Experiments were conducted to evaluate the promise of Tinnevelly senna, Cassia angustifolia Vahl, as an alternative crop for stressful agroecosystems. Effects of drought, foliar nitrogen application and crop type on sennoside yields were studied with simultaneous measurements of net photosynthesis. Short term drought increased sennoside A + B concentration (% dw). After drought-induced morphological changes had occurred, long term drought did not influence sennoside A + B concentration but severe loss of leaf biomass caused 78% reduction of the sennoside yield per plant. Foliar nitrogen application increased the total sennoside A + B content per plant by 140% when the plants were not water stressed, but in severely droughted plants, no effect of foliar nitrogen application was detected. Although foliar nitrogen application increased sennoside A + B per plant, the sennoside concentration (% dw) decreased. The latter effect was still persistent three months after the nitrogen treatments were discontinued. In a comparison among three crop types of Tinnevelly senna, ratoon plants had the highest sennoside A + B concentration in leaves followed by seedlings and cuttings. However, seedlings produced the highest sennoside A + B yield per plant due to the higher leaf biomass. Except in long term drought, sennoside levels were higher in leaves with lower net photosynthesis, and were increased by treatments that induced physiological stress. Lower net photosynthesis occurred in short term and long term drought, and with deprivation of foliar nitrogen supplement. In contrast, sennoside yields per plant are readily increased by treatments that increase the total leaf biomass. Short term drought, nitrogen stress and ratooning are promising component technologies for field and on-farm investigations with the goal of increasing sennoside yields.

Manual deflowering and leaf maturity were evaluated for effect on the yields of the bioactive sennosides A and B in Tinnevelly senna (Cassia angustifolia Vahl). Deflowering increased sennoside A and B concentration (percent dry weight) in leaves by 25%, the total leaf dry mass by 63%, and the harvest index by 22%, with the result that the sennoside A and B yield (grams) per plant doubled in response to deflowering. During the same time, net photosynthesis remained consistently lower in the deflowered plants. Youngest leaves had the greatest sennoside A and B concentration. A clone raised from cuttings of one seedling had lower sennoside A:B ratio than the plants raised from the seedlings. Although crop type and possibly environmental conditions influenced the sennoside A:B ratio, deflowering and leaf maturity had no effect. The sennoside A and B concentrations in the dried leaves of deflowered plants harvested in 1.5-hour intervals appeared to increase during the course of the day. Deflowering, harvesting of young leaves, and harvesting time of day constitute promising component technologies for field investigations.