Identification of unique alleles and assessment of genetic diversity of rabi sorghum accessions using simple sequence repeat markers

Genetic diversity among 42 sorghum accessions representing landraces (19), advanced breeding lines (16), local cultivars (2) and release varieties (5) with 30 simple sequence repeat (SSR) markers revealed 7.6 mean number of alleles per locus showing 93.3% polymorphism and an average polymorphism information content of 0.78 which range from 0.22 (Xtxp12) and 0.91(Xtxp321). The average heterozygosity and effective number of alleles per locus were 0.8 and 6.65 respectively. Cluster analysis based on microsatellite allelic diversity clearly demarcated the accessions into ten clusters. A total of 24 unique alleles were obtained from seven SSR loci in 23 accessions in a size range of 110–380 bp; these unique alleles may serve as diagnostic tools for particular region of the genome of respective genotypes. Selected SSR markers from different linkage groups provided an accurate way of determining genetic diversity at the molecular leve

Requirement of Whole-Genome Sequencing and Background History of the National and International Genome Initiatives

Chickpea is the second most important grain legume for food and nutritional security in the arid and semi-arid regions of the world. The genome sequence provides the basis for a wide range of studies, from the important goal of accelerated breeding to identifying the molecular basis of key agronomic traits, in addition to understanding the basic legume biology. The discussions during 5th International Conference on Legume Genetics and Genomics, held during July 8–10, 2010 in Asilomar, USA, provided the platform for the genesis of International Chickpea Genome Sequencing Consortium (ICGSC http://ceg.icrisat.org/gt-bt/ICGGC/ICGSC.htm), and as result of global research partnership co-led by ICRISAT, UC-Davis, and BGI-Shenzhen, involving 49 scientists from 23 organizations in 10 countries the draft genome of kabuli genotype CDC Frontier was published. On the other hand, the Next Generation Challenge Programme on Chickpea Genomics (NGCPCG) initiative unraveled the genome sequence of desi genotype ICC 4958. This chapter summarizes the background history of two independent efforts to generate draft genome sequence of kabuli and desi chickpea genomes. In addition, the chapter also highlights key developments of application of genome sequence for crop improvement

Toward the sequence-based breeding in legumes in the post-genome sequencing era

Efficiency of breeding programs of legume crops such as chickpea, pigeonpea and groundnut has been considerably improved over the past decade through deployment of modern genomic tools and technologies. For instance, next-generation sequencing technologies have facilitated availability of genome sequence assemblies, re-sequencing of several hundred lines, development of HapMaps, high-density genetic maps, a range of marker genotyping platforms and identification of markers associated with a number of agronomic traits in these legume crops. Although marker-assisted backcrossing and marker-assisted selection approaches have been used to develop superior lines in several cases, it is the need of the hour for continuous population improvement after every breeding cycle to accelerate genetic gain in the breeding programs. In this context, we propose a sequence-based breeding approach which includes use of independent or combination of parental selection, enhancing genetic diversity of breeding programs, forward breeding for early generation selection, and genomic selection using sequencing/genotyping technologies. Also, adoption of speed breeding technology by generating 4–6 generations per year will be contributing to accelerate genetic gain. While we see a huge potential of the sequence-based breeding to revolutionize crop improvement programs in these legumes, we anticipate several challenges especially associated with high-quality and precise phenotyping at affordable costs, data analysis and management related to improving breeding operation efficiency. Finally, integration of improved seed systems and better agronomic packages with the development of improved varieties by using sequence-based breeding will ensure higher genetic gains in farmers’ fields

Genome-wide association mapping of seed oligosaccharides in chickpea

Chickpea (Cicer arietinum L.) is one of the major pulse crops, rich in protein, and widely consumed all over the world. Most legumes, including chickpeas, possess noticeable amounts of raffinose family oligosaccharides (RFOs) in their seeds. RFOs are seed oligosaccharides abundant in nature, which are non-digestible by humans and animals and cause flatulence and severe abdominal discomforts. So, this study aims to identify genetic factors associated with seed oligosaccharides in chickpea using the mini-core panel. We have quantified the RFOs (raffinose and stachyose), ciceritol, and sucrose contents in chickpea using high-performance liquid chromatography. A wide range of variations for the seed oligosaccharides was observed between the accessions: 0.16 to 15.13 mg g-1 raffinose, 2.77 to 59.43 mg g-1 stachyose, 4.36 to 90.65 mg g-1 ciceritol, and 3.57 to 54.12 mg g-1 for sucrose. Kabuli types showed desirable sugar profiles with high sucrose, whereas desi types had high concentrations RFOs. In total, 48 single nucleotide polymorphisms (SNPs) were identified for all the targeted sugar types, and nine genes (Ca_06204, Ca_04353, and Ca_20828: Phosphatidylinositol N-acetylglucosaminyltransferase; Ca_17399 and Ca_22050: Remorin proteins; Ca_11152: Protein-serine/threonine phosphatase; Ca_10185, Ca_14209, and Ca_27229: UDP-glucose dehydrogenase) were identified as potential candidate genes for sugar metabolism and transport in chickpea. The accessions with low RFOs and high sucrose contents may be utilized in breeding specialty chickpeas. The identified candidate genes could be exploited in marker-assisted breeding, genomic selection, and genetic engineering to improve the sugar profiles in legumes and other crop species

