Backcross Breeding Research Articles

Advancement in the Breeding, Biotechnological and Genomic Tools towards Development of Durable Genetic Resistance against the Rice Blast Disease.

Rice production needs to be sustained in the coming decades, as the changeable climatic conditions are becoming more conducive to disease outbreaks. The majority of rice diseases cause enormous economic damage and yield instability. Among them, rice blast caused by Magnaportheoryzae is a serious fungal disease and is considered one of the major threats to world rice production. This pathogen can infect the above-ground tissues of rice plants at any growth stage and causes complete crop failure under favorable conditions. Therefore, management of blast disease is essentially required to sustain global food production. When looking at the drawback of chemical management strategy, the development of durable, resistant varieties is one of the most sustainable, economic, and environment-friendly approaches to counter the outbreaks of rice blasts. Interestingly, several blast-resistant rice cultivars have been developed with the help of breeding and biotechnological methods. In addition, 146 R genes have been identified, and 37 among them have been molecularly characterized to date. Further, more than 500 loci have been identified for blast resistance which enhances the resources for developing blast resistance through marker-assisted selection (MAS), marker-assisted backcross breeding (MABB), and genome editing tools. Apart from these, a better understanding of rice blast pathogens, the infection process of the pathogen, and the genetics of the immune response of the host plant are very important for the effective management of the blast disease. Further, high throughput phenotyping and disease screening protocols have played significant roles in easy comprehension of the mechanism of disease spread. The present review critically emphasizes the pathogenesis, pathogenomics, screening techniques, traditional and molecular breeding approaches, and transgenic and genome editing tools to develop a broad spectrum and durable resistance against blast disease in rice. The updated and comprehensive information presented in this review would be definitely helpful for the researchers, breeders, and students in the planning and execution of a resistance breeding program in rice against this pathogen.

Introgression of the RppQ gene from field corn improves southern rust resistance in sweet corn

Southern rust, one of the most destructive foliar diseases of sweet corn (Zea mays convar. saccharata var. rugosa), is caused by Puccinia polysora Underw. and leads to enormous yield losses and reduced quality of sweet corn in China. Utilization of resistance genes is an effective and environmentally friendly strategy for improving southern rust resistance of sweet corn. However, improvement is hampered by a lack of resistance genes in Chinese sweet corn germplasm. In this study, we introgress the southern rust resistance gene RppQ from Qi319, an inbred line of southern rust–resistant field corn, into four elite sweet corn inbred lines (1401, 1413, 1434, and 1445) using marker-assisted backcross breeding. These are parental inbred lines of four popular sweet corn varieties: Yuetian 28, Yuetian 13, Yuetian 26, and Yuetian 27. We developed five RppQ-based markers (M0607, M0801, M0903, M3301, and M3402) and employed these markers for foreground selection; 92.3 to 97.9% of the recurrent parent genomes were recovered following three or four rounds of backcrossing. The four newly developed sweet corn lines all showed significant improvement of southern rust resistance compared with their respective parent lines. Meanwhile, there was no significant difference in phenotypic data for agronomic traits. In addition, reconstituted hybrids derived from the converted lines retained resistance to southern rust, while other agronomic traits and sugar content remained unchanged. Our study provides an example of successful development of southern rust–resistant sweet corn using a resistance gene from field corn.

Incorporation of Two Bacterial Blight Resistance Genes into the Popular Rice Variety, Ranidhan through Marker-Assisted Breeding

The bacterial blight (BB) disease of rice is a major disease that reduces yield heavily in susceptible varieties. Ranidhan is a late maturing popular rice variety but shows high susceptibility to the disease. Two BB resistance genes were transferred into the variety through a marker-assisted backcross breeding approach. Tightly linked molecular markers were deployed to track the BB resistance genes in the plants carrying the target genes in each backcross generation. Foreground screening detected 17, 16 and 15 progenies to carry the 3 BB resistance genes in BC1F1, BC2F1 and BC3F1 generations, respectively. The selected BC3F1 plant was selfed and three different combinations of BB resistance genes were tracked in homozygous state in seven BC3F2 plants. The pyramided lines carrying three resistance genes in homozygous conditions were evaluated for BB disease resistance by inoculating with eight virulent Xoo strains. Five pyramided lines carrying two resistance gene combinations (Xa21+xa13 and Xa21+xa5) exhibited enhanced resistance against the BB pathogens. The disease resistance was in the order of Xa21+xa5 < Xa21+xa13 < xa13+xa5 gene combinations in conferring the resistance. The developed pyramided lines were similar to the recipient parent for the majority of the important agro-morphologic and grain quality traits.

