BPH Resistance Research Articles

High-resolution genetic mapping of a novel brown planthopper resistance locus, Bph34 in Oryza sativa L. X Oryza nivara (Sharma & Shastry) derived interspecific F2 population.

A BPH-resistant locus designated as Bph34 identified in Oryza nivara acc. IRGC104646 on long arm of chromosome 4 using high-resolution mapping with 50K SNP chip. BPH resistance contributed by locus showed dominant inheritance in F2 and F3. The Bph34 locus is 91kb in size and contains 11 candidate genes. In addition to SNP markers, SSR markers, RM16994 and RM17007 co-segregated with the BPH resistance. These two SSR markers can facilitate marker-assisted transfer of the Bph34 locus into elite rice cultivars in all labs. Brown planthopper (BPH, Nilaparvata lugen Stål) is one of the most destructive insects of rice (Oryza sativa L.) causing significant yield losses annually. Exploiting host plant resistance to BPH and incorporating resistant genes in susceptible commercial cultivars is economical and environmentally friendly approach to manage this pest. Here, we report high-resolution mapping of a novel genetic locus for resistance to BPH, designated as Bph34 on long arm of rice chromosome 4. The locus was mapped using an interspecific F2 population derived from a cross between susceptible indica cultivar PR122 and BPH-resistant wild species, O. nivara acc. IRGC104646. Inheritance studies performed using F2 and F2:3 populations revealed the presence of single dominant gene. Construction of high-density linkage map using 50K SNP chip (OsSNPnks) followed by QTL mapping identified single major locus at 28.8 LOD score between SNP markers, AX-95952039 and AX-95921548. The major locus contributing resistance to BPH designated as Bph34 and explained 68.3% of total phenotypic variance. The Bph34 locus is 91Kb in size on Nipponbare reference genome-IRGSP-1.0 and contains 11 candidate genes. In addition to associated SNP markers, two SSR markers, RM16994 and RM17007, also co-segregated with the Bph34 which can be used efficiently for markers assisted transfer into elite rice cultivars across the labs.

Multi-trait improvement in rice through marker-assisted breeding

Biotechnological tools like molecular markers can add precision to breeding and accelerate breeding efforts. Towards this objective, our research team at ICAR-IIRR has applied marker-assisted breeding (MAB) for improvement of multiple traits like resistance against bacterial blight, blast, gall midge and BPH, heterosis related traits, improvement of low soil P tolerance, grain quality and yield. Through marker-assisted backcross breeding (MABB), a high-yielding, bacterial blight resistant rice variety possessing fine-grain type and low glycemic index (GI), named Improved Samba Mahsuri (ISM) has been developed and released for cultivation by farmers. MABB has also been applied for improving bacterial blight resistance of a few important traditional and evolved Basmati rice varieties and hybrid rice parental lines. A novel bacterial blight resistance gene, Xa33 has been identified from an accession of the wild rice, O. nivara, fine-mapped and transferred into several elite genetic backgrounds. Novel sources of resistance against bacterial blight and blast diseases have been identified and characterized and major blast resistance have been transferred to several elite genetic backgrounds and a major QTL associated with neck blast resistance has been identified from wild rice. Additionally, genepyramid lines possessing resistance against gall midge have also been developed and a novel and highly effective BPH resistance gene has also been identified and mapped with molecular marker and few promising donors possessing resistance against sheath blight have been identified. A molecular marker-based assay has been designed for rapid and accurate determination of impurities in seed-lots of rice hybrids and their parental lines and functional markers have been developed for the traits relevant to hybrid rice, viz., wide-compatibility, wild-abortive cytoplasmic male sterility and fertility restoration. Functional markers have also been developed for major grain quality determining genes, fgr and GS3 and a major QTL controlling gelatinization temperature has been identified through molecular mapping. The major QTL responsible for low soil phosphorus (P tolerance, viz., Pup1 has been transferred to Improved Samba Mahsuri, MTU1010 and IR64 and novel, non-Pup1 type donors have been identified for the trait. Four major yield enhancing genes, viz., Gn1a, SCM2, OsSPL14 and GW5 have been transferred to elite rice cultivars, viz., Improved Samba Mahsuri, Swarna, MTU1010 and NDR359.