Identification of a non-redundant set of 202 in silico SSR markers and applicability of a select set in chickpea (Cicer arietinum L.)

The paucity of sequence information flanking the simple sequence repeat (SSR) motifs identified especially in the transcript sequences has been limiting factor in the development of SSR markers for plant genome analysis as well as breeding applications. To overcome this and enhance the genic SSR marker repertoire in chickpea, the draft genome sequence of kabuli chickpea (CDC Frontier) and publicly available transcript sequences consisting of in silico identified SSR motifs were deployed in the present study. In this direction, the 300 bp sequence flanking the SSR motifs were retrieved by aligning 566 SSR containing transcripts of ICCV 2 available in public domain on the reference chickpea genome. A set of 202 novel genic SSRs were developed from a set of 507 primer pairs designed, based on in silico amplification of single locus and having no similarity to the publicly available SSR markers. Further, 40 genic SSRs equally distributed on chickpea genome were validated on a select set of 44 chickpea genotypes (including 41 Cicer arietinum and 3 Cicer reticulatum), out of which 25 were reported to be polymorphic. The polymorphism information content (PIC) value of 25 polymorphic genic SSRs ranged from 0.11 to 0.77 and number of alleles varied from 2 to 9. Clear demarcation among founder lines of multi-parent advanced generation inter-cross (MAGIC) population developed at ICRISAT and near-isogenic nature of JG 11 and JG11 + demonstrates the usefulness of these markers in chickpea diversity analysis and breeding studies. Further, genic polymorphic SSRs reported between parental lines of 16 different mapping populations along with the novel SSRs can be deployed for trait mapping and breeding applications in chickpea

Resistance to Plant-Parasitic Nematodes in Chickpea: Current Status and Future Perspectives

Plant-parasitic nematodes constrain chickpea (Cicer arietinum) production, with annual yield losses estimated to be 14% of total global production. Nematode species causing significant economic damage in chickpea include root-knot nematodes (Meloidogyne artiella, M. incognita, and M. javanica), cyst nematode (Heterodera ciceri), and root-lesion nematode (Pratylenchus thornei). Reduced functionality of roots from nematode infestation leads to water stress and nutrient deficiency, which in turn lead to poor plant growth and reduced yield. Integration of resistant crops with appropriate agronomic practices is recognized as the safest and most practical, economic and effective control strategy for plant-parasitic nematodes. However, breeding for resistance to plant-parasitic nematodes has numerous challenges that originate from the narrow genetic diversity of the C. arietinum cultigen. While levels of resistance to M. artiella, H. ciceri, and P. thornei have been identified in wild Cicer species that are superior to resistance levels in the C. arietinum cultigen, barriers to interspecific hybridization restrict the use of these crop wild relatives, as sources of nematode resistance. Wild Cicer species of the primary genepool, C. reticulatum and C. echinospermum, are the only species that have been used to introgress resistance genes into the C. arietinum cultigen. The availability of genomic resources, including genome sequence and re-sequence information, the chickpea reference set and mini-core collections, and new wild Cicer collections, provide unprecedented opportunities for chickpea improvement. This review surveys progress in the identification of novel genetic sources of nematode resistance in international germplasm collections and recommends genome-assisted breeding strategies to accelerate introgression of nematode resistance into elite chickpea cultivars

The Chickpea Genome: An Introduction

Chickpea is the second most important cool season grain legume cultivated by small holder farmers in 59 countries across the globe. Chickpea production is adversely affected by several abiotic stresses like drought, temperature extremes (high and low temperatures), salinity, and biotic stresses, e.g., insect, fungal and viral diseases. Until recently breeding for tolerance/resistance to these stresses has been challenged by lower level of natural variation and lack of genomics tools to adopt genomics-assisted breeding. Nevertheless, during recent years large-scale genomic resources like molecular markers, genetic maps, draft genome sequence of both desi and kabuli chickpea have become available as a result of partnership among different institutes and advances in sequencing technologies. The chickpea genome book provides an up-to-date account on developments made over past ten years and presents the road map for future chickpea research. This chapter introduces the book and provides brief summary of 11 chapters included in the book

Whole genome re-sequencing reveals genome-wide variations among parental lines of 16 mapping populations in chickpea (Cicer arietinum L.)

