Improving seed germination of the eggplant rootstock Solanum torvum by testing multiple factors using an orthogonal array design

• The use of Solanum torvum as eggplant rootstock is difficulted by poor and irregular germination
• We use an orthogonal array experimental design to evaluate the main effects of seven factors.
• An improved protocol involving seed soaking, GA3 and KNO3 application, cold stratification, heat shock and germination under light is proposed.
• The improved treatment was validated under experimental and commercial conditions and resulted in a high and rapid germination.
• Orthogonal array designs may be of great utility to test multiple factors involved in seed germination.

Solanum torvum is a highly vigorous relative of eggplant that is resistant to a number of harmful soil-borne diseases and is compatible for grafting with eggplant. Being a potential rootstock, this plant frequently presents poor and erratic germination, which makes its practical use difficult. We used an L8 (27) orthogonal array design to evaluate the primary effects of seven factors (soaking of seeds, scarification with sodium hypochlorite (NaClO), application of gibberellic acid (GA3), use of potassium mitrate (KNO3) as a moistening agent, cold stratification, application of a heat shock, and light irradiation during germination) at two levels (L0 and L1) using four germination parameters (early and final germination, germination rate and vigour index) in fresh S. torvum seeds. S. torvum seeds had a strong dormancy with no germination in the untreated seeds and high early and final germination (approximately 100%) in certain treatments. An evaluation of the main effects revealed highly positive effects on germination from seed soaking, and the use of GA3, KNO3, and light irradiation, whereas NaClO scarification had a negative effect. The application of cold stratification and heat shock treatments also had a positive effect on seed germination but to a lesser extent than the other treatments. An improved proposed protocol that consisted of subjecting seeds to soaking, the application of GA3 and KNO3, cold stratification, heat shock, and light irradiation was validated and demonstrated to be highly effective, with seed germination success greater than 60% being observed at 3 days and final germination reaching a plateau at 6 days. A second validation experiment using a commercial growing substrate also showed a high emergence (approximately 50%) at 7 days and a final germination of approximately 80% was recorded with application of the improved protocol. The seed germination protocol that we have developed will facilitate the use of S. torvum as a rootstock for eggplant and its use in breeding programmes. Our results also reveal that orthogonal array designs are a powerful tool for establishing improved protocols for seed germination.