Onion Flower Research Articles

The development of onion (Allium cepa L.) Embryo sacs in vitro and gynogenesis induction in relation to flower size

The development of embryo sacs (ES) in vitro and induction of gynogenesis were studied in onion flower bud culture. Explants were divided into three groups according to their size at inoculation: (a) small flower buds (2.3–3.0 mm in diameter); (b) medium flower buds (3.1–3.7 mm); and (c) large flower buds (3.8–4.4 mm). For histological study, excised ovaries were fixed at inoculation and then at 3-d intervals until day 12, and after 2 and 3 wk of culture. Some explants were cultured until embryo emergence, i.e., 3–5 mo. In total, 2592 ovules were examined histologically. At inoculation, 83% of ovules in small flower buds contained a megaspore mother cell; in 17% of ovules, two-nucleate ES occurred. In medium flower buds two-nucleate, four-nucleate, and mature ES were present at frequencies of 15%, 46%, and 40%, respectively. In large flower buds, only mature ES occurred. In vitro conditions did not disturb meiosis and megagametophyte development in non-degenerated ovules. Regardless of the developmental stage at inoculation, only mature ES occurred on day 12. Gynogenic embryos were found after 2 wk of culture, indicating that embryos developed in mature ES exclusively. Embryos were detected in 5.4% of histological studied ovules; however, the number of embryos after 3–5 mo. was higher (12.4%). The parthenogenetic origin of the embryos is discussed. In addition, ES containing endosperm only (6.5%) and both endosperm and embryo (0.4%) were observed.

Patterns of Floral Nectar Production of Onion (Allium cepa L.) and the Effects of Environmental Conditions

Successful pollination of onion (Allium cepa L.) flowers greatly depends on adequate nectar production. In order to understand the nectar production dynamics of onion flowers, nectar was collected at regular intervals during a 24-hour period. Hourly nectar volumes were compared to a variety of environmental conditions, including amount of solar radiation, relative humidity, temperature, wind speed, and evapotranspiration. Production patterns showed mid- to late-morning peaks and late evening peaks in nectar volume. Nectar appeared to be reabsorbed by the flowers during the afternoon and overnight hours. Individual flowers produced the highest amount of nectar several days after initially opening. Nectar production was significantly and inversely related to relative humidity while the effects of temperature, evapotranspiration, wind speed and solar radiation on nectar production were not significant in this study.

Honey bee (Hymenoptera: Apidae) foraging in response to preconditioning with onion flower scent compounds.

Onion (Allium cepa L.) seed production has long been plagued with yield problems because of lack of pollination by the honey bee, Apis mellifera L. To attempt to attract more pollinators to the onion seed production field, honey bees were conditioned to associate onion floral odor components with a reward. Isolated nucleus hives of honey bees were fed 30% sucrose solutions scented with a 0.2% solution of onion floral odor compounds. After feeding on these solutions for 6 wk, bees were not found to prefer onion flowers to two competing food sources, carrot and alfalfa flowers, at the 5% significance level. However, there was an overall trend indicating a change in honey bee behavior, with fewer "trained" bees visiting alfalfa and carrot and more visiting onion. Thus, it may be possible to alter honey bee behavior with preconditioning but probably not to a degree that would be economically significant.

Honey Bee (Hymenoptera: Apidae) Foraging in Response to Preconditioning with Onion Flower Scent Compounds

Honey Bee (Hymenoptera: Apidae) Foraging in Response to Preconditioning with Onion Flower Scent Compounds

Effect of Nectar Composition and Nectar Concentration on Honey Bee (Hymenoptera: Apidae) Visitations to Hybrid Onion Flowers

Floral nectar characteristics of nine inbred lines of onion (Allium cepa L.) were examined to determine their influence on the attractiveness of the onion flowers to honey bees (Apis mellifera L.). Potassium concentrations and sugar concentrations of the nectar did not significantly correlate with the number of bee visits received by an umbel. The average amount of nectar produced by both the umbels and the individual florets was significantly positively correlated with the number of bee visits. Our results suggest that selection for flowers with high nectar production may lead to a higher rate of pollination of the onion seed crop.

The Role of Temperature and Free Moisture in Onion Flower Blight

The cardinal temperatures at which onion umbels were blighted (after inoculation when two-thirds of the florets were open) with Botrytis squamosa, B. cinerea, and B. allii (isolated from blighted onion florets) were near 9, 21, and 27 C for B. squamosa, near 12, 21, and 30 C for B. cinerea, and near 9, 24, and 30 C for B. allii. The cardinal temperatures for mycelial growth (potato-dextrose agar) of B. squamosa, B. cinerea, and B. allii were near 5, 22, and 30 C for each fungus. The cardinal temperatures for conidial germination (on purified water agar) were near 6, 15, and 30 C for B. squamosa; 3, 18, and 33 C for B. cinerea; and 6, 24, and 33 C for B. allii. When the duration of free moisture on umbels after inoculation with the three pathogens was increased from 0 to 96 hr. the percentages of unopened florets, open florets, and immature seed capsules blighted at 21 C were increased significantly. Free moisture durations of 12-24, 6-12, and 6-12 hr were necessary for blighting of unopen florets, open florets, and immature seed capsules, respectively, by each pathogen at 21 C. A positive correlation between the amount of July rainfallmore » and the natural incidence of onion flower blight was observed in Orange County, New York, from 1976 to 1981. 10 references, 2 figures, 1 table.« less

