Recurrent Parent Research Articles

Identification of powdery mildew resistance quantitative trait loci in melon and development of resistant near-isogenic lines through marker-assisted backcrossing

BackgroundMelon (Cucumis melo L.), an important cucurbit crop, faces production limitations due to powdery mildew (PM). Developing resistant varieties offers a sustainable, genetics-based alternative to chemical treatments. Therefore, identifying PM resistance quantitative trait loci (QTL) and creating trait-associated markers are essential for efficient melon PM resistance improvement through marker-assisted backcrossing (MABC).ResultsThree F2 populations, A6, B2, and C4, were generated for QTL mapping of PM resistance. Major QTL were identified on chromosome 2 in A6, chromosome 5 in B2, and chromosomes 5 and 12 in C4. A series of TaqMan® assays targeting regions on chromosomes 2, 5, and 12 were developed and validated for foreground and recombinant selection, complemented by the double digest restriction-site associated DNA genotyping system to evaluate the recurrent parent genome recovery. Three MABC programs using resistant donor parents from A6 and C4 crossed with elite susceptible recurrent parents with green and orange fruit flesh were implemented. After two to three cycles of MABC, individual QTL was successfully introgressed into elite genetic backgrounds, giving six PM resistance lines in each green- and orange-fleshed background. PM inoculation on the twelve near-isogenic lines confirmed their resistance to PM.ConclusionsWe have identified major PM resistance QTL for melon on chromosomes 2, 5, and 12 and have introgressed individual QTL to elite genetic backgrounds using MABC in three and a half years. This study demonstrates the power of combining high-throughput genotyping with breeding efforts and showcases the efficiency of molecular breeding.

Fine mapping of a major QTL, qECQ8, for rice taste quality

BackgroundRice ECQ (eating and cooking quality) is an important determinant of rice consumption and market expansion. Therefore, improvement of ECQ is one of the primary goals in rice breeding. However, ECQ-related quantitative trait loci (QTL) have not yet been fully revealed. The present study aimed to identify a major effect QTL for rice taste, an important component of ECQ via genotyping-by-sequencing, to reveal the associated molecular mechanisms, and to predict key candidate genes.ResultsA population of F9 recombinant inbred lines resulting from a cross between R668 (national standard of high-quality third class) and R838 (common edible rice) was used to construct a high-density genetic map (2,295.062 cM). The map comprises 639,504 markers distributed on 12 linkage elements with an average genetic distance of 0.004 cM. We detected a major taste-related QTL, qECQ8, which explained 41.4% of phenotypic variance and had LOD values of 4.42–7.73. Using a five-generation NIL population from the backcross of “Ganxiangzhan No. 1” carrying qECQ8 with the recurrent parent R838 (without qECQ8), we narrowed qECQ8 to a 187.5 kb interval between markers M33 and M37 on Chr8. Comparative transcriptomic analysis revealed that photosynthesis, glyoxylate and dicarboxylate metabolism, carbon fixation in photosynthetic organisms, and alpha-linolenic acid metabolism were induced in developing seeds of lines containing qECQ8. Furthermore, we identified two candidate genes in the qECQ8 region, including LOC_Os08g30550 (zinc knuckle family protein), a major candidate for genetic-assisted breeding of high-quality rice.ConclusionOur findings provide important genetic resources for targeted improvement of rice taste quality and may facilitate the genetic breeding of rice ECQ.

Structural, molecular, and physicochemical properties of starch in high-amylose durum wheat lines

