The Inheritance of N2 Fixation Efficiency in Crimson Clover1

Abstract

Host plant genetics of N2 fixation efficiency in the crimson clover‐Rhizobium trifolii symbiosis was investigated using a diallel mating design and mass selection. Dinitrogen fixation was evaluated using the acetylene reduction assay. Plants were grown for 60 days prior to the assay in plastic pouches containing N free nutrient solution. Live plants were assayed using the plastic pouch to contain the gas mixture.Crosses differed significantly in acetylene reduction rate. In a combining ability analysis, both general and specific combining abillty were significant sources of variation. Only one of the six parental lines showed a significant, positive general combining ability effect. This line uniformly transmitted its high acetylene reducing ability to all but one of its progeny. In terms of variance components, specific combining ability was more important in determining the acetylene reduction rate than general combining ability for all lines tested. After one cyle of mass selection, acetylene reduction rate was increased 8%. The realized heritability of this trait was 63.1%.