BC1F1 Plants Research Articles

Marker-assisted introgression of bacterial blight and blast resistance into DRR17B, an elite, fine-grain type maintainer line of rice

DRR17A is a stable wild-abortive cytoplasmic male sterile line with medium-slender grain type. DRR17A and its maintainer line DRR17B are highly susceptible to two of the major rice diseases, bacterial blight (BB) and blast. To improve DRR17B for resistance against BB and blast, we have introgressed a major dominant gene each conferring resistance against BB (Xa21) and blast (Pi54) into the maintainer line through marker-assisted backcross breeding using RP-Bio-Patho-2 (a near-isogenic line of Samba Mahsuri possessing Xa21 and Pi54) as the donor parent. PCR-based molecular markers tightly linked to Xa21 and Pi54 were used for foreground selection of the resistance plants at each backcross generation, while molecular markers tightly linked to the major fertility restorer genes, Rf3 and Rf4, were used for negative selection (i.e. selection of plants possessing non-fertility-restoring alleles at the two loci) at BC1 generation. After foreground selection for the target genes at each backcross generation, the ‘positive’ plants were screened with parental polymorphic markers for identifying backcross plants possessing maximum recovery of DRR17B genome. Marker-assisted backcrossing was continued till BC3 generation, and a single BC3F1 plant possessing the target genes with ~94 % recovery of recurrent parent genome was identified and selfed to generate BC3F2s. A total of six homozygous BC3F2 plants were identified and advanced. At BC3F5, six promising, stable, backcross-derived lines possessing high level of resistance against BB and blast, high yield, short plant stature, fine-grain type, have been identified; their maintenance ability and heterotic potential validated through test crosses and these lines are being converted to CMS lines through marker-assisted breeding.

Marker Assisted Transfer of Two Powdery Mildew Resistance Genes PmTb7A.1 and PmTb7A.2 from Triticum boeoticum (Boiss.) to Triticum aestivum (L.).

Powdery mildew (PM), caused by Blumeria graminis f. sp. tritici, is one of the important wheat diseases, worldwide. Two PM resistance genes, designated as PmTb7A.1 and PmTb7A.2, were identified in T. boeoticum acc. pau5088 and mapped on chromosome 7AL approximately 48cM apart. Two resistance gene analogue (RGA)-STS markers Ta7AL-4556232 and 7AL-4426363 were identified to be linked to the PmTb7A.1 and PmTb7A.2, at a distance of 0.6cM and 6.0cM, respectively. In the present study, following marker assisted selection (MAS), the two genes were transferred to T. aestivum using T. durum as bridging species. As many as 12,317 florets of F1 of the cross T. durum /T. boeoticum were pollinated with T. aestivum lines PBW343-IL and PBW621 to produce 61 and 65 seeds, respectively, of three-way F1. The resulting F1s of the cross T. durum/T. boeoticum//T. aestivum were screened with marker flanking both the PM resistance genes PmTb7A.1 and PmTb7A.2 (foreground selection) and the selected plants were backcrossed to generate BC1F1. Marker assisted selection was carried both in BC1F1 and the BC2F1 generations. Introgression of alien chromatin in BC2F1 plants varied from 15.4 - 62.9 percent. Out of more than 110 BC2F1 plants showing introgression for markers linked to the two PM resistance genes, 40 agronomically desirable plants were selected for background selection for the carrier chromosome to identify the plants with minimum of the alien introgression. Cytological analysis showed that most plants have chromosome number ranging from 40-42. The BC2F2 plants homozygous for the two genes have been identified. These will be crossed to generate lines combining both the PM resistance genes but with minimal of the alien introgression. The PM resistance gene PmTb7A.1 maps in a region very close to Sr22, a stem rust resistance gene effective against the race Ug99. Analysis of selected plants with markers linked to Sr22 showed introgression of Sr22 from T. boeoticum in several BC2F1 plants. Thus, in addition to PM resistance, these progeny might also carry resistance to stem rust race Ug99.

Pyramiding of three bacterial blight resistance genes for broad-spectrum resistance in deepwater rice variety, Jalmagna.

