A Review on Drought Stress in Seed Spices: Impacts, Mechanisms and Mitigation Strategies

Abstract

Drought stress is a major abiotic constraint affecting seed spice crops, particularly in arid and semi-arid regions where rainfall is erratic and irrigation resources are limited. Seed spices such as coriander, cumin, fennel, fenugreek, ajwain, dill, celery, anise, nigella and caraway are economically important crops, but their productivity and quality are often reduced by water deficit. Drought stress affects germination, vegetative growth, physiological activity, reproductive development, seed yield and essential oil production. The magnitude of yield loss differs among crops, growth stages, genotypes and stress intensity. Seed spice crops respond to drought through several adaptive mechanisms, including improved root development, reduced transpirational water loss, maintenance of relative water content, osmotic adjustment, antioxidant defence, chlorophyll stability and changes in secondary metabolism. Considerable genetic variability has been reported in several seed spice crops, especially coriander, fenugreek, cumin and fennel, indicating opportunities for selection and breeding of drought-tolerant cultivars. Management strategies such as seed priming, foliar application of osmolytes and plant growth regulators, integrated nutrient management, plant growth-promoting rhizobacteria, hydrogels and selected nanoparticle-based applications have been reported to reduce drought-induced damage under experimental conditions. However, their effectiveness depends on crop type, stress severity, application method, dose and local growing conditions. This review summarises the effects of drought stress on seed spices, describes major tolerance mechanisms and discusses genetic, physiological, agronomic, microbial and emerging technological approaches for drought mitigation. Integration of drought-tolerant genotypes with practical water- and nutrient-efficient management strategies is essential for sustaining seed spice production under changing climatic conditions.