BREEDING HORTICULTURAL CROPS FOR ABIOTIC STRESS TOLERANCE: GENETIC RESOURCES, MECHANISMS AND FUTURE PROSPECTS: A REVIEW

Abstract

Abiotic stresses are one of the major limitations affecting the productivity, quality, profitability and sustainability of horticultural crops. Rising temperatures, erratic precipitation, drought, salinity in soil and water, low temperatures and chilling/frost, waterlogging, imbalance in nutrients and heavy metal toxicity are the growing stresses experienced by fruit, vegetable, spice, plantation, ornamental and medicinal crops. The impact of such stresses is particularly pronounced in horticultural crops since apart from the total yield, the size, color, texture, flavor, nutritive value and marketable quality of fruits and vegetables are of considerable importance. Climate change has made such stresses even more unpredictable, severe and frequent, making it necessary to develop horticultural varieties with stable yields and quality under stress conditions. The genetic stock, which includes landraces, traditional varieties, wild relatives, introduced species, mutants and germplasm collections, is a major source of alleles for development of stress tolerant varieties. Abiotic stresses are tolerated by plants through a variety of physiological, biochemical and molecular mechanisms, which include osmoregulation, ionic regulation, antioxidative defenses, membrane stability, root system modifications, photosynthetic control and phytohormonal signaling. At the molecular level, transcription factors, stress response genes, transporters, protein kinases, reactive oxygen species and calcium-based signaling pathways play an important role. Traditional breeding techniques still hold significance, however, the efficiency of such techniques can be improved by adopting marker assisted selection, quantitative trait locus analysis, genome wide association studies, genomic selection and phenomics. The recent advances in genomics, pangenomics, transcriptomics, proteomics, metabolomics and epigenomics have made it easier to find out the candidate genes and favourable alleles that confer stress tolerance traits. Genome editing technology including the CRISPR/Cas system, base editing and prime editing has opened up new avenues for manipulating the genes of interest in stress adaptation. The combination of genetic resources, physiology, genomics, multi-omics, phenomics, artificial intelligence and genome editing will help develop more resilient cultivars in horticulture against the changing climatic conditions. This review article covers the important abiotic stresses impacting horticulture crops, genetic resources for crop breeding, physiological and molecular mechanisms of stress tolerance, traditional and advanced breeding techniques and future strategies for breeding resilient horticultural crops using genome editing technology.