James B. Holland1, E. T. Bingham2
1Dep. of Crop Science Box 7620, North Carolina State Univ. Raleigh NC 27695‐7620
2Dep. of Agronomy 1575 Linden Dr., Univ. of Wisconsin‐Madison Madison WI 53706‐1597
Tóm tắt
Alfalfa (Medicago sativa L.) exhibits inbreeding depression for forage yield and also tends to set fewer seeds following self‐pollination than following cross‐pollination. The objectives of this study were to estimate changes in yield potential, inbreeding depression for yield, and self‐ and cross‐fertilities of alfalfa cultivars adapted to Wisconsin and representing different eras of breeding from 1898 to 1985. In addition, two University of Wisconsin‐Madison experimental cultivars with well‐known breeding histories were included in the study. The S0 and S1 populations derived from each cultivar were evaluated for 3 yr for forage yield. Self‐ and cross‐fertilities of some S0 populations were measured in a greenhouse study. Both S0 and S1 populations of modern (Era 3) cultivars yielded greater than those of the oldest (Era 1) cultivars. Era 3 S0 populations generally yielded more than those of cultivars released in the 1940s and 1950s (Era 2) but this was not true for S1 populations. These results suggest that favorable alleles have accumulated in modern alfalfa cultivars but that this mostly occurred between Eras 1 and 2. Inbreeding depression decreased between Eras 1 and 2 and increased between Eras 2 and 3. Increased heterozygosity or exploitation of nonadditive genetic effects may account for much of the improvement in cultivar yield potential that occurred between Eras 2 and 3. Era 3 cultivars had a significantly lower ratio of self‐fertility to cross‐fertility than Era 1 cultivars. Therefore, modern cultivars appear to have improved capacity to produce high proportions of cross‐pollinated seed when nonself pollen is available, compared with older cultivars.