Honeybee Colony Populations and Foraging Rates on Onion Seed-Fields in Arizona

SummaryData collected during 2 years showed that the frequency with which honeybee (Apis mellifera) foragers were caught on onion flowers (Allium cepa) and tagged was proportional to colony population. In each year, 3 sizes of population were studied by using hives with single, double or triple brood chambers. Nearly 3000 metal tags were recovered each year from foragers returning to the test colonies after having been tagged at stations within each of the onion fields. The number of tags recovered per colony was proportional to colony population in one year and almost proportional in the other. Colony weight gains and bees/min flying from hive entrances were also proportional to colony populations. Thus, it is concluded that the rate of remuneration for beekeepers providing honeybee colonies for onion pollination in Arizona should be directly proportional to the strength of the colony.

Effects of No-tillage and Herbicides on Carrot and Onion Seed Production1

Abstract Carrot roots (Daucus carota L.) and onion bulbs (Allium cepa L.) were planted in Kidman silt loam immediately after DCPA (dimethyl tetrachloroterephthalate), ethofumesate (2-ethoxy-2,3-dmydro-3,3-dimethyl-5-benzofuranol methanesulfonate), linuron (3-(3,4-dichlo-rophyenyl)-l-methoxy-l-methylurea), napropamide (2-(a-naphthoxy)N,N-diethylpropiona-mide), or trifluralin (a,a,a-trifluoro-2,6 dinitro-N,N-dipropyl-p-toluidine) had been soil incorporated. In a second experiment, carrot roots and onion bulbs were planted in a conventionally-prepared seed bed or among vigorously growing wheat plants (7 to 10 cm tall). DCPA, linuron, and oryzalin (3,5-dinitro-N4,N4-dipropylsulfanilamide) plus glyphosate (N-(phos-phonomethyl)glycine) were surface applied to these seedbeds after planting but prior to crop emergence. Methazole (2-(3,4-dichlorophenyl)-4-methyl-l,2,4-oxadiazolidine-3,5-dione) and nitrofen (2,4-dichlorophenyl-p-nitrophenyl ether) were applied postemergence. Chemical treatments significantly altered the seed yields within the no-tillage method. Carrots grown in the tilled plots exhibited no effect of chemical treatments on seed yield. Comparison of tillage methods indicated a highly significant reduction in carrot seed yield relative to the no-tillage plots. Those on the non-weeded control and no-tillage plots showed a highly significant reduction in seed yield. Many of the onion bulbs from male-fertile lines failed to develop seedstalks in the plots sprayed with linuron and napropamide and those that did were delayed in development. Linuron and ethofumesate reduced the numbers of onion flowers per umbel. Onions grown in the tilled plots exhibited no effect of chemical treatments on seed yield. Those on the non-weeded control and no-tillage plots showed a highly significant reduction in onion seed yield. Comparison of tillage methods indicated a highly significant reduction in onion seed yield relative to the no-tillage plots.

Underlying Benefits of Foraging Aggression in Egrets

tiveness of onion flowers to honey bees. Journal of the American Society for Horticultural Science 97:535-539. Watt, W. B., P. C. Hoch, and S. G. Mills. 1974. Nectar resource use by Colias butterflies. Oecologia 4:353-374. White, J. W., Jr., and 0. N. Rudyj. 1978. Proline content of United States honey. Journal of Apicultural Research 17:89-93. Wolf, L. L. 1975. Energy intake and expenditures in a nectar-feeding sun bird. Ecology 56:92-104. . 1978. Aggressive social organization in nectarivorous birds. American Zoologist 18:765-778. Wolf, L. L., F. R. Hainsworth, and F. B. Giil. 1975. Foraging efficiencies and time budgets in nectar-feeding birds. Ecology 56:117-128.

Etiology and Control of Onion Flower Blight

Etiology and Control of Onion Flower Blight

Potassium in Onion Nectar and its Probable Effect on Attractiveness of Onion Flowers to Honey Bees1

Abstract Levels of K in nectar of onion (Allium cepa L.) varied from 3600-13,000 ppm, about 10 times higher than that of nectar from competing flora tested. An open-pollinated amphidiploid derived from the interspecific cross A. cepa X A. fistulosum L. was the only onion with nectar K level as low as that of competing flora and it was more attractive to honey bees than was the common onion, A. cepa. Addition of K salts to sugar solutions at the rate of 1500, 3000, 4500, 6000, or 7500 ppm K clearly reduced uptake of these solutions by honey bees foraging at artificial-flower feeders. Thus, it appears that the levels of K in onion nectar are high enough to reduce the attractiveness of onion flowers to honey bees. It is suggested that pollination of onion flowers might be improved if nectar K levels can be reduced, either through a program of selective breeding or by altering cultural practices. An alternative solution might be to provide pollinators that readily accept the high K level present in onion nectar. This might be accomplished by preconditioning honey bees to accept high K levels in sugar solutions before they are moved to the onion seed fields, by developing a strain of honey bees with a preference for onion (high K) nectar, or by utilizing other species of pollinators.