The relationship between bitterness and drought resistance of almond (Prunus dulcis Mill.)

Cynogenesis has been suggested to be an adaptive response to drought stress in some plants. To determine the possibility of cyanogenic compounds role in almond resistance to drought stress, three different irrigation levels including moderate and severe stress (soil water potential, _soil = -1.2 and -1.8 MPa, respectively) and a control treatment (_soil = -0.33 MPa) were applied for five weeks to six different almond seedling genotypes including Bitter (homozygote bitter), Butte (heterozygote sweet), `Shahrood’12 (SH12), `Shahrood’18 (SH18), `Shahrood’21 (SH21) and White (all heterozygote sweet). Cyanogenic compounds including amygdalin and prunasin and the nitrogen content in the roots and shoots were measured throughout the study. Results showed that nitrogen content tend to be lower in leaves and higher in roots however; differences were not significantly different between genotypes. Severe stressed plants generally showed higher root N content although this was only significantly different for SH18, SH12 and White. There was no amygdalin in vegetative parts of plants. Bitter genotype had the highest prunasin content in its roots compared to the other genotypes. Water stress had no effect on the content of cyanogenic compounds in the leaves of all genotypes, while in roots of all genotypes except Butte and White; water stress caused a decrease in prunasin content. Hence bitterness does not play any role in drought tolerance mechanisms in almond.