governing rice-planthopper interactions, aiming to contribute substantialplanthopper control and facilitate breeding for resistance to planthoppers in rice.

Abstract

The rice planthopper is the most destructive pest of rice and a substantial threat to rice production. The brown planthopper (BPH), white-backed planthopper (WBPH) and small brown planthopper (SBPH) are three species of delphacid planthoppers and important piercing-sucking pests of rice. Host-plant resistance has been recognized as the most practical, economical and environmentally friendly strategy to control planthoppers. Until now, at least 30, 14 and 34 major genes/quantitative trait loci for resistance to BPH, WBPH and SBPH have been identified, respectively. Recent inheritance and molecular mapping of gene analysis showed that some planthopper-resistance genes in rice derived from different donors aggregate in clusters, while resistance to these three species of planthoppers in a single donor is governed not by any one dominant gene but by multiple genes. Notably, Bph14, Bph26, Bph3 and Bph29 were successfully identified as BPH-resistance genes in rice. Biological and chemical studies on the feeding of planthoppers indicate that rice plants have acquired various forms of defence against planthoppers. Between the rice-planthopper interactions, rice plants defend against planthoppers through activation the salicylic acid-dependent systemic acquired resistance but not jasmonate-dependent hormone response pathways. Transgenic rice for the planthopper-resistance mechanism shows that jasmonate and its metabolites function diversely in rice’s resistance to planthopper. Understanding the genetic and biochemical mechanisms underlying resistance in rice will contribute to the substantial control of such pests and facilitate breeding for rice’s resistance to planthopper more efficiently.

     

High-resolution mapping of a gene conferring strong antibiosis to brown planthopper and developing resistant near-isogenic lines in 9311 background

The brown planthopper (BPH), Nilaparvata lugens Stål, is one of the most destructive pests to the rice production in the world. Thus, there is an urgency to identify new resistant genes for breeding. AC-1613 is an indica variety that has been reported to confer broad-spectrum resistance to BPH. In the present study, we found that AC-1613 exhibited strong antibiosis towards BPH insects. The body weight was significantly decreased when the insects fed on AC-1613 plants. By using BPH weight gain as an index of phenotyping, a novel dominant locus for resistance to BPH, designed as Bph30, was identified and its near-isogenic line (NIL) in 9311 background was developed. The F₂ population derived from a cross between AC-1613 and 9311 was used for mapping the gene. Through QTL scan, we located the gene on the short arm of chromosome 4 between RM16278 and RM16425, which explained 42.7% of the phenotypic variance (PEV) of BPH resistance in the F₂ population. The gene was finally located in a region flanking by simple sequence repeat (SSR) markers SSR-28 and SSR-69 through high-resolution mapping, the distance between the two markers in Nipponbare genome is 37.5 kb. In addition, SSR markers RM16294 and RM16299 tightly linked to Bph30 were applied effectively in introgressing Bph30 into elite rice cultivars. The developed NILs showed a strong antibiosis and high resistance to BPH.     

Identification and mapping of two brown planthopper resistance genes in rice

The brown planthopper (BPH) is one of the most serious insect pests of rice. In this study, we conducted a molecular marker-based genetic analysis of the BPH resistance of ’B5’, a highly resistant line that derived its resistant genes from the wild rice Oryza officinalis. Insect resistance was evaluated using 250 F₃ families from a cross between ’B5’ and ’Minghui 63’, based on which the resistance of each F₂ plant was inferred. Two bulks were made by mixing, respectively, DNA samples from highly resistant plants and highly susceptible plants selected from the F₂ population. The bulks were surveyed for restriction fragment length polymorphism using probes representing all 12 chromosomes at regular intervals. The survey revealed two genomic regions on chromosome 3 and chromosome 4 respectively that contained genes for BPH resistance. The existence of the two loci were further assessed by QTL (quantitative trait locus) analysis, which resolved these two loci to a 14.3-cM interval on chromosome 3 and a 0.4-cM interval on chromosome 4. Comparison of the chromosomal locations and reactions to BPH biotypes indicated that these two genes are different from at least nine of the ten previously identified BPH resistance genes. Both of the genes had large effects on BPH resistance and the two loci acted essentially independent of each other in determining t he resistance. These two genes may be a useful BPH resistance resource for rice breeding programs. Received: 6 March 2000 / Accepted: 28 July 2000