Blast Resistance Quantitative Trait Loci Research Articles

Resistance QTLs controlling leaf and neck blast disease identified in a doubled haploid rice population

One of the biotic constraints in rice production worldwide is blast disease which can control by planting resistant varieties. To find out effective resistance, blast resistance quantitative trait loci (QTL) were mapped against 20 and 3 virulent isolates for leaf blast and neck blast, respectively, using 111 doubled haploid lines from the cross of IR64 and Azucena. QTLs associated with leaf blast were found on chromosomes 1, 2, 4, 7, 8, 10, 11, and 12 (%R2 = 3.6 – 64.3), while neck blast linked QTLs were identified on chromosomes 1, 6, 10, and 12 (%R2 = 6.4 – 22.6). The new QTLs were identified on chromosome 1; however, most QTLs were mapped in the vicinity of resistance genes in previous references. The genetic relationship of leaf and neck blast was explained by the coincidence of detected QTLs and positive value of pathogenicity correlation (r = 4.5 – 4.7). This study provides reliable QTLs locations that will benefit rice breeding programs to develop new cultivars containing durable and broad-spectrum resistance to leaf and neck blast disease.

Genetic Association between Blast Resistance and Yield Traits in Rice Detected Using a High-Density Bin Map

Avoiding linkage drag of the resistance genes will facilitate the use of gene resources for rice breeding. This study was conducted to confirm the avoidance of linkage drag due to Pi26 and Pi25 blast resistance genes, and to analyze the association of Pi26, Pi25, Pib and Pita with quantitative trait loci (QTL) for yield traits. A recombinant inbred line population was derived from an indica rice cross Dan 71/Zhonghui 161. A linkage map consisting of 1219 bin markers, 22 simple sequence repeats and five gene markers was constructed. A total of 75 QTL were identified, including 2 for leaf blast resistance and 73 for eight yield traits. The two QTL for blast resistance were closely linked and located in the Pi26 and Pi25 regions, explaining 69.06 and 12.73% of the phenotypic variance, respectively. In a region covering Pi26 and Pi25, QTL were detected for grain yield and its key components. The alleles for enhancing blast resistance and grain yield were all from Dan 71. Not only was the linkage drag due to Pi26 and Pi25 avoided, but the results also indicate that these resistance genes may be used for simultaneously enhancing blast resistance and grain yield in rice. In the Pib and Pita regions, QTL was not detected for blast resistance, but was for yield traits. In each region, the allele for improving trait performance was derived from the parent carrying the resistance allele. In addition, four QTL clusters for grain weight and size, qGL4/qGW4.1, qGL11.2/qRLW11, qTGW11/qGW11 and qGL12/qGW12/qRLW12, were shown to be promising candidates for map-based cloning.

A high-density linkage map of finger millet provides QTL for blast resistance and other agronomic traits.

Finger millet [Eleusine coracana (L.) Gaertn.] is a critical subsistence crop in eastern Africa and southern Asia but has few genomic resources and modern breeding programs. To aid in the understanding of finger millet genomic organization and genes underlying disease resistance and agronomically important traits, we generated a F2:3 population from a cross between E. coracana (L.) Gaertn. subsp. coracana accession ACC 100007 and E. coracana (L.) Gaertn. subsp. africana , accession GBK 030647. Phenotypic data on morphology, yield, and blast (Magnaporthe oryzae) resistance traits were taken on a subset of the F2:3 population in a Kenyan field trial. The F2:3 population was genotyped via genotyping-by-sequencing (GBS) and the UGbS-Flex pipeline was used for sequence alignment, nucleotide polymorphism calling, and genetic map construction. An 18-linkage-group genetic map consisting of 5,422 markers was generated that enabled comparative genomic analyses with rice (Oryza sativa L.), foxtail millet [Setaria italica (L.) P. Beauv.], and sorghum [Sorghum bicolor (L.) Moench]. Notably, we identified conserved acrocentric homoeologous chromosomes (4A and 4B in finger millet) across all species. Significant quantitative trait loci (QTL) were discovered for flowering date, plant height, panicle number, and blast incidence and severity. Sixteen putative candidate genes that may underlie trait variation were identified. Seven LEUCINE-RICH REPEAT-CONTAINING PROTEIN genes, with homology to nucleotide-binding site leucine-rich repeat (NBS-LRR) disease resistance proteins, were found on three chromosomes under blast resistance QTL. This high-marker-density genetic map provides an important tool for plant breeding programs and identifies genomic regions and genes of critical interest for agronomic traits and blast resistance.