BackgroundJalmagna is a popular deepwater rice variety with farmers of India because of its good yield under waterlogged condition. However, the variety is highly susceptible to bacterial blight (BB) disease. The development of resistant cultivars has been the most effective and economical strategy to control the disease under deepwater situation. Three resistance genes (xa5 + xa13 + Xa21) were transferred from Swarna BB pyramid line, using a marker-assisted backcrossing (MAB) breeding strategy, into the BB-susceptible elite deepwater cultivar, Jalmagna.ResultsMolecular marker integrated backcross breeding program has been employed to transfer three major BB resistance genes (Xa21, xa13 and xa5) into Jalmagna variety. During backcross generations, markers closely linked to the three genes were used to select plants possessing these resistance genes and markers polymorphic between donor and recurrent parent were used to select plants that have maximum contribution from the recurrent parent genome. A selected BC3F1 plant was selfed to generate homozygous BC3F2 plants with different combinations of BB resistance genes. The three-gene pyramid and two gene pyramid lines exhibited high levels of resistance against the BB pathogen. Under conditions of BB infection, the three-gene pyramided lines exhibited a significant yield advantage over Jalmagna. The selected pyramided lines showed all agro-morphologic traits of Jalmagna without compromising the yield.ConclusionThe three major BB resistance genes pyramided lines exhibited high level of resistance and are expected to provide durable resistance under deep water situation where control through chemicals is less effective. High similarity in agro-morphologic traits and absence of antagonistic effects for yield and other characters were observed in the best pyramided lines.

Intersubgeneric hybridization between Glycine max and G. tomentella: production of F₁, amphidiploid, BC₁, BC₂, BC₃, and fertile soybean plants.

This paper describes methods for unlocking genetic treasure from wild perennial Glycine species of Australia for soybean improvement. The genetic resources of the ca. 26 species of the genus Glycine subgenus Glycine have not been exploited to broaden the genetic base of soybean (Glycine max; 2n = 40). The objectives of this study were to develop methods for producing F1, amphidiploid, BC1, BC2, BC3, and fertile soybean plants from crosses of soybean and the genus Glycine subgenus Glycine species, in order to utilize the subgenus Glycine germplasm in soybean breeding. Soybean cultivars were hybridized with six accessions of 78-chromosome G. tomentella as well as one accession each of 40-chromosome G. tomentella, G. argyrea and G. latifolia. They were chosen because they exhibit resistance to soybean rust. We were successful in producing fertile soybean from soybean cv. 'Dwight' and 78-chromosome G. tomentella accession PI 441001, while other hybrids were discontinued either at F1 or amphidiploid stage. The F1 seeds aborted prior to reaching maturity, so developing seeds from 19 to 21 day old pods were cultured aseptically in various media formulations. Seed maturation and multiple embryo generation media were developed. F1 plants with shoots and roots (2n = 59) were transplanted to pots in greenhouse. Amphidiploid (2n = 118) plants were backcrossed to 'Dwight'. BC1 (2n = 79) plants were propagated through in vitro and 43 mature BC2F1 seeds were harvested. Fifteen surviving BC2F1 plants were morphologically distinct, sterile, and had chromosome numbers ranging 2n = 56-59. Chromosome numbers of the BC3F1 plants ranged 2n = 40-49. Derived fertile soybeans were first planted in the field in 2008 and are being evaluated for yield, resistance to pathogens and pests and tolerance to salt through material transfer agreement.

Rice tungro spherical virus resistance into photoperiod-insensitive japonica rice by marker-assisted selection.

