Single-Stem Training Combined with High Plant Density Enhances Canopy Development and Yield of Parthenocarpic Eggplant Under a Constant Stem Density

In eggplant production, parthenocarpic cultivars are increasingly adopted to reduce labor associated with exogenous hormone applications for fruit set. Although optimizing training systems is essential to maximize the potential of these cultivars, associated quantitative evaluations of key physiological determinants, such as dry matter production and source–sink balance, remain limited. In this study, we investigated the effects of stem numbers on the yield and physiology of parthenocarpic eggplants grown in a soilless culture. Three treatments were established with varying stem numbers per plant (one, two, and four stems) and uniform stem density per area (3.75 stems m−2). The total yield and fruit number per unit area were highest in the one-stem treatment (1S) (8.5 kg m−2 and 60.0 fruits m−2, respectively), followed by the two-stem (2S) (7.1 kg m−2 and 50.9 fruits m−2) and four-stem (4S) (6.4 kg m−2 and 46.6 fruits m−2) treatments. Total dry matter production (TDM) varied similarly and was significantly higher in the 1S treatment than in the other systems. The 1S treatment exhibited rapid canopy development, reaching a higher leaf area index in the early stages, which contributed to greater cumulative light interception. Light use efficiency did not differ significantly among the treatments (5.2, 4.6, and 4.3 g MJ−1 for the 1S, 2S, and 4S treatments, respectively). Correlation analysis revealed a strong positive relationship between TDM and yield, whereas dry matter partitioning to fruit remained stable across treatments. These results indicated that the yield under these conditions was strongly driven by source capacity. We conclude that this single-stem training system represents an effective strategy for enhancing the canopy development and yield of parthenocarpic eggplants.