Allelopathic effects of Juniper essential oils on seed germination and seedling growth of some weed seeds

Abstract

Plant essential oils (EOs) are often used as ingredients in the development of new biopesticides. The objective of this study was to investigate the allelopathic effects of three EOs of two juniper species against weed seeds. The EOs were extracted from Juniperus sabina L. Male (M) and Female (F) and J. excelsa Bieb. by means of steam distillation in a semi-commercial extractor. The monoterpenes and sesquiterpenes were the predominant classes of J. excelsa EO. The major class of J. sabina EO was monoterpenes (sabinene). The bioherbicidal activities of the three EOs were tested in four concentrations (0, 30, 60, and 90 µL) against three weed species; Melilotus officinalis L., Trigonella besseriana Ser., and Myosotis arvensis (L.) Hill. The three EOs used in the experiment exhibited different inhibitory effects on weed seeds. The tested juniper EOs enhanced the germination energy of M. officinalis seeds. Compared with the 15% germination energy in the non-treated (control) treatment, germination energy (measured at Day 4) increased by up to 70–100% with increasing EO application rate. However, after Day 7, an inhibitory effect occurred, and the seed germination of the treated seeds was reduced to 12–37% compared with the 63% in the non-treated control. In M. arvensis seeds, J. sabina EO reduced germination energy and germination itself, while J. excelsa EO stimulated germination. ЕОs оf J. sabina, M (30, 60, and 90 µL) showed greater inhibition on the germination of seeds of T. besseriana. Sprout and root lengths of the three weed species varied with juniper species and EO concentration. Overall, J. sabina (M, F) EOs showed the highest inhibitory effect on seed germination, as well as on sprout and root lengths. The tested juniper EOs showed promise as ingredients to be included in new certified organic weed control products.