Allelopathic effects of leachates of Casuarina glauca Sieb. ex Spreng. and Populus nigra L. on germination and seedling growth of Triticum durum Desf. under laboratory conditions

The decline in soil fertility and the poor distribution of precipitation during the growth and maturation of cereal crops are major constraints to improving yields in the Mediterranean zone in North Africa. The use of agroforestry species is one strategy for enhancing agronomic productivity and supporting a range of ecosystem services and environmental benefits. However, to our knowledge, the allelopathic effects of these agroforestry species on cereals are poorly documented under Mediterranean conditions. The effects of three aqueous extracts (leaves, roots and litter) from two agroforestry species (Casuarina glauca Sieb. Ex Spreng. and Populus nigra L.) have been evaluated for their allelopathic potential on seed germination and seedling growth of Triticum durum Desf. under laboratory conditions. These allelopathic effects were evaluated using several parameters including seed germination, total dry mass, root and shoot length, chlorophyll and protein concentrations in T. durum seedlings along with phenolic compounds in different parts (leaves, roots and litter) of the two allelopathic species. Exposure to the different extracts of C. glauca and P. nigra significantly reduced germination kinetics, dry mass production, root and shoot length, and chlorophyll and protein concentrations in T. durum seedlings. This reduction was significantly more pronounced for the different extracts from P. nigra. Our results showed a significant negative correlation between dry mass accumulation in T. durum seedling and polyphenol concentration. Overall, the findings of the present study support the introduction of C. glauca into the agroforestry system. However, field monitoring under natural conditions would be necessary to confirm in practice the results obtained with the bioassays.