There is growing interest in the development of high-amylose cereals such as wheat due to their functional properties and nutritional value in foods. The increase in amylose content is associated with significant changes in the physicochemical, molecular, and structural characteristics of wheat starch which could affect its processing quality. The present study aimed to analyze the physicochemical, molecular, and structural characteristics of high-amylose starch from three durum wheat near isogenic lines (NILs), each obtained using three different recurrent parents. Morphology, granule size distribution, pasting and thermal properties, X-ray diffraction, and structural features were determined. The NILs showed the highest amylose content (65.3 and 69.8%), granules with an elongated shape, size between the wild-type and the mutant, restricted swelling in the pasting profile, the highest average and final gelatinization temperature, and B-polymorphism. The starches from the NILs showed the highest molar mass of amylopectin (AP) (7.0–7.6 × 107 Da) and the lowest amylose (AM) (1.1–1.8 × 106 Da), an issue associated with the biosynthesis of both components. The study on the debranched sample by high-performance size-exclusion chromatography showed that the high-amylose starch had the highest content of long B2 and B3 chains of AP (23.9–26.6%), which was corroborated with the high-performance anion-exchange chromatography analysis where the chains with degree of polymerization >37 had the highest content (18.3–19.1%). The PC1 is highly associated with the MwAM and the AM fraction in the debranched starch analyzed by HPSEC. Characterizing high-amylose durum wheat starch provides information to determine the structure-function relationship and design strategies to produce crosses with structural characteristics of AM and AP for specific applications.

Marker Assisted Selection in Advanced Backcross Population of Rice Variety, MTU1010 for Bacterial Blight and Blast Resistance

The present study was aimed for identification of the bacterial blight and blast resistant lines in the advanced back cross population of MTU-1010 using marker assisted foreground selection and also for evaluation of agro-morphological characters. The M-16-59 introgressed line (derived from an intercrossing of BC2F1 plants of MTU-1010 x GPP2 and MTU-1010 x NLR 145) is developed under ongoing DBTDBSRR subproject -IV possessing Xa21, xa13, Pi1 and Pi54 resistance genes having broad spectrum resistance to bacterial blight and blast is used as a donor parent and MTU-1010 was used as a recurrent parent for the back cross. Before attempting the backcross both the parents were verified for the target genes along with the original donors GPP2 and NLR 145 using gene specific/linked molecular markers viz., xa13-promo for xa13 gene, pTA248 for Xa21 gene, RM 224 for Pi1 and Pi54 MAS for Pi54. under the F1 generation (equivalent to BC3F1 because two backcrosses were completed earlier), 120 plants were screened, and 16 plants were confirmed for xa13, Xa21, Pi1, and Pi54 genes under heterozygous conditions. These confirmed plants were assessed for agro-morphological characteristics such as yield, grain features, and plant type. The results showed that the confirmed heterozygous plants were comparable to MTU-1010 and passed to the next round of selection and evaluation. The BC1F1-198th plant (96.8%) was selfed to produce BC1F2 population. Twenty five plants were advanced to BC1F3 generation based on BB resistance and above other phenotypic characters. The selected BC1F3 progenies were screened for blast and BB resistance. Four BC1F3 progenies with four target genes (xa13xa13Xa21Xa21Pi54Pi54Pi1Pi1) showed very high level of resistance to both the diseases. BC1F2-198-52nd line found similar to MTU1010 with respect to yield and yield related characters besides showing resistance to both BB and blast.Improved lines of MTU1010 can be advanced for multi-location testing under All India Coordinated Rice Improvement Project (AICRIP) for their evaluation and possible release for the benefit of rice farmers.

Recurrent Parent Phenome Recovery Analysis in Six Different Backcross Populations of Bell Pepper Having Genetic Male Sterile ms10 Gene

Recurrent Parent Phenome Recovery Analysis in Six Different Backcross Populations of Bell Pepper Having Genetic Male Sterile ms10 Gene

Introgression of Herbicide-Resistant Gene from Genetically Modified Brassica napus L. to Brassica rapa through Backcrossing.

