Delaying onion planting to control onion maggot (Diptera: Anthomyiidae): efficacy and underlying mechanisms

Onion maggot, Delia antiqua (Meigen) (Diptera: Anthomyiidae), is an important pest of onion, Allium cepa L., in northern temperate areas, especially in the Great Lakes region of North America Management of D. antiqua relies on insecticide use at planting, but insecticide resistance can cause control failures that threaten the long-term viability of this strategy. Delaying the time onions are planted was investigated as an alternative management approach for D. antiqua and the ecological and behavioral mechanisms underlying host age and insect relationships were examined in laboratory and field experiments. Delaying onion planting by two to four weeks reduced damage to onions by 35 and 90%, respectively. Onions planted later emerged later and this reduced the period overwintered flies had to oviposit on the plants. Moreover, flies tended to lay few to no eggs on these young, late-planted onions. As anticipated, D. antiqua laid 4-8 times more eggs on older onions than on young onions, and older onions were more resilient to injury caused by D. antiqua neonates compared with younger onions. However, the resiliency to maggot attack lessened as the density of D. antiqua increased from 2 to 10 eggs per plant, which probably explains why greater levels of maggot damage are typically observed in early onion plantings compared with later plantings. Delaying onion planting until mid-May reduced D. antiqua damage without jeopardizing the period required to produce marketable yield, but this cultural tactic must be combined with other management strategies to prevent economic loss.     

The response of growth rate to temperature in seedlings of several Allium crop species

Relative growth rates (R_w), leaf area ratios (LAR), net assimilation rates (NAR), and leaf weight ratios (LWR) were estimated for seedlings of onion, leek, Japanese bunching onion and chives grown at constant temperatures of 10, 12, 15, 19, 23, 27 and 31 C. R_w was greatest at 19 C in Japanese bunching onion and chives, and at 27 C in onions and leeks. R_w increased approximately linearly between 10 and 19 C in all species; between 19 and 27 C it either increased further, decreased or remained constant depending on species but at 31 C R_w was lower than the maximum in all cases. LAR's were greatest at 27 C in onions and leeks and at 23 C in the other two species. Between 10 and 19 C both LAR and NAR increased in all species. Between 19 and 27 C increases in LAR were compensated for by decreases in NAR with the result that R_w showed little change with temperature. Averaging over all temperatures the species were ranked in order of decreasing R_w, NAR and LWR as onion, leek, Japanese bunching onion and chives. For LAR this ordering was reversed with respect to onions and leeks. Plant to plant variability increased in the order onion, leek, Japanese bunching onion then chives. Although onions were the fastest growing of the Alliums tested their R_w was lower than that of several other vegetable species for which R_w was similarly measured.     

Fate of foodborne pathogens on green onions and tomatoes by electrolysed water

Aims: To investigate the efficacy of electrolysed water (EW) in killing Escherichia coli O157:H7, Salmonella typhimurium and Listeria monocytogenes on the surfaces of spot‐inoculated green onions and tomatoes. Methods and Results: Green onions and tomatoes were inoculated with a cocktail of three strains each of E. coli O157:H7, Salm. typhimurium and L. monocytogenes and treated with acidic electrolysed water (AC‐EW), alkaline electrolysed water (AK‐EW), alkaline electrolysed water followed by acidic electrolysed water (AK‐EW + AC‐EW), deionized water followed by acidic electrolysed water (DW + AC‐EW) and deionized water (control, DW) for 15 s, 30 s, 1 min, 3 min and 5 min at room temperature (22 ± 2°C). The relative efficacy of reduction was AC‐EW > DW + AC‐EW ≈ AK‐EW + AC‐EW > AK‐EW > DW. Conclusions: Acidic EW treatment was able to significantly reduce populations of the three tested pathogens from the surfaces of green onions and tomatoes with increasing exposure time. Significance and Impact of the Study: Rinsing in acidic EW reveals an effective method to control the presence of E. coli O157:H7, Salm. typhimurium and L. monocytogenes on the surfaces of fresh green onions and tomatoes, without affecting their organoleptic characteristics. This indicates its potential application for the decontamination of fresh produce surfaces.     

