Abstract
Natural variations in photosynthesis-related traits at an early vegetative stage of 8 grain sorghum varieties were examined. These varieties were divided into 3 phylogenetic groups according to the analysis of genetic polymorphisms using differences in 15 simple sequence repeats loci. Three varieties collected in Japan and Korea were clustered in one group while 5 varieties from 4 African countries were classified into 3 groups. There were significant differences among varieties in photosynthetic rate and 5 photosynthesis-related traits (ribulose-1,5-bisphosphate carboxylase/oxygenase, phosphoenolpyruvate carboxylase, nitrogen, soluble protein and chlorophyll contents per leaf area). However, there were no clear trends among the 3 genetic groups. Additionally, no correlations were detected between plant length (an indicator of growth rate) and photosynthesis-related traits, and plant length had a significant positive correlation with photosynthetic rate. In sorghum varieties, natural variation in photosynthesis-related traits might be used for breeding methods. At least at the early vegetative stage, growth rate was not limited by these photosynthesis-related traits. Therefore, other traits (e.g. sink) might be the target for improvement in the growth rate at the early vegetative stage.
