Marker-assisted Backcross Breeding Research Articles

Stacking Multiple Genes Improves Resistance to Chilo suppressalis, Magnaporthe oryzae, and Nilaparvata lugens in Transgenic Rice.

The ability of various pests and diseases to adapt to a single plant resistance gene over time leads to loss of resistance in transgenic rice. Therefore, introduction of different pest and disease resistance genes is critical for successful cultivation of transgenic rice strains with broad-spectrum resistance to multiple pathogens. Here, we produced resistance rice lines with multiple, stacked resistance genes by stacking breeding and comprehensively evaluated their resistance to Chilo suppressalis (striped rice stemborer), Magnaporthe oryzae (rice blast), and Nilaparvata lugens (brown planthopper) in a pesticide-free environment. CRY1C and CRY2A are exogenous genes from Bacillus thuringiensis. Pib, Pikm, and Bph29 are natural genes in rice. CH121TJH was introduced into CRY 1C, Pib, Pikm, and Bph29. CH891TJH and R205XTJH were introduced into CRY 2A, Pib, Pikm, and Bph29. Compared with those observed in their recurrent parents, CH121TJH significantly increased the mortality of borers. The other two lines CH891TJH and R205XTJH are the same result. Three lines introduction of Pib and Pikm significantly reduced the area of rice blast lesions, and introduction of Bph29 significantly reduced seedling mortality from N. lugens. Introduction of the exogenous genes had relatively few effects on agronomic and yield traits of the original parents. These findings suggest that stacking of rice resistance genes through molecular marker-assisted backcross breeding can confer broad spectrum and multiple resistance in differently genetic backgrounds.

Marker assisted pyramiding of qDTY QTLs governing yield under drought stress into rice variety ADT(R)45

Drought occurrence during reproductive stage of rice leads to significant yield loss. Rice production has to be doubled to feed the ever increasing human population. As the yield levels are stagnated under favourable production system, improvement of yield under unfavourable environment is key to attain the projected target. Therefore, the present study was undertaken to improve the drought tolerance of popular rice variety ADT(R)45 by introgressing major effect quantitative trait loci (QTLs) conferring yield under drought (qDTY1.1, qDTY3.1 and qDTY12.1) through marker assisted backcross breeding (MABB). Through MABB, 117 BILs in the background of ADT(R)45 were developed with different combinations of qDTY QTLs.  The BILs were evaluated under rainfed target production environment and observations on nine biometrical and yield traits were recorded. Variability analysis revealed presence of additive gene action for the traits viz., total number of tillers per plant, number of productive tillers per plant, hundred grain weight, yield per hectare and single plant yield. Hence, selection based on these traits will be effective to improve yield under drought stress. Association analysis showed total number of tillers per plant, number of productive tillers per plant, panicle length, hundred grain weight and spikelet fertility percentage were highly correlated with yield per plant. Comparison of BILs with different QTL combinations showed that BILs with single QTL (qDTY12.1) was better for most of the traits studied. BILs with single or two QTL combinations were found to perform better under rainfed condition, when compared to BILs with all the three QTLs. Keywords: Reproductive stage drought, Rainfed, qDTYs, rice, BILs, MABB

Performance of improved versions of Swarna introgressed with yield enhancing genes in multi-location trials

Swarna (MTU7029), an Indian mega-variety of rice, is cultivated on an estimated 8Mha of land. There is a pressing need to address yield stagnation and wider adaptability to irrigated lowland and rainfed ecologies as a result of the negative consequences of climate change and population growth. The present study was aimed at improving Swarna for two yield-related traits through marker-assisted backcross breeding strategy by introgression of OsSPL14 (panicle branching) and SCM2 (stronger culm). Foreground and background selection was carried out at each generation. Homozygous BC2F2 plants harbouring both yield-enhancing genes were identified and advanced through pedigree selection till BC2F5 and evaluated in station trials. Three promising lines possessing higher yield over recurrent parent were identified, and a single line, IET 27661 exhibited superior yield in multi-location trials of the All India Coordinated Rice Improvement Programme (AICRIP) and was found to be promising.

Development of bread wheat (Triticum aestivum L) variety HD3411 following marker-assisted backcross breeding for drought tolerance.