Identification of Blast Resistance QTLs Based on Two Advanced Backcross Populations in Rice

BackgroundRice blast is an economically important and mutable disease of rice. Using host resistance gene to breed resistant varieties has been proven to be the most effective and economical method to control rice blast and new resistance genes or quantitative trait loci (QTLs) are then needed.ResultsIn this study, we constructed two advanced backcross population to mapping blast resistance QTLs. CR071 and QingGuAi3 were as the donor parent to establish two BC3F1 and derived BC3F2 backcross population in the Jin23B background. By challenging the two populations with natural infection in 2011 and 2012, 16 and 13 blast resistance QTLs were identified in Jin23B/CR071 and Jin23B/QingGuAi3 population, respectively. Among Jin23B/CR071 population, 3 major and 13 minor QTLs have explained the phenotypic variation from 3.50% to 34.08% in 2 years. And, among Jin23B/QingGuAi3 population, 2 major and 11 minor QTLs have explained the phenotypic variation from 2.42% to 28.95% in 2 years.ConclusionsSixteen and thirteen blast resistance QTLs were identified in Jin23B/CR071 and Jin23B/QingGuAi3 population, respectively. QTL effect analyses suggested that major and minor QTLs interaction is the genetic basis for durable blast resistance in rice variety CR071 and QingGuAi3.

Genome-wide association mapping of resistance against rice blast strains in South China and identification of a new Pik allele

BackgroundEffective management of rice blast, caused by the fungus Magnaporthe oryzae, requires an understanding of the genetic architecture of the resistance to the disease in rice. Rice resistance varies with M. oryzae strains, and many quantitative trait loci (QTLs) affecting rice blast resistance have been mapped using different strains of M. oryzae from different areas. However, little is known about the genetic architecture of rice resistance against the M. oryzae population in Hunan Province, which is a main rice production area in South China.ResultsIn this study, we used three isolates from Hunan Province and the rice diversity panel 1 to perform a genome-wide association study (GWAS) of blast resistance in rice. A total of 56 QTLs were identified. One of the QTLs is localized with the resistance gene Pik locus which confers resistance to all three isolates. Genomic sequence analysis of the resistant cultivars led to the identification of a new Pik allele, which we named Pikx. Yeast two-hybrid and co-immunoprecipitation assays between AvrPiks and Pikx confirmed that Pikx is a new allele at the Pik locus.ConclusionsOur GWAS has identified many new blast resistance QTLs. The identified new Pik allele Pikx will be useful for breeding cultivars with high resistance to blast in Hunan and other South China provinces. Further research on the relationship between AvrPiks and Pikx will provide new insights into the molecular mechanism of rice resistance to M. oryzae.

Development of Sakon Nakhon Rice Variety for Blast Resistance through Marker Assisted Backcross Breeding

