Characteristics of the ET, a new species created by interspecific hybridization of two wild eggplants

The eggplant tree (Solanum stockii, ET) is a dominant hybrid obtained by sexual hybridization, embryo rescue, and tissue culture between the maternal parent SWB (Solanum wrightii Benth) and the paternal parent ST (Solanum torvum). Compared with its parents, eggplant tree has a faster growth rate, more efficient nutrient and water absorption, higher grafting compatibility, as well as comparable resistance and perenniality, making it an ideal rootstock for simplified, labor-saving, and long-season production of vegetables. However, there is few studies reported about the eggplant tree. In this study, we aimed to explore the factors contributing to the rapid growth of the eggplant tree. We obtained the ET using the same method, which the leaf and flower sizes are comparable to those of SWB, but larger than those of ST and cultivated eggplant (G063). Ploidy analysis demonstrated that ET is diploid, but with a significant decrease in pollen viability, which may be the reason for the phenomenon of "flowering but not fruiting". Transcriptome and metabolome analysis revealed that 6177 differentially expressed genes (DEGs) and 563 differentially accumulated metabolites (DAMs) significantly changed in plant growth and development, and stress resistance. A key gene (Smechr0700070.1) that may indirectly promote scopolin synthesis in ET was identified according to an in-depth analysis of the phenylpropanoid biosynthesis pathway, which promotes plant growth in ET. These findings significantly improve our understanding of the characteristics of ET and lay a theoretical foundation for its commercial cultivation.