Rice tungro disease (RTD) is one of the destructive and prevalent diseases in the tropical region. RTD is caused by Rice tungro spherical virus (RTSV) and Rice tungro bacilliform virus. Cultivation of japonica rice (Oryza sativa L. ssp japonica) in tropical Asia has often been restricted because most japonica cultivars are sensitive to short photoperiod, which is characteristic of tropical conditions. Japonica1, a rice variety bred for tropical conditions, is photoperiod-insensitive, has a high yield potential, but is susceptible to RTD and has poor grain quality. To transfer RTD resistance into Japonica1, we made two backcrosses (BC) and 8 three-way crosses (3-WC) among Japonica1 and RTSV-resistant cultivars. Among 8,876 BC1F2 and 3-WCF2 plants, 342 were selected for photoperiod-insensitivity and good grain quality. Photoperiod-insensitive progenies were evaluated for RTSV resistance by a bioassay and marker-assisted selection (MAS), and 22 BC1F7 and 3-WCF7 lines were selected based on the results of an observational yield trial. The results demonstrated that conventional selection for photoperiod-insensitivity and MAS for RTSV resistance can greatly facilitate the development of japonica rice that is suitable for cultivation in tropical Asia.

Introgression of multiple disease resistance into a maintainer of Basmati rice CMS line by marker assisted backcross breeding

Globally, blast incited by Magnaporthe oryzae and sheath blight (ShB) by Rhizoctonia solani Kuhn forms two major fungal diseases that cause significant yield loss in rice. Pusa 6B, the Basmati quality maintainer line of the popular superfine grain aromatic rice hybrid Pusa RH10, is highly susceptible to both the diseases. The rice cultivar Tetep was used as the donor for transferring a major blast resistant gene, Pi54 and three ShB resistant quantitative trait loci (QTLs) namely, qSBR11-1, qSBR11-2 and qSBR7-1 into Pusa 6B using a marker assisted backcross breeding scheme with restricted number of backcrosses. Plants heterozygous for the alleles of interest and phenotypic similarity to the recurrent parent were used for generating BC1F2 population by selfing selected BC1F1 plants. Selected BC1F2 plants homozygous for Pi54 were selfed to generate BC1F3 families that were subjected to a step-wise reductive screening for the three ShB resistant QTLs. Final selections were advanced to BC1F5 generation through selfing while subjecting to stringent phenotypic selection. The advanced selections carrying blast and ShB resistant genes (Pi54, qSBR11-1, qSBR11-2, qSBR7-1) in the background of Pusa 6B were resistant to highly virulent strains of rice blast as well as ShB isolates without compromising the grain and cooking quality of Pusa 6B. Marker assisted transfer of blast and ShB resistance into Pusa 6B will aid in developing CMS lines with inbuilt resistance to these diseases. When combined with restorer lines possessing resistant genes/QTLs for these diseases, the improved Pusa6A lines will aid in development of improved Pusa RH10 and other novel aromatic hybrids with resistance to blast and ShB diseases. The present study demonstrates successful use of a restricted backcrossing strategy for introgression of multiple loci conferring resistance to two important fungal diseases in rice.

Inheritance of Dwarfiness and Erect Growth Habit in Progenies of Jatropha curcas × Jatropha integerrima

Jatropha (Jatropha curcas) is one of the most popular tree crops for seed production as a source of oil for biodiesel. However, currently grown cultivars are too large in canopy size and thus have very low harvest index. Alteration of canopy height and size can lead to identification of a desirable plant architecture for jatropha. A study was conducted to determine genetic control of dwarfiness and erect growth habit in jatropha populations derived from an interspecific cross between J. curcas with tall-erect (TL-ER) plant type and J. integerrima with dwarf-spreading (DW-SP) plant type. Crosses were made between both species to develop F1, F2, BC1F1, and BC1F2 generations. The F2 plants segregated at a 1:2:1 ratio for tall (TL), intermediate (ID), and dwarf (DW) plant types as well as for spreading (SP), upright (UP), and erect (ER) canopy angles. Both characters segregated independently producing nine phenotypes including TL-ER, TL-UP, TL-SP, ID-ER, ID-UP, ID-SP, DW-ER, DW-UP, and DW-SP at a 1:2:1:2:4:2:1:2:1 ratio. The BC1F1 (J. curcas × F1) plant segregated into TL-ER, TL-UP, ID-ER, and ID-UP at a 1:1:1:1 expected ratio. Six BC1F2 lines were also evaluated to confirm the results by selfing two trees each of BC1F1 showing TL-ER, TL-UP, and ID-ER growth habits. The progenies of TL-ER trees were all TL-ER; the progenies of TL-UP trees segregated into TL-ER, TL-UP, and TL-SP at an expected 1:2:1 ratio, whereas the progenies of ID-ER trees segregated into TL-ER, ID-ER, and DW-ER at an expected 1:2:1 ratio. The results indicated that dwarfiness and erect growth habit were each controlled by independent genes with incomplete dominant action. The knowledge and progenies obtained from this study can be used in breeding jatropha for desirable canopy size and shape.