Cyromazine seed treatments to control onion maggot, Delia antiqua, on green onions

Cyromazine seed treatments were evaluated for onion maggot control in green onion crops. The more tolerant to organophosphates of two populations of onion maggots was chosen for further research, based on the results of adult assays in a Potter spray tower. In the laboratory, first-instar mortality was compared between film-coated seed treatment and soil drench treatment. The LC50 for the film-coated seed treatment was approximately one fourth that of the soil drench treatment. In choice assays, no significant difference was observed between the number of eggs deposited on seedlings grown from film-coated seeds with cyromazine and film-coated seeds without cyromazine. Field studies demonstrated that all rates of cyromazine seed treatment resulted in protection of onion plants from onion maggot damage. Green onions may not require as high a rate of cyromazine for control of onion maggots as the rate established for use in dry onions for two reasons: the seeding rate is much higher for green onions resulting in more AI/ha for a given amount of AI/kg of seed, and a given percentage of stand loss is more difficult to detect in green onions than in dry onions.     

Cultural and insecticidal control of Thrips tabaci on onions in the Sudan

Onion thrips (Thrips tabaci) is the major pest of onions in the Sudan. In the Gezira Scheme onions are normally transplanted between October and January when the thrips population is very low. Later, thrips commence to breed. Early transplanted onions were well established before infestations became severe and, without the need for insecticidal control, produced significantly higher yields. Onions transplanted later, when thrips began to multiply, produced lower yields. Depending on the duration and intensity of infestation three to five sprays applied at fortnightly intervals were required to control thrips on the late transplanted crop. The effect of spray frequency on the development and yield of onions was investigated and the response found to be solely due to the extent of thrips control achieved. The toxicant itself had no effect on growth. Although the leaves were unaffected by the various treatments, spraying when most thrips were present increased fresh and dry leaf weights, bulb weight and, in the Hudeiba cultivar, the proportion of flowering plants. With the late-transplanted crop, light infestations led to yield losses of at least 39% whilst severe thrips attacks reduced the crop by 57%.     

Gold color in onions (<Emphasis Type="Italic"> Allium cepa</Emphasis>): a natural mutation of the chalcone isomerase gene resulting in a premature stop codon

Unusual gold-colored onions were selected from a F₃ family originating from a cross between US-type yellow and Brazilian yellow onions. HPLC analysis showed that the gold onions contained a significantly reduced amount of quercetin, the most abundant flavonoid in onions. This result indicated that an early step in the flavonoid biosynthesis pathway might be abnormal in these onions. The expression of flavonoid synthesis genes isolated from onions was examined in gold onions and compared to that in onions of other colors by RT-PCR. The results showed that all genes were transcribed in gold onions as in red onions. In order to identify any critical mutations in flavonoid synthesis genes encoding enzymes involved in early steps of the pathway, the genomic sequence of chalcone isomerase (CHI) was obtained. A premature stop codon and a subsequent single base-pair addition causing a frameshift were identified in the coding region of the CHI gene in the gold onions. Co-segregation of the mutant allele of the CHI gene and the gold phenotype was investigated in the original F₂ segregating population. Genotyping of three color groups (red, yellow and gold) of F₂ onions revealed perfect co-segregation of the mutant CHI allele with the gold phenotype. All tested gold F₂ onions were homozygous for the mutant CHI allele. This perfect co-segregation implies that the presence of a premature stop codon in the gold CHI gene results in an inactive CHI. Inactivation of CHI results in a block in the flavonoid biosynthesis pathway and the accumulation of chalcone derivatives, including a yellow pigment which might be responsible for the gold color in onions.Communicated by R. Hagemann     

Overwintering locations and hosts for onion thrips (Thysanoptera: Thripidae) in the onion cropping ecosystem in New York

Identifying locations where onion thrips, Thrips tabaci Lindeman (Thysanoptera: Thripidae), overwinter and subsequently disperse is important for designing control strategies. In upstate New York from 2003 through 2006, potential overwintering sites in the commercial onion, Allium cepa L., cropping system were investigated early in the spring before onion seedling emergence and again late in the season after onions were harvested. Onion thrips adults were sampled directly from the soil and indirectly from the soil by using emergence cages. Sampling locations included onion field interiors and edges and areas outside of these fields, including woods. Host material sampled included onion culls; volunteer onions, which sprout from cull onions left behind after harvest; and weeds. Onion thrips adults were found in all sections of onion fields and in locations outside of onion fields, with the fewest emerging from woods. Emergence began in early May and extended into June. Peak emergence occurred during the last half of May, at which time 50-75% of the population had emerged. Adults colonized volunteer onions as early as late March and as late as mid-November. No adults were found overwintering in onion cull piles. Adults also colonized several weed species, especially pigweed, Amaranthus hybridis L., and lambsquarters, Chenopodium album L., late in the fall. Our results indicate that onion thrips adults overwinter in the soil within and near onion fields and that they probably colonize volunteer onion plants before subsequent generations infest the onion crop in the spring. Volunteer onions and weeds also provide onion thrips with a host after onions are harvested. Consequently, onion thrips management strategies should include tactics that reduce volunteer onion and weed abundance.     

