Foreground Selection Research Articles

Improvement of Stable Restorer Lines for Blast Resistance through Functional Marker in Rice (Oryza sativa L.).

Two popular stable restorer lines, CB 87 R and CB 174 R, were improved for blast resistance through marker-assisted back-cross breeding (MABB). The hybrid rice development program in South India extensively depends on these two restorer lines. However, these restorer lines are highly susceptible to blast disease. To improve the restorer lines for resistance against blasts, we introgressed the broad-spectrum dominant gene Pi54 into these elite restorer lines through two independent crosses. Foreground selection for Pi54 was done by using gene-specific functional marker, Pi54 MAS, at each back-cross generation. Back-crossing was continued until BC3 and background analysis with seventy polymorphic SSRs covering all the twelve chromosomes to recover the maximum recurrent parent genome was done. At BC3F2, closely linked gene-specific/SSR markers, DRRM-RF3-10, DRCG-RF4-8, and RM 6100, were used for the identification of fertility restoration genes, Rf3 and Rf4, along with target gene (Pi54), respectively, in the segregating population. Subsequently, at BC3F3, plants, homozygous for the Pi54 and fertility restorer genes (Rf3 and Rf4), were evaluated for blast disease resistance under uniform blast nursery (UBN) and pollen fertility status. Stringent phenotypic selection resulted in the identification of nine near-isogenic lines in CB 87 R × B 95 and thirteen in CB 174 R × B 95 as the promising restorer lines possessing blast disease resistance along with restoration ability. The improved lines also showed significant improvement in agronomic traits compared to the recurrent parents. The improved restorer lines developed through the present study are now being utilized in our hybrid development program.

Recovery of Recurrent Parent Genome in a Marker-Assisted Backcrossing Against Rice Blast and Blight Infections Using Functional Markers and SSRs.

The most vital aspect of marker-assisted backcross breeding is the recurrent parent genome recovery. This enables the selection of only parents with recovered recipient/recurrent parent genome in addition to the targeted genes. The recurrent parent genome recovery (RPGR) ensures that non-desirable genomic segments are removed while the gene of interest is sustained in the recombined progenies without further segregations. This work was aimed at quantifying the RPGR of backcross populations with introgression of bacterial leaf blight resistance genes. Putra-1, a Malaysian elite variety, high yielding with inherent resistance to blast but susceptible to bacterial leaf blight (BLB), was crossed with IRBB60 which is resistant to BLB disease. The IRBB60 has four Xoo resistance genes—Xa4, xa5, xa13 and Xa21. Tightly linked polymorphic functional and SSR markers were used for foreground selection at every stage of backcrossing to select progenies with introgressed target genes. Background selection was done to quantify the percentage of RPGR in the selected lines using 79 confirmed polymorphic microsatellites. Result obtained showed that the percentage of RPGR was 80.11% at BC1F1, 95.30% at BC2F1 and 95.9% at BC2F2. The introgression of Xa4, xa5, xa13 and Xa21 Xoo resistance genes were faster through the adopted marker-assisted backcross breeding compared to what could be obtained through conventional breeding. All the 16 selected lines displayed resistance to BLB with three lines showing high resistance to the disease. The blast resistance contained in the genetic background of Putra-1 was also sustained in all the selected lines. The newly developed lines were recommended as new rice varieties for commercial cultivation.

Enhancing β-Carotene Concentration in Parental Lines of CO6 Maize Hybrid Through Marker-Assisted Backcross Breeding (MABB).