BAC and RNA sequencing reveal the brown planthopper resistance gene BPH15 in a recombination cold spot that mediates a unique defense mechanism.

BackgroundBrown planthopper (BPH, Nilaparvata lugens Stål), is the most destructive phloem-feeding insect pest of rice (Oryza sativa). The BPH-resistance gene BPH15 has been proved to be effective in controlling the pest and widely applied in rice breeding programs. Nevertheless, molecular mechanism of the resistance remain unclear. In this study, we narrowed down the position of BPH15 on chromosome 4 and investigated the transcriptome of BPH15 rice after BPH attacked.ResultsWe analyzed 13,000 BC2F2 plants of cross between susceptible rice TN1 and the recombinant inbred line RI93 that carrying the BPH15 gene from original resistant donor B5. BPH15 was mapped to a 0.0269 cM region on chromosome 4, which is 210-kb in the reference genome of Nipponbare. Sequencing bacterial artificial chromosome (BAC) clones that span the BPH15 region revealed that the physical size of BPH15 region in resistant rice B5 is 580-kb, much bigger than the corresponding region in the reference genome of Nipponbare. There were 87 predicted genes in the BPH15 region in resistant rice. The expression profiles of predicted genes were analyzed. Four jacalin-related lectin proteins genes and one LRR protein gene were found constitutively expressed in resistant parent and considered the candidate genes of BPH15. The transcriptomes of resistant BPH15 introgression line and the susceptible recipient line were analyzed using high-throughput RNA sequencing. In total, 2,914 differentially expressed genes (DEGs) were identified. BPH-responsive transcript profiles were distinct between resistant and susceptible plants and between the early stage (6 h after infestation, HAI) and late stage (48 HAI). The key defense mechanism was related to jasmonate signaling, ethylene signaling, receptor kinase, MAPK cascades, Ca2+ signaling, PR genes, transcription factors, and protein posttranslational modifications.ConclusionsOur work combined BAC and RNA sequencing to identify candidate genes of BPH15 and revealed the resistance mechanism that it mediated. These results increase our understanding of plant–insect interactions and can be used to protect against this destructive agricultural pest.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2164-15-674) contains supplementary material, which is available to authorized users.

Genetic analysis and chromosome mapping of a thermo-sensitive genic male sterile gene in wheat

BS20-T is a thermo-sensitive genic male sterile (TGMS) wheat line (Triticum aestivum L.) used in hybrid wheat breeding in northern China. BS20-T was crossed with common wheat variety ZN7. F1 plants were highly fertile. The segregation ratio of male fertile and male sterile individuals in F2 and BC1F1 plants were close to 3:1 and 1:1, respectively. Other crosses of BS20-T also segregated for a single gene. Bulked sergeant analysis with SSR markers indicated the sterility gene was located on chromosome 2BL. It was named tmsBS20T. Screening of 162 extremely sterile and 30 extremely fertile F2 plants with linked markers indicated flanking by gwm403 and gwm374 with genetic distances of 2.2 and 4.5 cM, respectively. tmsBS20T was transferred into several common wheat varieties by using traditional hybridization combined with marker assisted selection with these two markers. Further identification of derived TGMS lines is ongoing.