Sources of resistance against brown plant hopper Nilaparvata lugens stal.

Fifty eight rice genotypes comprising of released varieties, elite breeding lines and genotypes obtained from different screening nurseries were evaluated against brown plant hopper under glasshouse conditions at Punjab Agricultural University, Ludhiana during kharif 2015 and kharif 2016. Based on two years screening, twelve entries showed resistant to moderately resistant reaction. From these, three genotypes, RP2068-303, RP2068-295 and KAUM182-1 were found to be resistant while nine other genotypes, CR3006-8-2, PAU5815-56-2, PAU5815-39-3, CT18139-8-5-1-5-1-1-M, PAU6002-32-1, PAU5815-39-2, PAU6002-32-4, IR71033-121-15-B and IR82858-B-B-2 showed resistant to moderately resistant reaction during two years of screening trial. The potential donors identified in the present study are expected to be a valuable source of BPH resistance.

Gene expression and plant hormone levels in two contrasting rice genotypes responding to brown planthopper infestation

BackgroundThe brown planthopper (BPH; Nilaparvata lugens Stål) is a destructive piercing-sucking insect pest of rice. The plant hormones salicylic acid (SA) and jasmonic acid (JA) play important roles in plant–pest interactions. Many isolated rice genes that modulate BPH resistance are involved in the metabolism or signaling pathways of SA, JA and ethylene. ‘Rathu Heenati’ (RH) is a rice cultivar with a high-level, broad-spectrum resistance to all BPH biotypes. Here, RH was used as the research material, while a BPH-susceptible rice cultivar ‘Taichung Native 1’ (TN1) was the control. A cDNA microarray analysis illuminated the resistance response at the genome level of RH under BPH infestation. The levels of SA and JA in RH and TN1 seedlings after BPH infestation were also determined.ResultsThe expression pattern clustering indicated that 1467 differential probe sets may be associated with constitutive resistance and 67 with the BPH infestation-responsive resistance of RH. A Venn diagram analysis revealed 192 RH-specific and BPH-inducible probe sets. Finally, 23 BPH resistance-related gene candidates were selected based on the expression pattern clustering and Venn diagram analysis. In RH, the SA content significantly increased and the JA content significantly decreased after BPH infestation, with the former occurring prior to the latter. In RH, the differential genes in the SA pathway were synthesis-related and were up-regulated after BPH infestation. The differential genes in the JA pathway were also up-regulated. They were jasmonate ZIM-domain transcription factors, which are important negative regulators of the JA pathway. Comparatively, genes involved in the ET pathway were less affected by a BPH infestation in RH. DNA sequence analysis revealed that most BPH infestation-inducible genes may be regulated by the genetic background in a trans-acting manner, instead of by their promoters.ConclusionsWe profiled the analysis of the global gene expression in RH and TN1 under BPH infestation, together with changes in the SA and JA levels. SA plays a leading role in the resistance response of rice to BPH. Our results will aid in understanding the molecular basis of RH’s BPH resistance and facilitate the identification of new resistance-related genes for breeding BPH-resistant rice varieties.

Mapping of QTLs conferring resistance in rice to brown planthopper, Nilaparvata lugens