Vitamin A deficiency (VAD) is a global health problem; many people around the world, especially children and pregnant women, are VAD deficient or insufficient. Maize is known as an important source of provitamin A for humans. Hence, enhancement of provitamin A carotenoids (pVAC) in maize varieties through breeding or biofortification is a good option for alleviating VAD in developing countries, especially India. So far, numerous maize hybrids have been developed in India. Among them, CO6, derived from UMI1200 × UMI1230, is a popular maize hybrid and adapted to different agro-climatic zones of India, especially Tamil Nadu, a southern state of India. However, CO6 is deficient for pVAC carotenoid β-carotene. Thus, the objectives of this study were to increase the β-carotene concentration in UMI1200 and UMI1230 and generate the β-carotene enriched hybrids through marker-assisted backcross breeding (MABB). For this purpose, the maize genotype HP467-15 was used as the donor for transferring the β-carotene gene, crtRB1, into UMI1200 and UMI1230. In the MABB scheme, we used one gene-specific marker (crtRB1 3′TE) and 214 simples sequence repeat (SSR) markers for foreground and background selection, respectively. As a result, six improved lines with recurrent parent genome recovery (RPGR) ranging from 90.24 to 92.42%, along with good agronomic performance, were generated. The β-carotene concentration of the improved lines ranged from 7.056 to 9.232 μg/g. Furthermore, five hybrid combinations were generated using improved lines and evaluated in a comparative yield trial (CYT) and multi-location trials (MLT) along with the original hybrid CO6 and commercial hybrids. It was revealed that ACM-M13-002 was a superior hybrid with a 7.3-fold increase in β-carotene concentration and with a comparable yield to CO6. In summary, the improved maize inbreds can be used as possible donors for the development of β-carotene-rich cultivars in maize breeding programs and the β-carotene enriched hybrid developed in this study will hold great promise for food and nutritional security.

Marker‐assisted introgression of QTLs for yield under moisture stress into elite varieties of rice (Oryza sativa)

AbstractRice production is severely constrained by the moisture stress. The present study was undertaken to transfer two important QTLs viz., (qDTY2.2 and qDTY4.1), which controls yield under moisture stress (DTY) into two elite varieties, that is, MTU1010 and NLR34449 through marker‐assisted breeding. Foreground and background selections of backcross generations, that is, BC1F1, BC2F1 and BC2F2 identified several promising introgression lines (ILs) with two QTLs and single QTLs with an appreciable level of recovery of recipient parent genome. In ILs, the recovery of MTU1010 genome content was estimated to be 83%–93% while the recovery of NLR34449 was 84%–92%. The two‐QTL ILs of MTU1010 and NLR34449 backgrounds (qDTY2.2 and qDTY4.1) have shown substantial yield advantage (32 to 84%) over the single‐QTL ILs (either qDTY2.2 or qDTY4.1) under moisture stress conditions. Among all, two ILs, MBC‐124 and NBC‐127 are the best high yielding lines under moisture stress conditions. These outyielded ILs have the potential to be released as varieties in rainfed ecosystem and also can be used as donors in the existing breeding programme in rice.

Marker Assisted Development and Characterization of Herbicide Tolerant Near Isogenic Lines of a Mega Basmati Rice Variety, \u201cPusa Basmati 1121\u201d

BackgroundDirect-seeded rice (DSR) is a potential technology for sustainable rice farming as it saves water and labor. However, higher incidence of weed under DSR limits productivity. Therefore, there is a need to develop herbicide tolerant (HT) rice varieties.ResultsWe used marker assisted backcross breeding (MABB) to transfer a mutant allele of Acetohydroxy acid synthase (AHAS) gene, which confers tolerance to imidazolinone group of herbicides from the donor parent (DP) “Robin” into the genetic background of an elite popular Basmati rice variety, Pusa Basmati 1121 (PB 1121). Foreground selection was done using the AHAS gene linked Simple Sequence Repeat (SSR) marker RM6844 and background selection was performed using 112 genome-wide SSR markers polymorphic between PB 1121 and Robin. Phenotypic selection for agronomic, Basmati grain and cooking quality traits in each generation was carried out to improve the recovery of recurrent parent phenome (RPP). Finally, a set of 12 BC4F4 near isogenic lines (NILs), with recurrent parent genome (RPG) recovery ranging from 98.66 to 99.55% were developed and evaluated. PB 1121-HT NILs namely 1979-14-7-33-99-10, 1979-14-7-33-99-15 and 1979-14-7-33-99-66 were found superior to PB 1121 in yield with comparable grain and cooking quality traits and herbicide tolerance similar to Robin.ConclusionOverall, the present study reports successful development of HT NILs in the genetic background of popular Basmati rice variety, PB 1121 by introgression of mutated AHAS allele. This is the first report on the development of HT Basmati rice. Superior NILs are being evaluated in the national Basmati trials, the release of which is likely to provide a viable option for the adoption of DSR technology in Basmati rice cultivation.

