Effects of Persian walnut leaf extracts on seed germination, seedling growth, and some physiological characteristics of the basil (Ocimum basilicum L.) cultivar ‘Genovese’

Abstract

SummaryThis study was conducted to elucidate the allelopathic effects of a series of dilutions of Persian walnut (Juglans regia) leaf extracts [i.e., undiluted, 1:2 (v/v), 1:4 (v/v), or 1:8 (v/v) dilutions] and distilled water (control) on the characteristics of seed germination, seedling growth, and subsequent physiological changes in the basil (Ocimum basilicum L.) cultivar, ‘Genovese’. The results indicated that all aqueous leaf extracts of walnut had statistically significant inhibitory effects on the germination of basil seeds and on seedling growth characteristics. Seed germination percentages, the lengths and fresh weights (FWs) of the plumule and the radicle, the FWs and dry weights (DWs) of the shoots and roots, and leaf areas decreased significantly with increasing concentrations of aqueous walnut leaf extract. The DWs of the plumules and radicles were increased by the undiluted walnut leaf extract. Moreover, it was found that the yields of essential oils and total phenolics, and the anti-oxidant activities of basil seedlings increased with increasing concentrations of aqueous walnut leaf extract, whereas the relative water contents of basil leaves, leaf water potentials, as well as the total chlorophyll and carotenoid contents of basil leaves decreased significantly. The highest protein contents and peroxidase (POD) activities were achieved using undiluted or 1:2 (v/v) diluted aqueous walnut leaf extracts, respectively. The results of this study suggest that cultivation of the basil cultivar, ‘Genovese’ may be appropriate for walnut tree-based intercropping systems, based on the increases in anti-oxidant capacity and the accumulation of secondary metabolites.