Grain Shape as a Predictor of Salt Tolerance in Sunflower

To determine whether sunflower (Helianthus annuus L.) grain shape should be considered as a predictor of salt tolerance, seeds of three grain shapes, namely long seeds (DC6009 and RH3146 with a width-length ratio [WLR] of 0.39), long ovate seeds (SH909 and 135 with a WLR of 0.49) and broadly ovoid seeds (RH118 with a WLR of 0.61) were exposed to 0, 1000, and 2000 mg L-1 NaCl for 30 d. Increases in the WLR increased the 100-seed weight and kernel/hull rate (KHR) but decreased the water absorption rate (WAR). A level of 2000 mg L-1 NaCl delayed the seed mean germination time (MGT), reduced the germination percentage (GP) and germination index (GI) and caused shorter root length (RL). A level of 1000 mg L-1 NaCl improved the GP and GI compared with the no NaCl-stressed control with the exception of the long ovate seeds. RL decreased with increasing NaCl levels, and plants with broadly ovoid seeds had longer roots than those with other shapes. The activities of superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) were lower in the NaCl-stressed plants than the controls. The malondialdehyde (MDA) contents increased with the NaCl levels in all cultivars. The broadly ovoid seeds exhibited the greatest enzyme activities and the highest net photosynthetic rate (Pn) at both NaCl levels. Based on emergence, early seedling growth and physiological characteristics, the long ovate seeds had a higher salt tolerance than those of the other two shapes, followed by those with long seeds.