Biofortification of sweet corn hybrids for provitamin-A, lysine and tryptophan using molecular breeding

Traditional sweet corn is poor in provitamin-A, lysine and tryptophan, deficiency of which causes serious health problems. Here, parental lines of two shrunken2 (sh2) -based sweet corn hybrids viz., ASKH-1 and ASKH-2 were targeted for introgression of crtRB1 and opaque2 (o2) genes through marker-assisted backcross breeding. Gene-based markers; umc1066 (SSR) and 3′TE-InDel were utilized for foreground selection of o2 and crtRB1, respectively in BC1F1, BC2F1 and BC2F2 generations. Background selection employing 102–113 polymorphic SSRs led to >90% recovery of recurrent parent genome. Reconstituted hybrids recorded high mean provitamin-A (18.98 μg/g) with a maximum of 7.7-fold increase over original hybrids (3.12 μg/g). High mean lysine (0.39%) and tryptophan (0.10%) with an average enhancement of 1.71- and 1.79-fold, respectively was recorded among reconstituted hybrids over original versions (lysine: 0.23%, tryptophan: 0.06%). Improved hybrids exhibited high phenotypic resemblance with their original hybrids. The average cob yield (11.82 t/ha) and brix (17.66%) of improved hybrids was at par with their original versions (cob yield: 11.27 t/ha, brix: 17.04%). These biofortified sweet corn hybrids rich in provitamin-A, lysine and tryptophan hold immense significance as multinutrient-rich balanced food. This is the first report to stack sh2, crtRB1 and o2 genes to improve nutritional quality in sweet corn.

Molecular marker aided selection for developing rust resistant genotypes by pyramiding Lr19/Sr25 and Yr15 in wheat (Triticum aestivum L.)

The study was aimed to develop rust resistant genotypes with genome of prominent wheat variety HS240 by pyramiding of linked leaf rust and stem rust resistance genes Lr19 and Sr25 with stripe rust resistance gene Yr15. The genotypes FLW13 and FLW20 were used as gene donors for transfer of Yr15 and Lr19/Sr25, respectively. The molecular markers scs265, wmc221, PSY1-E1, and Gb linked to Lr19/Sr25 and barc8 and gwm11 linked to Yr15 were used for foreground selection. Background selection, involving 58 simple sequence repeat (SSR) markers polymorphic between HS240 and FLW20; 72 between HS240 and FLW13 was carried out to recover the genome of HS240 in advanced bulks derived from a cross HS240*2/FLW20//HS240*2/FLW13. The SSR based genome recovery in selected advanced breeding lines, WBM3682 and WBM3684 was 90.8% and 93.3%, respectively. The 35 K SNP array based analysis of genomic regions of HS240 also substantiated the results of genomic recovery estimated through SSR markers. The selected line WBM3682 recorded average grain yield of 25.7q/ha and showed its superiority over parental check HS240 under rainfed situations. This study has led to development of rust resistant wheat carrying genome of HS240.

Marker aided introgression of \u2018Saltol\u2019, a major QTL for seedling stage salinity tolerance into an elite Basmati rice variety \u2018Pusa Basmati 1509\u2019

Marker assisted backcross breeding was used to transfer Saltol, a major QTL for seedling stage salinity tolerance from the donor FL478 to Pusa Basmati 1509 (PB 1509), a high yielding and early maturing Basmati rice variety. Foreground selection was carried out using three markers namely, AP3206f, RM3412b and RM10793, linked to Saltol. In addition, 105 genome-wide SSR markers polymorphic between FL478 and PB 1509 were used in background selection. Among the BC3F4 near isogenic lines (NILs) developed, recurrent parent genome recovery ranged from 96.67 to 98.57%. Multi-season evaluation identified some of the NILs showing significantly higher yield with grain and cooking quality comparable to PB 1509. All the NILs exhibited tolerance to salinity with significantly higher relative water content, membrane stability index and proline content as compared to PB 1509. The root and shoot concentration of Na+, K+ and Na+/K+ in NILs was at par with FL478 under stress conditions. The gene OsHKT1;5 located in the Saltol region showed higher expression levels under stress indicating its role in conferring salinity tolerance. Salt tolerant NILs of PB 1509 will be useful in stabilizing production in salt affected areas.

