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.
Multiple pest resistant alfalfa (Medicago sativa L.) cultivars in commercial production were used to study cross‐pollination along contiguous borders using contrasting levels of disease and insect resistance. Twenty‐eight seed samples were obtained from each of 3 cultivars and 26 from the fourth cultivar. In 110 sample comparisons with foundation and certified lots, only five departures from expected levels of resistance were found. Departures appeared to be random in relation to distance from foreign pollen source and leafcutter bee, Megachile rotundata (F.), locations and were interpreted as sampling variations. Thus the data indicated that isolation requirements for production of certified seed in fields larger than 2 ha using M. rotundata (F.) as pollinators could be less stringent than current standards without sacrificing the integrity of the cultivar.
The purpose of this study was to compare seed yields from breeder and foundation seed classes of eight alfalfa (Medicago sativa L.) cultivars, ‘Agate’, ‘Arc’, ‘Cody’, ‘Dawson’, ‘Kanza’, ‘Ramsey’, ‘Ranger’, and ‘Vernal’. Breeding methods used in developing the cultivars and generations of synthesis of breeder and foundation seed classes varied among cultivars. Breeder and foundation seed of the eight alfalfa cultivars were seeded at 2.2 kg/ha in a randomized block split‐plot design of cultivars as main plots and seed classes as subplots with three replications in a field near Caldwell, Idaho, in the spring of 1976. The experiment was managed to maximize seed yield. Seed yields were determined in 1977 and 1978. Seed yields obtained from breeder seed averaged over eight alfalfa cultivars were lower than those obtained from foundation seed in 1977 and for the 1977–1978 average. Seed yields obtained from breeder seed were lower than those obtained from foundation seed for two of eight cultivars, Ramsey and Vernal, in 1977 and for the 1977–1978 averages. Alfalfa breeders need to conduct seed yield tests that include at least one commercial seed generation of their experimental cultivars compared with a check cultivar.
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