Scientific name: Cajanus cajan (L.) Millsp.
Family: Fabaceae (Leguminosae)
Chromosome number: 2n = 22
Pigeonpea is a warm-season pulse crop of major importance across tropical and subtropical regions. Valued for its relatively high seed protein, ability to fix atmospheric nitrogen, and resilience under marginal conditions, pigeonpea is used as a grain pulse, vegetable (green pods), forage, and green-manure crop. Its mixed mating system (predominantly insect-mediated outcrossing with partial selfing), wide phenotypic diversity and adaptability make it a prime target for both varietal and hybrid improvement.
The primary centre of origin of pigeonpea is the Indian subcontinent, particularly peninsular India. Archaeobotanical records and genetic diversity surveys indicate domestication in South Asia, from where the crop spread to Africa and later to the Americas and Australia. India continues to be the major centre of diversity, hosting numerous landraces and locally adapted farmer selections.
Pigeonpea is widely cultivated across South Asia (India, Pakistan, Bangladesh, Myanmar), East and Southern Africa (Tanzania, Malawi, Kenya), Latin America (Brazil, Caribbean), and parts of Australia. It thrives under rainfed conditions on a wide range of soils — from well-drained loams to low-fertility and shallow soils — and is often integrated in mixed or intercropping systems with cereals and other crops.
The cultivated gene pool is dominated by Cajanus cajan. Farmers and breeders recognize diversity across growth habit, maturity, seed type and intended use. Important categories include:
- Growth habit: determinate, semi-determinate and indeterminate. Determinate and semi-determinate types provide synchronous pod maturity and suit mechanical or consolidated harvests; indeterminate types are suited for staggered harvests and ratooning.
- Maturity groups: early (≈90–120 days), medium (≈120–180 days) and late (>180 days). Choice depends on cropping system, rainfall pattern and farmer preference.
- Seed types: variation in seed size, shape and colour — from small cream seeds to large brown and speckled types. Market preferences drive selection for size and appearance.
- Use types: grain-only varieties, dual-purpose cultivars (grain + fodder), vegetable types for green pod consumption, and cover/green-manure types.
This intra-specific variation forms the basis for genetic improvement through selection, hybridization and pre-breeding.
The genus Cajanus contains several wild relatives — C. cajanifolius (closest progenitor), C. scarabaeoides, C. platycarpus, C. lineatus, C. reticulatus, among others. These wild species are reservoirs of alleles for resistance to diseases and pests, abiotic stress tolerance (drought, salinity), and novel traits for root architecture or seed quality. However, incorporation of wild alleles often requires pre-breeding to overcome crossing barriers and to reduce linkage drag of undesirable traits.
Pigeonpea is usually a semi-woody shrub (0.6–2.5 m tall) or an erect annual habit depending on genotype and environment. Key botanical features include:
- Leaves: pinnate with 1–3 pairs of leaflets (commonly a single pair which may appear simple); leaflets elliptic to oblong.
- Inflorescence: racemes or panicles with papilionaceous flowers (yellow, cream, orange or pink shades).
- Flowers: bisexual, zygomorphic; primarily insect-pollinated, enabling cross-pollination that facilitates heterosis exploitation.
- Pods: 2–5 cm long, usually 1–3 seeds per pod; many cultivars have dehiscent pods at maturity.
- Seeds: variable in size and colour; protein content typically 20–25% making it a valuable pulse for nutrition.
- Roots: prominent taproot with lateral branches; nodulation by rhizobia allows biological nitrogen fixation and improves soil fertility.
Pigeonpea supports smallholder livelihoods across many tropical regions. Its major economic roles:
- Nutrition: Important source of protein, calories and micronutrients where animal protein is scarce.
- Income: Cash from dried grain sales, green pods, and fodder; often a stable income crop due to drought tolerance.
- Soil health: Nitrogen-fixing ability benefits subsequent crops in rotation and enhances soil organic matter.
- Risk mitigation: Performs under erratic rainfall and poor soils, providing yield stability where cereals may fail.
Breeding goals are framed by farmer needs, market demands and production constraints. Principal objectives include:
- Higher and stable grain yield: across seasons and environments.
- Appropriate maturity durations: early and medium-duration types to fit rotations and escape terminal drought.
- Biotic stress resistance: durable resistance to Fusarium wilt, Sterility Mosaic Disease (SMD), Phytophthora blight and insect pests such as pod borer (Helicoverpa spp.).
- Abiotic stress tolerance: drought tolerance, heat tolerance and adaptation to low-fertility or saline soils.