Biochemical and molecular characterization of sub-tropical maize germplasm for tocopherols

Vitamin E (α-tocopherol) deficiency is one of the serious health concerns among malnutrition in human beings. Exploration of genetic variation for vitamin E in maize germplasm will prove a long-term and cost-effective approach for developing biofortified cultivars. In the present study, 64 maize inbreds were characterized for tocopherols by RP-HPLC and other parameters. A significant genetic variability for α-, γ-, β-, and δ- tocopherols was observed in the germplasm. Maximum δTcontent was present in I188 (7503 ppm) while VL109126 (1499 ppm) showed higher αT content. A positive correlation was observed between αT and carotenoid pigments present in the kernels, whereas αT and oil content showed a negative association. Molecular characterization for αT using VTE4 (ϒ-tocopherol methyltransferase) gene-based InDel marker grouped the germplasm into four distinct haplotypes viz., 0/0 (23), 7/118 (19), 0/118 (14), and 0/7 (8). Three (VL109126, PML224, PML384) and two (MIL41, PML1228) inbreds had 0/0 and 0/118 haplotype, respectively, for the highest αT content. The identified inbreds with favorable αT haplotype could be deployed in maize biofortification programs for the enhancement of vitamin E and also along with other nutritional traits like QPM and β-carotene through marker-assisted backcross breeding to provide nation nutritional security.

Multi-trait multi environment analysis for stability in MABC lines of Chickpea (Cicer arietinum)

Fusarium wilt (Fusarium oxysporum f. sp. ciceris) is a major disease that can cause up to 90% yield loss in Chickpea (Cicer arietinum L.). The presence of 8 physiological races of Foc (0, 1A, 1B/C, 2, 3, 4, 5 and 6) makes it a complex task in the development of disease-resistant cultivar. Thus, Pyramiding of Foc races 1, 2, 3, 4 and 5 was undertaken using WR 315 as donor and Pusa 372 as recurrent parent through Marker assisted backcross (MABC) breeding approach. A total of 20 genotypes, including 17 MABC derived lines of Pusa 372 × WR 315, susceptible parent (Pusa 372), resistant check (WR 315) and national check (JG 16) were used. Multi-location testing of advanced MABC lines at 4 different regions (Amla, Badnapur, Sehore, IARI-New Delhi) was carried out using randomised block design (RBD) in two replications during 2020–21 winter (rabi) season. Usually, multi environment testing is performed involving a single trait, which provides lower reliability in selection of lines, compared to multi-trait analysis. The present study identifies highly stable Fusarium wilt resistant lines with higher yield advantage using MTSI (Multi trait stability index) and GGE (Genotype main effect and genotype × environment interaction) biplot methodology. From GGE biplot analyses the PC1 explains 84.97% and PC2 explains 8.96% of variability. MTSI results revealed that genotype (G) 1, 4 and 3 were stable for the multiple characters studied. But, based on GGE-mean stability value G 11, 12 and 3 were identified for higher yield and better stability values. Based on MTSI and GGE, G 3 may be considered as a stable line for multiple traits including yield superiority.

