Purple‐flowered genotypes of alfalfa (Medicago saliva L.) that were simplex at the P locus (Pppp) were spaced planted and open‐pollinated within a seed production field of Blazer XL alfalfa. Self‐pollination in the field environment was estimated by the frequencies of purple‐ and cream‐flowered progeny from simplex plants. Natural purple‐flower color avoided pollinator preferences found with recessive flower colors. The background level of cream gametes (pp) in Blazer XL and the spaced simplex plants was 5% based on cream progeny of two cream (pppp) male‐sterile clones also planted in the field. Selfing averaged 28% based on greenhouse classified with no competition. Based on progeny that were transplanted in the field, selfing averaged 25% while selfing based on progeny seeded in the field averaged 13%. Direct seeding resulted in fewer cream progeny reflecting decreased survival in competition with hybrid progeny. We observed lower selfing percentages than previous estimates which used recessive flower color markers, but our results were similar to a recent allozyme study.
A recently discovered female‐sterile trait in alfalfa (Medicago sativa L.) was used as a male pollenizer along with three cytoplasmic male‐sterile clones to study the feasibility of mixed plantings for hybrid alfalfa seed production. Rows with mixed stands of male‐sterile (seed parent) and female‐sterile (pollenzier) clones produced significantly more seed than alternate rows of seed parent and pollenizer clones. Leafcutter bees [Megachile rotundata (Fabricius)] served as pollinators. Significant differences were noted among cytoplasmic male‐sterile clones for seed set. Their average yield was only 76% of the first‐year seed yield in an adjacent experiment. Commercial lines with the femalesterile trait and more attractive cytoplasmic male‐steriles are needed before hybrid seed yields will equal those of conventional synthetics.
Two alfalfa (Medicago sativa L.) cultivars in commercial production were used to study isolation distance for foundation seed production using insect resistance traits as genetic markers. Twenty‐one seed samples were obtained for comparison with foundation and certified seed lots. Spotted alfalfa aphid [Therioaphis maculata (Buckton)] resistance values indicated adequate isolation at 0.4 km (1,320 feet) and no shift in resistance from breeder seed to the foundation seed generation. Resistance to pea aphid [Acyrthosiphon pisum (Harris)] could not be used to measure cross‐fertilization between cultivars because the range of resistance overlapped between cultivars.
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