Interspecific hybridization between two different Brassicaceae species, namely Brassica rapa ssp. pekinensis (♀) (AA, 2n = 2x = 20) and genetically modified Brassica napus (♂) (AACC, 2n = 4x = 38), was performed to study the transmission of a herbicide resistance gene from a tetraploid to a diploid Brassica species. Initially, four different GM B. napus lines were used for hybridization with B. rapa via hand pollination. Among the F1 hybrids, the cross involving the B. rapa (♀) × GM B. napus (♂) TG#39 line exhibited the highest recorded crossability index of 14.7 ± 5.7. However, subsequent backcross progenies (BC1, BC2, and BC3) displayed notably lower crossability indices. The F1 plants displayed morphological characteristics more aligned with the male parent B. napus, with significant segregation observed in the BC1 generation upon backcrossing with the recurrent parent B. rapa. By the BC2 and BC3 generations, the progeny stabilized, manifesting traits from both parents to varying degrees. Cytogenetic analysis revealed a substantial reduction in chromosome numbers, particularly in backcrossing progenies. BC1 plants typically exhibited 21-25 chromosomes, while BC2 progenies showed 21-22 chromosomes, and by the BC3 generation, stability was achieved with an average of 20 chromosomes. SSR marker analysis confirmed the progressive reduction of C-genome regions, retaining minimal C-genome-specific bands throughout successive backcrossing. Despite the extensive elimination of C-genome-specific genomic regions, the glyphosate resistance gene from the male parent B. napus was introgressed into BC3 progenies, suggesting that the glyphosate resistance gene located and introgressed in A-chromosome/genome regions of the Brassica plants.

A novel strategy to map a locus associated with flowering time in canola (Brassica napus L.).

Flowering time is an important agronomic trait for canola breeders, as it provides growers with options for minimizing exposure to heat stress during flowering and to more effectively utilize soil moisture. Plants have evolved various systems to control seasonal rhythms in reproductive phenology including an internal circadian clock that responds to environmental signals. In this study, we used canola cultivar 'Westar' as a recurrent parent and canola cultivar 'Surpass 400' as the donor parent to generate a chromosome segment substitution line (CSSL) and to map a flowering time locus on chromosome A10 using molecular marker-assisted selection. This CSSL contains an introgressed 4.6 mega-bases (Mb) segment (between 13 and 17.6Mb) of Surpass 400, which substantially delayed flowering compared with Westar. To map flowering time gene(s) within this locus, eight introgression lines (ILs) were developed carrying a series of different lengths of introgressed chromosome A10 segments using five co-dominant polymorphic markers located at 13.5, 14.0, 14.5, 15.0, 15.5, and 16.0Mb. Eight ILs were crossed with Westar reciprocally and flowering time of resultant 16 F1 hybrids and parents were evaluated in a greenhouse (2021 and 2022). Four ILs (IL005, IL017, IL035, and IL013) showed delayed flowering compared to Westar (P < 0.0001), and their reciprocal crosses displayed a phenotype intermediate in flowering time of both homozygote parents. These results indicated that flowering time is partial or incomplete dominance, and the flowering time locus mapped within a 1Mb region between two co-dominant polymorphic markers at 14.5-15.5Mb on chromosome A10. The flowering time locus was delineated to be between 14.60 and 15.5Mb based on genotypic data at the crossover site, and candidate genes within this region are associated with flowering time in canola and/or Arabidopsis. The co-dominant markers identified on chromosome A10 should be useful for marker assisted selection in breeding programs but will need to be validated to other breeding populations or germplasm accessions of canola.

Rapid transfer of the leaf rust resistance gene Lr52 for the improvement of bread wheat cultivar HD3086

For varietal improvement, parental genotypes are crossed and advanced to generate homozygous lines with selection for desirable traits like disease resistance and yield. In the current study, leaf rust resistance gene Lr52 from Lr52/Yr47/2*Mace, the donor parent (DP), transferred to the recurrent parent (RP) HD3086, a popular Indian wheat cultivar, which has become susceptible to leaf rust. During the backcross breeding, the plants were grown sequentially under natural field conditions during the winter season and under controlled environmental conditions to take two crop generations during the summer season. Generations comprising F1, BC1F1, and BC2F1-3 plants were developed by crossing and successive backcrossing with RP HD3086 and further selfing to generate homozygous resistant lines. Plants with leaf rust resistance in backcross generations were selected phenotypically to identify the superior or similar plants as of RP HD3086. The Lr52/Yr47-linked SSR marker icg16c004_2 was initially utilised to confirm hybridity and foreground analysis in the BC1F1 generation but was found to be recombinant. Homozygous resistant (HR) lines in BC2F3 generation were selected based on leaf rust disease score and phenome recovery. Finally, the SSR markers unveiling parental polymorphism across the genome were employed to estimate the background recovery of phenotypically selected superior plants, revealing a recovery of 91.48 to 94.81 % of RP genome. The selected improved lines of HD3086+Lr52 displayed similar performance for most agro-morphological traits, and a few lines were also found to yield significantly superior to that of RP HD3086. Overall, the study shows the practical utility of phenotypic selection with intermittent selection under controlled and natural field conditions for improving popular cultivars with relatively higher speed and precision.

