Introduction
Sweet potato (Ipomoea batatas (L.) Lam.) ranks among the world’s most significant root and tuber crops, particularly in tropical, subtropical, and developing regions. Its importance stems from its high nutritional value (rich source of vitamin A (β-carotene), vitamin C, fiber, potassium, and phenolic antioxidants), adaptability to diverse and marginal environments, and critical role in food and nutritional security. This review provides an in-depth analysis of sweet potato agronomy, physiology, genetics, and integrated management practices, focusing on contemporary research challenges and innovations.
1. Botanical Classification & Genetic Architecture
Family: Convolvulaceae (Morning glory)
Genus: Ipomoea
Species: Ipomoea batatas (L.) Lam.
Ploidy: Hexaploid (2n=6x=90), indicating complex hybrid origin.
Genome: A reference genome (~4.4 Gb) has been sequenced (Yang et al., 2017), revealing high complexity and facilitating genomic studies.
Genetic Relatives: Closely related to wild diploid species Ipomoea trifida and Ipomoea triloba, which serve as vital sources of stress-resistance genes.
2. Physiology & Development
Tuberization: The initiation and development of storage roots are regulated by intricate interactions between internal factors (phytohormones: GAs, CKs, ABA, florigenic signals) and external cues (photoperiod, temperature, water stress, nutrients). Key genes identified include IbFT, IbSPR1, and IbMADS1.
Photoperiod Response: Classified as a short-day plant (SDP), but many modern cultivars are day-length neutral. Molecular mechanisms of photoperception influencing flowering and tuberization are under active investigation.
Stress Physiology: Exhibits advanced physiological, biochemical, and molecular adaptations to abiotic (drought, salinity, heat, cold) and biotic (pests, diseases) stresses. Mechanisms include osmolyte accumulation, HSPs, antioxidant activation (SOD, CAT, POD), and stress-responsive gene expression (DREB, WRKY, NAC).
3. Breeding & Genetic Improvement
Objectives: yield enhancement, nutritional quality (β-carotene, Fe, Zn), disease resistance (soft rot, scab, viruses: SPFMV, SPCSV), pest resistance (weevils: Cylas spp., nematodes), abiotic stress tolerance, improved shelf life, and sensory traits.
Conventional Methods: Hybridization and selection remain foundational. Challenges include flowering barriers in some genotypes.
Advanced Biotechnologies:
Genetic Diversity Assessment: Molecular markers (SSRs, SNPs, AFLPs) for germplasm characterization and parental selection.
Marker-Assisted Selection (MAS): Introgression of genes/QTLs (e.g., IbOr for β-carotene stability, disease resistance genes).
Genomic Selection (GS): Genome-wide marker-based prediction of breeding values.
Gene Editing (CRISPR/Cas9): Precise modification of target genes (e.g., reducing internal discoloration, enhancing disease resistance).
Tissue Culture: Rapid propagation of elite clones, virus-free plantlet production, and germplasm conservation.
4. Environmental Requirements & Crop Management
Climate: Thrives in warm climates (25-30°C optimum). Frost-sensitive. Requires 4-6 frost-free months. High light intensity is essential.
Soil: Prefers well-drained sandy loams (pH 5.5-6.5). Tolerant of low-fertility soils but responsive to fertilization.
Propagation: Primarily via vine cuttings. Tissue-cultured plantlets for disease-free establishment.
Planting: Cuttings planted on ridges/beds. Density: 30,000–50,000 plants/ha.
Water Management: Sensitive to waterlogging but moderately drought-tolerant. Supplemental irrigation (drip preferred) is critical during tuber initiation/bulking. Deficit irrigation may enhance quality.
Nutrient Management:
Nitrogen (N): Essential for vegetative growth; excess delays tuberization.
Phosphorus (P): Critical for root/tuber development.
Potassium (K): Vital for yield, dry matter, and quality.
Calcium (Ca): Improves tuber quality and disease resistance.
Micronutrients: Fe, Zn, and B are crucial on deficient soils.
Biofertilizers: P-solubilizing bacteria, Azospirillum, and AM fungi enhance nutrient use efficiency.
Weed Control: Critical during early growth (first 6-8 weeks). Integrated use of mechanical, chemical (selective herbicides), and mulch-based strategies.
5. Major Pests, Diseases & Integrated Pest Management (IPM)
Key Pests:
Sweet Potato Weevils (Cylas spp.): Most destructive pest. Research focuses on pheromones, biocontrol (Steinernema carpocapsae, Beauveria bassiana), and resistant cultivars (hairy stems, thick periderm).
Leaf-Feeding Caterpillars (Acraea acerata, Bedellia spp.).
Root-Knot Nematodes (Meloidogyne spp.).
Key Diseases:
Fungal: Soft Rot (Rhizopus, Fusarium), Scab (Streptomyces ipomoeae), Black Rot (Ceratocystis fimbriata), Leaf Blight (Alternaria), Downy Mildew (Peronosclerospora).
Viral: Sweet potato feathery mottle virus (SPFMV), sweet potato chlorotic stunt virus (SPCSV—synergistic with SPFMV causes SPVD), and tomato spotted wilt virus (TSWV). Control: Virus-free planting material, resistant cultivars, and vector management.
Bacterial: Bacterial soft rot (Dickeya, Pectobacterium).
IPM Strategies: Resistant cultivars, crop rotation, sanitation, biological control, judicious chemical use, and monitoring.
6. Harvest, Curing & Storage
Harvest: At physiological maturity (leaf senescence), pre-frost. Manual or mechanical (modified potato diggers). Minimize wounding.
Curing: Critical post-harvest treatment (28-32°C, 85-95% RH, 4-7 days). Induces suberization and wound periderm formation, reducing pathogen entry and water loss. Research focuses on optimizing conditions and molecular mechanisms.
Storage: After curing, 13-16°C, 85-90% RH, ventilation. Chilling injury (<10°C) causes internal discoloration and flavor loss. Research areas: chilling-tolerant cultivars, modified atmospheres (MAP), and edible coatings.
7. Nutritional Quality & Utilization
Composition: High in complex carbohydrates, dietary fiber (pectin), β-carotene (orange-fleshed), vitamin C, potassium, and manganese. Rich in antioxidants (anthocyanins—purple-fleshed, chlorogenic acid, and caffeic acid).
Health Benefits: Supports vision, immunity, cardiovascular health, and blood glucose regulation; anti-inflammatory and anticancer properties.
Utilization:
Human Food: Fresh, boiled, baked, fried, pureed, or flour (bakery).
Animal Feed: Vines, culled roots.
Industry: Starch extraction, natural colorants (β-carotene, anthocyanins), bioethanol, biodegradable plastics.
8. Current Challenges & Future Research Directions
Climate Change Resilience: Breeding/engineering for heat, drought, salinity, and flooding tolerance.
Sustainable Pest/Disease Management: Enhanced biocontrol, deciphering resistance mechanisms, advanced IPM, and virus resistance.
Nutrition & Post-Harvest: Biofortification (Fe, Zn), stabilizing phytonutrients during storage/processing, and developing slow-sugar-conversion and chilling-tolerant cultivars.
Reducing Post-Harvest Losses: Improved curing/storage tech, processing innovations, efficient value chains.
Leveraging Genetic Diversity: Collection, characterization, and conservation of wild relatives and landraces in gene banks.
Sustainable Intensification: Climate-smart practices, precision agriculture for water/nutrient efficiency.
Value-Added Products: Novel food and industrial applications to boost demand.