Phytochemical profile and allelopathic activity of eight Eucalyptus species on the performance of initial growth stage of four local species in the southern Tunisia

Abstract

We aimed thought this survey 1) to investigate and compare the phytotoxicity features of eight Eucalyptus species frequently planted in southern Tunisia (Eucalyptus camaldulensis Dehn., Eucalyptus gomphocephala DC., Eucalyptus torquata Luehm., Eucalyptus microtheca F.Muell., Eucalyptus occidentalis Endl., Eucalyptus diversifolia Bonpl., Eucalyptus sargentii Maiden., and Eucalyptus torwood) on seed germination and radicle growth of Medicago sativa L., Corchorus olitorius L., Cenchrus ciliaris L., Peganum harmala L., and 2) to classify those species according to their allelopathic efficiency. The laboratory experiment was conducted using aqueous extracts made from dried and ground plant leaves to obtain concentrations of 5 % and 10 %. These were prepared alongside control treatments for comparison. Afterward, methanol extracts were utilized in the chemical composition identification procedure via HPLC-DAD-ESI-MS. Different responses were obtained for the species studied for germination and extraction. Results highlighted that C. ciliaris and P. harmala were the most susceptible to eucalypt extracts, while, M. sativa and C. olitorius were more resistant. Statistically, lower concentrations were less effective, but higher ones had noticeable inhibitory effects on seedling growth parameters. We assumed that E. occidentalis, E. gomphocephala, E. torquata and E. camaldulensis were recognized as the most noxious species, E. sargentii and E. microtheca produced moderate effects, while E. torwood and E. diversifolia were regarded as benign species. Phytochemicals especially ellagitannins and flavonols derivatives were the major compounds identified accounted for 21–78 % and 8–59 %, but hydroxycinnamic acids derivatives, gallic acid derivatives, total flavonols content and non-phenolic acids were acknowledged as the major causes for the observed outcomes.