Marker aided introgression of opaque 2 (o2) allele improving lysine and tryptophan in maize (Zea mays L.).

Maize is the predominant food source for the world population, but lack of lysine and tryptophan in maize endosperm cannot fulfill the nutritional requirements of humans. Hence, the improvement of lysine and tryptophan content is the ultimate goal of maize biofortification programs. In the present study, the marker-assisted backcross (MABC) breeding strategy wasused to enhance the lysine and tryptophan content of the elite maize inbred line UMI1230 by introgressing opaque 2 (o2) gene from the VQL1. During the transfer of the gene into UMI1230, SSR marker umc1066 tightly associated with o2 used for foreground selection. Background recovery was estimated using 168 SSR markers. Phenotype screening for morphological traits was adopted to choose plants parallel to UMI1230. As a result, four BC2F3 improved lines (DBT5-1-14/25-5/25-8/25-8/25, DBT5-1-14/25-5/25-8/25-7/25, DBT5-1-14/25-5/25-8/25-10/25 and DBT5-1-14/25-5/25-8/25-12/25) with o2 were developed. The improved line's background genome recovery varied between 90.60 and 94.80%. Also, the improved lines had better agronomic performance along with increased lysine (0.311-0.331%) and tryptophan (0.040-0.048%) contents. In summary, the MABC breeding strategy has successfully improved the levels of lysine and tryptophan in UMI1230 without affecting agronomic performance. The improved line's hold great potential as donors in biofortification programs in maize.

Breeding of a novel clubroot disease-resistant <italic>Brassica napus</italic> variety Huayouza 62R

<p indent=0mm>The rapeseed clubroot disease incidence in China is about 0.67 million hectare, accounting for 10% of the canola production area, which become a serious threat for the safety of <italic>Brassica napus</italic> industry. Based on this, we used CR Shinki, a Chinese cabbage material containing <italic>CRb</italic> clubroot disease resistance locus, as the donor parent, and Pol.CMS restorer line Bing409, the parent of <italic>Brassica napus</italic> national approved varieties Huayouza 62, as the recipient parent, and the <italic>CRb</italic> resistance locus was introduced into Bing409 by breeding programs such as crossing, backcrossing, self-cross with the foreground and genetic background selection. In the BC₃F₂ generation, a new restorer line Bing409R with a genetic background close to Bing409 containing <italic>CRb</italic> resistance locus was obtained, and Huayouza 62R, the first rapeseed hybrid resistant to clubroot disease in China was successfully developed. The results were as follows: <italic>CRb</italic> disease resistance locus appeared as a dominant single-gene inheritance in <italic>B</italic>.<italic> napus</italic> background, and the genetic improvement of resistance to clubroot disease did not at the expense of yield and quality losses for new restorer line Bing409R and its hybrid Huayouza 62R. Bing409R and Huayouza 62R were showed immune-resistance to physiological races of <italic>Plasmodiophora brassicae</italic> in Sichuan, Hubei, and Anhui provinces in China. This study will provide valuable resources for the breeding of rapeseed in China, and supplemented important support to overcome the threat of rapeseed clubroot disease.

Marker Assisted Gene Pyramiding (MAGP) for bacterial blight and blast resistance into mega rice variety "Tellahamsa".

