Symbiont-mediated adaptation by planthoppers and leafhoppers to resistant rice varieties

For over 50 years, host plant resistance has been the principal focus of public research to reduce planthopper and leafhopper damage to rice in Asia. Several resistance genes have been identified from native varieties and wild rice species, and some of these have been incorporated into high-yielding rice varieties through conventional breeding. However, adaptation by hoppers to resistant rice has been phenomenally rapid, and hopper populations with virulence against several resistance genes are now widespread. Directional genetic selection for virulent hoppers seems unlikely given the rapid pace of adaptation reported from field and laboratory studies. Among the alternative explanations for rapid hopper adaptation are changes (genetic, epigenetic, or community structure) in endosymbiont communities that become advantageous for planthoppers and leafhoppers that feed on resistant rice varieties. This review examines the nature of these symbiont communities and their functions in planthoppers and leafhoppers—focusing on their likely roles in mediating adaptation to plant resistance. Evidence from a small number of experimental studies suggests that bacterial and eukaryotic (including yeast-like) symbionts can determine or mediate hopper virulence on rice plants and that symbiont functions could change over successive generations of selection on both resistant and susceptible plants. The review highlights the potential complexity of rice hopper–symbiont interactions and calls for a more careful choice of research materials and methods to help reduce this complexity. Finally, the consequences of symbiont-mediated virulence adaptation for future rice breeding programs are discussed.     

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。     

Detection and analysis of QTLs for resistance to the brown planthopper, Nilaparvata lugens, in a doubled-haploid rice population

 We used a mapping population of 131 doubled-haploid lines, produced from a cross between an improved indica rice variety (IR64) and a traditional japonica variety (Azucena), to detect quantitative trait loci (QTLs) for resistance to the brown planthopper (BPH), Nilaparvata lugens. We evaluated the parents and mapping population with six tests that measure varying combinations of the three basic mechanisms of insect host plant resistance, i.e., antixenosis, antibiosis, and tolerance. To factor-out the effect of the major resistance gene Bph1 from IR64, the screening was done with two BPH populations from Luzon Island, The Philippines, that are almost completely adapted to this gene. A total of seven QTLs associated with resistance were identified, located on 6 of the 12 rice chromosomes. Individual QTLs accounted for between 5.1 and 16.6% of the phenotypic variance. Two QTLs were predominantly associated with a single resistance mechanism: one with antixenosis and one with tolerance. Most of the QTLs were derived from IR64, which has been shown to have a relatively durable level of moderate resistance under field conditions. The results of this study should be useful in transferring this resistance to additional rice varieties. Received: 10 May 1998 / Accepted: 4 June 1998     

Non-specific resistance in brown planthopper resistant indica rice varieties against Plodia interpunctella (Lepidoptera: Phycitidae)

Mechanisms of host plant resistance against insect pests can be manifold. Resistance screenings generally use single target insect pests, but the resistance thus screened may not always be specific to the target insect species. We conducted a test for non‐specific resistance in indica rice varieties with resistance genes against brown planthopper (BPH), by using the Indian meal moth, Plodia interpunctella. The test system was very simple, and only required the non‐pest moth to be reared on rice flour. We compared the survival rate, developmental period and adult weight of the moth on three rice varieties: ‘Nipponbare’, a BPH‐susceptible japonica variety, and ‘Thai Collection 11’ and ‘Pokkali’, two resistant indica varieties. Our results were straightforward and demonstrate that resistance in the two resistant rice varieties is not BPH specific, because development of the moth was retarded and adult body weight was reduced.     

RAPD markers linked to brown planthopper Nilaparvatha lugens resistance locus in rice

Brown plant hopper, a major pest in rice causes "hopper burn" in the field. The resistance gene for brown planthopper was mapped by using 20 recombinant inbred lines (RIL's) derived from a cross between resistant line Oryza. officinalis derivative (IR 54742-2-21-12-17-6) and a susceptible rice cultivar ASD 16 using bulked segregant analysis. On an average of 4 loci were amplified and two RAPD primers amplified loci that co-segregated with resistance/susceptibility. The segregating RAPD loci were mapped using Mapmaker programme into 13 groups. The expected and the 95% confidence level were found to be 15.2 and 47.7 cM respectively, confirming the location of the brown planthopper resistant gene on the region of chromosome 4. These RAPD markers will accelerate breeding programme for brown planthopper resistance.     

