SUMMARY
Medicinal and aromatic plants are known to be used by a large portion of global population for their medicinal therapeutic effects. Water is among the most important factors for the development, yield and quality of medicinal plants since its deficiency may cause serious growth damages and yield losses. The objective of the present study was to evaluate the effect of two irrigation rates on the development and characteristics of the root system of medicinal plants Hyssopus officinalis L. and Passiflora incarnata L. The experiments were conducted in 2013 in western Greece in the region of Agrinio according to completely randomized design. The root parameters that were determined were root density, root diameter, root surface and root volume, while some soil parameters and abscular mycorrhiza colonization were also measured. The results indicated that for both medicinal plants the increase of irrigation rate had a positive effect on density and volume of the root system, and the other characteristics of the root correlated with the growth and the forage yield of the plants. In conclusion, irrigation can positively affect the growth and development of the root system of H. officinalis and P. incarnate with a beneficial impact on overall plant growth and productivity.