Bacterial blight (BB) and fungal blast diseases are the major biotic constraints that limit rice productivity. To sustain yield improvement in rice, it is necessary to developed yield potential of the rice varieties by incorporation of biotic stress resistance genes. Tellahamsa is a well-adapted popular high yielding rice variety in Telangana state, India. However, the variety is highly susceptible to BB and blast. In this study, simultaneous stepwise transfer of genes through marker-assisted backcross breeding (MABB) strategy was used to introgress two major BB (Xa21 and xa13) and two major blast resistance genes (Pi54 and Pi1) into Tellahamsa. In each generation (from F1 to ICF3) foreground selection was done using gene-specific markers viz., pTA248 (Xa21), xa13prom (xa13), Pi54MAS (Pi54) and RM224 (Pi1). Two independent BC2F1 lines of Tellahamsa/ISM (Cross-I) and Tellahamsa/NLR145 (Cross-II) possessing 92% and 94% recurrent parent genome (RPG) respectively were intercrossed to develop ICF1—ICF3 generations. These gene pyramided lines were evaluated for key agro-morphological traits, quality, and resistance against blast at three different hotspot locations as well as BB at two locations. Two ICF3 gene pyramided lines viz., TH-625-159 and TH-625-491 possessing four genes exhibited a high level of resistance to BB and blast. In the future, these improved Tellahamsa lines could be developed as mega varieties for different agro-climatic zones and also as potential donors for different pre-breeding rice research.

Introgressed Saltol QTL Lines Improves the Salinity Tolerance in Rice at Seedling Stage.

Rice is a staple food crop in Asia and plays a crucial role in the economy of this region. However, production of rice and its cultivating areas are under constant threat of soil salinity. A major QTL, Saltol, responsible for salinity tolerance at seedling stage has been mapped on chromosome 1 using Pokkali/IR29 Recombinant Inbred Lines (RIL) population. The present study was aimed to incorporate Saltol Quantitative Trait Loci (QTL) in two high yielding mega rice varieties i.e. Pusa44 and Sarjoo52 through Marker Assisted Backcross Breeding (MABB). To improve the seedling stage salinity tolerance in these cultivars, we introgressed the Saltol QTL from donor parent FL478 a derivative of Pokkali. A total of three backcrosses (BC3) followed by selfing have led to successful introgression of Saltol QTL. Foreground selection at each breeding cycle was done using micro-satellite markers RM3412 and AP3206 to confirm Saltol QTL. The precise transfer of Saltol region was established using recombinant selection through flanking markers RM493 and G11a. Finally, 10 Saltol near isogenic lines (NILs) of Pusa44 and eight NILs of Sarjoo52 were successfully developed. These NILs (BC3F4) were evaluated for seedling stage salinity under hydroponic system. The NILs PU99, PU176, PU200, PU215, PU229, PU240, PU241, PU244, PU252, PU263 of Pusa44 and SAR17, SAR23, SAR35, SAR39, SAR77, SAR87, SAR123, SAR136 NILs of Sarjoo52 confirmed tolerance to salinity with low salt injury score of 3 or 5. Ratio of Na+/K+ content of Saltol NILs ranged from 1.26 to 1.85 in Pusa44 and 1.08 to 1.69 in Sarjoo52. The successfully developed NILs were further phenotyped stringently for morphological traits to estimate Phenotypic Recovery. Background selection of NILs along with parents was carried out with 50K SNP chip and recovered 94.83–98.38% in Pusa44 NILs and 94.51 to 98.31% in Sarjoo52 NILs of recurrent genome. The present study of MAB has accelerated the development of salt tolerant lines in the genetic background of Pusa44 and Sarjoo52. These NILs could be used for commercial cultivation in saline affected area.

Chlorophyll fluorescence and photosynthetic gas exchange in submergent tolerant CO 43 Sub1 lines

The study was aimed at developing submergence tolerant version of popular rice variety of Tamil Nadu namely CO 43, through marker assisted introgression of Sub1 locus from a submergence tolerant FR13A. Selfed progenies of BC2 generations were genotyped and phenotyped for submergence tolerance. Foreground selection was done using rice marker RM219 and ART 5. Background Selection (BGS) was done using 25 genome wide SSR markers with three markers covering per chromosome. BGS resulted in the identification of superior six BC2F2 plants possessing > 80% of CO43 genome. These lines were selfed to generate BC2F3 progenies for further phenotyping studies under simulated submergence conditions. Most of the BC2F3 progenies and FR13A plants exhibited 100% survival for flooding stress of 13 days. All the survived plants of BC2F3 generations were evaluated for plant height, chlorophyll contents, chlorophyll fluorescence, photosynthetic rate, stomatal conductance and transpiration rates before and after flooding. The findings of the study showed that the backcross progenies (BC2F3) with minimum underwater elongation were associated with increased survival percentage, higher chlorophyll contents and comparable fluorescence values as that of FR13A. Most of the BC2F3 individuals recorded higher photosynthetic rate coupled with higher conductance and transpiration rates.

