Synthetic Seeds for Plant Propagation: Biotechnological Progress, Persistent Constraints and Translational Applications

Abstract

Synthetic seed technology seeks to convert in vitro-derived plant propagules into storable, transportable and sowable units. Its conceptual attraction lies in combining the clonal fidelity and year-round production of micropropagation with handling attributes associated with botanical seed. This critical narrative review evaluates the biological foundations, capsule engineering, storage strategies, quality assurance and practical applications of synthetic seeds, while distinguishing laboratory regeneration from meaningful propagation performance. Verified peer-reviewed literature published from 1 January 1977 to 29 May 2026 was identified through life-science and multidisciplinary scholarly sources and appraised according to propagule definition, experimental controls, conversion endpoints, storage conditions, ex vitro validation and genetic-fidelity assessment. The evidence shows that calcium alginate remains the dominant encapsulation matrix because it is inexpensive, biocompatible and readily ionically gelled, but matrix optimisation alone rarely resolves the principal constraint: inconsistent developmental competence of the enclosed propagule. Somatic embryos most closely reproduce the bipolar organisation and autonomous conversion expected of a seed analogue, whereas encapsulated shoot tips, nodal segments and related micropropagules are better understood as protected clonal delivery units that still require rooting and acclimatisation. Recent advances include stress-assisted embryo maturation, bioreactor production, slow-growth storage, liquid conversion systems, integrated biochemical and molecular fidelity testing, and exploratory machine-learning models. Nevertheless, many studies remain species-specific, report in vitro regrowth rather than ex vitro establishment, use limited marker systems, and omit cost, transport, phytosanitary and field-performance data. Synthetic seeds therefore have their strongest current value in germplasm exchange, short- to medium-term conservation, propagation of elite or threatened genotypes, and integration with established tissue-culture pipelines. Direct field sowing at broad commercial scale remains insufficiently supported. Progress will depend on standardised stage-specific metrics, mechanistic control of propagule maturation, automated manufacture, non-sterile conversion trials and comparative economic evaluation against conventional micropropagation and vegetative propagation.