Effective components of services for recurrent care experienced parents: A literature review of what works

Recurrent care services aim to reduce the number of repeat removals amongst birth parents who have already ‘lost’ a child through care proceedings. This literature review aimed to identify published evidence about effective components of services to support parents who have experienced repeat removals of their children to care.Searches identified 19 studies that included content relating to the components of service provision within recurrent care services. Across all studies, a range of perspectives were included: birth parents (n = 425); practitioners (n ≥ 151); other professionals (n = 109).The evidence reviewed indicates the importance of relationship-based practice, building a trusted relationship between parents and practitioners, continuity and tenacity in engaging with mothers and a non-judgemental approach. Services should be flexible, holistic and client led, with a long duration of support and a flexible end date. Services should: have a trauma-informed approach; recognise unresolved loss, complex grief and trauma experienced by mothers who have ‘lost’ their children through care proceedings; and provide emotional support, therapeutic support, practical support and advocacy. Services need to have a skilled and multi-disciplinary workforce with robust supervision and ongoing training.

Identification and Validation of Blast Resistance Loci from the Durable Resistance Cultivar Hahng Yi 71

One of the effective strategies for developing blast disease-resistant cultivars to mitigate the yield losses caused by Pyricularia oryzae is the discovery of new genetic resources containing resistance genes. In the present study, a Thai landrace glutinous rice cultivar Hahng Yi 71 (HY71) was used as a durable, broad resistance source to identify QTLs against blast fungus and crossed with a susceptible recurrent parent cultivar RD6, generating 56 BC4F5 lines. The BC4F5 population was tested with six blast isolates, including THL54, THL583, THL658, THL690, THL795, and THL1119, and evaluated with 161 SSR markers to identify resistance regions using modified bulk segregation analysis. Single marker analysis showed 7 markers linked to a resistance reaction located on chromosomes 2, 4, and 5, then tentatively designated as qBL2-RD6, qBL4-HY71, and qBL5-HY71, respectively. Two introgressed lines from the mapping population, KKN97057-7-1-1-2-5-NKI-4-1 and KKN97057-7-1-1-2-5-NKI-5-1, were the qBL5-HY71 donor for introgressing into two rice lines, RGD07123-MS12-MS22-MS1, and RGD07123-MS12-MS22-MS9, which generated two single crosses and a backcross population by marker-assisted selection (MAS) using the linked markers RM39 and RM164. Three improved lines, RGD10021-MS18-B-MS8-MS40, RGD10031-MS-MS3-B-MS9-MS42 (single cross), and RGD11086-MS-MS15-MS10-MS19 (backcross), carrying qBL5-HY71, were tested for their resistance against leaf and neck blast disease by 62 and 8 blast isolates, respectively. The disease screening results showed that qBL5-HY71 was very effective in controlling leaf and neck blast. This study demonstrates the effectiveness of resistance loci qBL5-HY71 from HY71 on chromosome 5 and their linked markers in improving durable blast resistance in rice breeding programs.

Development of high oleic Spanish bunch groundnut (Arachis hypogaea L.) through marker-assisted backcrossing

ABSTRACT Groundnut (Arachis hypogaea L.) is an important oilseed crop. A specific type of groundnut, known as high-oleate groundnut, is particularly sought-after for its antioxidant properties and benefits to human health due to its favorable fatty acid profile. To breed high-oleic acid varieties of groundnut, two elite varieties of Tamil Nadu, India, TMVGn 13 and GJG 33, were hybridized with a high-oleic groundnut donor released in India, Girnar 4. The resulting progenies were then backcrossed with their recurrent parents for two generations, using marker-assisted backcross selection. Six progenies in the TMVGn 13 × Girnar 4 cross and nine progenies in the GJG 33 × Girnar 4 cross were identified as homozygous mutants for ahFAD2A and ahFAD2B genes, respectively. Three lines with high oleic acid content (>70%), good oil content (48–50%), and pod yield per plant were selected from these progenies. Following multi-location and adaptive research yield trials, these lines may be released as high-oleic acid varieties.