Marker-assisted backcross breeding enables selective insertion of targeted traits into the genome to improve yield, quality, and stress resistance in wheat. In the current investigation, we transferred four drought tolerance quantitative trait loci (QTLs) controlling traits, viz canopy temperature, normalized difference vegetative index, chlorophyll content, and grain yield from the drought-tolerant donor line, C306, into a popular high-yielding, drought-sensitive variety, HD2733. Marker-assisted selection coupled with stringent phenotypic screening was used to advance each generation. This study resulted in 23 improved lines carrying combinations of four drought tolerance QTLs with a range of 85.35%-95.79% background recovery. The backcross-derived lines gave a higher yield under moisture-deficit stress conditions compared with the recipient parent. They also showed higher phenotypic mean values for physiological traits and stability characteristics of HD2733. A promising genotype, HD3411, derived from this cross was identified for release after national multi-location coordinating trials under the All India Coordinated Wheat Improvement Project. Our study is a prime example of the advantages of precision breeding using integrating markers and phenotypic selection to develop new cultivars with desirable traits like drought tolerance.

Developing Early Morning Flowering Version of Rice Variety CO 51 to Mitigate the Heat-Induced Yield Loss

By 2050, the rice production needs to be increased by at least 50% in order to meet the growing food demands of the global population. Among various yield limiting factors, high temperature is fast becoming a major threat to sustain rice yields due to its increased frequency of occurrence and severity of stress events. The development of heat-resilient rice cultivars has been slow due to the lack of relevant donors for heat tolerance traits and limited information regarding the genetic basis of these component traits. The early morning flowering (EMF) trait, contributing to heat escape by promoting flowering/anthesis during cooler hours in the morning is demonstrated to offer protection against high-temperature-induced failure of pollination and fertilization. In this study, evaluation of CO 51, IR64 and IR64-qEMF3 (NIL of IR64 harboring QTL promoting EMF revealed that qEMF3 promoted early morning flowering in IR64-qEMF3 (1½ to 2 h earlier than IR64) and thereby reduced the sterility by about 8.15%. Attempts through marker-assisted backcross breeding led to development of advanced backcross progenies (NILs) of CO 51, harboring qEMF3. Evaluation of 88 BC3F2 progenies identified 19 progenies harboring qEMF3 under homozygous conditions. Evaluation of NILs of CO 51 harboring qEMF3 during summer 2019 revealed that the NILs exhibited early (7.30 a.m.) onset of anthesis by 1½ h and completed its peak anthesis well around cooler hours (9.30 a.m.) of the day and thereby recorded reduced spikelet sterility (7.8–9.0%) than their recurrent parent CO 51 (19.2%). The current study clearly demonstrated the efficacy of early morning flowering in the mitigation of yield losses under high-temperature conditions in a farmer preferred rice variety.

Backcrossing with Marker Assistance to Introduce Broad-Spectrum Bacterial Leaf Blight Resistance in the Malaysian Elite Variety MR297

A significant part of marker-assisted backcross breeding (MABB) is recurrent parent genome recovery (RPGR). The purpose of this study was to introduce MABB-mediated resistance genes against numerous bacterial leaf blight (BLB) pathogens. Here, we examine the introgression of four Xoo resistance genes to the high-yielding Malaysian MR297 lineage Xa21, xa13, xa5, and Xa4 from the IRBB60 lineage. To accomplish both foreground and background selection, we employed polymorphic functional linked markers to target genes and simple sequence repeat (SSR) markers. We used 83 of the 475 authorized polymorphic microsatellite markers to determine the proportion of RPGR in the chosen lines. According to the data, the RPGR at BC1F1, BC2F1, and BC2F2 are 81.94, 92.30, and 95.04%, respectively. Incorporating the four BLB resistance genes into the newly created lines would result in long-lasting and comprehensive protection against BLB. Therefore, a resistant gene may be introduced into a population more quickly with MABB than through conventional breeding. All ten lines tested showed a significant level of resistance to BLB, with three lines displaying very high levels of resistance. Consequently, it was recommended that new lines should be used to produce commercially viable rice varieties.

Molecular Breeding for Incorporation of Submergence Tolerance and Durable Bacterial Blight Resistance into the Popular Rice Variety 'Ranidhan'.