The Sakon Nakhon (SKN) rice cultivar is non-photosensitive, rich in aroma, and an excellent choice for cooking quality; which adapts well to both upland and lowland conditions. Furthermore, it has been adopted by Thailand’s sugarcane growers, as it has proved fit for an upland crop preceding the sugarcane cropping system. However, SKN is very susceptible to blast disease caused by Pyricularia oryzae. The purpose of this study was to breed SKN for blast resistance, using marker-assisted backcrossing, together with phenotypic selection. The breeding population was constructed by crossing the SKN (recurrent) with the RD6 introgression line (donor), which contained four blast resistant quantitative trait loci (QTLs). Franking microsatellite markers for blast resistance QTLs on chromosomes 1, 2, 11 and 12 were used for selection through BC2F2. Thirteen BC2F3 selected lines were evaluated under greenhouse conditions, and seven lines of BC2F4 were evaluated against blast, along with their agronomic traits, under field conditions (upland and lowland). SKN 39-10-19-29-12 and SKN 39-10-19-29-13 presented high resistance to leaf and neck blast; and were non-photosensitive, with the same agronomic traits as the SKN. This study successfully demonstrates the improvement of the recommended SKN variety blast resistance, while maintaining similar agronomic traits.

Pid3-I1 is a race-specific partial-resistance allele at the Pid3 blast resistance locus in rice.

The rice blast resistance QTL detected on chromosome 6 in MC276 is Pid3-I1, one of the multiple alleles at the Pid3 locus. Pid3-I1 shows race-specific partial resistance. Many of the quantitative trait loci (QTLs) for rice blast resistance reported to date remain unidentified. In the present study, we focused on qBRM6.2, a known blast-resistance QTL in experimental resistant rice line MC276. A CO39 near-isogenic line (NIL) carrying qBRM6.2 from MC276 was developed here, and we showed that qBRM6.2 resistance was partial but race specific to Japanese blast isolates using the NIL. Because defense genes in the NIL were expressed sooner than those in CO39 after inoculation with a blast isolate, qBRM6.2 resistance appeared to be an induced resistance. Next, we demonstrated that qBRM6.2 was located within a 123-kb interval on chromosome 6. Among the six genes annotated in the interval, only four genes appeared to be functional. Among these four, a polymorphism between CO39 and the NIL for qBRM6.2 at the amino acid sequence level was detected only in Os06g0330400 that encodes a fatty acid hydroxylase domain-containing protein and in Os06g0330100, the blast resistance locus Pid3, that encodes a nucleotide-binding site-leucine-rich repeat protein. Moreover, the allele at the Pid3 locus in the NIL was Pid3-I1, originally identified as a complete blast resistance gene in Kasalath. To clarify whether Pid3-I1 is qBRM6.2, we investigated the resistance phenotype of Pid3-I1 to Japanese isolates using Nipponbare transgenic lines that express Pid3-I1. The results showed that Pid3-I1 was a race-specific but partial-resistance allele at the Pid3 locus, suggesting strongly that Pid3-I1 is qBRM6.2. The discrepancy in the phenotype of Pid3-I1 between the present and previous reports is also discussed.

Functional Interactions Between Major Rice Blast Resistance Genes, Pi-ta and Pi-b, and Minor Blast Resistance Quantitative Trait Loci.

Major blast resistance (R) genes confer resistance in a gene-for-gene manner. However, little information is available on interactions between R genes. In this study, interactions between two rice blast R genes, Pi-ta and Pi-b, and other minor blast resistance quantitative trait loci (QTLs) were investigated in a recombinant inbred line (RIL) population comprising 243 RILs from a Cybonnet (CYBT) × Saber (SB) cross. CYBT has the R gene Pi-ta and SB has Pi-b. Ten differential isolates of four Magnaporthe oryzae races (IB-1, IB-17, IB-49, and IE-1K) were used to evaluate disease reactions of the 243 RILs under greenhouse conditions. Five resistance QTLs were mapped on chromosomes 2, 3, 8, 9, and 12 with a linkage map of 179 single nucleotide polymorphism markers. Among them, qBR12 (Q1), was mapped at the Pi-ta locus and accounted for 45.41% of phenotypic variation while qBR2 (Q2) was located at the Pi-b locus and accounted for 24.81% of disease reactions. The additive-by-additive epistatic interaction between Q1 (Pi-ta) and Q2 (Pi-b) was detected; they can enhance the disease resistance by an additive 0.93 using the 0 to 9 standard phenotyping method. These results suggest that Pi-ta interacts synergistically with Pi-b.

