Assessing the impact of salinity stress on Na+, K+, and Ca2+ contents of 125 rice genotypes

The ionic balance of Na⁺, K⁺, and Ca²⁺ affects salinity tolerance in rice. This study examined the content of Na⁺, K⁺, and Ca²⁺ in seedling dry matter in 121 traditional rice accessions and four improved rice genatypes under salinity stress and control conditions. The experiment was conducted as a randomized complete block design with four replicates. Seedlings were raised for three days in Yoshida solution with an electrical conductivity (EC) of 6 dS/m and then exposed to a EC 12 dS/m salinity level for fourteen days. Salinity tolerance was assessed using a standard visual scoring system. Na⁺, K⁺, and Ca²⁺ contents were measured using a flame photometer. Salinity tolerance levels were inversely correlated with Na⁺, Ca²⁺, and Na:K ratio, and positively correlated with K⁺. Inverse relationships were observed between K⁺ and both Na⁺ and Ca²⁺, suggesting antagonism, while a positive correlation existed between Na⁺ and Ca²⁺. Analyzing shoot dry matter, Na⁺, K⁺, and Ca²⁺ contents in rice help to identify and select salinity tolerant rice genotypes by prioritizing those with higher K⁺ and lower Na⁺ and Ca²⁺ levels. The order of Na⁺, K⁺, and Ca²⁺ in the dry matter of tolerant and moderately tolerant rice genotypes highlights that the ion balance is genotype dependent and not the sole determinant of salinity tolerance in rice.  Further research is needed to determine the susceptibility of accessions to salinity stress, focusing on demonstrating decreased Na⁺ and Ca²⁺ contents, and increased K⁺ content across various stress scenarios and growth phases to understand their potential for salinity tolerance.