Stress-induced changes of growth, yield and bioactive compounds in lemon balm cultivars.

The aim of the present study was to investigate the impact of water deficiency on five Melissa officinalis genotypes. For three months water supply of 70% (control) and 40% (stress) of soil water capacity treatments have been adjusted in a pot experiment. Considering the morphological data, the different genetic potentials of cultivars were manifested only under optimum water regimes while under drought they merged into one homogeneous basic population representing the species. The biomass data decreased for all cultivars under drought stress, but the degree of loss was genotype specific. Genotype dependence of the change in essential oil accumulation was clearly proved by the data. Three of the cultivars ('Gold Leaf', 'Lorelei' and 'Quedlinburger Niederliegende') showed the same essential oil content both in control and stress treatments. Under drought stress the cultivar 'Lemona' produced only 35% of its essential oil content, however cv. 'Soroksár' reacted with 58% increase of essential oil accumulation to drought treatment. Considering the non-volatile bioactive compounds a unique response of the investigated accessions to drought stress was demonstrated. Cultivar 'Lorelei' showed an increased accumulation of total hydroxicinnamic acid derivatives content while cv. 'Gold Leaf' and 'Soroksár' clearly reacted with higher accumulation of total flavonoid fraction. In the case of cv. 'Quedlinburger Niederliegende' the remarkable decline in total flavonoid content is the most obvious stress reaction. The rosmarinic acid content of all genotypes showed lower accumulation level in consequence of lower water supply.