Introgression of a drought insensitive grain yield QTL for improvement of four Indian bread wheat cultivars using marker assisted breeding without background selection

In wheat, a major yield QTL (Qyld.csdh.7AL) contributing ~ 20% to the variation for grain yield under drought was introgressed into each of the four Indian wheat cultivars (HUW234, HUW468, K307 and DBW17) with an objective to develop high yielding drought tolerant genotypes. The marker Xwmc273.3 linked to the yield QTL was used for marker assisted foreground selection, which was followed by phenotypic selection leading to the development of 55 advanced lines. These lines were evaluated during the crop seasons 2015–2016 and 2016–2017 under irrigated and rainfed conditions at two locations (Meerut and Niphad), which differed for agro-climatic conditions. Under irrigated condition at Niphad, three lines gave 14.9–25.7% higher yield relative to the corresponding genotypes HUW234 and DWB17 that were used for introgression. Similarly, under rainfed condition at Meerut, one line gave 25.5% higher yield relative to the corresponding genotype HUW234. The high yield in the selected lines was attributed to number of grains per ear, grain weight, tiller number, biomass and lower canopy temperature. The line giving higher yield under rainfed condition also had low stress sensitivity index suggesting its ability to tolerate water-stress. The high yielding lines may be used for testing in a variety development programme. The study is yet another example of the successful use of MAS in combination with phenotypic selection for development of high yielding wheat genotypes for rainfed and irrigated conditions.

Introgression of QTLs determining sorghum downy mildew (SDM) resistance into elite maize line UMI 79 through marker-assisted backcross breeding (MABC)

Sorghum downy mildew (SDM), caused by Peronosclerospora sorghi is one of the important diseases in maize. Here, we illustrate the transfer of two QTLs for SDM on chromosome 3 and 6 from UMI 936 (w) into an elite maize inbred line UMI 79 through marker-assisted backcross breeding (MABC). For foreground selection, plants carrying heterozygote allele for the QTLs for SDM were selected from F1 and three back cross (BC1-BC3) generations using simple sequence repeat (SSR) markers linked to the targeted QTLs region of SDM. Consequently, foreground positive plants from BC3F1 generation selfed to produce BC3F2 and plants carrying the favorable alleles for the QTLs for SDM were selected followed by stringent phenotyping against SDM and advanced to BC3F3. As a result, two improved lines (79/936–1–7-7-7-46-46 and 79/936–1–7-7-10-80-80) possessing QTLs for SDM were obtained. Background selection using 146 SSR markers distributed evenly across the maize genome revealed 92.45% and 89.68% recovery of recurrent parent genome (RPG) in two improved lines. Phenotypic characterization of the improved lines showed more than 90% of recovery of the recurrent parents in morphological traits and a resistance to SDM. In conclusion, the newly developed SDM resistant inbred lines are a potential source for improving SDM resistance in maize breeding programs.