DRR Dhan 58, a Seedling Stage Salinity Tolerant NIL of Improved Samba Mahsuri Shows Superior Performance in Multi-location Trials

BackgroundImproved Samba Mahsuri (ISM) is an elite, high-yielding, bacterial blight resistant, fine-grained rice variety with low glycaemic index. It is highly sensitive to salt stress, particularly at seedling stage, which significantly reduces its yield potential in coastal areas. A salinity tolerant QTL, Saltol, associated with seedling stage tolerance was previously mapped on chromosome 1 (10.6–11.5 Mb) from the Indian landrace, Pokkali and is effective in different genetic backgrounds. The objective of this study was to enhance salinity tolerance of ISM by incorporating the Saltol QTL through marker-assisted backcross breeding using the breeding line, FL478 (Pokkali/IR29).ResultsForeground selection was carried out at each generation using five Saltol-specific markers and three bacterial blight resistance genes, Xa21, xa13 and xa5. Background selection was conducted using 66 well distributed polymorphic SSR markers and at the BC3F2 generation, a single plant with maximum recurrent parent genome recovery (95.3%) was identified and advanced to the BC3F4 generation. Based on bacterial blight resistance, seedling stage salinity tolerance and resemblance to ISM, four advanced breeding lines were selected for testing in replicated experiments near Hyderabad, India. A promising near-isogenic line, DRR Dhan 58, was evaluated in multi-location trials-coastal salinity and it showed significant salinity tolerance, resistance to bacterial blight disease, high yield and excellent grain quality during the 2019 and 2020 trials. DRR Dhan 58 was 95.1% similar to ISM based on genotyping with the 90 K SNP chip. Whole genome resequencing analysis of Pokkali and FL478 which were salinity tolerant checks, ISM and DRR Dhan 58 showed a high degree of relatedness with respect to the candidate gene loci for Saltol and OsSKC1 (Shoot K+Concentration 1).ConclusionDRR Dhan 58, possessing Saltol and three bacterial blight resistance genes (Xa21, xa13 and xa5) in the genetic background of the Indian mega-variety of rice, Samba Mahsuri, was developed for potential cultivation in areas prone to seedling stage salinity, as well as areas with endemic bacterial blight disease. This entry had a 24% yield advantage over the recurrent parent ISM under coastal saline conditions in multi-location trials and was recently released for commercial cultivation in India.

Introgression of the low phytic acid locus (lpa2) into elite maize (Zea mays L.) inbreds through marker-assisted backcross breeding (MABB)

Phytic acid (PA) is an important antinutritional component in maize that affects the availability of major micro-nutrients like di- and multi-valent mineral cations like iron (Fe) and zinc (Zn). The long-term consumption of maize as a staple food crop leads to micronutrient malnutrition especially iron and zinc deficiency in the human population. In addition, it also acts as a storehouse of a major part of mineral phosphorous (P), approximately 80% of the total P stored as phytate P is not available to mono-gastric animals like humans and poultry birds, and it gets excreted as such, leading to one of the major environmental pollution called eutrophication. Of the various low phytic acid (lpa) mutants, lpa2-2 generated through mutagenesis reduces PA by 30%. BML 6 and BML 45, the parents of the popular maize hybrid DHM 121 with high PA were selected to introgress lpa2-2 through marker-assisted backcross breeding (MABB). The percent recurrent parental genome (RPG) in the selected BC2F2 plants ranged from 88.68 to 91.04% and 90.09–91.51% in the genetic background of BML 6 and BML 45, respectively. Based on the highest percentage of RPG, best five BC2F2 plants, viz., #3190, #3283, #3230, #3263 and #3292 with RPG 88.68–91.04% in the genetic background of BML 6 and #3720, #3776, #3717, #3828 and #3832 with RPG 90.09–91.51% in the genetic background of BML 45 were advanced to BC2F3. The newly developed near-isogenic lines (NILs) possessed low phytate content (2.37 mg/g in BML 6 and 2.40 mg/g in BML 45) compared to 3.59 mg/g and 3.16 mg/g in recurrent parents BML 6 and BML 45, respectively thereby reducing the phytate by an average of 34 and 24 per cent, respectively. These newly developed progenies were similar to their recurrent parents for various morphological traits. These inbreds assume great significance in alleviating Fe and Zn deficiencies in worldwide.