Methodology for creating alloplasmic soybean lines by using Glycine tomentella as a maternal parent

AbstractSoybean breeders have not exploited the diversity of the 26 wild perennial species of the subgenus Glycine Willd. that are distantly related to soybean [Glycine max (L.) Merr.] and harbour useful genes. The objective of this study was to develop a methodology for introgressing cytoplasmic and genetic diversity from Glycine tomentella PI 441001 (2n = 78) into cultivated soybean using ‘Dwight’ (2n = 40) as the male parent. Immature seeds (19–21 days post‐pollination) were cultured in vitro to produce F1 plants (2n = 59). Amphidiploid (2n = 118) plants, induced by colchicine treatment, were vigorous and produced mature pods and seeds after backcrossing with ‘Dwight’. The BC1 plants (2n = 79) produced mature seeds in crosses with ‘Dwight’. Chromosome numbers in BC2F1 plants ranged from 2n = 41–50. From BC2F2 to BC3F1, the number of plants in parentheses with 2n = 40 (275), 2n = 41 (208), 2n = 42 (80), 2n = 43 (27), 2n = 44 (12) and 2n = 45 (3) were identified. Fertile lines were grown in the field during 2012 and 2013. This is the first report of the successful development of new alloplasmic soybean lines with cytoplasm from G. tomentella.

Quantitative trait loci for quality and agronomic traits in two advanced backcross populations in oat (Avena sativa L.)

AbstractUsing the advanced backcross quantitative trait loci (AB‐QTL) strategy, we successfully transferred and mapped valuable allelic variants from the high β‐glucan (BG) accession IAH611 (PI 502955), into the genome of cultivar ‘Iltis’. By backcrossing one BC1F1 plant to ‘Iltis’, we developed two BC2F2‐6 populations A and B, comprising 98 and 72 F2‐individuals, respectively. Genotyping of BC2F2 individuals with predominantly AFLP markers resulted in 12 linkage groups with a map size of 455.4 cM for Population A and 11 linkage groups with a map size of 313.5 cM for Population B. Both populations were grown at three sites in Germany over a three‐year period. Individuals were then phenotyped for 13 traits including grain yield (YD) and β‐glucan content (BG). QTL analysis via stepwise regression detected a total of 33 QTLs, most of which were clustered in three linkage groups. Two dense linkage groups A1 and B13 were found to be putatively homologous to groups KO_6 and KO_11 of the ‘Kanota’/‘Ogle’ map, respectively.

Fine mapping of qRC10-2, a quantitative trait locus for cold tolerance of rice roots at seedling and mature stages.

Cold stress causes various injuries to rice seedlings in low-temperature and high-altitude areas and is therefore an important factor affecting rice production in such areas. In this study, root conductivity (RC) was used as an indicator to map quantitative trait loci (QTLs) of cold tolerance in Oryza rufipogon Griff., Dongxiang wild rice (DX), at its two-leaf stage. The correlation coefficients between RC and the plant survival rate (PSR) at the seedling and maturity stages were –0.85 and –0.9 (P = 0.01), respectively, indicating that RC is a reliable index for evaluating cold tolerance of rice. A preliminary mapping group was constructed from 151 BC2F1 plants using DX as a cold-tolerant donor and the indica variety Nanjing 11 (NJ) as a recurrent parent. A total of 113 codominant simple-sequence repeat (SSR) markers were developed, with a parental polymorphism of 17.3%. Two cold-tolerant QTLs, named qRC10-1 and qRC10-2 were detected on chromosome 10 by composite interval mapping. qRC10-1 (LOD = 3.1, RM171-RM1108) was mapped at 148.3 cM, and qRC10-2 (LOD = 6.1, RM25570-RM304) was mapped at 163.3 cM, which accounted for 9.4% and 32.1% of phenotypic variances, respectively. To fine map the major locus qRC10-2, NJ was crossed with a BC4F2 plant (L188-3), which only carried the QTL qRC10-2, to construct a large BC5F2 fine-mapping population with 13,324 progenies. Forty-five molecular markers were designed to evenly cover qRC10-2, and 10 markers showed polymorphisms between DX and NJ. As a result, qRC10-2 was delimited to a 48.5-kb region between markers qc45 and qc48. In this region, Os10g0489500 and Os10g0490100 exhibited different expression patterns between DX and NJ. Our results provide a basis for identifying the gene(s) underlying qRC10-2, and the markers developed here may be used to improve low-temperature tolerance of rice seedling and maturity stages via marker-assisted selection (MAS).Key MessageWith root electrical conductivity used as a cold-tolerance index, the quantitative trait locus qRC10-2 was fine mapped to a 48.5-kb candidate region, and Os10g0489500 and Os10g0490100 were identified as differently expressed genes for qRC10-2.