AbstractBrown planthopper (BPH), Nilaparvata lugens Stål (Hemiptera: Delphacide), is a destructive insect pest of rice, Oryza sativa L. (Poaceae), in rice‐producing areas worldwide. Host plant resistance is a major aspect of managing this pest. In this study, a mapping population consisting of 150 F3 lines, derived from a cross of MR276 and Rathu Heenati, was used to detect and analyse quantitative trait loci (QTLs) for the resistance to BPH. Composite Interval Mapping (CIM) was used for QTL detection. In total 10 QTLs controlling BPH resistance were mapped on chromosomes 1, 3, 6, 7, 9, 10, and 12. Four QTLs – qBph‐1‐1, qBph‐3‐1, qBph‐6‐1, and qBph‐7‐1 – were mapped on chromosomes 1, 3, 6, and 7 in the standard seedbox screening test, explaining 41% of the phenotypic variance. Two QTLs, qBph‐6‐1 and qBph‐9‐1, were detected on chromosomes 6 and 9 in the honeydew test, accounting for 32% of the total phenotypic variance. Moreover, four QTLs – qBph‐3‐1, qBph‐6‐1, qBph‐10‐1, and qBph‐12‐1 – were identified on chromosomes 3, 6, 10, and 12 expressing antixenosis to BPH and explaining 41% of the phenotypic variance. QTL qBph‐3‐1 was located in the chromosomal region between markers RM231 and RM3872 on chromosome 3, and QTL qBph‐6‐1 was located in the region between RM588 and RM204 on chromosome 6, indicating that these regions have a major effect in controlling the resistance to BPH in the population studied. The molecular markers linked to QTLs that are identified will be useful in the development of varieties resistant to BPH. Our study contributes to the development of genetic material for breeding programmes and marker‐assisted selection (MAS) in rice to improve BPH resistance.

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.

Determination of brown planthopper resistant genes in some rice varieties by molecular markers

Brown plant hopper (Nilaparvata lugens Stal.) is the one of dangerous pests for rice that were reported in most of rice growing countries. Twenty seven BPH resistance genes have been detected in cultivated and wild rice. However, each resistance gene is able to resist with only strain or certain biotype. Besides, many studies indicated that the toxicity of BPH strains tend to change and loss the resistance of rice lines. The breeding of rice varieties that resist to many BPH biotypes is being the breeders towards. With helping of the development of molecular markers and genetic engineering, the breeders are hopping to identify the molecular markers that linked tightly with BPH resistance genes and develop the rice varieties can gather many resistance genes in a well genomic platform. In this study, we assessed the resistance of rice lines of Vietnam and imported rice lines. The resistance was ditermined by using assessement method in the galvanized box and molecular markers linkage with resistance genes (Bph1, bph2, Bph3, Bph9 and Bph17). The results showed that there was a high affinity between the two methods with 70.59% and 86.27% of lines that have the resistance (respectively). Among of 51 surveyed rice lines, 44 lines (86.27%) were determined to have at least one marker linkage with resistance genes. 19 lines (37.25%) harbored two or three markers linkage with resistance genes. These lines will be a good genetic resource for screening and breeding the resistant rice varieties.

Exploring genetic diversity of rice cultivars for the presence of brown planthopper (BPH) resistance genes and development of SNP marker for Bph18

AbstractBrown planthopper (BPH) is the most devastating insect pest in rice‐growing areas. Information on availability of BPH resistance alleles and their sources enhances BPH‐resistant breeding programmes. In this study, 260 highly diversified rice cultivars or breeding lines were screened for the presence of five major BPH resistance genes (Bph10, Bph13, Bph18, Bph20 and Bph21) using gene‐specific markers. The analysis revealed that 137 of the 260 cultivars possess at least one BPH resistance gene. Bph10 was predominant while Bph20 was the least distributed. Moreover, two and three different resistance gene combinations were found in the cultivars. Molecular markers play an important role in molecular breeding programmes. A tightly linked PCR‐based co‐dominant Bph18 marker was developed, which is cost effective and time effective and simpler than available Bph18 CAPS marker (7312.T4A). We strongly believe that the identified BPH‐resistant cultivars can be used as alternative resistance gene sources and also as resource for novel BPH resistance genes. The developed Bph18 marker will be highly useful in molecular breeding applications of BPH‐resistant breeding programmes.