Introgressing blue mold resistance into elite apple germplasm by rapid cycle breeding and foreground and background DNA-informed selection

Apple blue mold causes significant postharvest economic losses worldwide. A blue mold resistance locus, qM-Pe3.1, was previously identified on chromosome 3 of Malus sieversii PI 613981, a wild accession with inferior fruit quality. Introgression of the resistance allele into elite breeding germplasm is difficult and success of introgression and the effect of the PI 613981 genome on fruit quality cannot be phenotypically evaluated until fruiting, which occurs approximately 5 years from seed. In this study, introgression of the qM-Pe3.1 resistance allele was achieved by rapid cycle breeding, utilizing the transgenic line T1190 constitutively expressing the BpMADS4 early-flowering gene. This was supported by DNA-based diagnostic information that enabled marker-assisted selection for blue mold resistance using a locus-specific DNA test developed to detect the qM-Pe3.1 resistance allele in offspring (foreground selection). Of 75 second-generation ([‘Gala’ × PI 613981] × T1190) offspring carrying BpMADS4, 43 also carried the qM-Pe3.1 resistance allele. DNA tests for other trait loci were used to identify other desirable alleles related to fruit quality in progeny and 6874 genome-wide SNP markers (from an apple 20K Illumina® SNP array) were used to identify undesirable genomic segments of PI 613981 (background selection). Three individuals identified with favorable recombination close to qM-Pe3.1 and less than 25% of M. sieversii unimproved genome were selected as best suited for the elimination of unimproved DNA segments in subsequent generations. Our pipeline for introgression of qM-Pe3.1, facilitated by marker-assisted foreground and background selection, successfully advanced this promising germplasm in readiness for the next generation.

Marker assisted introgression of genes governing resistance to bacterial blight and blast diseases into an elite Basmati rice variety, ‘Pusa Basmati 1509’

In the present study, we introgressed two genes each governing resistance to major diseases of rice namely, bacterial blight (BB) (xa13 and Xa21) and blast (Pi2 and Pi54) into a popular Basmati cultivar, Pusa Basmati 1509 (PB 1509) through marker assisted backcross breeding (MABB). Through foreground selection, seven plants homozygous for all the four genes were selected from a large population of 1832 BC2F2 plants and subjected to background selection coupled with phenotypic selection for agronomic and grain quality traits of the recurrent parent. BC2F2 selections were further advanced to BC2F4 generation to develop near-isogenic lines (NILs). Six NILs from the BC2F4 families with an RPG recovery ranging from 82.5% to 90.5% were evaluated in multi-location trials for agronomic performance, grain quality traits and disease resistance. The level of resistance to BB and blast diseases in all the selected NILs was similar to that of the donor parent. Three BB races, race 2, 4 and 6, respectively produced on average 1.8, 2.3 and 2.5 cm of lesion length in the NILs as against 15.6, 18.1 and 20.8 cm in PB1509. Further, the NILs recorded a disease score of 1.0 and 1.7 for two blast isolates Mo-nwi-38 and Mo-nwi-kas, respectively, as against the score of 4.0 in PB 1509 for both the isolates. The NILs were similar to PB 1509 for major agronomic and grain quality traits with the advantage of resistance to BB and blast diseases.

Marker-assisted selection of qMrdd8 to improve maize resistance to rough dwarf disease.

Maize rough dwarf disease (MRDD) is caused by viruses in the Fijivirus genus in the family Reoviridae. MRDD resistance can be improved by a combination of marker-assisted selection (MAS) and conventional breeding strategies. In our previous study, we fine-mapped a major QTL qMrdd8 and developed the functional Indel marker IDP25K. In the present study, qMrdd8 from the donor parent X178 was introgressed into elite inbred lines derived from the three corn heterotic groups using multi-generation backcrossing and MAS. Recipient lines included Huangzao4, Chang7-2, Ye478, Zheng58, Zhonghuang68, B73, and Ji846. Markers used for foreground selection included IDRQ4, IDRQ47, IDP25K, and IDP27K. Background selection was carried out in the BC3 or BC4 using 107 SSR markers to select lines with the highest rate of recovery of the particular recurrent parent genome. Plants from BC4F2 and BC3F2 that carried the shortest qMrdd8 interval from X178 and those with the highest rate of recovery of the recurrent parent genome were then selected to create converted homozygous inbred lines. In 2017, seven converted inbred lines and five hybrids exhibited enhanced resistance to MRDD, while other agronomic traits were not affected under nonpathogenic stress conditions. Thus, the MRDD resistance allele at the qMrdd8 locus, or IDP25K, should be valuable for maize breeding programs in China.

