A Salt Tolerance Evaluation Method for Sunflower (Helianthus annuus L.) at the Seed Germination Stage

Abstract

Salinity is a major abiotic stress that affects plant growth and development and leads to crop yield loss. Many crop species are more sensitive to salinity stress at the seed germination stage than at other developmental stages. Some studies have shown that sunflower is tolerant to salinity to a certain degree. However, no systematic screening data for sunflower germplasms are available for salinity stress. In this study, 552 sunflower germplasms with different genetic backgrounds were evaluated for salt tolerance. Among them, 30 and 53 sunflower germplasms were identified as highly salt-tolerant and salt-tolerant germplasms, respectively, while 80 and 23 were grouped as salt-sensitive and highly salt-sensitive materials, respectively. Of all the traits tested, the germination index and the germination vigor index were the two most reliable traits, showing the highest correlation with salt tolerance during the seed germination stage of sunflower. Thus, a highly efficient and reliable method for evaluating salinity tolerance of sunflower seed germination was established. These results provided a good foundation for studying salt-tolerance mechanisms and breeding highly salt-tolerant sunflower cultivars.

Figure 1

The optimum NaCl concentration for salt tolerance evaluation was determined according to the two indexes of germination rate and germination phenotype with the parental breeding line ZSADT. (A) Germination rate and (B) germination phenotype of ZSADT seeds treated with different NaCl concentrations for seven days. **Indicated significant difference (p < 0.01) between treatment and control.

Figure 2

Classification of 552 sunflower germplasm lines based on mean membership function values (mean MFV). (A) Distribution of mean MFVs. (B) Classification of 552 sunflower germplasms according to salt tolerance based on mean MFVs. HST, highly salt-tolerant; ST, salt-tolerant; MST, moderately salt-tolerant; SS, salt-sensitive; HSS: highly salt-sensitive.

Figure 3

A linear correlation analysis between the STI values of each parameter and mean MFV. (A) Relationship between the STI of germination rate (STI_GR) and mean MFV; (B) Relationship between the STI of germination index (STI_GI) and mean MFV; (C) Relationship between the STI of the germination energy (STI_GE) and mean MFV; (D) Relationship between STI of root length (STI_RL) and mean MFV; (E) Relationship between STI of germination vitality index (STI_GVI) and mean MFV; (F) Relationship between STI of fresh weight (STI_FW) and mean MFV; (G) Relationship between the STI of water content (STI_WC) and mean MFV; R²(L) is the coefficient of determination.