Characterization and QTL identification in eggplant introgression lines under two N fertilization levels

Lowering nitrogen inputs is a major goal for sustainable agriculture. In the present study, a set of 10 Solanum melongena introgression lines (ILs) developed using Solanum incanum as the exotic donor parent were grown under two nitrogen fertilization doses supplied with the irrigation system: 1) 8.25 mmol · L−1 NH4NO3, corresponding to the high nitrogen treatment (HN), and 2) no external nitrogen supply, corresponding to the low nitrogen treatment (LN). Twenty traits, including plant growth and yield parameters, fruit size and morphology, nitrogen and carbon content in leaf and fruit, and phenolics content in fruit, were evaluated. The aim was to select of potential materials for eggplant breeding under low N inputs, as well as to identify and locate putative QTLs associated with the traits evaluated. No significant differences were observed between the soil characteristics of the HN and LN treatments, except for nitrogen and iron content, which was slightly lower in the HN, probably as a consequence of higher nutrient removal from soil by plants in the latter group. Analysis of variance showed that lowering nitrogen inputs did not significantly affect the final yield, fruit morphology, size and phenolics content. Most agronomic traits were highly and positively correlated with each other under both treatments, as well as total phenolics with chlorogenic acid content. The assessment of the differences between each IL and the recipient parent resulted in the identification of 36 QTLs associated with most of the traits—12 were specific to the HN, 17 specific to the LN, and 7 were stable across treatments. The introgressed fragment of S. incanum generally had a negative effect on the trait, except for QTLs for fruit dry matter, for fruit length on chromosome 10 under the HN, and for fruit pedicel length on chromosome 9 under the LN. The increase over AN-S-26 of the allele of S. incanum for the QTLs detected ranged between −73.98% and 26.03% in HN and −73.67% and 34.43% in LN. These findings provide useful tools for the utilization of S. incanum in eggplant breeding under lower nitrogen fertilization.