Marker assisted backcross selection for genetic removal of lipoxygenase-2 from popular soybean (Glycine max) variety JS 97-52: Parental polymorphism survey and hybridity validation

Lipoxygenase-2 is the prime contributor to the off- flavour associated with the soy products. With the aim to introgress null allele of lipoxygenase-2 into popular soybean variety JS 97-52 through marker assisted backcross selection (MABC), parental polymorphism was surveyed for JS 97- 52 (recipient parent) and PI 596540 (the donor of null allele of lipoxygenase-2). A total of 264 SSR markers dispersed across 20 linkage groups were screened. Of these, 130 SSR markers showed polymorphism. SSR markers Satt522 and Satt656 reported to be in the vicinity of Lox2 locus were found to be polymorphic for JS 97-52 and PI 596540 and were used for confirming true F1 and BC1F1 plants. The polymorphic SSR markers identified in the study would be utilized for retrieving the genetic background of JS 97-52 in the backcross generations.

Fast‐Track Introgression of “QTL‐hotspot” for Root Traits and Other Drought Tolerance Traits in JG 11, an Elite and Leading Variety of Chickpea

A “QTL‐hotspot” containing quantitative trait loci (QTL) for several root and drought tolerance traits was transferred through marker‐assisted backcrossing into JG 11, a leading variety of chickpea (Cicer arietinum L.) in India from the donor parent ICC 4958. Foreground selection with up to three simple sequence repeat markers, namely TAA170, ICCM0249, and STMS11, and background selection with up to 10 amplified fragment length polymorphism primer combinations was undertaken. After undertaking three backcrosses with foreground and background selection and selfing, 29 BC3F2 plants homozygous for two markers (ICCM0249 and TAA170) were selected and referred as introgression lines (ILs). Root trait phenotyping of these ILs showed higher rooting depth (RDp) (average 115.21 ± 2.24 cm) in all 29 ILs, better root length density (RLD) (average 0.41 ± 0.02 cm cm−3) in 26 ILs, and higher root dry weight (RDW) (average 1.25 ± 0.08 g per cylinder) as compared to the recurrent parent, JG 11 (111.70 cm for RDp, 0.39 cm cm−3 for RLD, and 1.10 g per cylinder for RDW), as well as the donor parent, ICC 4958 (114.20 cm for RDp, 0.45 cm cm−3 for RLD, and 1.25 g per cylinder for RDW). These ILs, developed in 3 yr, after multilocation field trials may be released as improved variety with enhanced drought tolerance.

Marker‐assisted simultaneous but stepwise backcross breeding for pyramiding blast resistance genes Piz5 and Pi54 into an elite Basmati rice restorer line ‘PRR78’

AbstractMarker‐assisted simultaneous but stepwise backcross breeding (MASS‐BB) was utilized in the present study for pyramiding blast resistance genes, Piz5 and Pi54, from non‐Basmati donors, C101A51 and Tetep, respectively, into PRR78, an elite Basmati restorer line of rice hybrid, Pusa RH10. Marker‐assisted foreground selection coupled with stringent phenotypic selection and background analysis was carried out for hastening the recovery of recurrent parent phenome (RPP) and genome (RPG) in two separate backcross series to produce BC2F1 plants with individual blast resistance gene. The best BC2F1 plant from each backcross series was intercrossed, and the resultant F1 was selfed to pyramid both blast‐resistance genes into PRR78. The plants homozygous for both the genes in the F2 were advanced through pedigree selection to produce superior blast‐resistant F5 lines. Background analysis revealed that the RPG recovery was up to 91.6%. Improved versions of Pusa RH10 developed using the improved PRR78 lines (PRR78+Piz5+Pi54) performed on par with the original Pusa RH10 and showed resistance to blast disease both under artificial screening and at hot spot locations.

