Seed Production Fields Research Articles

Occurrence of the Wheat Stem Maggot, Meromyza americana Fitch (Diptera: Chloropidae), in Intermediate Wheatgrass, Thinopyrum intermedium (Host) Barkworth and D. R. Dewey (Poaceae), in Oklahoma1

The wheat stem maggot is primarily an economic pest of wheat, Triticum aestivum L.; barley, Hordeum vulgare L.; and cereal rye, Secale cereale L. (Poaceae) (Gilbertson, 1925; Allen and Painter, 1937; Rockwood et al., 1947). The larva of the wheat stem maggot enters the culm above the terminal node and feeds within the culm. Consequently, the developing inflorescence withers and dies and turns white in color. The aborted inflorescences are very noticeable among non-infested inflorescences. In Oklahoma, wheat stem maggot infestations have been reported to occur in seed production fields of bermudagrass, Cynodon dactylon var. dactylon (L.) Pers., and weeping love grass, Eragrostis curvula (Schrad.) Nees (Arnold and Ahring, 1987; Kindler et al., 1989). These were the first reported cases of wheat stem maggot to economically impact important warm-season forage grasses. Kindler et al. (1989) reported the percentage of aborted inflorescence in weeping lovegrass ranged from 3.2 to 22.6%. Intermediate wheatgrass, Thinopyrum intermedium (Host) Barkworth and D.R. Dewey, is an introduced forage grass that is used for pasture and hay for livestock in the Northern Great Plains, the Central and Southern High Plains, and much of the western United States. In the Southern Plains, research has shown that perennial, cool-season forage grasses do not persist through prolonged drought. Gillen and Berg (2005) reported a 95% reduction in stand due to drought where precipitation from September 2001 through May 2002 measured 62% of normal. Seeds from surviving plants from pastures used by Gillen and Berg were harvested in June 2002 and increased at the USDA-ARS Southern Plains Range Research Station, Woodward, Oklahoma. It was anticipated that progeny from these plants would have increased tolerance to drought. In late June 2006, aborted inflorescences of intermediate wheatgrass were found in a seed production block at Woodward. Aborted inflorescences were collected from the plot on 30 June, placed in Erlenmeyer flasks containing about 300 ml of tap water, and caged by placing them in a clear plastic bag with a nylon mesh screen on two sides to determine which insect was responsible (Kindler et al., 1989). Adult flies emerged 15–20 days later and were identified as wheat stem maggot using the keys of Sabrosky (1935) and Fedoseeva (1971). The percentage of aborted inflorescences was determined from randomly sampling 10 quadrats (30 3 30 cm) and ranged from 10 to 28%. Accordingly, the wheat stem maggot was confirmed as a pest of intermediate wheatgrass in Oklahoma which is a new host record. Voucher specimens were deposited at the K. C. Emerson Entomological Museum, Oklahoma State University, Stillwater.

Carrot seed germination and vigor in response to temperature and umbel orders

Several factors may influence carrot (Daucus carota L.) crop establishment. High temperatures (35 - 40°C), for instance, may delay or inhibit carrot seed germination in the field and so compromise the stand establishment. Carrot seeds from superior umbel orders usually have better physiological quality than those of lower umbel orders. These seeds from superior umbel orders may also show a better performance in adverse conditions. In addition, seeds from different ages show differences in vigor, which affect the stand establishment, mainly under adverse conditions. The aim of this study was to verify the germination at high temperatures and the carrot seed vigor of different umbel orders of 'Brasília', as well as the different 'Alvorada' seed lots. Preliminarily, 'Brasilia' seeds were incubated at temperatures ranging from 20 to 36°C. Also, seeds from the primary, secondary and tertiary umbel orders harvested separately from a basic seed production field and seeds from lots harvested in 1998, 1999 and 2000 were analyzed to the following tests: germination at 20°C (optimum) and 35°C (adverse), accelerated aging, cold test, seedling emergence in greenhouse and mass of 100 seeds. High temperatures reduced carrot seed germination. Seeds germinated better at 20°C than 35 or 36ºC. Seeds from primary and secondary orders, as well as less aged seed lots, had higher vigor and germination at high temperature.