Effect of Onions on Blood Fibrinolytic Activity

Twenty-two convalescent patients at rest were given a fat-enriched breakfast with and without the addition of 60 g. of fried or boiled onions. Both forms of onions were found to prevent the expected decrease in fibrinolytic activity, and indeed the latter was actually increased.     

Temperature-dependent survival of hepatitis A virus during storage of contaminated onions

Pre- or postharvest contamination of green onions by hepatitis A virus (HAV) has been linked to large numbers of food-borne illnesses. Understanding HAV survival in onions would assist in projecting the risk of the disease associated with their consumption. This study defined HAV inactivation rates in contaminated green onions contained in air-permeable, moisture-retaining high-density polyethylene packages that were stored at 3, 10, 14, 20, 21, 22, and 23°C. A protocol was established to recover HAV from whole green onions, with 31% as the average recovery by infectivity assay. Viruses in eluates were primarily analyzed by a 6-well plaque assay on FRhK-4 cells. Eight storage trials, including two trials at 3°C, were conducted, with 3 to 7 onion samples per sampling and 4 to 7 samplings per trial. Linear regression correlation (r(2) = 0.80 to 0.98) was observed between HAV survival and storage time for each of the 8 trials, held at specific temperatures. Increases in the storage temperature resulted in greater HAV inactivation rates, e.g., a reduction of 0.033 log PFU/day at 3.4 ± 0.3°C versus 0.185 log PFU/day at 23.4 ± 0.7°C. Thus, decimal reduction time (D) values of 30, 14, 11, and 5 days, respectively, were obtained for HAV in onions stored at 3, 10, 14, and 23°C. Further regression analysis determined that 1 degree Celsius increase would increase inactivation of HAV by 0.007 log PFU/day in onions (r(2) = 0.97). The data suggest that natural degradation of HAV in contaminated fresh produce is minimal and that a preventive strategy is critical to produce safety. The results are useful in predicting the risks associated with HAV contamination in fresh produce.     

Control of stem nematode, Ditylenchus dipsaci, in onions, by granular nematicides applied to the soil

Aldicarb at 1.4–5.6 kg a.i. ha^-l or oxamyl at 1.3–5.2 kg a.i. ha^-1 applied over the seed furrows during sowing prevented much of the damage resulting from stem nematode attack in spring-sown onions. Rotting of bulbs in store due to stem nematode infestation was sometimes lessened by these treatments. Neither sowing onion seeds on soil ridges, nor applying aldicarb in two equal doses, one over the seed furrows during sowing, the other over the plants mid-season, controlled the nematode better or increased onion yields more than a single equivalent dose over the seed furrows. Applied as two doses in this way, aldicarb was sometimes more effective against the nematode in summer-sown onions than was an equivalent amount applied over the seed furrows during sowing. Only 2.5 kg or less aldicarb ha^-1 can be applied to onions without leaving unacceptable residues (>0.15 μg g^-1) in the harvested bulbs.     

The role of onion-associated fungi in bulb mite infestation and damage to onion seedlings

In Israel Rhizoglyphus robini is considered to be a pest in its own right, even though the mite is usually found in association with fungal pathogens. Plant protection recommendations are therefore to treat germinating onions seedlings, clearly a crucial phase in crop production, when mites are discovered. The aim of this study was to determine the role of fungi in bulb mite infestation and damage to germinating onion seedlings. Accordingly we (1) evaluated the effect of the mite on onion seedling germination and survival without fungi, (2) compared the attraction of the mite to species and isolates of various fungi, (3) assessed the effect of a relatively non-pathogenic isolate of Fusarium oxysporum on mite fecundity, and (4) determined the effects of the mite and of F. oxysporum separately and together, on onion seedling germination and sprout development. A significant reduction of seedling survival was recorded only in the 1,000 mites/pot treatment, after 4 weeks. Mites were attracted to 6 out of 7 collected fungi isolates. Mite fecundity on onion sprouts infested with F. oxysporum was higher than on non-infested sprouts. Survival of seedlings was affected by mites, fungi, and their combination. Sprouts on Petri dishes after 5 days were significantly longer in the control and mite treatments than both fungi treatments. During the 5-day experiment more mites were always found on the fungi-infected sprouts than on the non-infected sprouts. Future research using suppressive soils to suppress soil pathogens and subsequent mite damage is proposed.     