Simultaneous transfer, introgression, and genomic localization of genes for resistance to stem rust race TTKSK (Ug99) from Aegilops tauschii to wheat

Wheat production is currently threatened by widely virulent races of the wheat stem rust fungus, Puccinia graminis f. sp. tritici, that are part of the TTKSK (also known as 'Ug99') race group. The diploid D genome donor species Aegilops tauschii (2n = 2x = 14, DD) is a readily accessible source of resistance to TTKSK and its derivatives that can be transferred to hexaploid wheat, Triticum aestivum (2n = 6x = 42, AABBDD). To expedite transfer of TTKSK resistance from Ae. tauschii, a direct hybridization approach was undertaken that integrates gene transfer, mapping, and introgression into one process. Direct crossing of Ae. tauschii accessions with an elite wheat breeding line combines the steps of gene transfer and introgression while development of mapping populations during gene transfer enables the identification of closely linked markers. Direct crosses were made using TTKSK-resistant Ae. tauschii accessions TA1662 and PI 603225 as males and a stem rust-susceptible T. aestivum breeding line, KS05HW14, as a female. Embryo rescue enabled recovery of F1 (ABDD) plants that were backcrossed as females to the hexaploid recurrent parent. Stem rust-resistant BC1F1 plants from each Ae. tauschii donor source were used as males to generate BC2F1 mapping populations. Bulked segregant analysis of BC2F1 genotypes was performed using 70 SSR loci distributed across the D genome. Using this approach, stem rust resistance genes from both accessions were located on chromosome arm 1DS and mapped using SSR and EST-STS markers. An allelism test indicated the stem rust resistance gene transferred from PI 603225 is Sr33. Race specificity suggests the stem rust resistance gene transferred from TA1662 is unique and this gene has been temporarily designated SrTA1662. Stem rust resistance genes derived from TA1662 and PI 603225 have been made available with selectable molecular markers in genetic backgrounds suitable for stem rust resistance breeding.

Introgression of Transgenic Resistance for Rice Tungro Disease into Mega variety, ASD 16 of Tamil Nadu through Marker Assisted Backcross Breeding

Rice Tungro is a viral disease caused by the joint infection of Rice tungro bacilliform virus (RTBV) and Rice tungro spherical virus (RTSV). In order to obtain transgenic resistance against RTBV, indica rice cultivar, Pusa Basmati-1 (PB-1) was transformed to express the coat protein gene of an Indian isolate of RTBV. The transformed PB-1 showed a concomitant reduction of tungro symptoms. The present study was attempted to diversify this transgenic resistance against tungro disease from PB-1 into superior but highly susceptible variety, ASD 16 by following marker assisted backcross breeding. ASD 16, was crossed with transgenic PB1 and the F1 plants were repeatedly backcrossed with the recurrent parent ASD 16 to obtain BC3F1 population. The transgenic plants that contained the RTBV resistant transgene were identified in BC3F1 and BC3F2 population by PCR analysis using functional marker associated with that gene. These foreground selected plants were subjected to background analysis and it revealed that there was 100 per cent recovery of the recurrent parent genome in BC3F2 plants.

Marker-assisted development and characterization of a set of Triticum aestivum lines carrying different introgressions from the T. timopheevii genome