Development of Broad Spectrum and Durable Bacterial Blight Resistant Variety through Pyramiding of Four Resistance Genes in Rice

Bacterial blight (BB) disease caused by Xanthomonas oryzae pv. oryzae is a major biotic constraint on obtaining higher grain yields in rice. Marker-assisted backcross breeding (MABB) was performed by the pyramiding of Xa4, xa5, xa13 and Xa21 resistance genes in the popular variety, Ranidhan. A foreground selection in BC1F1, BC2F1, and BC3F1 progenies detected all the target genes in 12, 7 and 16 progenies by using the closely linked markers from a population size of 446, 410, and 530, respectively. The BB-positive progenies carrying the target genes with a maximal similarity to the recipient parent was backcrossed in each backcross generation. A total of 1784 BC3F2 seeds were obtained from the best BC3F1 progeny. The screening of the BC3F2 progenies for the four target genes resulted in eight plants carrying all the four target genes. A bioassay of the pyramided lines conferred very high levels of resistance to the predominant isolates of bacterial blight disease. In addition, these pyramided lines were similar to Ranidhan in 16 morpho-quality traits, namely, plant height, filled grains/panicle, panicles/plant, grain length, grain breadth, grain weight, milling, head rice recovery, kernel length after cooking, water uptake, the volume expansion ratio, gel consistency, alkali-spreading value, and the amylose content.

Wheat breeding for early heading: Does it improve grain yield under drought stress and well-watered conditions?

Terminal drought stress strongly affects wheat grain yield under Mediterranean conditions. Therefore, developing early-heading bread wheat cultivars in these conditions is an important breeding strategy. In the present research, earliness was transferred from the Australian cultivar, Excalibur, to three Iranian cultivars, Roshan, Kalheydari and Mahdavi, in separate backcross (BC) breeding programs from 2012 to 2018. The earliest and latest heading genotypes of each BC 3 population, were selected as near-isogenic lines (NILs). NILs and their parents were assessed under diverse field conditions including rain-fed, moderate drought stress and well-watered conditions in three locations, Kerman, Sepidan and Semirom, during two growing seasons, 2018–2019 and 2019–2020. Breeding for early heading significantly improved earliness in all genetic backgrounds and increased grain yield by 36.4% and 9.6%, in the rain-fed and moderate drought stress conditions, respectively. Whereas, grain yield was not significantly affected by early heading under well-watered conditions. Results showed that breeding for early heading, a highly heritable trait, is an appropriate method to increase grain yield and reduce water consumption under drought stress and well-watered conditions, respectively. Based on these findings, we recommend transferring early heading to high yield late heading commercial cultivars using backcrossing. • For the first time, near isogenic lines of early heading were developed. • Breeding for early heading increased grain yield by 36.4% in rain-fed conditions. • Early heading increased grain yield by 9.6% in moderate drought stress conditions. • Early heading did not affect grain yield under well-watered conditions in Kerman.

Lines for blast resistance genes with genetic background of Indica Group rice as international differential variety set

AbstractTwenty‐one near‐isogenic lines (NILs) for 18 resistance genes—Pia, Pii, Pi3, Pi5(t), Pik‐s (two lines from two donors), Pik‐m, Pi1, Pik‐h, Pik, Pik‐p, Pi7(t), Pi9(t), Piz, Piz‐5, Piz‐t, Pita‐2, Pita (three donors) and Pi20(t)—to blast disease were developed through introduction into the genetic background of a semi‐dwarf susceptible rice line, US‐2, by recurrent backcross breeding. US‐2 is derived from a cross between an Indonesian Tropical Japonica Group cultivar, 'Kencana', and an improved high‐yielding and semi‐dwarf Indica Group cultivar, 'Takanari', bred in Japan. The reactions of US‐2 NILs to standard differential blast isolates were clearly defined than previous differential varieties (DVs) such as monogenic lines. US‐2 and its NILs are adapted well to wide environmental conditions from temperate to subtropical regions. They will be useful and easier to handle and manage as the first DV set with genetic background of Indica Group rice for pathology studies and as gene sources for rice breeding programme.

Genetic improvement for blast resistance in high-yielding cold-tolerant rice (Oryza sativa L.) cultivar Himalaya 741 by marker-assisted backcross breeding.

The online version contains supplementary material available at 10.1007/s13205-022-03244-w.

Efficient marker-assisted breeding for clubroot resistance in elite Pol-CMS rapeseed varieties by updating the PbBa8.1 locus.

