Berry productivity and molluscicidal saponin yield ofPhytolacca Dodecandra (Phytolaccaceae) under different sunlight,watering and nutrient conditions

The cultivation ofPhytolacca dodecandra has been studied in Zimbabwe in order to initiate local production of the berries from which molluscicidal saponins can be extracted and used in schistosomiasis control programs. The effect of shading, water and nutrient type on growth and berry yield of an imported Ethiopian and a Zimbabwean cultivar were monitored. The molluscicidal potency and saponin concentration of the aqueous extracts of berries, harvested at the full grown, unripe development stage, were determined. There was a marked seasonal variation in berry production with both cultivars being highly productive in the dry season. The best growth and the highest berry yield was obtained with plants grown in full sunlight, under irrigation and with application of cattle manure. The Ethiopian cultivar showed in general better growth and higher berry yield than the Zimbabwean cultivar. Cultivation in shade gave a substantially lower berry yield and saponin concentration in both cultivars, compared to full sunlight. Irrigation was beneficial to the berry yield in both cultivars but lowered the saponin concentration in berries of the Ethiopian cultivar. However, it did not counteract the advantage of irrigation on the total yield. Addition of manure did significantly increase the growth and the berry yield of both cultivars compared to fertilizer application and to the control. The saponin concentration was in general lower with addition of manure, with exception of irrigated Ethiopian plants. The combination of cattle manure and irrigation resulted in the highest saponin yield. Although the two cultivars had different saponin patterns, these patterns and the relative proportions of the saponins were constant, irrespective of the treatments.