A set of common wheat introgression lines carrying one or two introgressions from Triticum timopheevii was produced by means of marker-assisted backcross selection. The starting material consisted of two BC1F20 (T. aestivum*2/T. timopheevii) lines with resistance to leaf rust, stem rust, powdery mildew, spot blotch, and loose smut and containing multiple 1At, 2At, 2G, 3AtL, 3GL, 4GL, 5AtL, 5GL, and 6G T. timopheevii chromosome fragments. The two lines were crossed with, and backcrossed three times to common wheat cultivar Saratovskaya 29. In total, 275 BC2F1 and BC3F2 plants were characterized by microsatellite markers and in situ hybridization. Molecular and cytological analyses revealed 38 plants with a single introgression from chromosomes 2G, 5GL, or 6G of T. timopheevii and 72 plants, each with two introgressions, among them three plants carrying a T. timopheevii translocation involving the D genome (2DS.2GL). It was observed that the lengths of fragments introgressed from the At genome were more than halved in the BC2 generation, while the lengths of 2G and 5GL introgressed fragments were only slightly reduced after the third backcross. The introgression lines were tested for resistance to the native Puccinia triticina population of the Western Siberian region of Russia. Lines with a single introgressed 5GL region carrying the major leaf rust resistance locus, QLr.icg-5B, were completely resistant. The presence of two minor resistance loci, QLr.icg-2A and QLr.icg-1A, suppressed disease development and reduced the number of urediniospores by up to 25 % but did not lead to a hypersensitive response. The introgression lines therefore constitute promising sources of new resistance to Puccinia triticina.

Genetics of Leaf Rust Resistance in the Winter Wheat Line CI13227

ABSTRACTThe winter wheat (Triticum aestivum L.) line CI13227 with slow rusting resistance to leaf rust, caused by Puccinia triticina Eriks., was crossed and backcrossed to ‘Thatcher’ (Tc) wheat. Backcross F2 families were tested for seedling resistance and segregated in a 1:1 ratio for families that segregated for resistance and families that were homozygous susceptible. The BC1F2 resistant seedlings were progeny tested for infection type (IT) as BC1F3 lines and compared for IT with near‐isogenic lines of Tc with alleles at the Lr3 locus. The BC1F3 lines and the Tc line with Lr3ka had nearly identical IT. The F2 progeny of a resistant BC1F3 plant and a Tc line with Lr3ka did not segregate for IT confirming that CI13227 had an allele at the Lr3 locus. The BC1F2 plants from families that were homozygous susceptible as seedlings were tested as adults for leaf rust IT. Resistant BC1F2 adult plants were selected and advanced to BC1F6 by single seed descent. A single BC1F6 plant was crossed with Tc, and the Tc*3/CI13227 population advanced to F6. The F6 recombinant inbred lines (RILs) were tested for leaf rust resistance at two locations. Molecular mapping with Diversity Arrays Technology (DArT) and simple sequence repeat (SSR) markers detected a major locus for resistance on chromosome 1BL. A polymerase chain reaction (PCR) marker specific for Lr46 also mapped in the 1BL region associated with resistance. Quantitative trait loci on 2DS, 2B, and 7BL for slow rusting resistance in CI13227 detected in previous experiments were not detected in this study. CI13227 has seedling resistance gene Lr3ka and likely has the adult plant resistance gene Lr46.

Incorporation of blast resistance into “PRR78”, an elite Basmati rice restorer line, through marker assisted backcross breeding

Pusa RH10, a popular high yielding superfine grain aromatic rice hybrid and its parents Pusa6A and PRR78 are highly susceptibility to blast disease. Marker assisted backcross breeding (MABB) approach was employed to incorporate blast resistance genes viz., Piz-5 and Pi54, from the donor lines C101A51 and Tetep into the genetic background of PRR78 to develop Pusa1602 (PRR78+Piz5) and Pusa1603 (PRR78+Pi54), respectively. Foreground selection for the genes Piz-5 and Pi54 was effected using tightly linked molecular markers, AP5930 and RM206, respectively in two independent backcross series. Further, foreground selection was coupled with stringent phenotypic selection for agronomic, grain and cooking quality traits, to accelerate recurrent parent phenome recovery. Five superior BC2F2 plants homozygous from each of the backcross series were selected and advanced to BC2F5 generation through pedigree selection to develop improved versions of PRR78 with blast resistance. Background analysis revealed the recurrent parent genome recovery up to 89.01% and 87.88% in Pusa1602 and Pusa1603 lines, respectively. The hybrids produced by crossing Pusa6A with improved lines of PRR78, were on par with original Pusa RH10 in terms of yield, grain and cooking quality traits with an added advantage of blast resistance.