Application of marker‐assisted backcross to introgress Bph3, Bph14 and Bph15 into an elite indica rice variety for improving its resistance to brown planthopper

AbstractTo improve brown planthopper (Nilaparvata lugens Stål; BPH) resistance of an elite indica cultivar of South China, Hemeizhan (HMZ), we applied marker‐assisted backcross (MABC) to incorporate three BPH‐resistance genes (Bph3, Bph14 and Bph15) into the genetic background of HMZ. In the third backcross (BC3) generation, we obtained near‐isogenic lines (Bph3‐NIL, Bph14‐NIL, Bph15‐NIL and Bph14 + Bph15‐NIL) with more than 96% recovery of recurrent parent genome, and pyramided lines (Bph3 + Bph14‐PYL, Bph3 + Bph15‐PYL and Bph3 + Bph14 + Bph15‐PYL) with more than 89% recovery of recurrent parent genome. These lines showed stronger resistance against BPH than HMZ at seedling and booting stages. The rank of resistance gene effect was Bph3 + Bph14 + Bph15 ≥ Bph3 + Bph15 ≥ Bph3 +Bph14 ≥ Bph14 + Bph15 ≥ Bph3 ≥ Bph15 ≥ Bph14 > none. Compared with HMZ, only Bph3 + Bph14 + Bph15‐PYL had a significant difference in yield per plant, and the lines carrying Bph3 had higher amylose contents, indicating that Bph3 was tightly linked to Wxa allele. These improved lines are good intermediate sources of broad‐spectrum and durable BPH resistance to improve other indica cultivars. Our results demonstrate that MABC is a very efficient approach to improve BPH resistance of elite rice cultivar.

Donor validation studies on rice differential varieties against rice brown planthopper, Nilaparvata lugens (Stal.)

Six differential varieties along with standard checks were evaluated for donor validation against rice brown plant hopper at glasshouse, Department of Entomology, IGKV, Raipur during 2013- 14. All the differentials were resistant to Raipur BPH population. Among the differential tested, ARC 10550 exhibited list plant damage score (0.64) followed by Sinna Sivappu (0.75). Honeydew excretion values were minimum in Sinna Sivappu (15.3 mm 2 ) followed by Rathu Heenati (15.8 mm 2 ). The average probing marks were maximum in Sinna Sivappu (38.3) followed by Rathu Heenati (30.7) which were significantly higher than TN1, while nymphal survival value was minimum in variety INRC 3021 (29.21%). All the differentials showed resistant reaction in all the tests performed against Raipur population. These differentials were designated as the potential donors for BPH resistance.

Fine mapping and pyramiding of brown planthopper resistance genes QBph3 and QBph4 in an introgression line from wild rice O. officinalis

The brown planthopper (Nilaparvata lugens Stal; BPH) has become the most destructive insect pest in rice-producing areas. Finding, characterizing and pyramiding BPH resistance genes have become increasingly recognized as an efficient approach to cope with the frequent infestations by BPH. Introgression line IR02W101 is derived from the wild rice Oryza officinalis. Using a BC1F2:3 population from a cross between Zhenshan 97 and IR02W101, we firstly mapped QBph3 on the long arm of chromosome 3, and QBph4 on short arm of chromosome 4, explaining 28 and 35 % of the variation in BPH response, respectively. We further used two BC2F2:3 populations to fine-map QBph3 to a 47-kb region co-segregating with marker c3-14, and QBph4 to a 200-kb region. Furthermore, we developed eight near-isogenic lines and four pyramided lines (PLs) containing both or either of QBph3 and QBph4 with Bph14 and Bph15 in the backgrounds of Zhenshan 97 and 9311, by marker-assisted backcrossing (MABC). The BPH bioassay showed that the PL-QBph3/QBph4 was the most resistant of the lines. The fine mapping and pyramiding of QBph3 and QBph4 will facilitate map-based cloning of these genes, which can be used immediately in hybrid breeding and production.

