Evaluation of salinity tolerance index of sunflower in Hetao Irrigation District

Soil salinization is a vital non-biological factor restricting crops yield and quality improvements across the world. The most effective and economic way of exploiting saline soils has been breeding and planting salt-tolerant species. Yet the lack of reliable, inexpensive and convenient screening method has limited progress in salt-tolerant breeding programs. Screening the applicability of different salt-intolerant indexes of cultivar under different salt stresses was critical for providing requisite scientific evidence of breeding salt-tolerant species and molecular marker in selective breeding. In this paper, the applicability of different salinity tolerance indexes of sunflower was screened. This laid the scientific relevance of salinity tolerance breeding and marker-assisted selection. To determine salinity tolerance indexes of sunflower in Hetao Irrigation District, the main local cultivar 'LD 5009' was cropped and observed in fourteen representative fields over a period of two years. The fields included non-saline, mild-saline, saline and severe-saline zones. Twelve indexes, including yield, biomass, plant height, leaf area index, face plate diameter, SOD activity and contents of leaf chlorophyll, proline, Na⁺ and K⁺ were analyzed in response to salinity conditions and indexes which reduced with increased soil ECe selected. Nonlinear least squares numerical approximation method was used to establish an S-shaped salinity tolerance function which reflected the relationship between salinity tolerance indexes and soil ECe in different layers. The results indicated that yield, biomass, plant height, leaf area index, disc diameter, and leaf and stem K⁺ contents decreased with increasing soil salinity. The coefficient of determination of salinity tolerance function between biomass and ECe in the 0-20 cm soil layer was highest. There was no obvious impact of salinity on chlorophyll content. Under salinity conditions, Na⁺ content gradually increased, while proline content and SOD activity increased followed by a decrease. In conclusion, this study verified the suitability of biomass as a key index of sunflower salinity tolerance analysis in Hetao Irrigation District.