Development of high-yielding fennel synthetic cultivars based on polycross progeny performance

Bitter fennel (Foeniculum vulgare var. Vulgare), hereafter just called fennel, is an open-pollinated plant, and controlling pollination can be very difficult. Most fennel growers are reliant on local landraces, as there is no commercial cultivar. Here, we developed five fennel synthetic cultivars with different maturity habits, three with the goal of high essential oil yield, and the other two with the goal of high seed yield in drought. For each of the five synthetic cultivars, elite parents based on General combining ability (GCA) for either essential oil yield or seed yield in drought conditions were selected, and allowed to freely cross-pollinate. After developing the first generation of synthetic cultivars, their performances were evaluated against some of their elite parents under both well-irrigated and drought conditions. Altogether, the five synthetic cultivars had higher essential oil yield and seed yield than their parents in drought stress, although SynEMOY (16.5 l/ha, 848.3 kg/ha) and SynEMSY (20 l/ha, 562.9 kg/ha) were more promising. In well-irrigated conditions, SynMMOY gave the highest essential oil yield (49.94 l/ha) and seed yield (2357.1 kg/ha), and performances of the synthetic cultivars were like their elite parents. Our result here showed synthetic cultivar has the potential to be an efficient, reliable, and sustainable breeding method to develop high-yielding and drought-tolerant fennel cultivars, especially for early and medium maturities.