RFLP-facilitated investigation of the quantitative resistance of rice to brown planthopper ( Nilaparvata lugens)

Quantitative trait loci (QTLs), conferring quantitative resistance to rice brown planthopper (BPH), were investigated using 160 F₁₁ recombinant inbred lines (RILs) from the Lemont/Teqing cross, a complete RFLP map, and replicated phenotyping of seedbox inoculation. The paternal indica parent, Teqing, was more-resistant to BPH than the maternal japonica parent, Lemont. The RILs showed transgressive segregation for resistance to BPH. Seven main-effect QTLs and many epistatic QTL pairs were identified and mapped on the 12 rice chromosomes. Collectively, the main-effect and epistatic QTLs accounted for over 70% of the total variation in damage scores. Teqing has the resistance allele at four main-effect QTLs, and the Lemont allele resulted in resistance at the other three. Of the main-effect QTLs identified, QBphr5b was mapped to the vicinity of gl1, a major gene controlling leaf and stem pubescence. The Teqing allele controlling leaf and stem pubescence was associated with resistance, while the Lemont allele for glabrous stem and leaves was associated with susceptibility, indicating that this gene may have contributed to resistance through antixenosis. Similar to the reported BPH resistance genes, the other six detected main-effect QTLs were all mapped to regions where major disease resistance genes locate, suggesting they might have contributed either to antibiosis or tolerance. Our results indicated that marker-aided pyramiding of major resistance genes and QTLs should provide effective and stable control over this devastating pest. Received: 10 December 2000 / Accepted: 7 May 2001     

Molecular progress on the mapping and cloning of functional genes for blast disease in rice (Oryza sativa L.): current status and future considerations

Rice blast disease, which is caused by the fungal pathogen Magnaporthe oryzae, is a recurring problem in all rice-growing regions of the world. The use of resistance (R) genes in rice improvement breeding programmes has been considered to be one of the best options for crop protection and blast management. Alternatively, quantitative resistance conferred by quantitative trait loci (QTLs) is also a valuable resource for the improvement of rice disease resistance. In the past, intensive efforts have been made to identify major R-genes as well as QTLs for blast disease using molecular techniques. A review of bibliographic references shows over 100 blast resistance genes and a larger number of QTLs (～500) that were mapped to the rice genome. Of the blast resistance genes, identified in different genotypes of rice, ～22 have been cloned and characterized at the molecular level. In this review, we have summarized the reported rice blast resistance genes and QTLs for utilization in future molecular breeding programmes to introgress high-degree resistance or to pyramid R-genes in commercial cultivars that are susceptible to M. oryzae. The goal of this review is to provide an overview of the significant studies in order to update our understanding of the molecular progress on rice and M. oryzae. This information will assist rice breeders to improve the resistance to rice blast using marker-assisted selection which continues to be a priority for rice-breeding programmes.     

辽宁水稻品种抗灰飞虱鉴定及其抗性机制研究

为探明辽宁地区水稻品种对本地灰飞虱Laodelphax striatellus(Fallén)的抗性水平及其抗虫机制,本研究利用改进的苗期集团鉴定法,以IR36为抗虫对照品种、武育粳3号为感虫对照品种,对42份辽宁地区主栽水稻品种和研究待推广品种进行了水稻苗期对灰飞虱抗性鉴定,并从中选取20份不同抗性水平的品种进行了排趋性和抗生性的测定。结果表明:从42份水稻材料中仅筛选出1份抗虫材料辽优5218,中抗品种11份,其余均为感虫或高感品种。在不同水稻类型中,杂交稻的抗虫性普遍较常规稻强,而从水稻株型上看,抗性品种大多为披散型。抗虫机制研究发现,抗虫品种辽优5218和中抗品种港育129兼具排趋性和抗生性,是非常理想的抗性种质资源,中抗品种港源8号和粳优558具有很强的排趋性,也是较为理想的抗性资源,为抗性机制的深入研究提供了材料。但大部分省内主栽主推品种不具备对灰飞虱的抗性,应引起重视。     

Pyramided rice lines harbouring Allium sativum (asal) and Galanthus nivalis (gna) lectin genes impart enhanced resistance against major sap-sucking pests