Ranidhan is a popular late-maturing rice variety of Odisha state, India. The farmers of the state suffer heavy loss in years with flash floods as the variety is sensitive to submergence. Bacterial blight (BB) disease is a major yield-limiting factor, and the variety is susceptible to the disease. BB resistance genes Xa21, xa13, and xa5, along with the Sub1 QTL, for submergence stress tolerance were transferred into the variety using marker-assisted backcross breeding approach. Foreground selection using direct and closely linked markers detected the progenies carrying all four target genes in the BC1F1, BC2F1, and BC3F1 generations, and the positive progenies carrying these genes with maximum similarity to the recipient parent, Ranidhan, were backcrossed into each segregating generation. Foreground selection in the BC1F1 generation progenies detected all target genes in 11 progenies. The progeny carrying all target genes and similar to the recipient parent in terms of phenotype was backcrossed, and a total of 321 BC2F1 seeds were produced. Ten progenies carried all target genes/QTL in the BC2F1 generation. Screening of the BC3F1 progenies using markers detected 12 plants carrying the target genes. A total of 1270 BC3F2 seeds were obtained from the best BC3F1 progeny. Foreground selection in the BC3F2 progenies detected four plants carrying the target genes in the homozygous condition. The bioassay of the pyramided lines conferred very high levels of resistance to the predominant isolates of bacterial blight pathogen. These BB pyramided lines were submergence-tolerant and similar to Ranidhan in 13 agro-morphologic and grain quality traits; hence, they are likely to be adopted by farmers.

Evaluation of Salinity-Tolerant Backcrossed Inbre Lines (BILs) For Fertility Restoration Using Molecula Markers

Fertility restoration is a very important trait for the WA-CMS system in hybrid rice. Fifty-five BILs derived from KMR3 and FL478 cross combination possessing Saltol1 generated through Marker Assisted Backcross Breeding (MABB) approach were screened using Rf4 and Rf3 markers during Rabi 2021. The use of molecular markers tightly linked with fertility restoration aided in identifying promising groups of restorers, maintainers, partial restorers, and partial maintainers. The presence of both Rf4 and Rf3 alleles among the nineteen BILs was 35% which showed a clear difference in the marker distribution among the BILs. The BILs namely TCP32, TCP34, TCP35, TCP36, TCP36-3, TCP37-2, TCP38, TCP13, TCP18, TCP19, TCP45, TCP46, TCP48, TCP54, TCP56, TCP57-1, TCP60, TCP61, TCP61-3 were identified as promising restorers possessing both Rf4 and Rf3 genes. The current study reflects that Rf4 and Rf3 genes in combination help in the breeding of WA-CMS-based hybrids in Saltol introgressed restorers with better heterosis under various ecologies, especially coastal saline areas.

Genetic Diversity, Conservation, and Utilization of Plant Genetic Resources.

Plant genetic resources (PGRs) are the total hereditary material, which includes all the alleles of various genes, present in a crop species and its wild relatives. They are a major resource that humans depend on to increase farming resilience and profit. Hence, the demand for genetic resources will increase as the world population increases. There is a need to conserve and maintain the genetic diversity of these valuable resources for sustainable food security. Due to environmental changes and genetic erosion, some valuable genetic resources have already become extinct. The landraces, wild relatives, wild species, genetic stock, advanced breeding material, and modern varieties are some of the important plant genetic resources. These diverse resources have contributed to maintaining sustainable biodiversity. New crop varieties with desirable traits have been developed using these resources. Novel genes/alleles linked to the trait of interest are transferred into the commercially cultivated varieties using biotechnological tools. Diversity should be maintained as a genetic resource for the sustainable development of new crop varieties. Additionally, advances in biotechnological tools, such as next-generation sequencing, molecular markers, in vitro culture technology, cryopreservation, and gene banks, help in the precise characterization and conservation of rare and endangered species. Genomic tools help in the identification of quantitative trait loci (QTLs) and novel genes in plants that can be transferred through marker-assisted selection and marker-assisted backcrossing breeding approaches. This article focuses on the recent development in maintaining the diversity of genetic resources, their conservation, and their sustainable utilization to secure global food security.

