Phenology and Reproductive Biology of Aconitum violaceum - A Threatened Endemic Medicinal Herb of the Northwestern Himalaya

The study of reproductive biology provides essential paradigms for biodiversity conservation, reclamation, and restoration. The present study was undertaken with the aim of studying the phenology, floral biology, pollination ecology, and breeding behavior of an endemic threatened medicinal plant of Ladakh Himalaya. The present study revealed that Aconitum violaceum Jacq. ex Stapf is a biennial medicinal herb that completes its life cycle within 127–160 days. Flowers are typically hermaphrodite and partially protandrous. Pollens were spheroidal, monad, tricolpate, granulate, and exhibited 94–95% viability at the time of anther dehiscence. Boric acid and calcium nitrate at concentrations ranging between 100–500 ppm were optimal for in vitro pollen germination. The highest percentage of in vitro pollen germination was reported on the M7 medium (49.5%), followed by M4 (33.15%). The stigmas were highly receptive between 5th – 8th days after anthesis. The greatest pollen-ovule ratio was observed in the Khawous population with 3729.72 ± 48.92:1 pollen per ovule. Pollination indices, including foraging (FB), insect visiting efficiency (IVE), foraging speed (FS), visitor visitation frequency (VVF), and pollen load (PL) on the bodies of insect visitors, revealed that Bombus species were the chief pollinators of A. violaceum , accounting for 78.6% of pollination. The values of the self-incompatibility index (ISI), selfing rate (SR), greatest pollen ovule ratio, and breeding experiments revealed that A. violaceum is cross-fertile and partially self-compatible. The maximum proportion of fruit formation (86.66%) with a 94.87% seed set rate was recorded in open pollination, followed by induced xenogamy (68.88%) with 82.25% seed set, demonstrating that the species favoured cross-pollination. The present study first reported the phenological episodes and reproductive strategies operative in A. violaceum which will be crucial paradigms for its conservation, domestication, and sustainable utilization. It also aids in the development of specific techniques to overcome the challenges that limit its regeneration.