QTL mapping of panicle blast resistance in japonica landrace heikezijing and its application in rice breeding

The rice blast caused by Magnaporthe oryzae is one of the most devastating diseases worldwide, and the panicle blast could result in more loss of yield in rice production. However, the quantitative trait loci (QTLs) and genes related to panicle-blast resistance have not been well studied due to the time-consuming screening methodology involved and variation in symptoms. The QTLs for panicle blast resistance have been mapped in a population of 162 RILs (recombination inbreeding lines), derived from a cross between a highly blast-resistant rice landrace, Heikezijing, and a susceptible variety, Suyunuo. Two QTLs for panicle-blast resistance, qPbh-11–1 and qPbh-7-1, were identified, which were distributed on chromosomes 11 and 7. The QTL qPbh-11–1 was stably detected in three independent experiments, at Nanjing in 2013 and 2014 and at Hainan in 2014, located between the region of RM27187 and RM27381 on the distal end of chromosome 11 far from the reported resistant loci Pb1 and qPbm11 for panicle blast. The QTL qPbh-7-1 was detected only at Nanjing in 2013 and located between the region of M18 and RM3555 on chromosome 7. With marker-assisted selection (MAS) three introgression lines with the major panicle blast-resistance QTL qPbh-11–1 were developed from a recurrent parent Nanjing 44 (NJ44) and the panicle resistance of introgression lines was improved 46.36–55.47 % more than NJ44. Based on the results provided, Heikezijing appears to be a valuable source for panicle blast resistance.

Confirming and Identifying New Loci for Rice Blast Disease Resistance using Magnaporthe oryzae Field Isolates in the US

ABSTRACTQuantitative trait loci (QTL) play important roles in controlling rice blast disease. In the present study, 10 field isolates of the races IA1, IB1, IB17, and IC1 of US rice blast fungus Magnaporthe oryzae collected in 1996 and 2009 were used to identify blast resistance QTL with a recombinant inbred line (RIL) population consisting of 227 F7 individuals derived from the cross of rice (Oryza sativa L.) cultivars Lemont and Jasmine 85. Jasmine 85 is an indica cultivar that is moderately resistant, and Lemont is a tropical japonica cultivar susceptible to rice blast in greenhouse inoculation. Disease reactions of the parents and RILs were evaluated under greenhouse conditions. A total of six resistance QTL, qBLR8, qBLR10‐1, qBLR10‐2, qBLR10‐3, qBLR12‐1, and qBLR12‐2, were identified on chromosomes 8, 10, and 12, respectively. Phenotypic variation, conditioned by these six resistance QTL, ranged from 5.37 to 39.18%. Among them, qBLR12‐1 and qBLR12‐2 provided the strongest resistance to the newest isolates of the most virulent race IA1 of M. oryzae. Three of these resistance QTL have been identified using different blast isolates in a previous study. qBLR10‐1, qBLR10‐2, and qBLR10‐3 have not been previously found in this cross. These confirmed and new resistance QTL will be useful for the development of rice cultivars with improved effective resistance to rice blast via a marker‐assisted selection (MAS) approach.

Mapping and evaluating quantitative trait loci for blast resistance under natural infection conditions using an advanced backcross population in rice

Blast (caused by Magnaporthe oryzae B. Couch) is an economically important and mutable disease of rice (Oryza sativa L.). To analyze the genetic mechanism of blast resistance in rice cultivar CR185; we used CR185 as a donor parent to establish a BC3F1 and derived BC3F2 backcross population in the Zhenshan 97B (ZS97B) background. By challenging the population with natural infection in 2008 and 2009, 11 blast resistance quantitative trait loci (QTLs) were identified. Among them, four major QTLs, qBR-1a, qBR-4d, qBR-6a, and qBR-12a, had large effects during four observation times. QTL effect analyses suggested that resistance increased with the number of QTLs. The major QTL, qBR-6a, which had the largest effect, was fine-mapped to a 100-kb DNA fragment that encompassed the Pi2/Pi9 locus. Sequence comparisons revealed that the Pi allele in CR185 was different from the known alleles of Pi2/Pi9. Our results revealed that accumulation of several QTLs is an effective way to develop highly resistant cultivars.

