Two sorghum varieties( Liaoza 10 and Liaoza 19) were used as the plant materials and exogenous auxin( IAA) was sprayed on the plant leaves at the three-leaf stage with three concentrations of exogenous IAA( 0,100,200 mg·L~(-1),respectively). Effects of exogenous IAA application on endogenous hormone contents and tillering in sorghum were determined. Results showed that exogenous IAA application significantly affected the endogenous hormone contents of sorghum. Exogenous IAA application substantially increas...