Although alfalfa (Medicago sativa L.) is considered
an outcrossing species, the self-pollination
incidence during insect pollination can be
substantial, with an observed 30% average
selfing rate. Despite this, alfalfa breeders utilizing
space-plant evaluation nurseries make no
attempt to discriminate self-pollination-derived
progeny (selfs) from outcross progeny. Due to
alfalfa’s substantial inbreeding depression, the
selfed individuals have much lower breeder utility.
This study examines an alfalfa space-plant
breeding nursery in which selfed and outcross
progeny had been identified using DNA markers
for the following phenotypic traits: plant
vigor, fall height, fall dormancy, first and second
winter survival, plant lodging, and profusion of
flowering. Trait means, phenotypic and additive
variances, and narrow-sense heritabilities on a
halfsib mean basis were determined for selfed
and outcross progeny. For most traits, inbreeding
depression was severe, with approximately
80% reductions in performance. Selfed progeny
for most traits had reduced phenotypic variances
compared with outcross progeny. No differences
in estimated additive variance and heritabilities
were observed between the two types of progeny.
Assuming a 30% selfing rate and a selection
intensity less than or equal to 10%, we would
expect to select few if any selfed progeny from
a space-plant nursery that had plant vigor phenotypic
distributions observed in this study. The
estimated maximum loss in genetic gain due to
the presence of selfed progeny in breeding nurseries
for selection intensities from 1 to 10% was
estimated at a 10% genetic gain reduction. We
conclude that selfed progeny in breeding nurseries
are a hindrance, and if possible, they should
be minimized or eliminated.