Physiology and Transcriptomics of Salt Tolerance in ‘Yannong Jinxia’ × ‘Yannong Jinzhan’ Groundcover Chrysanthemum Hybrids

Abstract Salinity stress is a major abiotic factor that significantly constrains plant growth and development. Hybridization within the genus Chrysanthemum produces hybrid offspring exhibiting salt tolerance levels that are intermediate between those of the parental. However, the molecular mechanisms underlying this phenomenon remain unreported. In this study, the salt-sensitive variety ‘Yanong Jinxia’ (JX) and the salt-tolerant variety ‘Yannong Jinzhan’ (JZ) were selected as parental plants for crossbreeding. The hybrid offspring were identified using SRAP-PCR analysis. After the hybrid offspring and their parent plants were treated with salt, transcriptome sequencing was used to analyze the salt tolerance mechanism. Results indicated that under salt stress, the antioxidant enzyme activity in the hybrid progeny ZJ was significantly higher than that in JX but lower than that in JZ. Meanwhile, malondialdehyde (MDA) accumulation in ZJ was lower compared to JX. In the transcriptome KEGG enrichment analysis, significant differential gene enrichment in metabolic pathways such as galactose metabolism was observed in the JZ vs. ZJ comparison. In contrast, the differential gene enrichment of metabolic pathways including isoflavonoid biosynthesis and fatty acid elongation was specifically and significantly detected in the JX vs. ZJ comparison. Meanwhile, analysis of key gene expression in the SOS signaling pathway revealed that the expression level of the SOS gene in the hybrid offspring ZJ was intermediate between those of the parental plants. This study elucidates the molecular regulatory network associated with salt tolerance in hybrid offspring of ground-cover daisies, laying a theoretical foundation for the development of salt-tolerant chrysanthemum germplasm.