Inheritance of Ineffective Nodulation in Crimson Clover1

Abstract

A single plant of crimson clover (Trifolium incarnation L.) appearing to have ineffective nodules was identified under nil‐N conditions from a 1000‐pIant population of the cultivar Chief. The plant (designated CH‐I) had tiny, white, beaded nodules and only 2 cm of topgrowth. With the addition of N this plant was grown to maturity and self‐pollinated. S1 plants were inoculated with 11 different Rhizobium trifolii strains in replicated experiments, all resulting in an ineffective symbiosis. No segregation for effectiveness occurred in the S1 or S2 generations of the CH‐I line. Crosses were made between normal crimson clover lines and S1 lines of CH‐I. F1 populations were nodulated effectively with R. trifolii strain 162K13. The Fz generation segregated for symbiotic effectiveness when nodulated with strain 162K13. F2 populations from two crosses showed a good fit to a 3:1 ratio of normal to ineffective nodulation. Results indicate that non‐strain‐specific ineffective nodulation of crimson clover is controlled by a single recessive gene pair (rt1 rt2) with possible modifiers. Plants with this trait should be useful as non‐Nj fixing controls in 15N isotope dilution experiments and to study individual steps in N2 fixation.