Phytotoxicity of exotic species on the physiological potential of crambe seeds (Crambe abyssinica Hochs).
Biological invasions of exotic plants can seriously contribute to ecological imbalances within areas to which they have been introduced, affecting, in addition to native plants, cultivated species. Consequently, the objective of the current study was to evaluate effects of allelopathic extracts of three exotic species on the physiological quality of crambe seeds. Aqueous extracts of Prosopis juliflora (Sw.) DC (algaroba) were formulated; Azadirachta indica A. Juss (Nim) and Cryptostegia madagascariensis Bojer ex Decne (viuvinha) at 20% (200 g of dried leaves per liter of distilled water) placed in B.O.D at 25°C for 24 h. Petri dishes, lined with germitest paper sheets, were moistened with aqueous extracts at 2,5 times de paper weight. In the experimental trial, we used the completely randomized, with four treatments (three extracts + control treatment) and four replicates of 25 seeds. The first and second germination counts were evaluated in the fourth and tenth days respectively; germination rate index (GRI), allelopathic effect index (AEI), seedling length and dry mass. P. juliflora and C. madagascariensis reduced germination by 84 and 91%, respectively, in the first count. The GRI was affected by the three species, while the AEI showed greater allelopathy for C. madagascariensis, reaching -0.90. Seedlings lengths were reduced in the presence of P. juliflora and C. madagascariensis. For crambe seeds, all extracts negatively affected their physiological potential.