Improved marker-assisted selection efficiency of multi-resistance in doubled haploid rice plants

During rice cultivation, brown planthopper (BPH, Nilaparvata lugens Stal.) and white-backed planthopper (WBPH, Sogatella furcifera) infestations cause decreased yield and rice quality. In this study, we attempted to develop multi-resistance plants and increase the marker-assisted selection (MAS) efficiency. The frequency of callus induction in 95 F1 doubled haploid lines (DHLs) derived from JSNDH13 (BPH resistance)/CNDH32 (WBPH resistance) ranged from 3.8 to 15.2 %. The plant regeneration rates varied from 2.9 to 39.3 %. Selected 75 DH plants were used to compare the results of WBPH bioassay and DNA marker reaction. The DHL bioassay showed continuous gene distribution and resistance score ranged from 0.5 to 9.0 (mean, 4.2). The broad-sense heritability for WBPH resistance was 51.7 %. The DHLs from the cross of JSNDH13/CNDH32 were segregated into 39 resistant (R):36 susceptible (S) to WBPH, i.e., 1 RR:SS. For the bioassay and MAS, RM11669 with WBPH resistance was selected. Genetically, the use of resistant cultivars, MAS, and DH breeding has proven to be environment friendly, efficient, and economical. This study confirmed the genetic basis for MAS to improve WBPH resistance in DHLs of WBPH/BPH resistant rice plants.

Bahasa Indonesia

Development of resistant rice varieties to brown planthopper (BPH, Nilaparvata lugens Stal) must be countinuously conducted to overcome the spatial and temporal genetic change in BPH into more virulent ones which can adapt to resistance rice. The availability of linked molecular markers with BPH resistant trait can speed up selection of hybridization progenies. Close-linked markers with trait of interest can be identified using association studies between markers and phenotypic data of unrelated individuals without the need to generate hybridization progenies as an alternative method to linkage studies which use mapping population. The objective of this study was to analyze the association of rice simple sequence repeat (SSR) markers with resistance to BPH. Forty-four rice varieties and promising lines with known resistance degree to BPH biotype 3 were assessed using 30 rice microsatellite markers previously mapped in the rice chromosomal regions with effects on resistance to BPH. Association test between SSR markers and BPH resistance scores revealed eight markers (RM17, RM38, RM125, RM144, RM250, RM287, RM328, dan RM536) which were significantly associated with BPH resistance (R2=0,18 to 0,89; P<0,05). Twenty-one varieties and 11 promising lines were detected to contain SSR alleles that were associated with BPH resistance. Marker RM17 was detected in 15 varieties and 11 promising lines which were scored as resistant and moderately resistant to BPH and therefore it is potentially the most useful as early diagnostic marker to detect BPH resistance alleles. Nevertheless, to obtain SSRs that can be used as reliable selection markers for BPH resistance, marker analysis in segregating populations for the eight markers is still needed as well as association test of more SSR markers widely distributed in rice chromosomes.

Fine mapping of the rice brown planthopper resistance gene BPH7 and characterization of its resistance in the 93-11 background

The brown planthopper (Nilaparvata lugens Stal; BPH) is a severe constraint to rice (Oryza sativa) production. A particularly important approach to controlling this insect pest is the identification and characterization of BPH resistance genes and the subsequent incorporation of the most effective ones into cultivars. Rice var. T12 has been reported to carry resistance gene BPH7 (previously designated bph7) that has not yet been assigned to a chromosome location and whose resistance mechanism is still unknown. In the study reported here we identified and mapped this gene using F2 and backcrossing populations and characterized its resistance in the rice var. 93-11 genetic background using near isogenic lines (NILs). Our analysis of the 93-11/T12 F2 population revealed that the BPH7 gene is located on the long arm of chromosome 12 between simple sequence repeat markers RM28295 and RM313. Subsequent fine mapping placed this gene more precisely in a region flanked by the markers RM3448 and RM313 which are 150 kb apart in the Nipponbare genome and 300 kb apart in the 93-11 genome. BPH7 explained 38.3 % of the phenotypic variance of BPH resistance in the F2 populations. Characterization of the BPH7-mediated resistance revealed that the settlement of the BPH on plants and the survival rate and population growth rate of the BPH were not different significantly between NIL-BPH7 and 93-11 plants. The NIL-BPH7 plants showed significant tolerance to the insects at the seedling and adult stages compared with the susceptible parent 93-11. Our results demonstrate that tolerance is the major component in the resistance conferred by BPH7. The gene mapping of BPH7 should be of great benefit for gene map-based cloning and in plant breeding programs for BPH-resistant rice lines.

