**2. Materials and Methods**

#### *2.1. Plant Material*

The eggplant F1 hybrid Scarlatti (black cylindrical shape) (EnzaZaden, The Netherlands) was used as the scion cultivar as well as the rootstock and ungrafted control. Five rootstocks were evaluated, which included materials corresponding to the three species *S. melongena* (F1 hybrid Scarlatti ), *Solanum torvum*, and *Solanum aethiopicum* gr. *gilo* (two accessions, named accession 1 and accession 2), and one interspecific hybrid of *S. melongena* × *S. aethiopicum* gr. *gilo*, which is a double haploid line obtained from another culture of the tetraploid backcrosses from the somatic hybrid eggplant cv

Dourga(+) *S. aethiopicum* gr. *gilo* accession 2 with a tetraploid plant of the eggplant line DR2 [13,18]. The materials used as rootstocks originated from the germplasm collection of the Consiglio per la Ricerca in Agricoltura e l'Analisi dell'Economia Agraria CREA-GB, Centro di Ricerca Genomica e Bioinformatica (Montanaso Lombardo, Italy).

### *2.2. Seedlings Production and Grafting*

For the production of the grafted plant material, on 10 February 2014 and 9 February 2015, *S. aethiopicum* gr. *gilo* and *S. torvum* rootstock seeds were planted in 40-cell seedling trays (cell volume of 83 cm3), under a temperature regime of 25 ◦C/18 ◦C (day/night) in a propagation greenhouse. After 20 days, seeds of the F1 Scarlatti eggplant were planted in 104-cell trays (cell volume of 33 cm3) under the same temperature regime and planting method as the rootstocks. Due to the faster germination and growth, the *S. melongena* × *S. aethiopicum* gr. *gilo* hybrid rootstock was sown simultaneously to the F1 Scarlatti hybrid. Trays were watered manually every day to maintain the substrate at water holding capacity. Seventy-five days after the sowing of *S. torvum* and *S. aethiopicum* gr. *gilo* (accessions 1 and 2), all seedlings had reached an adequate diameter for grafting. The eggplant cultivar Scarlatti was grafted onto Scarlatti rootstocks (self-grafted), *S. torvum*, *S. aethiopicum* gr. *gilo* (accession 1 and accession 2), and *S. melongena* × *S. aethiopicum* gr. *gilo* rootstocks using the tube grafting method described by Lee [20] and modified by Miceli et al. [21]. Plants at the 3–4 leaf stage were used as rootstocks. The grafted plantlets were misted, incubated within a plastic tunnel in a greenhouse, and maintained at a temperature of 20 ◦C and a humidity rate of 95% for 7 days. After 7 days, the grafted plantlets were acclimatized to the natural conditions of the greenhouse by slowly dropping the humidity (RH 70–80%) for 3 days, until they were ready for transplant.

#### *2.3. Cultivation Conditions*

 Scarlatti plants ungrafted, self-grafted, and grafted onto *S. melongena*, *S. torvum*, and accession 1 and 2 of *S. aethiopicum* gr. *gilo* rootstocks were transplanted on 5 May 2014 and 4 May 2015 on a Typic Rhodoxeralf soil in the experimental farm of the Department of Agricultural, Alimentary and Forest Sciences (SAAF) (longitude 13◦19 E, latitude 38◦09 N), of the University of Palermo, Italy. The field trials were conducted in a sandy clay loam soil (46.5% sand, 22.3% silt, 31.2 clay) at pH 7.2 in a completely randomized design with 4 replications of 10 plants (40 plants per treatment). In both years, the preceding crop was cauliflower. Plants were spaced 1.0 m between rows and 0.5 m apart within the row and drip irrigated. Fertilization was applied with drip irrigation throughout the growing cycle and consisted of 250 kg nitrogen ha−1, 150 kg phosphorous pentoxide ha−1, and 250 kg potassium oxide ha−<sup>1</sup> (Yara, Oslo, Norway). Standard horticultural practices for eggplant production in the Mediterranean environment were adopted [22].

Average daily temperature during the experimental period from May to August of 2014 and 2015 was obtained from the meteorological station of the experimental farm of the Department SAAF (Figure S1). In terms of temperatures, the weather during the experimental period in 2014 and 2015 was similar to the long term average. Nevertheless, the average monthly temperatures showed the highest negative deviation in June (1.8 and 2.2 ◦C in 2014 and 2015, respectively).
