Stress modification of allelopathy ofHelianthus annuus L. debris on seedling biomass production ofAmaranthus retroflexus L.

When added to soil,Helianthus annuus debris from plants grown under various nutrient stresses in the greenhouse and field had a significant negative effect onAmaranthus retroflexus seedling dry weight production. The regression models for dry weight versus total phenolic compounds and the variation in N, P, and K contents of theHelianthus debris were significant. It was possible to partially simulate debris inhibition ofA. retroflexus seedling dry weight production when chlorogenic acid alone was added to the soil instead ofHelianthus debris. The inhibition ofAmaranthus growth byHelianthus debris and chlorogenic acid was not evident when nutrient solution was applied to the soil.     

Lipid changes during pre-germination and germination ofstriga asiatica seeds

Witchweed (Striga asiatica L. Kuntze) seeds were incubated at 28 C in a moist environment for a 14-day period, after which seeds germinated only when exposed to specific natural or synthetic germination stimulants. Changes in lipid composition were determined during germination of witchweed seeds and during early seedling growth. Witchweed seeds contained 37.5% (w/w) oil. Increased levels of monogalactosyl-diacylglycerol and phosphatidylglycerol suggested the enlargement or multiplication of plastids after witchweed seeds had germinated. In contrast to the usual course of events in seeds with high oil reserves, witchweed seeds did not hydrolyze triacylglycerol rapidly during or after germination. These findings indicated that triacylglycerol in germinating witchweed seeds was conserved for subsequent use during haustorial formation and host invasion.