The online version contains supplementary material available at 10.1007/s11032-022-01305-9.

Development of tryptophan rich maize lines through simple sequence repeat marker aided introgression of opaque2 trait

  Maize is the main staple food of the world but it is nutritional deficient due to the scarcity of two essential amino acids viz., lysine and tryptophan. Under this study, opaque2 gene from QPM donor (CML-169) was transferred into normal maize (BAJIM-08-26) through marker aided backcross breeding method. The opaque2 specific SSR marker (phi057) was used for foreground selection in BC1F1 and BC2F1 generations. The heterozygous offspring were self-pollinated to produce the BC2F2 generation. Further plants on the basis of 25% opaqueness were selected and selfed to develop BC2F3 and BC2F4 progenies. The background selection using a series of SSR markers showed 97% recovery in the recurrent parent genome of backcrossed generation. Tryptophan content and total protein in the endosperm of BC2F4 progenies were  found to be ranged from 0.75 to 0.93% and 7.0 to 9.6 %, respectively. As an outcome, three promising MAS derived QPM lines viz., B76-22-2, B70-5-8 and B42-3-1 were developed that showed a high percentage of tryptophan, grain yield and recovery of recurrent parent genome. The  worldwide problem of protein malnutrition could be improved by adopting a molecular breeding approach for the development of nutritionally rich maize over the normal maize. Keywords: Marker assisted backcrossing, opaque2, tryptophan content, SSR markers, QPM lines and normal Maize

Identification of Candidate Genes Regulating Drought Tolerance in Pearl Millet.

Pearl millet is an important crop of the arid and semi-arid ecologies to sustain food and fodder production. The greater tolerance to drought stress attracts us to examine its cellular and molecular mechanisms via functional genomics approaches to augment the grain yield. Here, we studied the drought response of 48 inbreds representing four different maturity groups at the flowering stage. A set of 74 drought-responsive genes were separated into five major phylogenic groups belonging to eight functional groups, namely ABA signaling, hormone signaling, ion and osmotic homeostasis, TF-mediated regulation, molecular adaptation, signal transduction, physiological adaptation, detoxification, which were comprehensively studied. Among the conserved motifs of the drought-responsive genes, the protein kinases and MYB domain proteins were the most conserved ones. Comparative in-silico analysis of the drought genes across millet crops showed foxtail millet had most orthologs with pearl millet. Of 698 haplotypes identified across millet crops, MyC2 and Myb4 had maximum haplotypes. The protein–protein interaction network identified ABI2, P5CS, CDPK, DREB, MYB, and CYP707A3 as major hub genes. The expression assay showed the presence of common as well as unique drought-responsive genes across maturity groups. Drought tolerant genotypes in respective maturity groups were identified from the expression pattern of genes. Among several gene families, ABA signaling, TFs, and signaling proteins were the prospective contributors to drought tolerance across maturity groups. The functionally validated genes could be used as promising candidates in backcross breeding, genomic selection, and gene-editing schemes in pearl millet and other millet crops to increase the yield in drought-prone arid and semi-arid ecologies.

Marker-Assisted Backcross Breeding for Improving Bruchid (Callosobruchus spp.) Resistance in Mung Bean (Vigna radiata L.)

Mung bean is vulnerable to bruchids (Callosobruchus spp.), resulting in low quality and losses worldwide. Developing resistant cultivars is the most effective, economical, and eco-friendly way to protect mung bean seeds from the damage of bruchids. Previously, we identified two gene loci that are tightly linked with bruchid resistance, which makes new cultivar development possible using molecular assisted selection (MAS). In the present study, marker-assisted backcross (MABC) breeding was employed to introgress the bruchid resistance gene VrPGIP2 locus from the donor parent V2802 into a popular cultivar, Kamphaeng Saen 1. Markers VrBR-SSR013 and DMB-SSR158 were used for foreground selection, and phenotypic selection was used for background selection. Three advanced inbred lines (R67-11, R67-22, and R92-15) carrying the resistance gene VrPGIP2 were developed from the BC3F6 population. Further analysis showed that the line R67-22 performed best; it was highly resistant to bruchids and showed excellent agronomic traits in the field. Therefore, R67-22 could be further evaluated in large-scale trials for release as a variety.

