Inbreeding and Heterosis in Red Clover¹

The effects of inbreeding and heterosis in red clover ( Trifolium pratense L.) were investigated in two experiments. Objectives were to study the effects of one generation of selfing on pseudo‐self‐compatibility (PSC) and on seed and forage characteristics, and to ascertain the degree of hybrid vigor obtained and its relation to persistence in single crosses of I 1 parents. In the first experiment, five I 0 parental clones and four I 1 clones from each of the five parents were compared in spaced‐planted field plots for PSC, cross‐compatibility, florets per head, and heads per plant. In all characteristics, some inbred families contained clones which equalled or exceeded their non‐inbred parents. In the second experiment, a diallel cross was made among four I 0 clones, and another among four I 1 clones (one from each I 0 ). Plants from these crosses and from open‐pollinated seed of the four I 0 's, and three varietal checks were compared for yield and persistence in spaced‐planted field plots, which also included vegetative propagules of the four I 0 and four I 1 clones. Hybrid vigor was expressed in the I 1 single crosses, but their yields were no greater than the single crosses of the parental I 0 clones. I 1 clones yielded as much and were as persistent as I 0 clones, but both yield and persistence were less than other non‐inbred materials, except for the varietal checks and O.P.'s of I 0 clones. It was inferred that inbred parental lines may be maintained either by seed through PSC or by vegetative reproduction, and that yield and persistence lowered by selfing will be regained in single crosses.