Small and strong: Dwarf cultivars as a strategic response to shade avoidance syndrome through molecular, hormonal, and breeding innovations

Abstract

Dwarfism is a valuable trait in crop breeding, offering improved lodging resistance, higher planting density, and better adaptation to resource-limited environments. The Green Revolution gene sd1 has long been central to modern rice (Oryza sativa) breeding, but overreliance on a single gene risks genetic diversity, sustainability, and yield under changing environmental conditions. Recent efforts across various crops have identified new dwarfing genes and regulatory networks as promising alternatives. In rice, key gibberellin (GA)- and brassinosteroid (BR)-related genes such as D18, EUI1, D1, D11, and D61 have been identified, alongside SlGAI, SlBRI1, SlRR6, and SlARF5 in tomato (Solanum lycopersicum). Hormonal pathways involving GA, BR, and auxin are major determinants of stem elongation and internode architecture, with cross-regulatory components such as DELLA, PIFs, and BZR1 central to the shade avoidance response (SAS). This review explores the genetic, physiological, and molecular mechanisms of dwarfism in monocots and dicots, focusing on recent findings in rice, tomato, and other crops. We highlight advances in understanding how cell elongation, cell wall biosynthesis, and hormone interactions regulate culm length and structural strength. Novel mutants that preserve yield and fruit size while minimizing height offer potential for smart farming and dense planting systems. We also examine trade-offs such as reduced biomass or fertility and stress the need to balance compactness with productivity. Future directions include high-throughput phenotyping, functional validation, and multi-environment testing to enable deployment of diverse dwarfing alleles in breeding.