Small brown planthopper resistance loci in wild rice (Oryza officinalis)

Host-plant resistance is the most practical and economical approach to control the rice planthoppers. However, up to date, few rice germplasm accessions that are resistant to the all three kinds of planthoppers (1) brown planthopper (BPH; Nilaparvata lugens Stål), (2) the small brown planthopper (SBPH; Laodelphax striatellus Fallen), and (3) the whitebacked planthopper (WBPH, Sogatella furcifera Horvath) have been identified; consequently, the genetic basis for host-plant broad spectrum resistance to rice planthoppers in a single variety has been seldom studied. Here, one wild species, Oryza officinalis (Acc. HY018, 2n = 24, CC), was detected showing resistance to the all three kinds of planthoppers. Because resistance to WBPH and BPH in O. officinalis has previously been reported, the study mainly focused on its SBPH resistance. The SBPH resistance gene(s) was (were) introduced into cultivated rice via asymmetric somatic hybridization. Three QTLs for SBPH resistance detected by the SSST method were mapped and confirmed on chromosomes 3, 7, and 12, respectively. The allelic/non-allelic relationship and relative map positions of the three kinds of planthopper resistance genes in O. officinalis show that the SBPH, WBPH, and BPH resistance genes in O. officinalis were governed by multiple genes, but not by any major gene. The data on the genetics of host-plant broad spectrum resistance to planthoppers in a single accession suggested that the most ideally practical and economical approach for rice breeders is to screen the sources of broad spectrum resistance to planthoppers, but not to employ broad spectrum resistance gene for the management of planthoppers. Pyramiding these genes in a variety can be an effective way for the management of planthoppers.

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

The brown planthopper (BPH; Nilaparvata lugens Stal) 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.

A Global Perspective of Rice Brown Planthopper Management Ⅱ- After Green Revolution Era

Rice Brown Plant hopper, Nilaparvata lugens (Stal) (BPH) has started becoming a major pest in tropical rice growing countries only after major areas were covered by dwarf varieties or high yielding varieties (HYVs). Detailed discussion both historical and experimental evidence on several possible causes like Changed architecture of rice plant, Associated change in agricultural practices, change in micro-climate in rice crop ecosystem, Lack of insect resistance in dwarf varieties, Increased use of insecticides, Consequent destruction of natural enemies, Development of insecticide resistance is presented. Among these, microclimatic factors in rice ecosystem, notably optimum temperature, low wind movement, high water vapor pressure and consequent high relative humidity among abiotic factors and nitrogen rich plant sap among biotic factors appeared to be the most important. Lack of BPH resistance in HYVs does not appear to be the primary cause. Higher insecticide usage in HYVs appeared to be responsible for persistence of BPH menace partially due to destruction of natural enemies and more importantly through development of insecticide resistance and resurgence. However this seems to be secondary cause for BPH problem in all tropical rice growing countries of Asia including China and India.

Identification of a new locus conferring antixenosis to the brown planthopper in rice cultivar Swarnalata (Oryza sativa L.)

The brown planthopper [Nilaparvata lugens (Stål); BPH] has caused severe damage to rice production. The identification of resistance genes and the development of BPH-resistant varieties are economical and effective ways to manage this pest. Using an F2 population from a cross between the Indica cultivars 93-11 and Swarnalata, we mapped the Qbph-8 locus to a 7.3-cM region on chromosome 8 in two tests, flanked by the markers RM339 and RM515. In this population, Qbph-8 explained 7.7 and 6.6% of the phenotypic variance of BPH preference in both tests. In the BPH host choice test, the average number of settled BPHs on the Qbph-8 plants was less than that on the 93-11 plants over the 24- to 120-h observation period. Furthermore, less BPH insects were observed on the BPH6+Qbph-8 plant compared with the BPH6 plant or Qbph-8 plant, indicating a stronger antixenotic effect shown in the gene pyramiding plants. Hence, this locus can be pyramided with other BPH resistance genes and applied to breed-resistant varieties, which possibly can improve the resistance level and durable resistance to the BPH.