Agro-Physiological and DNA Methylation Responses to Salinity Stress in Wheat (Triticum aestivum L.), Aegilops cylindrica Host, and Their Introgressed Lines

Bottlenecks, including limited genetic variation and the ongoing loss of genetic diversity, have hindered the development of modern wheat cultivars., making it crucial to use genetic diversity from wild relatives to improve wheat’s adaptation to abiotic stress, such as salinity. This study assessed the phenotypic and epigenetic variation of introgressed wheat lines (BC4F2) derived from hybridizing two wheat cultivars with Aegilops cylindrica (AC). This study assessed the phenotypic and epigenetic variation of 156 introgressed wheat lines (BC4F2) derived from hybridization between wheat cultivars “Chinese Spring” (CS) and “Roshan” (R) and Aegilops cylindrica (AC). These lines and their recurrent parents (total of 158) were evaluated under normal and saline field conditions for the agronomic traits and stress tolerance indices. The data were used to select the most tolerant and most sensitive lines. Then, the selected BC4F2 lines and their parents (AC, CS, and R) were subjected to physiological, DNA cytosine methylation, and expression analysis of HKT1;5, NHX1, and SOS1 genes under control and salt stress conditions. Agro-physiological, epigenetic, and gene expression analyses showed the significant effects of salt stress and genetic background, as well as the differential response of the BC4F2 lines to salt stress. The variations in leaf and root K, Na, and K/Na ratios, and leaf Chla, Chlb, Car, and MDA levels, unlike DPPH radical scavenging levels, between salt-tolerant and salt-sensitive BC4F2 lines under saline conditions indicated a substantial distinction in salinity tolerance responses. RT-qPCR indicated higher expression levels of NHX1 and SOS1 genes in the leaf and root tissues of tolerant lines than those of sensitive lines. Global leaf and root DNA methylation analysis revealed the significant effects of salinity on the methylation modifications and confirmed the successful introgression of the salt-tolerance epigenome from Ae. cylindrica into wheat. Exploiting the genetic diversity of wild wheat relatives is a crucial goal for increasing genetic and epigenetic variation to enhance plant adaptation to salt stress.

Validation and identification of new QTLs for plant and fruit developmental and composition traits in eggplant under low N conditions

Enhancing plant adaptation to low input conditions is a fundamental goal for implementing sustainable agriculture. In the present study, two eggplant (Solanum melongena) accessions (MEL1 and MEL5), two introgression lines (ILs) derived from eggplant wild relatives S. dasyphyllum (IL-M1-D1) and S. insanum (IL-M5-I9), and a heterozygous version of this last IL (ILHet-M5-I9), along with hybrids among them were evaluated under low N (LN) conditions. IL-M1-D1 carries an introgressed fragment of 4.9 Mb in homozygosis from S. dasyphyllum on chromosome 2, while IL-M5-I9 and ILHet-M5-I9 carry an introgression of 21.5 Mb on chromosome 9 in homozygosis and heterozygosis, respectively, from S. insanum. Multiple quantitative trait loci (QTLs) for several traits of interest were associated with both introgressions under LN conditions in a previous study with segregating advanced backcrosses. Here we evaluated the performance of these materials for 22 agronomic and developmental traits under low N fertilization (LN) conditions. Hybrids with the ILs enabled the study of genetic background effects on QTLs expression. The materials evaluated showed a significant phenotypic variation, particularly within hybrids segregating for the introgression from S. insanum in chromosome 9. Statistical analysis revealed no significant differences among hybrids carrying or not the introgression on chromosome 2 of S. dasyphyllum, and only slight differences were observed between the IL-M1-D1 and its recurrent parent S. melongena MEL1, suggesting a limited impact of this introgression on chromosome 2 on the phenotype variation. However, the differences observed between IL-M5-I9 and its recurrent parent S. melongena MEL5, together with the association between genotypic and phenotypic variation in hybrids segregating for this introgression, allowed the identification of 13 QTLs on chromosome 9. These results successfully validated the previously identified QTLs for flavonol content in leaves, nitrogen balanced index, fruit mean weight, and nitrogen content in leaves and, also revealed nine new QTLs associated with the introgressed genomic region in chromosome 9. This study emphasizes the influence of environmental conditions, genotypes, and genetic backgrounds on the phenotypic expression of eggplant QTLs introgressed from wild relatives and highlights the importance of QTL validation. These findings contribute valuable insights for developing new eggplant cultivars for a more sustainable agriculture, particularly with adaptation to LN conditions.