Development of β-carotene, lysine, and tryptophan-rich maize (Zea mays) inbreds through marker-assisted gene pyramiding

Maize (Zea mays L.) is the leading cereal crop and staple food in many parts of the world. This study aims to develop nutrient-rich maize genotypes by incorporating crtRB1 and o2 genes associated with increased β-carotene, lysine, and tryptophan levels. UMI1200 and UMI1230, high quality maize inbreds, are well-adapted to tropical and semi-arid regions in India. However, they are deficient in β-carotene, lysine, and tryptophan. We used the concurrent stepwise transfer of genes by marker-assisted backcross breeding (MABB) scheme to introgress crtRB1 and o2 genes. In each generation (from F1, BC1F1–BC3F1, and ICF1–ICF3), foreground and background selections were carried out using gene-linked (crtRB1 3′TE and umc1066) and genome-wide simple sequence repeats (SSR) markers. Four independent BC3F1 lines of UMI1200 × CE477 (Cross-1), UMI1200 × VQL1 (Cross-2), UMI1230 × CE477 (Cross-3), and UMI1230 × VQL1 (Cross-4) having crtRB1 and o2 genes and 87.45–88.41% of recurrent parent genome recovery (RPGR) were intercrossed to generate the ICF1-ICF3 generations. Further, these gene pyramided lines were examined for agronomic performance and the β-carotene, lysine, and tryptophan contents. Six ICF3 lines (DBT-IC-β1σ4-4-8-8, DBT-IC-β1σ4-9-21-21, DBT-IC-β1σ4-10-1-1, DBT-IC-β2σ5-9-51-51, DBT-IC-β2σ5-9-52-52 and DBT-IC-β2σ5-9-53-53) possessing crtRB1 and o2 genes showed better agronomic performance (77.78–99.31% for DBT-IC-β1σ4 population and 85.71–99.51% for DBT-IC-β2σ5 population) like the recurrent parents and β-carotene (14.21–14.35 μg/g for DBT-IC-β1σ4 and 13.28–13.62 μg/g for DBT-IC-β2σ5), lysine (0.31–0.33% for DBT-IC-β1σ4 and 0.31–0.34% for DBT-IC-β2σ5), and tryptophan (0.079–0.082% for DBT-IC-β1σ4 and 0.078–0.083% for DBT-IC-β2σ5) levels on par with that of the donor parents. In the future, these improved lines could be developed as a cultivar for various agro-climatic zones and also as good genetic materials for maize nutritional breeding programs.

Marker-Assisted Improvement of Bread Wheat Variety HD2967 for Leaf and Stripe Rust Resistance.

The mega wheat variety HD2967 was improved for leaf and stripe rust resistance by marker-assisted backcross breeding. After its release in 2011, HD2967 became susceptible to stripe rust and moderately susceptible to leaf rust. The leaf rust resistance gene LrTrk was transferred into HD2967 from the durum wheat genotype Trinakria. Then, HD2967 was crossed with Trinakria to produce F1 plant foreground selection for LrTrk and background selection for the recurrent parent genotype was carried out in BC1F1, BC2F1 and BC2F2 generations. Foreground selection was carried out with the linked marker Xgwm234, while polymorphic SSR markers between parents were used for background selection. Background selection resulted in the rapid recovery of the recurrent parent genome. A morphological evaluation of 6 near isogenic lines (NILs)—2 resistant to leaf and stripe rust, and 4 resistant to leaf rust only—showed no significant differences in yields among NILs and the recurrent parent HD2967. All of the 6 NILs showed the presence of 2NS/2AS translocation, carrying the linked genes Lr37/Sr38/Yr17 present in HD2967 and the targeted leaf rust resistance gene LrTrk. Two NILs also showed additional resistance to stripe rust. Therefore, these NILs with rust resistance and an at par yielding ability of H2967 can replace the susceptible cultivar HD2967 to reduce yield losses due to disease.

