Effectiveness of Exogenous Salicylic Acid on Root and Shoot Growth Attributes, Productivity, and Water Use Efficiency of Water-deprived Fennel Genotypes

This study was carried out to investigate the response of fennel (Foeniculum vulgare Mill.) to water deficit and exogenous application of salicylic acid (SA). Six fennel genotypes, from Iran (namely Urmia, Hamadan, Kerman, Shiraz, Birjand and Yazd) were subjected to two levels of irrigation consisting of either irrigation after 35% (control) or 75% depletion of available soil water (water deficit) and 3 levels of treatment with SA (0.0, 0.5 and 1.0 mM). Root growth attributes, yield and yield components as well as irrigation water use efficiencies for seed, oil and dry masses of the shoot and whole plant were studied. Shoot dry mass, grain yield and essential oil yield were decreased due to water deficit. Furthermore, root growth attributes were decreased under water deficit, except for root diameter and dry mass, and root/shoot ratio. With the exception of irrigation water use efficiency for seed yield, all irrigation water use efficiency aspects were increased when fennel was subjected to water deprivation. Fennel genotypes were grouped according to their stress susceptibility indices (SSI) into drought-tolerant, moderately drought-tolerant and drought-sensitive groups. The largest drought-induced decreases in root length, root dry mass, root length density, number of fruits per umbel, seed yield, 1000-seed weight, seed essential oil yield, and irrigation water use efficiency for seed and oil yield were observed in genotype Hamadan from the drought-sensitive group. Salicylic acid led to increases in root growth and yield attributes, seed essential oil content and yield, and irrigation water use efficiency aspects under both moisture conditions. Overall, foliar application of SA appeared to attenuate the negative effects of drought stress on fennel through increases in most of the root growth and yield attributes and the attenuation was more substantial in the drought-tolerant set of fennel genotypes.