We have developed transgene pyramided rice lines, endowed with enhanced resistance to major sap-sucking insects, through sexual crosses made between two stable transgenic rice lines containing Allium sativum (asal) and Galanthus nivalis (gna) lectin genes. Presence and expression of asal and gna genes in pyramided lines were confirmed by PCR and western blot analyses. Segregation analysis of F₂ progenies disclosed digenic (9:3:3:1) inheritance of the transgenes. Homozygous F₃ plants carrying asal and gna genes were identified employing genetic and molecular methods besides insect bioassays. Pyramided lines, infested with brown planthopper (BPH), green leafhopper (GLH) and whitebacked planthopper (WBPH), proved more effective in reducing insect survival, fecundity, feeding ability besides delayed development of insects as compared to the parental transgenics. Under infested conditions, pyramided lines were found superior to the parental transgenics in their seed yield potential. This study represents first report on pyramiding of two lectin genes into rice exhibiting enhanced resistance against major sucking pests. The pyramided lines appear promising and might serve as a novel genetic resource in rice breeding aimed at durable and broad based resistance against hoppers.     

GENE SILENCING BY PARENTAL RNA INTERFERENCE IN THE GREEN RICE LEAFHOPPER,Nephotettix cincticeps (HEMIPTERA: CICADELLIDAE)

RNA interference (RNAi) has been widely used for investigating gene function in many nonmodel insect species. Parental RNAi causes gene knockdown in the next generation through the administration of double‐strand RNA (dsRNA) to the mother generation. In this study, we demonstrate that parental RNAi mediated gene silencing is effective in determining the gene function of the cuticle and the salivary glands in green rice leafhopper (GRH), Nephotettix cincticeps (Uhler). Injection of dsRNA of NcLac2 (9 ng/female) to female parents caused a strong knockdown of laccase‐2 gene of first instar nymphs, which eventually led to high mortality rates and depigmentation of side lines on the body. The effects of parental RNAi on the mortality of the nymphs were maintained through 12–14 days after the injections. We also confirmed the effectiveness of parental RNAi induced silencing on the gene expressed in the salivary gland, the gene product of which is passed from instar to instar. The parental RNAi method can be used to examine gene function by phenotyping many offspring nymphs with injection of dsRNA into a small number of parent females, and may be applicable to high‐efficiency determination of gene functions in this species.     

利用抑制差减杂交技术分离受水稻抗性调控的褐飞虱基因

为分离受水稻抗性调控的褐飞虱Nilaparvata lugens基因, 以取食感虫水稻台中1号和高抗水稻B5的2叶1芯秧苗24 h的褐飞虱4龄若虫为起始材料, 采用抑制差减杂交技术构建了两个群体间的正反向差减cDNA文库。通过斑点杂交从差减文库中筛选代表受水稻抗性调控的基因的cDNA克隆, 进行测序和功能分析, 挑选具功能的基因进行Northern杂交验证。结果表明, 通过斑点杂交筛选到的98个阳性克隆代表92个互不重复的单基因, 其中25个与动物的已知蛋白基因存在较高的同源性。Northern杂交表明, 这25个基因有11个表达上调, 8个表达下调, 提示它们可能在褐飞虱适应抗性水稻过程中发挥了重要作用。本研究结果为克隆上述新基因的全长cDNA序列及进一步研究其在褐飞虱与水稻互作中的功能奠定了基础。     

QTL analysis and mapping of pi21, a recessive gene for field resistance to rice blast in Japanese upland rice