Introgressing cry1Ac for Pod Borer Resistance in Chickpea Through Marker-Assisted Backcross Breeding.

The gram pod borer Helicoverpa armigera is a major constraint to chickpea (Cicer arietinum L.) production worldwide, reducing crop yield by up to 90%. The constraint is difficult to overcome as chickpea germplasm including wild species either lacks pod borer resistance or if possessing resistance is cross-incompatible. This study describes conversion of elite but pod borer-susceptible commercial chickpea cultivars into resistant cultivars through introgression of cry1Ac using marker-assisted backcross breeding. The chickpea cultivars (PBG7 and L552) were crossed with pod borer-resistant transgenic lines (BS 100B and BS 100E) carrying cry1Ac that led to the development of BC1F1, BC1F2, BC1F3, BC2F1, BC2F2, and BC2F3 populations from three cross combinations. The foreground selection revealed that 35.38% BC1F1 and 8.4% BC1F2 plants obtained from Cross A (PBG7 × BS 100B), 50% BC1F1 and 76.5% BC1F2 plants from Cross B (L552 × BS 100E), and 12.05% BC2F2 and 82.81% (average) BC2F3 plants derived from Cross C (PBG7 × BS 100E) carried the cry1Ac gene. The bioassay of backcross populations for toxicity to H. armigera displayed up to 100% larval mortality. BC1F1 and BC1F2 populations derived from Cross B and BC2F3 population from Cross C segregated in the Mendelian ratio for cry1Ac confirmed inheritance of a single copy of transgene, whereas BC1F1 and BC1F2 populations obtained from Cross A and BC2F2 population from Cross C exhibited distorted segregation ratios. BC1F1 plants of Cross A and Cross B accumulated Cry1Ac protein ranging from 11.03 to 11.71 µgg−1 in leaf tissue. Cry1Ac-positive BC2F2 plants from Cross C demonstrated high recurrent parent genome recovery (91.3%) through background selection using SSR markers and phenome recovery of 90.94%, amongst these 30% plants, were homozygous for transgene. The performance of BC2F3 progenies derived from homozygous plants was similar to that of the recurrent parent for main agronomic traits, such as number of pods and seed yield per plant. These progenies are a valuable source for H. armigera resistance in chickpea breeding programs.

Pyramiding of genes for grain protein content, grain quality, and rust resistance in eleven Indian bread wheat cultivars: a multi-institutional effort.

The online version contains supplementary material available at 10.1007/s11032-022-01277-w.

Improvement of large-seeded waxy corn (Zea mays L. var. ‘Ceratina Kulesh’) populations for food and industrial purposes

Improving large-seeded waxy corn for food and industrial purposes is one way to increase the value and utilization of new corn cultivars in Thailand. This study aimed to evaluate the agronomic traits, yield and yield components, and response to downy mildew (DM) disease caused by Peronosclerospora sorghi of the developed breeding lines of large-seeded waxy corn. A total of 33 waxy corn breeding lines with different seed sizes, row numbers, and kernel colors were selected from 2015 to 2018. The yield experiment was conducted at the Khon Kaen University, Khon Kaen, Thailand in the 2019/20 dry season and the 2020 rainy season. The breeding lines were also screened for DM resistance through artificial inoculation with spore suspension at farmers’ fields in two locations, namely, Sok Muang and Nong Bua, in the 2020 rainy season. Genotype had a significant effect on yields, yield components, and agronomic traits. However, the interactions between genotype and season were not significant for 1000-kernel dry weight and the number of rows per ear. ‘DRP-4’, RLW-4’, ‘RLW-6’, ‘RLW-7’, and ‘RLW-10’ showed the highest 1000-kernel dry weight and the optimal number of rows. Corn grown at Sok Muang Village had higher disease severity than that grown at Nong Bua Village due to the high rainfall, low temperature, and high humidity at the area. The resistant check cultivar ‘Nei9008’ exhibited moderate resistance to DM at both locations. Although the inbred lines were susceptible to DM disease, they appeared to be a good source of large seeds. Therefore, the backcross breeding method is still needed to obtain DM-resistant germplasm for the further development of waxy corn cultivars.