Ugradnja Ga1-S gena u roditeljske linije hibrida kukuruza belog zrna pomoću molekularnih markera

Maize Research Institute Zemun Polje has a marker-assisted backcross breeding (MABB) program aimed to incorporate the strong allele of incompatibility gene Ga1 into parental components of the hybrids with specific traits (white kernel). The main objective of this research was marker-assisted development of the white maize hybrid's parental lines with complete cross-incompatibility to foreign pollens. Ga1-S-tightly-linked molecular markers successfully identified heterozygous plants with a percentage of approximately 50% after all three backcrossings. Regarding the background selection, 69% of progenies had recurrent parent's genome (RPG) above the theoretical value for BC3 generation. Also, a few individuals even had 99%, the value theoretically achieved in the BC6 generation, showing that MABB made a genetic gain in RPG recovery. Foreground selection in this generation aimed to identify homozygous dominant individuals. Out of 264 BC3 F2 plants, 70 (26.5%) were dominant homozygotes, which is in accordance with the expected Mendelian ratio. Progenies of the BC3 F2 homozygous dominant plants were planted alternatively with yellow-kernel maize of the same maturity to check cross-incompatibility. Unfortunately, none of the dominant progenies had a 100% white kernel, most likely due to the presence of modifier genes that increase/decrease the effectiveness of pollen exclusion or that, alternatively, modifiers are lost during the backcrossing. It could be expected that successfully employed functional markers (developed from the sequence polymorphisms present within a functional gene(s) associated with phenotypic trait variations) would outbalance the noted impediments and enhance MABB efficiency to transfer the desired gene(s) controlling simple or complex trait(s) into cultivated varieties.

Development of low-phytate maize inbred lines through marker-assisted introgression of lpa1

Context Phytic acid is the major storage form of phosphorus in cereals and is considered an anti-nutritional factor because it chelates major mineral micronutrient cations, resulting in micronutrient malnutrition in humans. For monogastric animals fed maize (Zea mays L.) grains, the stored phosphorus does not release into the digestive tract, leading to phosphorus deficiency and environmental pollution. Aims The aim of the study was to develop maize lines with a lower level of phytic acid that might substantially enhance the nutritional value of maize. Methods The lpa1 mutant allele conferring low phytic acid was transferred into the parental lines of popular maize hybrid DMH 121 (i.e. BML 6 and BML 45) through marker-assisted backcross breeding. Foreground selection was performed using a co-dominant single nucleotide polymorphism marker through a high-resolution melting approach, and background selection was undertaken using 50–55 polymorphic sequence-tagged microsatellite site markers. Key results Near-isogeneic lines were produced with >90% recurrent parental genome and reduction of phytic acid content by up to 44–56% compared with the original lines. Conclusions The near-isogeneic lines carrying lpa1 can be used to reconstitute DHM 121 with low phytate content. Implications The low-phytate maize hybrids produced can be useful in reducing micronutrient malnutrition in humans, as well as environmental pollution.

Marker assisted backcross breeding to develop the drought tolerant version of IR58025B, a popular maintainer line of hybrid rice

Drought stress has become more important abiotic factor affecting rice yield under present changing climate conditions. IR58025B is a maintainer line of widely used WA CMS line IR58025A and widely used in commercial rice hybrids production in India. Most of the rice hybrids are released for the irrigated ecosystem consequently, these derived hybrids suffer drastic yield decline under moisture stress conditions. To facilitate the efficient use of complex polygenic traits in hybrid rice molecular breeding research, we undertook development of introgression lines in background of IR58025B with tolerance to moisture stress by introgression of major QTL qDTY3.1 controlling grain yield under moisture stress. The present study reports the development and evaluation of 230 introgression lines (BC2F2) lines in IR58025B background for improvement of grain yield under moisture stress condition. Among 230 ILs, 24 introgression lines were found positive for qDTY3.1 and negative for fertility restoration (rf4 & rf3).Promising BILs exhibited earliness of 7 days under moisture stress with grain yield advantage of 8.54g to 10.78g in comparison to the recurrent parent. This suggested that the efficacy of introgressed drought tolerant QTL qDTY3.1 in enhancing grain yield under moisture stress conditions. Further, breeding lines of IR58025B possessing qDTY3.1 could also serve as good donors for development of drought tolerant rice hybrids for unfavorable ecologies.