Preinoculation of lettuce and onion with VA mycorrhizal fungi reduces deleterious effects of soil salinity

The hypothesis that inoculation of transplants with vesicular-arbuscular mycorrhizal (VAM) fungi before planting into saline soils alleviates salt effects on growth and yield was tested on lettuce (Lactuca sativa L.) and onion (Allium cepa L.). A second hypothesis was that fungi isolated from saline soil are more effective in counteracting salt effects than those from nonsaline soil. VAM fungi from high- and low-salt soils were trap-cultured, their propagules quantified and adjusted to a like number, and added to a pasteurized soil mix in which seedlings were grown for 3–4 weeks. Once the seedlings were colonized by VAM fungi, they were transplanted into salinized (NaCl) soil. Preinoculated lettuce transplants grown for 11 weeks in the saline soils had greater shoot mass compared with nonVAM plants at all salt levels [2 (control), 4, 8 and 12 dS m^–1] tested. Leaves of VAM lettuce at the highest salt level were significantly greener (more chlorophyll) than those of the nonVAM lettuce. NonVAM onions were stunted due to P deficiency in the soil, but inoculation with VAM fungi alleviated P deficiency and salinity effects; VAM onions were significantly larger at all salt levels than nonVAM onions. In a separate experiment, addition of P to salinized soil reduced the salt stress effect on nonVAM onions but to a lesser extent than by VAM inoculation. VAM fungi from the saline soil were not more effective in reducing growth inhibition by salt than those from the nonsaline site. Colonization of roots and length of soil hyphae produced by the VAM fungi decreased with increasing soil salt concentration. Results indicate that preinoculation of transplants with VAM fungi can help alleviate deleterious effects of saline soils on crop yield.     

Social facilitation of fur rubbing behavior in white-faced capuchins

In their natural environment, capuchins select certain plants, containing secondary compounds with bactericide, insecticide or fungicide properties, to rub their pelage energetically (i.e. fur rubbing). Fur rubbing can be performed in solitary, or collectively in subgroups of variable size and composition, and most of the time fur rubbing happens in synchrony with other group members. The aim of this study is to understand the underlying mechanisms of this phenomenon, and, more particularly, to determine the processes involved in its synchronization. For this purpose, we designed a set of experiments where white-faced capuchins (Cebus capucinus) were presented with onions (Allium cepa) that they use to fur rub. We conducted a detailed kinetic study of fur rubbing behavior to determine if its synchronization is the consequence of simultaneous responses of different individuals to the same stimulus or if, on the contrary, there is a real collective phenomenon where individuals respond to conspecific behavior. Our results reveal that fur rubbing is a collective behavior with a mimetic underlying mechanism. If fur rubbing with onions (a plant with antifungal and repellent properties) allows capuchins to treat their fur against parasites or pathogens, its synchronization would optimize the treatment by acting as a group barrier to ectoparasite propagation.     

Experiments on the control of white rot (Sclerotium cepivorum Berk.) in onions

Experiments-made during 1943 and 1944 on the use of mercurous chloride (calomel) for the control of Sclerotium cepivorum in spring-sown onions are described. The application of 4% calomel dust to the seed drill at sowing time gave better results than seed treatment. 1 lb. of dust per 25 yd. of seed drill gave good disease control in bulb onions, and 1 lb./so yd. may suffice for salad onions.
The relation between disease control and the effective mercury content of the treated soil is discussed.     

The possible contribution of electron microscopy to the understanding of the mechanism of non-disjunction in man.

