2019 ASHS Annual Conference

We hypothesized that phasing of timing of salinity stress imposition will result in improved oxidative stress defence in an African leaf vegetable, Amaranthus cruentus L. We imposed salinity on the plants at 2-leaf stage, 4-leaf stage and 5-leaf stages of growth while plants that received no salinity treatment served as control. The five levels of salinity were 0 (control), 60, 100, 140 and 180 mM NaCl in four replications, corresponding to 1.2, 8.4, 12.5, 16.6 and 22.4 dS/cm electrical conductivities, respectively. Scanning electron microscopy (SEM) showed a concentration of discernible segmented trichomes on the veins of adaxial leaf surface while the trichomes are evenly distributed on the abaxial leaf surface. Significantly higher amounts of carotenoids, flavonoids, chlorophyll ‘a’, ‘b’ and total chlorophyll were found in the control plants and 5-leaf stage plants compared to plants that started receiving salinity treatment at 2-leaf and 4-leaf stage. Chlorophylls ‘a’ and ‘b’ were maintained in approximately ratio 5:1 irrespective of the salinity rate. It is noteworthy that the higher the salinity level (within a range of 0-180 mM), the lower the leaf tissue content of elemental Ca and the higher the K. The antioxidative potential, falavoniods, carotenoids, relative photochemical efficiency (Fv/Fm), net photosynthesis (A), intercellular carbon dioxide concentration (C_i) and stomata conductance (g_i) decreased as salinity level increased. The older the plant before the imposition of salt stress, the better the ability of the plant to tolerate the stress. These results can assist in appropriate transplanting decision in saline locations for A. cruentus leaf and seed production.