- Improved seed quality: desirable seed size, uniformity, reduced cooking time and enhanced nutritional composition (protein and amino-acid balance).
- Desirable plant architecture: synchronous maturity, reduced lodging, compact plant types for higher planting densities and mechanization.
- Hybrid vigour: development of commercially viable hybrids with significant heterosis.
- Post-harvest traits: reduced shattering and improved storability.
Conventional breeding laid the groundwork for pigeonpea improvement and remains central in many programs:
- Germplasm collection and evaluation: global and national gene banks maintain landraces and wild relatives that are systematically screened for target traits.
- Pedigree and pure-line selection: selection from segregating populations to fix desirable traits and develop stable cultivars.
- Backcross breeding: used to transfer specific resistance or quality genes into elite cultivars while minimizing undesirable background effects.
- Hybridization and recombination breeding: traditional crossing among diverse parents followed by selection to recombine favorable alleles.
- Mutation breeding: induced mutations have been used to create novel variation for traits like determinacy, earliness and plant architecture.
- Heterosis-based breeding: using male sterility or genic systems to develop hybrids that express increased yield and vigor.
Integrating new tools accelerates and refines improvement:
- Cytoplasmic male sterility (CMS) systems: CMS and matching maintainer/restorer lines enable large-scale hybrid seed production; stable sterility and effective restorer genes are prerequisites for commercial hybrids.
- Marker-assisted selection (MAS): DNA markers linked to major genes or QTLs speed up introgression and pyramiding of resistance loci and quality traits.
- Genomic selection (GS): genome-wide marker information is used to predict breeding values for complex traits (yield, drought tolerance) enabling early selection and shorter breeding cycles.
- High-throughput phenotyping: UAVs, canopy sensors and imaging help quantify biomass, phenology and stress responses across large breeding populations precisely and quickly.
- Pre-breeding and interspecific introgression: transferring favorable alleles from wild relatives using embryo rescue, bridge crosses and recurrent backcrossing followed by selection to remove linkage drag.
- Genome editing and transgenics: CRISPR/Cas and genetic transformation offer the ability to precisely modify endogenous genes (flowering time, shattering, susceptibility genes) or to introduce novel resistances — subject to regulatory frameworks and public acceptance.
- Speed-breeding and off-season nurseries: controlled-environment generation advancement and international offseason nurseries allow more breeding cycles per year and faster release of improved lines.
Hybrid pigeonpea offers potential yield gains through heterosis but requires concerted technical and seed-system support:
- Mating system and hybridization: the insect-pollinated nature supports heterosis. Reliable male-sterility (CMS or genic) systems simplify hybrid seed production by eliminating the need for manual emasculation.
- Parental selection: identify parents with high GCA (general combining ability) and complementary SCA (specific combining ability) for targeted traits — yield, maturity, pest resistance and seed quality.
- Seed production practices: spatial isolation, pollinator management and quality-control protocols are essential to produce pure hybrid seed at scale.
- Multi-environment testing: extensive METs are crucial to evaluate hybrid adaptability, stability and resistance under varied agro-ecologies and pest/disease pressures.
- Socio-economic integration: ensure hybrids match market preferences (seed size and colour), are cost-effective for farmers and supported by extension messages for management practices that realize heterosis potential (planting density, fertilization).
Despite progress, several challenges remain:
- Complex quantitative traits: yield and drought tolerance are controlled by many genes and interact strongly with the environment; genomic selection combined with strong phenotyping is promising for progress.
- Dynamic pests and diseases: pathogen evolution requires continual identification and combination of new resistance sources for durable protection.
- Utilization of wild relatives: pre-breeding to reduce linkage drag and to stabilize favourable introgressions is resource-intensive but necessary for tapping wild gene pools.
- Seed system and adoption: building robust hybrid seed production, certification and distribution networks is critical for farmer access and trust in hybrid performance.
- Climate change: breeding for heat tolerance, erratic rainfall resilience and new pest/disease spectra will grow in importance.
Effective pigeonpea improvement combines traditional breeding, modern genomics, participatory approaches and socio-economic considerations. Priorities include developing early- and medium-duration varieties and hybrids with durable biotic resistance, enhanced drought resilience, and improved seed quality. Investments in germplasm conservation, pre-breeding, genomic-enabled selection and strengthening hybrid seed systems will accelerate gains. Engaging farmers in selection and aligning breeding targets with market preferences will ensure adoption and tangible benefits for smallholder livelihoods.
