Allelopathic effect of Solanum Iycocarpum A. St.-Hil. leaves on the germination and growth of Sesamum indicum L. (Pedaliaceae) under different temperatures.

Allelopathy should be defined as any stimulatory or inhibitory effect by one plant on another through the production of chemical compounds released into the environment. Several Solanum species have shown some allelopathic property. Solanum Iycocarpum is largely distributed on disturbed areas of the Brazilian Cerrado. In the present study the ‘effects of aqueous extracts of Solanum Iycocarpum leaves on the germination and growth of Sesamum indicum were investigated. Aqueous leaf extracts at 1, 2, 3, 4 and 5% (w/v) were prepared. The osmolarity of the extracts were measured and solutions of polyethylene glycol (PEG 6000) of similar osmolarity were prepared to evaluate osmotic effects of the extracts on sesame germination and growth. For the germination experiments the number of germinated seeds was checked every 8 h. For the growth experiments sesame seeds were previously germinated in water and disposed to grow in the extracts. After five days of incubation the root and shoot length of the seedlings was measured. All the experiments were performed at 22, 30 and 38°C. The extracts did not affect the germinability but increased the average germination time in a dose-dependent manner at the 3 temperatures. Root growth was more affected by the extracts, showing tip-necrosis, absence of root hairs, and formation of secondary roots. These effects were more evident at 38°C. Using PEG 6000 it was shown that the observed effects were not due to osmotic properties of the leaf extracts.