Quantitative trait loci analysis suggests that partial resistance to rice blast is mostly determined by race–specific interactions

• The race specificity of quantitative trait loci (QTL) for partial resistance to blast (Magnaporthe grisea) disease was tested by using isolates for which no major resistance gene segregated in a mapping population based on rice (Oryza sativa) varieties Bala × Azucena. • Recombinant inbred lines were repeatedly inoculated with isolates CD100, CM28 and PH19 and scored for lesion type, lesion size and number of lesions. Composite interval mapping was employed to identify QTL. • Eighteen main effect QTL were detected. Of these, eight were detected in only one isolate, seven detected in two isolates and only three in all three isolates. Diallelic epistasis was identified as an important genetic component but had little discernible pattern. Fourteen main-effect QTL mapped to previously identified QTL for blast resistance and 10 to previously identified major resistance genes. • It is concluded that the majority of QTL detected are race-specific. The results also support the hypothesis that partial resistance genes might be defeated major genes, with residual effectiveness and race specificity.

Comparative analyses of genomic locations and race specificities of loci for quantitative resistance to Pyricularia grisea in rice and barley.

Comparative genomic analyses have revealed extensive colinearity in gene orders in distantly related taxa in mammals and grasses, which opened new horizons for evolutionary study. The objective of our study was to assess syntenic relationships of quantitative trait loci (QTL) for disease resistance in cereals by using a model system in which rice and barley were used as the hosts and the blast fungus Pyricularia grisea Sacc. as the pathogen. In total, 12 QTL against three isolates were identified in rice; two had effects on all three isolates, and the other 10 had effects on only one or two of the three isolates. Twelve QTL for blast resistance were identified in barley; one had effect on all three isolates, and the other 11 had effects on only one or two of the three isolates. The observed isolate specificity led to a hypothesis about the durability of quantitative resistance commonly observed in many plant host-pathogen systems. Four pairs of the QTL showed corresponding map positions between rice and barley, two of the four QTL pairs had complete conserved isolate specificity, and another two QTL pairs had partial conserved isolate specificity. Such corresponding locations and conserved specificity suggested a common origin and conserved functionality of the genes underlying the QTL for quantitative resistance and may have utility in gene discovery, understanding the function of the genomes, and identifying the evolutionary forces that structured the organization of the grass genomes.

QTL analysis of resistance to the rice blast pathogen in barley (Hordeum vulgare)

Barley is compatible with the rice blast pathogen (Pyricularia oryzae Cav.). Fiftyfour barley cultivars of diverse geographic origin and pedigree were inoculated with three isolates of the rice blast pathogen. All barley genotypes showed blast disease symptoms when inoculated at the seedling stage with each of the three isolates. However, one genotype showed quantitative resistance to all three isolates and three genotypes showed quantitative resistance to one or two of the isolates. By inoculating a set of doubled-haploid lines derived from the cross ’Harrington’ (susceptible) and ’TR306’ (resistant) with isolate Ken 54–20, we mapped quantitative trait loci (QTLs) determining seedling stage blast resistance. At all QTLs, TR306 contributed the resistance alleles. The four QTLs, when considered jointly, explained 43.6% of the phenotypic variation in blast symptom expression. A comparison of the blast resistance QTLs with other disease resistance QTLs reported in this population revealed a region on chromosome 4 (4H) with multiple disease resistance loci. It will be useful to capitalize on the syntenic relationship of rice and barley and to integrate information on species-specific resistance genes with information on the reaction of the two species to the same pathogen.