Evaluation of different pre-germination treatments, temperature and light conditions, to improve seed germination of Passiflora incarnata L.

Among the conservation agriculture practices, the introduction of perennials in crop rotation systems has been proposed as a viable opportunity to improve their long-term sustainability and productivity. In this context, perennial medicinal and aromatic plants (MAPs) may represent interesting environmentally friendly crops for the Mediterranean environments. Among MAPs, Passiflora incarnata L. (maypop) represents a very promising crop for its wide adaptability to diverse climatic conditions, low input requirements and high value and demand due to its unique medicinal properties (Dhawan, 2004). In Italy, maypop is grown mostly in the central regions (for a total area of 150-180 hectares, of which 50 ha under organic farming), where it behaves as perennial spring-summer crop with a stand duration of 5-7 years. The main problem in maypop large-scale cultivation is the poor seed quality with erratic and low seed germination, due to its apparent pronounced seed dormancy. Therefore, the aim of this work was to investigate different chemical and physical treatments for overpassing seed dormancy and enhancing seed germination rates of P. incarnata. The experiments were carried out at the Seed Research and Testing Laboratory of DiSAAA-a University of Pisa. Seeds of three P. incarnata accessions (F2016, FF2016, and A2016) grown in 2016 in Central Italy have been examined. The following treatments have been tested according ISTA Rules (2015): Pre-germination treatments: pre-chilling, GA3, leaching, scarification, control; Germination test conditions: light (L) and dark (D); constant temperature: 25°C L; 30°C L; 35°C L; 25°C D; 30°C D; 35°C D; alternating temperature 20/30°C for 16/8h D/L and for 8/16h D/L. The seeds were placed in 12 cm Petri dishes and incubated in climatic cabinets. Germination Percentage and Mean Germination Time (MGT) were evaluated. Data were subjected to analysis of variance. The results confirmed as P. incarnata seeds are photoblastically negative and have pronounced heat requirements for germination. Optimal germination percentages were in fact, achieved with 35°C under dark, while very low values were observed at constant temperature of 25°C. The time required for germination decreased progressively with increasing temperatures, but only under dark conditions. In addition, alternating temperature did not improve germination energy, except when combined with pre-chilling. Among accessions, the highest and faster germination rates were observed for F2016, followed by FF2016. Among the pre- treatments tested, prechilling, GA3 and leaching enhanced germination, while under scarification, the dead seeds percentage considerably increased in all accessions, due to embryo damaging. A significant interaction between pre-chilling and temperatures has been observed with significantly higher germination values and lower MGTs than control (+330% and -200%, respectively) at 20/30°C (16/8h). This study underlined that dark and suitable thermal conditions are necessary for high and rapid germination of P. incarnata seeds. Among pre-treatments, pre-chilling plus 20/30°C (16/8h) was the most effective in breaking dormancy of maypop seeds, enhancing both germination percentage and rate. These findings are useful for improving maypop seed propagation at nursery level. Furthermore, the information gathered can be incorporated in the ISTA (International Seed Testing Association) rules, still pending for this species.