AUTOTOXICITY OF MESQUITE (PROSOPIS-JULIFLORA) PERICARPS ON SEED-GERMINATION AND SEEDLING GROWTH

Autotoxicity, expressed as the inhibitory effects, of the pericarp on seed germination and seedling growth of mesquite, was investigated. The final germination of fresh mesquite seeds at 25 ± 2ºC in a distilled water control and four pericarp aqueous extracts, prepared by the extraction of 5, 20, 40 and 60 g dry pericarp in a litre of distilled water, revealed that more than 95% of the seeds had germinated in the distilled water control and in the least concentrated extract, whereas 100% germination inhibition was exhibited by the most concentrated extract. Likewise, both radicle and hypocotyl lengths were retarded significantly by the extracts. These lengths decreased with an increase in the extract concentration to be severely affected in the most concentrated extract. Using four NaCl-citric acid solutions, with the same pH and osmotic potentials as the extracts, resulted in more than 95% final seed germination. This was significantly higher than in their corresponding extracts, with the exception of the least concentrated one. As with the extracts, the radicles and hypocotyls decreased in length with an increase in the NaCl-citric acid concentration, but they were still significantly longer than in the corresponding extracts. These results clearly indicate that mesquite pericarp contains allelochemicals which inhibit seed germination and seedling growth of that species. The characterization and indentification of these allelochemicals will add to the understanding of their allelopathic mechanism and, hence, could make it possible to use the mesquite pod segments as propagules instead of the seeds which are difficult to extract. © 1994 Academic Press Limited.