Resistance to Pythium root rot and anthracnose among Kenyan common bean genotypes and marker-assisted introgression of resistance genes

ABSTRACT Common bean (Phaseolus vulgaris L.) is an important food legume crop and major protein source in Kenya and many parts of the world. However, the yields are low due to the diseases like anthracnose caused by Colletotrichum lindemunthianum and Pythium root rots. The study, therefore, sought to screen Kenyan common bean genotypes for anthracnose and Pythium resistance and to improve the resistance of local landraces to the two diseases. Local landraces and commercial cultivars were screened for resistance under greenhouse conditions for Pythium and in vitro for anthracnose. The results showed that majority of the landraces were moderately resistant to anthracnose and Pythium root rot. The study further utilized molecular markers linked to anthracnose and Pythium resistance, respectively, to determine their potential to detect specific resistance genes among the test genotypes. None of the markers amplified the test genotypes except the control genotypes pointing toward different resistance genes. Further, cultivars G2333 and KK8 were used as donor parents for anthracnose and Pythium resistance, respectively, in a marker-assisted backcross breeding program involving three high-yielding farmer-preferred landraces. A number of lines were developed that carry both resistance genes. These lines can be advanced for release as new cultivars to enhance common bean production in Kenya.

Marker-assisted pyramiding of southern leaf blight resistance QTLs qSLB3.1 and qSLB8.1 in maize (Zea mays)

Southern leaf blight (SLB) is one of the major diseases that cause substantial yield losses in maize (Zea mays L.) worldwide. Stacking broad-spectrum resistance genes/QTLs into prevalent cultivars is the prerequisite for durable disease resistance breeding programme. Therefore, a study was carried at the research farm and molecular biology laboratory of School of Agricultural Biotechnology, Punjab Agricultural University, Ludhiana, Punjab during 2017–21 to introgress SLB resistance QTLs from two donors, viz. CM139 (qSLB3.1) and LM5 (qSLB8.1) into CM140 inbred using marker-assisted backcross breeding (MABB). Crosses were made between CM139 × CM140 and LM5 × CM140 to generate two separate F1s. Each F1 was backcrossed twice to generate BC2F1 progenies. Foreground selection was performed at each step using linked flanking markers to each QTL and also evaluated for SLB resistance. The selected heterozygous BC2F1 plants from each cross were inter-crossed to combine qSLB3.1 and qSLB8.1 in the same genetic background. The F2 population was also evaluated phenotypically for SLB resistance and other morphological traits. A total of 18 plants were obtained having both the QTLs with homozygous donor alleles. The F2 plants having both QTLs and singly in the homozygous state were advanced to generate F3 progenies. The pyramided lines exhibited 29% lesser disease severity than the lines with either QTL. The present results indicated that additive effects of the QTLs for SLB resistance played an important role among these lines. To our best knowledge, this is the first report for the pyramiding of QTLs associated with SLB resistance. The pyramided lines would serve as potential donors in maize breeding programs.

Marker-assisted backcross breeding for heat tolerance in bread wheat (Triticum aestivum L.).

Manipulation of flowering time for adaptation through natural or genetic approaches may combat heat-stress damage that occurs at the reproductive stages in production conditions. HD2733, a popular wheat variety of the eastern plains of India, is largely sensitive to heat stress. Therefore, the current study aims to improve heat tolerance of HD2733 by introgression of QTLs associated with early anthesis and high kernel weight linked to markers Xbarc186 and Xgwm190, respectively, through marker-assisted backcross breeding (MABB) from a tolerant donor, WH730. A total of 124 simple sequence repeat (SSR) markers distributed evenly across the genome were used for the background selection. The alleles of Xbarc186 and Xgwm190 were fixed in BC2F1 and BC1F2 generations by selecting individual plants heterozygous for both marker loci and backcrossed with HD2733 and simultaneously selfed to generate BC2F1 and BC1F2 populations, respectively. Furthermore, the selected BC1F2 were selfed to generate the BC1F4 population. By background screening, a total of 39 BC2F3 and 21 BC1F4 families homozygous for the targeted QTLs with 90.9-97.9% and 86.8-88.3% RPG recoveries were selected. The best performing 17 BC2F3 and 10 BC1F4 lines were evaluated for various morpho-physiological traits. Phenotypic evaluation and multi-location trials of the introgressed lines under late sown conditions led to the selection of three promising lines with early anthesis and higher grain yield. The improved lines will serve as an excellent genetic material for functional genomics and expression studies to understand the molecular mechanisms and pathways underlying the stress tolerance.

