Genomics Approaches for Biotic and Abiotic Stress Improvement in Tea

Tea (Camellia sinensis) plants are continuously exposed to a wide range of biotic and abiotic stresses. Being a perennial monoculture crop, tea relatively provides a favorable niche for more than 1000 arthropod pests and numerous disease-causing microorganisms. Abiotic stress factors such as drought, temperature, waterlogging, salinity, and nutrient stress considerably constrain the growth, productivity, and quality of tea plants. At present, global climatic changes have made notable impact in tea with a decline in its productivity. The main biotic and abiotic stresses that affect tea plants in the field are being extensively studied. Each stress elicits a complex molecular cascade starting from perception of stress to initiation of signal transduction and its manifestation in cellular and metabolic level. Construction of genetic map, by application of conventional molecular marker technologies, has been difficult in tea due to the problems of self-incompatibility, the absence of pure inbreed lines, high heterozygosity, 15 pairs of chromosomes, and large genome size. However, novel approaches such as next-generation sequencing (NGS) technologies have successfully helped in identification of several candidate genes which are responsible for biotic and abiotic stress regulation in different plants. It has accelerated the process of large-scale single-nucleotide polymorphism (SNP) discovery and genotyping in tea, thus, facilitating the construction of high-density genetic maps. The landmark tea whole genome will lead to identification and mapping of quantitative trait loci related to agronomical important traits underlying biotic and abiotic stress. It will also aid in comparative genomic analysis, marker-assisted selection, and map-based cloning for developing stress-tolerant tea plants.