Abstract

Plumbago zeylanica L. is an important medicinal plant traditionally used for the treatment of various diseases. Phenology from seed germination via vegetative growth to reproductive development was studied under glasshouse and nursery conditions. Seeds rapidly germinated on a mixture of nursery soil and cattle dung in a ratio of 3:1 filled in pots or on cultivated soil under nursery conditions as a prerequisite for vegetative and flowering phenological studies. Hypogeal germination characterizes the emergence of seedlings. Subsequent vegetative and flowering phenology between glass house and nursery field populations showed significant difference (p <0.05) in terms of time, duration and yield. Glass house populations completed their phenophases (seasonally) (72.3 ± 1.03%) within 133 days (15 March to 20 July, 2006) being under controlled conditions while field-grown seedlings extended to 225 days (15 March to 30 November, 2006) after seed sowing.  Rainy season was the cause for the continuous damage of apical shoots, and consequently stunted vegetative growth of field-grown seedlings.  Plant size (≥ 95 cm in height), leaves number (33 - 38) and seasonal climate (cold season for field-grown populations) were found to be the most eliciting signals for the initiation of flowering buds. 100 ppm GA₃ was the most effective for early flowering (that is, before 6 days) and production of higher number of flowers (32.6 ± 1.6%) compared to the control (22.5 ± 1.33%). The mode of reproductive biology appeared to be cross-pollination and showed significant (p <0.05) compared to the control. The final flowering percentage (95.3 ± 1.71%) and/or seed-set (89.4 ± 1.41%) were obtained under glass house condition compared to the nursery, which dropped as low as 50% in flowering and seed-set. The study found that rainy season, plant size, leave number, low temperature, cross pollination and glass house conditions were found to be the most determining factors for the phenology of P. zeylanica.

Key words: Growth regulators, medicinal plant, seasonal climate, plant size, growth environment.