Introgression of tsv1 improves tungro disease resistance of a rice variety BRRI dhan71

Rice Tungro disease poses a threat to rice production in Asia. Marker assisted backcross breeding is the most feasible approach to address the tungro disease. We targeted to introgress tungro resistance locus tsv1 from Matatag 1 into a popular but tungro susceptible rice variety of Bangladesh, BRRI dhan71. The tsv1 locus was traced using two tightly linked markers RM336 and RM21801, and background genotyping was carried out using 7 K SNPs. A series of three back crosses followed by selfing resulted in identification of plants similar to BRRI dhan71. The background recovery varied at 91–95% with most of the lines having 95%. The disease screening of the lines showed moderate to high level of tungro resistance with a disease index score of ≤ 5. Introgression Lines (ILs) had medium slender grain type, and head rice recovery (59.2%), amylose content (20.1%), gel consistency (40.1 mm) and gelatinization temperature were within the acceptable range. AMMI and Kang’s stability analysis based on multi-location data revealed that multiple selected ILs outperformed BRRI dhan71 across the locations. IR144480-2-2-5, IR144483-1-2-4, IR144484-1-2-2 and IR144484-1-2-5 are the most promising lines. These lines will be further evaluated and nominated for varietal testing in Bangladesh.

Pyramiding Submergence Tolerance and Three Bacterial Blight Resistance Genes in Popular Rice Variety Hasanta through Marker-Assisted Backcross Breeding

Flash flooding (FF) along with bacterial blight (BB) outbreak are very destructive for rice production in the rainfed shallow-lowland (RSL) ecosystem. The presence of dynamic Xoo races with varying levels of genetic diversity and virulence renders their management extremely challenging under RSL. In this context, the marker-assisted improvement of plant resistance/tolerance has been proven as one of the most promising strategies towards the development of sustainable cultivars. The present study demonstrates the marker-assisted introgression of the submergence tolerant (Sub1) and three bacterial blight resistant genes (Xa21 + xa13 + xa5) into the genetic background of Hasanta, a long duration popular rice variety in the eastern coastal region of India. The rice genotypes, Swarna Sub1 (carrying Sub1) and IRBB66 (carrying Xa21 + xa13 + Xa7 + xa5 + Xa4) had maximum genetic similarity (0.84 and 0.73, respectively) with Hasanta; recurrent parent (RP) was used as donor. The forward analysis of target genes in F1s, IC1F1s and backcross (BC) generations was performed by linked/genic markers (Sub1bc2; pTA248, xa13prom and RM122), whereas background recovery of RP in each BC and segregating generations was performed utilizing 108 hypervariable SSR markers. Intervened speed breeding (SB) strategy and intensive phenotyping could lead the development of near isogenic lines (NILs) as to the RP in all basic traits. The performance of the near isogenic lines (NILs, BC2F3 and BC2F4), HS 232-411-391-756-37, HS 232-411-391-809-8, HS 232-411-391-756-18, HS 110-224-197-10-36, HS 232-411-391-809-81, HS 110-224-197-10-41 and HS 232-411-391-809-63 establishes the utility of marker-assisted backcross-breeding (MAB) and SB in accelerated trait introgression. The introgressed lines carrying Sub1 + Xa21 + xa13 + xa5 showed 76% to 91% survival under 14 days of submergence and durable BB resistance (percent disease index-PDI of 2.68 ± 0.26 to 6.22 ± 1.08 and lesion length, LL of 1.29 ± 0.12 to 4.2 ± 0.64 cm). Physiological analysis revealed that improved NILs, carrying Sub1 gene conquered adaptive physiological modulations, had reduced the consumption of soluble sugar and the degradation of total chlorophyll contents (TCC), and an enhanced level of Alcohol Dehydrogenase activity (ADH) and proline accumulation in all submergence regimes. The pyramided lines attained complete product profile of RP, that will contribute to sustainable rice production under RSL, particularly in the coastal region that has substantial acreage under the variety Hasanta.

Dissection of a grain yield QTL from wild emmer wheat reveals sub-intervals associated with culm length and kernel number.