Marker-assisted introgression to improve the oleic acid content in the TMV 7 groundnut (Arachis hypogaea L.) variety suitable for the oil industry

BackgroundImproving the quality and shelf life of groundnut oil is one of the foremost objectives of groundnut breeding programmes. This can be achieved by marker-assisted introgression, a technique that efficiently and precisely enables breeders to develop plants with enhanced qualities. This study focused on improving the oleic acid content of an elite groundnut variety, TMV 7, by introgressing a recessive mutation responsible for the increase in oleic acid from ICG 15419. Hybridization was performed between the donor and recurrent parents to develop the F1, BC1F1, BC2F1 and BC2F2 populations. Introgressed lines with increased oleic acid in the genetic background of TMV 7 were identified using allele-specific marker, F435-F, F435SUB-R and a set of SSR markers were employed to recover the genome of the recurrent parent. ResultsWith two backcrosses, a total of ten homozygous plants in the BC2F2 population were identified with oleic acid content ranging from 54.23 to 57.72% causing an increase of 36% over the recurrent parent. Among the ten lines, the line IL-23 exhibited the highest level of recurrent parent genome recovery of 91.12%.ConclusionsThe phenotypic evaluation of 10 homozygous introgressed lines indicated fewer differences for all other traits under study compared to the recurrent parent, except for oleic acid and linoleic acid content confirming the genetic background of the recurrent parent. The identified lines will be subjected to multilocation trials before their commercial release.

Performance Test of Vegetative Characteristics of Crossed Rice (Oryza sativa L.) Lines of Ciherang Variety X B11143D Line in Telagasari, Karawang Regency, Indonesia

One way to increase the genetic diversity of Ciherang as the superior variety is to cross Ciherang with the donor B11143D line as a New Plant Type (NPT) rice. This study aimed to obtain Ciherang X B11143D lines with the best vegetative characteristics in the field. The research was conducted in rice fields in Talagasari Village, Telagasari District, Karawang Regency, from May to September 2023. This experiment used a single-factor Randomized Block Design (RBD) with three replications of 22 treatments, consisting of 19 Ciherang X B11143D lines and three comparison varieties. The effect of treatment was studied using analysis of variance. The results showed that the rice lines significantly influenced the vegetative characters of Ciherang X B11143D lines in Telagasari, Karawang Regency. Based on the observed characters, several lines were selected i.e. 124.2.3, 94.3.3, and 20.4.4 lines. Those three lines chosen as backcrossing lines performed similarly compared to Ciherang as recurrent parent and inherited several important traits for rising productivity from the B11143D line as donor parent, namely the length and area of flag leaf, the total number of tillers, and the number of productive tillers, which were significantly higher than Ciherang.

Breeding of a Near-Isogenic Wheat Line Resistant to Wheat Blast at Both Seedling and Heading Stages Through Incorporation of Rmg8.

