Seed size effects on growth and N-2 fixation of juvenile sainfoin

Seed size of forage legumes influences seedling establishment and vigor. Two studies were conducted to examine the effects of seed size on growth and N-2 fixation of juvenile sainfoin (Onobrychis viciifolia Scop.). In two growth chamber experiments, 'Remont' sainfoin was evaluated for nodulation, plant height, dry matter yield, N concentration, and acetylene reduction activity (ARA). Seedlings from large seed emerged faster, had more nodules, and had higher N-2 fixation rates at most harvest dates up to 84 d. Across all harvests, seed size accounted for 60, 81, 87, 90, and 98% of the variability in mean ARA, nodule number, total plant N content, plant dry weight, and plant height, respectively. The superiority of seedlings from large seed was not due to increased relative growth rates. Two Remont seed lots that differed in seed weight distributions had similar ARA and shoot dry weight patterns, but varied in their correlations between ARA and seed size. It appears that the factors influencing seed size also affected subsequent seedling behavior of these two seed lots. Divergent individual plant selections for high or low ARA at 56, 70, or 84 d would have arisen from the largest or smallest seed size classes, respectively, if seed size effects had been ignored in a breeding program. Considerable variability for plant dry weight and ARA existed within seedlings from uniformly sized seed. We conclude that for breeding purposes, growth or ARA analyses of juvenile sainfoin should be conducted with sized seed in order to minimize seed-size effects and to better expose genetic variability in N-2 fixation.