Salinity stress and drought stress differentially affect biomass allocation, leaf orientation and performance of two sesame (Sesamum indicum L.) cultivars

Drought and salinity stresses are major threats to crop productivity in the arid lands. This work investigates the differential impact of salinity and drought on growth and performance of two sesame cultivars: Sohg and Shnd at water potentials of 0, -100, -250 and − 450 kPa with the same nutrient supply in a hydroponic sand culture. Under no stress, leaves of Sohg exhibited vertical orientation with higher pigment and soluble sugar contents but lower polysaccharide content relative to leaves of Shnd. Salinity and drought differentially affect leaf orientation only in Sohg, where drought induced horizontal leaf position but salinity led to the opposite effect. Whereas drought induced stronger reduction in foliage biomass than did salinity, with enhancement of root biomass, salinity reduced foliage and root biomass with favored allocation of plant biomass to root. Salinity reduced leaf pigment content, particularly in Sohg but drought either increased it or was without effect. Both drought and salinity, post a threshold of -100 kPa, reduced rates of photosynthesis and transpiration as well as stomatal conductance, with stronger impact of salinity than drought. The lowering in carbohydrate content under stress, being more aggressive under salinity than drought, was associated with increasing proportion of pectin at the expense of starch and variable changes in soluble sugar proportions.