Combining Ability in I₁ Single Crosses of Red Clover¹

A diallel cross involving 10 I 1 red clover ( Trifolium pratense L.) clones was evaluated for survival on four dates over a 3‐year period, 1973‐75, and vigor of growth on three dates in 1973 and 1974. Significant nonadditive genetic variance was found for survival in 1974 and 1975 and for vigor in 1973. This nonadditive portion of genetic variance was substantially greater than in a previous study involving I 0 clones and strengthens the case for production of hybrid red clover. Significant reciprocal effects were found for all traits except vigor in 1974. GCA effects of I 1 clones failed to agree with GCA effects of their I 0 parents in the previous study, possibly owing to chance selection of inferior I 1‐ segregates from superior I 0 clones, or to genotype ✕ environment interactions.