Evaluation of genetic diversity and potential salt stress tolerance in safflower (Carthamus tinctorius L.) genotypes using the molecular marker SCoT and germination indices

Objective
Genetic diversity and parental selection in breeding programs are crucial factors for the successful development of new crop varieties. Plants are exposed to a wide range of stresses at all stages of growth, leading to quantitative and qualitative reductions in yield and overall crop production. The present study aimed to evaluate the genetic diversity of safflower and assess its potential tolerance to NaCl salt stress, as well as to classify genotypes using germination indices and SCoT molecular markers.
Materials and Methods
In this study, a factorial experiment was conducted using a completely randomized design with three replications at the Genomics Laboratory of the Islamic Azad University, Khorramabad Branch, during the first half of 2022. Ten safflower genotypes were evaluated under control conditions and three salinity levels (50, 150, and 250 mM NaCl). For this purpose, 20 seeds of each genotype were placed in 12-cm sterile Petri dishes under different salinity levels with three replications. The samples were incubated for 10 days in a growth chamber at 25°C during the day and 20°C at night. Various traits and indices, including germination percentage, germination rate, shoot and root length and weight, stress tolerance index, seedling vigor, seedling length vigor index, seedling weight vigor index and reduction of germination, were measured and calculated. SCoT markers were employed to estimate genetic diversity, and genetic distances among safflower genotypes were analyzed and clustered based on germination indices and molecular data.
Results
The results of analysis of variance showed that the interaction effect of genotype and salinity stress was significant for most of the studied traits. Comparison of means showed that genotypes number 5 and 7 showed the highest and lowest significant decrease for the studied traits and indices, respectively. Genotype number 7, along with two genotypes 4 and 9, had greater tolerance to salinity stress. Based on the results of factor analysis, considering the loading of the first and second factors, the first factor was called stress tolerance or resistance and the second factor was called the weight factor. Based on the two principal components, the studied genotypes formed 5 groups. Genotype number 5 was located at a further distance from the other genotypes due to its greater resistance to different levels of salinity stress. In cluster analysis, the genotypes were placed in 4 groups. The first group had the highest decrease and the second group had the lowest decrease for the traits at salinity stress levels. The primers used showed 114 bands with 86% polymorphism. The highest and lowest similarity coefficients between genotypes were 66 and 34%, respectively. Based on cluster analysis using molecular markers, the genotypes were classified into 5 groups. The grouping obtained in both techniques showed a high correlation (R=0.87).
Conclusion
Overall, the results indicated that safflower genotypes possess high genetic diversity under salt stress conditions, and their responses to varying stress levels differed significantly. These genetic differences provide useful information regarding enhancing crop production and identifying salt-tolerant genotypes in breeding programs. Although safflower exhibits considerable tolerance to soil salinity, developing more tolerant cultivars remains necessary, and evaluating germplasm under saline conditions is essential. Despite the moderate concordance between molecular marker-based grouping and germination indices, their combined use is of great importance for identifying superior genotypes and enhancing breeding efficiency.