Abstract: Isatis indigotica is the primary ingredient of traditional Chinese drugs ‘Banlangen’ and ‘Daqingye’, and its cultivation relies on seed propagation. This research examined the flowering habit and pollination biology of I. indigotica cultivated in Minle county. The work included field observation and an artificial pollination experiment, in order to provide scientific and technical information to support seed production and heterosis utilization in this crop. It was found that the plant had an infinite inflorescence consisting of an upright main stem bearing raceme-like branches with new branches above as older matured branches below and 10-20 individual flowers per branch opening in an acropetal sequence over a flowering period of some 30 days. Flowers are bisexual with 6 stamens, four of which are long and two of which are short. There are 4 green calyces, 4 yellow petals with ovary superior, and 1 locule. The flower lifespan was 6-7 days but was shortened to 3-4 days under adverse climate conditions. The stigma matures just prior to the flowers opening. When the petals are just emerging from the calyx tube, bright fresh yellow pollen grains become visible and are dispersed by the flowering day. Anthers then begin to wither, and the ovary expands at the end of the flowering stage, growing a short pod with 0-2 seeds. Seed set was 95.0% for plants under natural conditions. Under covered conditions with paper bags, seed set was very low (approximately 4%) both with and without castration, but was 72.0% when plants were cross-pollinated after castration. When plants were cross-pollinated after castration, but the inflorescence was unbagged, seed set was 53.3%. The self-incompatibility index was assessed as 0.96-1.00. For bagged racemes, seed set was 5.0% without castration and increased to 13.7% after castration. The most common flower pollinator visitors were Episyrphus balteatus and Apis mellifer but various other insect species also visited. These results indicate that I. indigotica has strong self-incompatibility without apomixis, and can be considered a typical cross-pollinating plants needing pollinators, pollinated mainly by insects but supplemented by wind.

Key words: Isatis indigotica, diploid, floral habit, pollination, self-incompatibility