Genetic diversity in wheat has been depleted due to domestication and modern breeding. Wild relatives are a valuable source for improving drought tolerance in domesticated wheat. A QTL region on chromosome 2BS of wild emmer wheat (Triticum turgidum ssp. dicoccoides), conferring high grain yield under well-watered and water-limited conditions, was transferred to the elite durum wheat cultivar Uzan (T. turgidum ssp. durum) by a marker-assisted backcross breeding approach. The 2B introgression line turned out to be higher yielding but also exhibited negative traits that likely result from trans-, cis-, or linkage drag effects from the wild emmer parent. In this study, the respective 2BS QTL was subjected to fine-mapping, and a set of 17 homozygote recombinants were phenotyped at BC4F5 generation under water-limited and well-watered conditions at an experimental farm in Israel and at a high-throughput phenotyping platform (LemnaTec-129) in Germany. In general, both experimental setups allowed the identification of sub-QTL intervals related to culm length, kernel number, thousand kernel weight, and harvest index. Sub-QTLs for kernel number and harvest index were detected specifically under either drought stress or well-watered conditions, while QTLs for culm length and thousand-kernel weight were detected in both conditions. Although no direct QTL for grain yield was identified, plants with the sub-QTL for kernel number showed a higher grain yield than the recurrent durum cultivar Uzan under well-watered and mild drought stress conditions. We, therefore, suggest that this sub-QTL might be of interest for future breeding purposes.

Genetic improvement of traditional Basmati rice Ranbir Basmati for semi-dwarfism and blast resistance through molecular breeding

The traditional Basmati rices grown in north-western foothills of Himalayas in India are known world-wide for their exquisite aroma and exceptional eating and cooking qualities. These varieties are tall and suffer heavy losses due to their susceptibility to lodging as well as blast disease. In present study, we improved a popular traditional Basmati rice variety ‘Ranbir Basmati’ for semi-dwarfism and resistance to blast by incorporating the semi-dwarfing gene, sd1 and two blast resistance genes, Pi9 and Pi54 through marker-assisted backcross breeding. Combining marker-assisted background selection with stringent phenotypic selection for aroma and seed quality traits during backcrossing enabled faster recovery of recurrent parent genome and reconstitution of the genomic regions associated with Basmati quality traits in the gene pyramided lines. All pyramided lines were significantly short statured with a reduction of 23.46 to 40.26 cm in height, as compared to recurrent parent, with many of them exhibiting higher grain yield and superior quality attributes than Ranbir Basmati. The yield superiority of the pyramided lines primarily resulted from the improvement in panicle number and semi-dwarf stature conferred by sd1 gene. The gene pyramided lines showed complete resistance to five highly virulent blast races that collectively showed compatibility with 16 different resistance genes, suggesting the broad-spectrum resistance in these lines. The semi-dwarf, high yielding and blast resistant lines generated herein are potential candidates for release as cultivars for overcoming losses in Ranbir Basmati due to lodging and blast disease.

Genotypic and Phenotypic Selection of Newly Improved Putra Rice and the Correlations among Quantitative Traits

This experiment was conducted to genotypically and phenotypically select new rice lines pyramided with blast and bacterial leaf blight disease resistance genes after a marker-assisted backcross breeding programme. The inter-relationship among agro-morphological characteristics and their effect on yield was also studied. The polymorphic functional and microsatellite markers Xa21FR and pTA248 (Xa21), Xa13prom (xa13), RM21 (xa5), MP (Xa4), RM6836 (Pi2, Pi9 & Piz) and RM8225 (Piz) were first confirmed for the target genes. The selected markers were used for foreground selection of BC2F2 homozygous progenies with the target genes. Plants that had homozygous IRBB60 alleles for these markers were evaluated for their recovery of the recurrent parent genome. IRBB60 was used as the donor parent for bacterial blight resistance genes while Putra-1 served as a recipient/recurrent parent with background blast-resistance genes and high yield. After the foreground selection, 79 polymorphic simple sequence repeat markers identified from the marker polymorphism survey were used for marker-assisted background selection to determine the percentage recovery of the recurrent parent genome. In order to make a selection on a phenotypic basis, 14 agro-morphological traits were measured and recorded. The result obtained from the study showed that 16 lines received the seven resistance genes in sufficiently varied numbers and were selected. The distribution of yield per hectare showed that about 50% of the selected lines had yields as high as 5 t/ha and above. Some of the lines produced as high as 8.4 t/ha. These lines demonstrated the potential of recording uniform 8t/ha upon recombination at BC2F2. The study also indicated that the number of panicles per hill correlated strongly, significantly and positively with the number of tillers (r = 0.962 **), total grain weight per hill (r = 0.928 **) and yield per hectare (r = 0.927 **). It was concluded that the newly improved resistant lines which were selected have the capability to compete with Putra-1 in terms of its productivity and yield. The newly developed lines would be useful in future breeding programmes as donors for bacterial leaf blight and blast resistance genes. These lines are recommended for release to farmers in Malaysia and other rice-growing agro-ecologies for commercial cultivation.