Genotype-specific response of Foeniculum vulgare grain yield and essential oil composition to proline treatment under different irrigation conditions

Drought stress is a major environmental stress which severely affects growth, yield, as well as quality and quantity of crop products. Proline as a multifunction amino acid has a crucial role in ameliorating of drought stress. In order to study the effect of external proline on the response of fennel to drought stress, three fennel genotypes (namely Urmia, Shiraz, and Kerman) were exposed to two irrigation regimes (drought stress and non-stress control) and two levels of foliar-applied proline (0 and 20 mM) in a pot experiment. Drought led to significant decreases in umbels/plant, plant height, 1000-grains weight, harvest index, above-ground dry mass, grain weight and grain and dry mass WUE, root volume, root fresh and dry mass, ratio of shoot/root, grains and stems essential oil weight/plant and significant increases in root length and grains limonene content. Foliar-applied proline led to notable increases in harvest index and grain essential oil weight in the presence of drought. It also led to increases in umbels/plant, 1000-grains weight, harvest index, above-ground dry mass, grain weight and grain and dry mass WUE and ratio of shoot/root in Urmia and Shiraz genotypes. Anethole, limonene, fenchone, estragole and α-pinene were the main essential oil constituents in both grain and stems. Grain fatty acid and phytosterol compositions were not affected by experimental treatments. It may be concluded that drought stress suppresses fennel growth and grain weight, but foliar-applied proline is potent to mitigate the adverse reaction through increasing growth, grain weight/plant, WUE and grains limonene content in genotypes such as Urmia and Shiraz.