Analysis of root morphology characteristics of germplasm resources of different rice subspecies under salt stress

【Objective】This study aimed to analyze the root morphological characteristics of different rice subspecies under salt stress，elucidate their coping strategies，and identify germplasm resources with excellent root characteristics under salt stress， providing a theoretical basis for breeding salt-tolerant and high-yield rice varieties.【Method】Using 23 indica，35 japonica，and 17 AUS rice germplasm resources as experimental materials，and a hydroponic experiment of salt stress treatment at the seedling stage （adding 125 mmol/L NaCl to rice nutrient solution） was conducted， and 12 root morphological indexes were measured. Multiple statistical methods，including correlation analysis，principal component analysis （PCA），linear regression，and membership function were employed to comprehensively evaluate root morphological characteristics of different rice subspecies under salt stress.【Result】Among different rice subspecies，indica rice exhibited the highest mean values of salt tolerance level （5.0）， followed by japonica rice （4.0） and AUS rice （3.6）. The root total number，total length of 0-0.5 mm root，total length of 0.5-1.0 mm root，total root surface area， and total root volume of indica rice were extremely significantly higher than those of japonica rice and AUS rice （P<0.0001）. Correlations among the 12 root traits varied across the three rice subspecies. In PCA， two principal components for each subspecies were extracted，with cumulative contribution rates of 85.638% for indica rice，83.277% for japonica rice，and 80.342% for AUS rice. Linear regression identified four key indexes of root morphology under salt stress for different rice subspecies： for indica rice were root total number，total length of 0.5-1.0 mm root，total root surface area，and total root volume； for japonica rice were total root surface area，total length of 0.5-1.0 mm root，total surface area of 0-0.5 mm root， and root total number； for AUS were total volume of 0-0.5 mm root，total volume of 0.5-1.0 mm root，total root volume， and root average diameter. Through comprehensive evaluation of D values and salt tolerance level，salt-tolerant germplasms with excellent root morphological characteristics were identified in each subspecies： Vary Vato 462 （indica rice），Ta Mao Tsao （japonica rice），and DJ 24 （AUS rice）.【Conclusion】Under salt stress，indica rice generally outperform japonica rice and AUS rice in root morphological traits，with obviously different coping strategies among them.