Wheat blast caused by Pyricularia oryzae pathotype Triticum (MoT) has been transmitted from South America to Bangladesh and Zambia and is now spreading in these countries. To prepare against its further spread to Asian countries, we introduced Rmg8, a gene for resistance to wheat blast, into a Japanese elite cultivar, Chikugoizumi (ChI), through recurrent backcrosses and established ChI near-isogenic lines, #2-1-10 with the Rmg8/Rmg8 genotype and #4-2-10 with the rmg8/rmg8 genotype. A molecular analysis suggested that at least 96.6% of the #2-1-10 genome was derived from the recurrent parent ChI. The #2-1-10 line was resistant to MoT not only in primary leaves at the seedling stage but also in spikes and flag leaves at the heading stage. The strength of the resistance in spikes of this Rmg8 carrier was comparable to that of a carrier of the 2NS segment, which has been the only genetic resource released to farmers' fields for wheat blast resistance. On the other hand, the 2NS resistance was not expressed on leaves at the seedling stage nor flag leaves at the heading stage. Considering that leaf blast has been increasingly reported and regarded as an important inoculum source for spike blast, Rmg8 expressed at both the seedling and heading stages, or more strictly in both leaves and spikes, is suggested to be useful to prevent the spread of MoT in Asia and Africa.

Design of rice with low cadmium accumulation in grain using single segment substitution line

Rice (Oryza sativa L.) is a major dietary source of cadmium (Cd). Developing rice varieties with reduced Cd levels in the grain is a cost-effective and practical approach to enhance food safety, particularly in regions with high Cd contamination. However, the genetic mechanisms underlying Cd accumulation in rice grains are not fully understood. In this study, we identified eight quantitative trait loci (QTLs) associated with Cd accumulation in rice grains through substitution mapping using single segment substitution lines (SSSLs). These QTLs, named qCd‐2‐1, qCd‐3‐1, qCd‐3‐2, qCd‐5‐1, qCd‐6‐1, qCd‐7‐1, qCd‐8‐1, and qCd‐11‐1, are distributed across seven chromosomes. Notably, the qCd‐5‐1 and qCd‐6‐1 loci are reported for the first time. We performed a detailed haplotype analysis of candidate genes related to heavy metal metabolism, specifically focusing on Cd accumulation. All SSSLs carrying alleles from donor parents exhibited a significant reduction in Cd accumulation, with additive effects ranging from −0.061 to −0.105. To further develop rice varieties with lower Cd accumulation in the grain, we developed six pyramided lines through crossing and marker-assisted selection. These pyramided lines showed significantly reduced Cd content in the grain compared to the elite indica recurrent parent, Huajingxian74 (HJX74). Importantly, most agronomic characteristics of the pyramided lines were similar to those of HJX74. In conclusion, this study demonstrates that identifying and pyramiding QTLs associated with reduced Cd accumulation is an effective strategy for developing rice varieties with lower Cd content in the grain.

Molecular Mapping and Transfer of Quantitative Trait Loci (QTL) for Sheath Blight Resistance from Wild Rice Oryza nivara to Cultivated Rice (Oryza sativa L.).

Sheath blight (ShB) is the most serious disease of rice (Oryza sativa L.), caused by the soil-borne fungus Rhizoctonia solani Kühn (R. solani). It poses a significant threat to global rice productivity, resulting in approximately 50% annual yield loss. Managing ShB is particularly challenging due to the broad host range of the pathogen, its necrotrophic nature, the emergence of new races, and the limited availability of highly resistant germplasm. In this study, we conducted QTL mapping using an F2 population derived from a cross between a partially resistant accession (IRGC81941A) of Oryza nivara and the susceptible rice cultivar Punjab rice 121 (PR121). Our analysis identified 29 QTLs for ShB resistance, collectively explaining a phenotypic variance ranging from 4.70 to 48.05%. Notably, a cluster of four QTLs (qRLH1.1, qRLH1.2, qRLH1.5, and qRLH1.8) on chromosome 1 consistently exhibit a resistant response against R. solani. These QTLs span from 0.096 to 420.1 Kb on the rice reference genome and contain several important genes, including Ser/Thr protein kinase, auxin-responsive protein, protease inhibitor/seed storage/LTP family protein, MLO domain-containing protein, disease-responsive protein, thaumatin-like protein, Avr9/Cf9-eliciting protein, and various transcription factors. Additionally, simple sequence repeats (SSR) markers RM212 and RM246 linked to these QTLs effectively distinguish resistant and susceptible rice cultivars, showing great promise for marker-assisted selection programs. Furthermore, our study identified pre-breeding lines in the advanced backcrossed population that exhibited superior agronomic traits and sheath blight resistance compared to the recurrent parent. These promising lines hold significant potential for enhancing the sheath blight resistance in elite cultivars through targeted improvement efforts.