Sprout inhibition of onion bulbs can be effectively accomplished by low doses of radiation [2,3]. However, wholesomeness data on irradiated onions, particularly with respect to their mutagenic activity, are still insufficient for evaluation [6]. Therefore we examined the mutagenic activity of irradiated onions in bacterial systems. Because onion bulbs contain a considerable amount of free amino acids, we used indicator strains carrying the marker for mutagenicity other than the amino acid requirement.In this paper we describe the results on irradiated onions. We used tests with solid and liquid media, assaying for the streptomycin (SM) dependence in a strain having a tetracycline (TC)-resistance factor, as well as DNA repair tests using two sets of indicator strains.     

Control of Botrytis cinerea and Botrytis squamosa in overwintered salad onions by fungicide sprays

In 1974/75, 13 sprays of 0·2% a.i. thiram applied at 14 day intervals to overwintered salad onions reduced the incidence of Botrytis cinerea and significantly increased onion yields. In 1977/78 both B. cinerea and B. squamosa occurred, and 12 iprodione sprays at 0·1% a.i. applied at 14-day intervals or 6 sprays at 0·2% a.i. applied at 28-day intervals gave good control of B. cinerea and B. squamosa and significantly increased onion yields. Benomyl (0·1% a.i. at 14-day intervals, or 0·2% a.i. at 28-day intervals) failed to control either pathogen because of the development of carbendazim-insensitive strains of the fungi. Effective control of both pathogens and increased yields were obtained with an application of 0·4% a.i. thiram in October and November followed by an application of 0·2% a.i. iprodione in December and January.     

Marker-assisted genotype analysis of bulb colors in segregating populations of onions (Allium cepa)

Bulb color in onions (Allium cepa) is an important trait whose complex inheritance mechanism involves epistatic interactions among major color-related loci. Recent studies revealed that inactivation of dihydroflavonol 4-reductase (DFR) in the anthocyanin synthesis pathway was responsible for the color differences between yellow and red onions, and two recessive alleles of the anthocyanidin synthase (ANS) gene were responsible for a pink bulb color. Based on mutations in the recessive alleles of these two genes, PCR-based markers for allelic selection were developed. In this study, genotype analysis of onions from segregating populations was carried out using these PCR-based markers. Segregating populations were derived from the cross between yellow and red onions. Five yellow and thirteen pink bulbs from one segregating breeding line were genotyped for the two genes. Four pink bulbs were heterozygous for the DFR gene, which explains the continuous segregation of yellow and pink colors in this line. Most pink onions were homozygous recessive for the ANS gene, except for two heterozygotes. This finding indicated that the homozygous recessive ANS gene was primarily responsible for the pink color in this line. The two pink onions, heterozygous for the ANS gene, were also heterozygous for the DFR gene, which indicated that the pink color was produced by incomplete dominance of a red color gene over that of yellow. One pink line and six other segregating breeding lines were also analyzed. The genotyping results matched perfectly with phenotypic color segregation.     

Effects of pre-inoculation with a vesicular-arbuscular mycorrhizal fungus on growth of onions transplanted to the field as multi-seeded peat modules

Summary A 1984 field experiment tested the effect of inoculation with a vesicular-arbuscular mycorrhizal fungus on yield of onions (Allium cepa L. cv. Balstora) grown under commercial conditions from seedlings raised in peat modules. Roots in commercial blocking compost (M 64) could not be infected, so a modified peat, containing 50% of sterilized clay soil, was used to produce mycorrhizal seedlings. Treatments to seedlings were: uninoculated in M64 compost (K), uninoculated in modified medium (NM) and inoculated withGlomus mosseae in modified medium (M). There were two blocks of plots, one irrigated, one not. At harvest the yields of marketable (>20 mm bulb diameter) onions from M seedlings were generally about twice those from NM seedlings. On non-irrigated plots M seedlings yielded 30.3 tha⁻¹, slightly less than did K seedlings (36.6 t ha⁻¹). On irrigated plots M seedlings yielded 35.3 t ha⁻¹ and K seedlings 34.9 t ha⁻¹, but this difference was not significant. Differences in size of bulbs at harvest were small even though rates of vegetative growth differed markedly between treatments during crop development. Variations in final yield arose largely from differences in numbers of onions that failed to bulb (thicknecks). Irrigation increased mean bulb weight in all treatments but also markedly increased the number of thicknecks. Unexpectedly, the increase in thicknecks was much less in inoculated plants. This effect of mycorrhizal infection did not seem to be related to improved phosphorus nutrition.