Efficacy of Silicon Foliar Spray in Alleviating Salinity Stress in Sunflower (Helianthus annuus L.)

Abstract

Sunflower is a popular oilseed crop worldwide including Bangladesh. This crop is well-fitted with high yield in salt-affected southwestern (SW) coastal soil in Bangladesh where many other crops of the country cannot be grown due to several abiotic stresses including salinity. Similarly, the yield of sunflowers is gradually reduced due to increased soil salinity. To reduce the salt effect the efficient technology is to flush out salts from the root zone. Due to lack of fresh irrigation water in this region, alternative options need to be searched to ameliorate salinity. Silicon (Si)-mediated salinity amelioration could be a potential option. Thus a pot experiment was conducted by spraying Si on sunflower leaf. The current study included two levels of salinity (0 and 8 dS m⁻¹) and four levels of Si (0, 0.3, 0.6, and 0.9 mM) foliar spray. The result revealed that leaf chlorophyll content index ( SPAD value), plant biomass, seed yield, and yield attributes (head circumference, head parameter, seed number head⁻¹, 1000 seed weight, seed yield plant⁻¹) were reduced due to individual effects of salinity but these parameters were increased gradually due to application of Si and the highest seed yield was found in 0.9 mM Si foliar spray. The interaction of salinity and Si significantly affected head circumference, head diameter, and leaf chlorophyll content index, with the largest head circumference and diameter recorded in plants treated with 0.9 mM Si under control conditions, while the smallest values were observed in saline treatment with zero Si foliar spray, and the highest chlorophyll content index (42.3) found in zero salinity and 0.9 mM Si, which was statistically similar to saline treatment under 0.9 mM Si. Salinity increased shoot concentration of sodium (Na) and reduced the uptake of potassium (K), and Si; while Si application reduced the uptake of Na and increased the uptake of K and Si. The plant height and leaf number also reduced due to salinity and increased with the increasing levels of Si. The current study depicted that, salinity inhibited significantly sunflower growth and yield; however, the detrimental effects of salinity was mitigated by foliar application of Si. Thus, foliar application of Si at the rate of 0.9 or even 0.6 mM ameliorated the salinity effect in sunflower. Future research should also be done in the field.