Identification of transcription factors potential related to brown planthopper resistance in rice via microarray expression profiling

BackgroundBrown planthopper (BPH), Nilaparvata lugens Stål, is one of the most destructive insect pests of rice. The molecular responses of plants to sucking insects resemble responses to pathogen infection. However, the molecular mechanism of BPH-resistance in rice remains unclear. Transcription factors (TF) are up-stream regulators of various genes that bind to specific DNA sequences, thereby controlling the transcription from DNA to mRNA. They are key regulators for transcriptional expression in biological processes, and are probably involved in the BPH-induced pathways in resistant rice varieties.ResultsWe conducted a microarray experiment to analyze TF genes related to BPH resistance in a Sri Lankan rice cultivar, Rathu Heenati (RHT). We compared the expression profiles of TF genes in RHT with those of the susceptible rice cultivar Taichun Native 1 (TN1). We detected 2038 TF genes showing differential expression signals between the two rice varieties. Of these, 442 TF genes were probably related to BPH-induced resistance in RHT and TN1, and 229 may be related to constitutive resistance only in RHT. These genes showed a fold change (FC) of more than 2.0 (P<0.05). Among the 442 TF genes related to BPH-induced resistance, most of them were readily induced in TN1 than in RHT by BPH feeding, for instance, 154 TF genes were up-regulated in TN1, but only 31 TF genes were up-regulated in RHT at 24 hours after BPH infestation; 2–4 times more TF genes were induced in TN1 than in RHT by BPH. At an FC threshold of >10, there were 37 induced TF genes and 26 constitutive resistance TF genes. Of these, 13 were probably involved in BPH-induced resistance, and 8 in constitutive resistance to BPH in RHT.ConclusionsWe explored the molecular mechanism of resistance to BPH in rice by comparing expressions of TF genes between RHT and TN1. We speculate that the level of gene repression, especially for early TF genes, plays an important role in the defense response. The fundamental point of the resistance strategy is that plants protect themselves by reducing their metabolic level to inhibit feeding by BPH and prevent damage from water and nutrient loss. We have selected 21 TF genes related to BPH resistance for further analyses to understand the molecular responses to BPH feeding in rice.

Analysis of Quantitative Trait Loci for Resistance to Brown Planthopper in Dongxiang Wild Rice (Oryza rufipogon Griff.)

The wild species in genus Oryza are important resources of genes resistant to brown planthopper (Nilaparvata lugens, BPH). The objective of this study was to identify quantitative trait loci (QTLs) in Dongxiang wild rice (O. rufipogon Griff.). A BC1F5 population and a BC3F3 population were developed for QTL mapping from the cross between Dongxiang wild rice and an indica rice cultivar, Xieqingzao B (O. sativa L. subsp. indica) as the recurrent parent. The BC1F5 population was infested with BPH collected from paddy fields. Two QTLs were identified, of which qBph2 was located in the interval of RM29-RG157 on chromosome 2 and qBph7 in the interval of RM11-RM234 on chromosome 7. The alleles from Dongxiang wild rice on qBph2 and qBph7, which explained 21.8% and 67.1% of the phenotypic variations, respectively, and reduced seedling mortality by 22.2% and 43.7%. These QTLs were validated using the BC3F3 population infested by BPH biotypes I, II, and III. This result shows that qBph2 confers resistance to biotypes I and II, and qBph7 confers resistance to biotypes I and III. Both QTLs show a great potential for improving BPH resistance in rice cultivars.