Morphogenetic variation for artemisinin and volatile oil in Artemisia annua

Abstract

Seeds of Artemisia annua cv. Jeevanraksha were sown in the nursery in the middle of December in 1997, 1998 and 1999. About 1-month old seedlings were transplanted in the field having sandy loam soil in the subtropical agroclimate of Lucknow, India. The plant tops were sampled fortnightly for leaves during vegetative phase and for leaves and capitula during post-flowering stages for the estimation of artemisinin content. The A. annua plants continued to grow logarithmically in height from the end of rosette phase at about 9 weeks to the pre-flowering stage at about 44 weeks age and attained a height of 3.4 m. The artemisinin content of the leaves was observed to be high from 0.8 to 1.0% in May and 0.8 to 1.3% through late July to late September. Subsequently, plants entered the reproductive phase. While in the vegetative phase, 90% of artemisinin was in the leaves, in the mature plants, about 30% of the artemisinin was in the leaves and 40% was in capitula. In the vegetative stage plants the younger leaves born on the tops of secondary and higher order branches were richer in the artemisinin than the older leaves. The tops of A. annua plants in their vegetative growth phase possessed low levels of essential oil at about 0.2% as compared to 1.2% of essential oil in the full blooming stage plants. The extraction of artemisinin from leaves is more economic than from the mixture of leaves and capitula on account of higher levels of lipids in the extract of the latter. Since A. annua plants grew logarithmically all through vegetative phase from March to late September and artemisinin content in the leaves was high in May and from late July to late September, it is suggested that under the subtropical agroclimates, A. annua crops may be harvested more than once. The ratooning is expected to reduce losses in artemisinin yield resulting from senescence caused dropping of old leaves and favour preponderance of young leaves found richer in artemisinin content.