Enhancing kernel oil and tailoring fatty acid composition by genomics-assisted selection for dgat1-2 and fatb genes in multi-nutrient-rich maize: new avenue for food, feed and bioenergy.

Enhancing maize kernel oil is vital for improving the bioavailability of fat-soluble vitamins. Here, we combined favourable alleles of dgat1-2 and fatb into parental lines of four multi-nutrient-rich maize hybrids (APTQH1, APTQH4, APTQH5 and APTQH7) using marker-assisted selection (MAS). Parental lines possessed favourable alleles of crtRB1, lcyE, vte4 and opaque2 genes. Gene-specific markers enabled successful foreground selection in BC1F1, BC2F1 and BC2F2, while background selection using genome-wide microsatellite markers (127-132) achieved 93% recurrent parent genome recovery. Resulting inbreds exhibited significantly higher oil (6.93%) and oleic acid (OA, 40.49%) and lower palmitic acid (PA, 14.23%) compared to original inbreds with elevated provitamin A (11.77 ppm), vitamin E (16.01 ppm), lysine (0.331%) and tryptophan (0.085%). Oil content significantly increased from 4.80% in original hybrids to 6.73% in reconstituted hybrids, making them high-oil maize hybrids. These hybrids displayed 35.70% increment in oil content and 51.56% increase in OA with 36.32% reduction in PA compared to original hybrids, while maintaining higher provitamin A (two-fold), vitamin E (nine-fold), lysine (two-fold) and tryptophan (two-fold) compared to normal hybrids. Lipid health indices showed improved atherogenicity, thrombogenicity, cholesterolaemic, oxidability, peroxidizability and nutritive values in MAS-derived genotypes over original versions. Besides, the MAS-derived inbreds and hybrids exhibited comparable grain yield and phenotypic characteristics to the original versions. The maize hybrids developed in the study possessed high-yielding ability with high kernel oil and OA, low PA, better fatty acid health and nutritional properties, higher multi-vitamins and balanced amino acids, which hold immense significance to address malnutrition and rising demand for oil sustainably in a fast-track manner.

Transferring an Adult-Plant Stripe-Rust Resistance Gene Yr7VS from Chromosome 7V of Dasypyrum villosum (L.) to Bread Wheat.

Stripe rust (Puccinia striiformis West. f.sp. tritici, Pst) is a destructive disease that seriously threatens wheat production globally. Exploring novel resistance genes for use in wheat breeding is an urgent need, as continuous Pst evolution frequently leads to a breakdown of host resistance. Here, we identified a set of wheat-Dasypyrum villosum 01I139 (V#6) disomic introgression lines for the purpose of determining their responses to a mixture of Pst isolates CYR32, CYR33 and CYR34 at both seedling and adult-plant stages. The results showed that all introgression lines exhibited high susceptibility at the seedling stage, with infection-type (IT) scores in the range of 6-8, whereas, for chromosomes 5V#6 and 7V#6, disomic addition lines NAU5V#6-1 and NAU7V#6-1 displayed high resistance at the adult-plant stage, indicating that adult-plant resistance (APR) genes were located on them. Further, in order to transfer the stripe-rust resistance on chromosome 7V#6, four new wheat-D. villosum introgression lines were identified, by the use of molecular cytogenetic approaches, from the self-pollinated seeds of 7D and 7V#6, in double monosomic line NAU7V#6-2. Among them, NAU7V#6-3 and NAU7V#6-4 were t7V#6L and t7V#6S monosomic addition lines, and NAU7V#6-5 and NAU7V#6-6 were homozygous T7DS·7V#6L and T7DL·7V#6S whole-arm translocation lines. Stripe-rust tests and genetic analyses of chromosome 7V#6 introgression lines revealed a dominant APR gene designated as Yr7VS on the chromosome arm 7V#6S. Comparison with the homozygous T7DL·7V#6S translocation line and the recurrent parent NAU0686 showed no significant differences in yield-related traits. Thus, T7DL·7V#6S whole-arm translocation with the APR gene Yr7VS provided a valuable germplasm for breeding for resistance.