Marker-Assisted Introgression of Multiple Resistance Genes Confers Broad Spectrum Resistance against Bacterial Leaf Blight and Blast Diseases in PUTRA-1 Rice Variety

Bacterial leaf blight caused by Xanthomonas oryzae pv oryzae (Xoo) and blast caused by Magnaporthe oryzae are major diseases responsible for significant yield loss in rice production across all rice growing regions. Host plant resistance has been advocated as a sustainable means of guarding against the diseases. This experiment was conducted with the aim to introgress multiple resistance genes against bacterial leaf blight and blast diseases through marker-assisted backcross breeding. Two dominant (Xa4 and Xa21) and two recessive (xa5 and xa13) Xoo resistance genes were introgressed into a high yielding Malaysian rice variety Putra-1 with genetic background of three blast resistance (Piz, Pi2 and Pi9) genes. Eight polymorphic tightly linked functional and SSR markers were used for foreground selection of target genes. Seventy nine polymorphic SSR markers were used in background selection. The plants were challenged at initial stage of breeding and challenged again at BC2F2 with the most virulent Malaysian pathotypes of Xoo (P7.7) and Magnaporthe oryzae (P7.2) to test their resistance. Results obtained from foreground marker segregation analysis at BC1F1 and BC2F1 showed that the marker polymorphism both fitted into the Mendel’s single gene segregation ratio of 1:1 for both Xoo and blast resistance. At BC2F2, results indicated that foreground marker polymorphism fitted into the expected Mendelian ratio of 1:2:1 for blast resistance only. Marker-assisted background selection revealed high percentage of recurrent parent genome recovery (95.9%). It was concluded that the inheritance of blast resistance in the introgressed lines was mainly due to single gene action while the inheritance of Xoo resistance was substantially due to single nuclear gene action. The incorporation of four bacterial leaf blight and three blast resistance genes (Xa4 + xa5 + xa13 + Xa21; Pi9 + Pi2 + Piz) in the newly developed lines would provide for broad spectrum and durable resistance against the two major diseases studied.

INTROGRESSION OF BACTERIAL BLIGHT RESISTANCE GENES; Xa33 AND Xa38 INTO RICE GENOTYPE ADT 47 THROUGH MARKER ASSISTED SELECTION

Bacterial blight is one of the serious diseases of rice. Utilization of resistant varieties is considered to be the most effective method of control. ADT 47 rice genotype has nearly been improved with the blight resistance genes xa5, xa13 and Xa21, through marker assisted selection (MAS). As the objective of this study, marker assisted backcrossing breeding (MABB) was adopted for targeted introgression of the broad spectrum resistance genes, Xa33 and Xa38 to the Improved ADT 47 rice variety. The rice genotypes FBRI-15, PR114 were used as donors of Xa33 and Xa38 genes, respectively. The marker RMWR7.1 linked to Xa33 and the sequenced-tagged site marker Os04g53050-1 specific to Xa38 were validated in parents who were used for foreground selection. True F1 hybrids were selected using the polymorphic markers. Out of one hundred and thirty seven SSR markers, forty-two were polymorphic for Improved ADT 47 x FBRI-16 which was used for background selection. Foreground selection revealed that a single F1 plant was heterozygote in Improved ADT 47 x FBRI-15 and it was used to develop BC1 generation. At BC1F1, one plant was found to be heterozygous for Improved ADT 47 x FBRI-15. At BC2F1, a single plant was found heterozygous as well from the cross. In the final BC3F1 population, one heterozygous plant was validated from the cross, the plant was subjected to background selection for selecting plants having the genetic background similar to that of the recurrent parent (i.e., confirmation of recurrent parent genome recovery) using the forty-two dominant SSR markers. In BC3F1, there was a 92.80% parental genome recovery in the Improved ADT 47 x FBRI-15. This high parental genome line was selfed to produce BC2F2 for selection of homozygous lines for xa5, xa13, Xa21 and Xa33/Xa38. The study recommends that the BC2F2 plants will be selfed using pedigree method and then advance to preliminary yield trial (PYT), then Advanced yield trial (AYT) and finally to on farm assessment for release.