Background Chickpea (Cicer arietinum L.) is the second most important grain legume cultivated by resource poor farmers in South Asia and Sub-Saharan Africa. In order to harness the untapped genetic potential available for chickpea improvement, we re-sequenced 35 chickpea genotypes representing parental lines of 16 mapping populations segregating for abiotic (drought, heat, salinity), biotic stresses (Fusarium wilt, Ascochyta blight, Botrytis grey mould, Helicoverpa armigera) and nutritionally important (protein content) traits using whole genome re-sequencing approach. Results A total of 192.19 Gb data, generated on 35 genotypes of chickpea, comprising 973.13 million reads, with an average sequencing depth of ~10 X for each line. On an average 92.18 % reads from each genotype were aligned to the chickpea reference genome with 82.17 % coverage. A total of 2,058,566 unique single nucleotide polymorphisms (SNPs) and 292,588 Indels were detected while comparing with the reference chickpea genome. Highest number of SNPs were identified on the Ca4 pseudomolecule. In addition, copy number variations (CNVs) such as gene deletions and duplications were identified across the chickpea parental genotypes, which were minimum in PI 489777 (1 gene deletion) and maximum in JG 74 (1,497). A total of 164,856 line specific variations (144,888 SNPs and 19,968 Indels) with the highest percentage were identified in coding regions in ICC 1496 (21 %) followed by ICCV 97105 (12 %). Of 539 miscellaneous variations, 339, 138 and 62 were inter-chromosomal variations (CTX), intra-chromosomal variations (ITX) and inversions (INV) respectively. Conclusion Genome-wide SNPs, Indels, CNVs, PAVs, and miscellaneous variations identified in different mapping populations are a valuable resource in genetic research and helpful in locating genes/genomic segments responsible for economically important traits. Further, the genome-wide variations identified in the present study can be used for developing high density SNP arrays for genetics and breeding applications

Future Prospects for Chickpea Research

Advances in genomics technologies, coupled with the availability of several high-throughput genotyping and sequencing platforms during recent years, provided a kick start to the adoption of modern breeding approaches to develop climate-resilient crops. Chickpea is the most important grain legume crop for global food and nutritional security in the context of population explosion and climate vagaries. During last ten years, it has transformed from orphan legume to genomics resource-rich legume like any other model legume plants. There has been a paradigm shift in the outlook of the scientific community in translating the genomic resources including the genome sequence and re-sequence information for developing superior lines with enhanced resistance or tolerance to important abiotic and biotic stresses. In addition, pan-genome and re-sequencing information of several germplasm lines will enable tailoring climate smart chickpeas. In addition, efforts to broaden the genetic base and enhanced utilization of the available trait-specific germplasm lines, multi-parent advanced generation inter-cross (MAGIC), nested association mapping (NAM) populations in breeding programs will accelerate the genetic grains at a faster pace

The Chickpea Genome

This book sheds new light on the chickpea genome sequencing and resequencing of chickpea germplasm lines and provides insights into classical genetics, cytogenetics, and trait mapping. It also offers an overview of the latest advances in genome sequencing and analysis. The growing human population, rapid climate changes and limited amounts of arable land are creating substantial challenges in connection with the availability and affordability of nutritious food for smallholder farmers in developing countries. In this context, climate smart crops are essential to alleviating the hunger of the millions of poor and undernourished people living in developing countries. In addition to cereals, grain legumes are an integral part of the human diet and provide sustainable income for smallholder farmers in the arid and semi-arid regions of the world. Among grain legumes, the chickpea (Cicer arietinum) is the second most important in terms of production and productivity. Besides being a rich source of proteins, it can fix atmospheric nitrogen through symbiosis with rhizobia and increase the input of combined nitrogen. Several abiotic stresses like drought, heat, salinity, together with biotic stresses like Fusarium wilt, Ascochyta blight, and Botrytis grey mould have led to production losses, as the chickpeas is typically grown in the harsh climates of our planet’s semi-arid regions