Field resistance is defined as the resistance that allows effective control of a parasite under natural field conditions and is durable when exposed to new races of that parasite. To identify the genes for field resistance to rice blast, quantitative trait loci (QTLs) conferring field resistance to rice blast in Japanese upland rice were detected and mapped using RFLP and SSR markers. QTL analysis was carried out in F₄ progeny lines from the cross between Nipponbare (moderately susceptible, lowland) and Owarihatamochi (resistant, upland). Two QTLs were detected on chromosome 4 and one QTL was detected on each of chromosomes 9 and 12. The phenotypic variation explained by each QTL ranged from 7.9 to 45.7% and the four QTLs explained 66.3% of the total phenotypic variation. Backcrossed progeny lines were developed to transfer the QTL with largest effect using the susceptible cultivar Aichiasahi as a recurrent parent. Among 82 F₃ lines derived from the backcross, resistance segregated in the expected ratio of resistant 1 : heterozygous 2 : susceptible 1. The average score for blast resistance measured in the field was 4.2 ± 0.67, 7.5 ± 0.51and 8.2 ± 0.66, for resistant, heterozygous and susceptible groups, respectively. The resistance gene, designated pi21, was mapped on chromosome 4 as a single recessive gene between RFLP marker loci G271 and G317 at a distance of 5.0 cM and 8.5 cM, respectively. The relationship to previously reported major genes and QTLs conferring resistance to blasts, and the significance of marker-assisted selection to improve field resistance, are discussed. Received: 8 June 2000 / Accepted: 24 November 2000     

小粒野生稻导入系对稻飞虱的抗性鉴定与分析

稻飞虱是水稻生产最严重的害虫之一。野生稻拥有丰富的抗虫基因资源,导入系是鉴定和利用野生稻有利基因的有效途径。本研究通过对371份小粒野生稻导入系进行抗褐飞虱和白背飞虱接虫鉴定,分别筛选出了11份抗、72份中抗褐飞虱的材料和7份抗、45份中抗白背飞虱的材料,其中有5份材料兼抗褐飞虱和白背飞虱,这是从小粒野生稻中鉴定出抗白背飞虱材料的首次报道。通过对2份抗性导入系材料与感虫亲本杂交构建的F1和F2群体的抗虫鉴定和分析表明:K41对褐飞虱和白背飞虱的抗性受2对显性抗虫基因通过互补作用所控制;P114对褐飞虱和白背飞虱的抗性都是由1对主效的隐性基因控制。这些结果必将有利于小粒野生稻抗稻飞虱的基因定位和育种利用。     

褐飞虱致害性变异机制研究进展

褐飞虱Nilaparvata lugens Stal是危害水稻Oryza sativa L.的毁灭性害虫。种植抗虫水稻品种可以控制褐飞虱危害,技术手段绿色、经济且可持续。但是,褐飞虱致害性变异速度快且程度高,常导致抗虫水稻品种使用年限缩短。目前,针对褐飞虱致害性个体表型及分子标记、产生原因与机制、功能基因研究等已开展了大量研究。本文围绕褐飞虱致害性变异产生的遗传基础、分子标记、变异的主动机制和被动机制等方面进行综述,并对该领域未来方向进行展望。为更好地利用抗虫品种控制虫害,做好害虫的致害性监测及制定防治策略提供参考。     

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.     

Balancing selection and wild gene pool contribute to resistance in global rice germplasm against planthopper

Interactions and co-evolution between plants and herbivorous insects are critically important in agriculture. Brown planthopper (BPH) is the most severe insect of rice, and the biotypes adapt to feed on different rice genotypes. Here, we present genomics analyses on 1,520 global rice germplasms for resistance to three BPH biotypes. Genome-wide association studies identified 3,502 single nucleotide polymorphisms (SNPs) and 59 loci associated with BPH resistance in rice. We cloned a previously unidentified gene Bph37 that confers resistance to BPH. The associated loci showed high nucleotide diversity. Genome-wide scans for trans-species polymorphisms revealed ancient balancing selection at the loci. The secondarily evolved insect biotypes II and III exhibited significantly higher virulence and overcame more rice varieties than the primary biotype I. In response, more SNPs and loci evolved in rice for resistance to biotypes II and III. Notably, three exceptional large regions with high SNP density and resistance-associated loci on chromosomes 4 and 6 appear distinct between the resistant and susceptible rice varieties. Surprisingly, these regions in resistant rice might have been retained from wild species Oryza nivara. Our findings expand the understanding of long-term interactions between rice and BPH and provide resistance genes and germplasm resources for breeding durable BPH-resistant rice varieties.     

水稻品种对褐飞虱持续抗性的筛选技术

通过水稻品种苗期和分蘖期后对褐飞虱的抗性筛选,提出TN_1受害9级时受害1～5级的为抗性品种,TN_19级后苗期10天、分蘖期后24天内保持1～5级的为持抗品种,不具持抗的抗性品种为短期抗性品种。