OCORRÊNCIA DO NEMATÓIDE DE CISTO DA SOJA (Heterodera glycines) NOS MUNICÍPIOS DE VIANÓPOLIS E RIO VERDE (GO)

The soybean cyst nematode ( Heterodera glycines ) was found in Goias State in Chapadao do Ceu in 1991-1992. Until 1996-1997, this nematode had spread all over six towns of Goias State. Samples of soil were collected in Vianopolis and Rio Verde in 1997-1998. Samples from Vianopolis were collected in seed production fields and analised in the Laboratory of Phytopathology of Escola de Agronomia — Universidade Federal de Goias. Samples collected in Rio Verde were analised in the Laboratory of Phytopathology of ESUCRV - FESURV where the race 3 of H. glycines was identified. Up to now there are eight towns in Goias State with H. glycines occurrence. KEY-WORDS: Glycine max ; Heterodera glycines .

Tilletia vankyi, a new species of reticulate-spored bunt fungus with non-conjugating basidiospores infecting species of Festuca and Lolium

A bunt fungus, exhibiting a spore germination pattern unique to known reticulate-spored species of Tilletia was found infecting plants in seed production fields of Festuca rubra ssp. rubra (red fescue) and F. rubra ssp. fallax (Chewing's fescue) in Oregon, and in seed lots of Lolium perenne (perennial ryegrass) from Australia and Germany. Teliospores germinated to form 20–40 uninucleate, non-conjugating basidiospores, and colonies derived from single basidiospores produced teliospores in culture. In inoculation studies using single basidiospore colonies, perennial ryegrass and L. perenne ssp. multiflorum (Italian or annual ryegrass) were infected. A phylogenetic analysis, based on ITS region rDNA, eukaryotic translation elongation factor 1 alpha, and the second largest subunit of RNA polymerase II demonstrated that the fescue and ryegrass bunts are conspecific, and distinct from known species of Tilletia.

Impact of alpha‐cypermethrin on honey bees foraging on spring oilseed rape (Brassica napus) flowers in field conditions

Cruciferous oil-bearing crops have gained in importance worldwide. The expansion of the growing area of these crops has caused a proliferation of pests. Exposure to organophosphate, carbamate and pyrethroid insecticides has been associated with bee poisoning in food crops. This study examines the repellent effect of alpha-cypermethrin on the number of foraging honey bees, Apis mellifera L., on fields of spring oilseed rape, Brassica napus L. var. oleifera. The first experiment was conducted on differently sprayed 10 m(2) experimental plots where alpha-cypermethrin was applied at different times. Another experiment was conducted on a 4 ha seed production field divided into two parts: one part was treated with alpha-cypermethrin and the other was not treated with this insecticide. The results show that there was no difference in the number of honey bees between alpha-cypermethrin-treated and untreated patches. The result persisted through three observation years, regardless of varying flower and honey bee densities. No repellent effect of the insecticide on honey bees was found even 24 h after spraying. The density of oilseed rape flowers most likely played a major role in choosing the foraging area.

Simulating Source‐Limited and Sink‐Limited Kernel Set with CERES‐Maize

CERES‐Maize simulates kernel set as a source‐limited process based on average plant growth rate during the lag phase after flowering. Yet the number of kernels formed by maize (Zea mays L.) also depends on timely interaction between male and female flowers, which can limit formation of reproductive sinks under some conditions. Failure to account for sink‐limited kernel set may contribute to simulation error observed under conditions that affect dynamics of pollen shed or silking, but do not alter crop growth rate. We developed algorithms for a Flowering Model to simulate sink‐limited kernel set from flowering dynamics. This model was calibrated against kernel production in hybrid seed production fields and then linked to CERES‐Maize. The Modified CERES‐Maize was calibrated against two years of field data involving three hybrids, eight population densities, and seven N levels. Integrating the capacity to simulate sink‐limited kernel set with source‐limited kernel set increased simulation accuracy dramatically, relative to original CERES‐Maize. For 13 commercial fields tested, Modified CERES‐Maize decreased simulation error for kernels per plant from 17.1 to 2.3%, improved r2 between measured and simulated values from 0.77 to 0.87, and decreased simulation error indicators mean error, root mean square error, and mean square deviation by 85, 40, and 64%, respectively. Modified CERES‐Maize accounts for a much greater range of variability in the biological processes controlling kernel set.

Stalk Rot of Sugar Beet Caused by Fusarium solani on the Pacific Coast.

In 2006, symptoms of stalk blight (2) were observed on sugar beet (Beta vulgaris L.) plants from roots produced in Oregon that were being grown for seed production in a greenhouse in Salinas, CA using Salinas Valley soil. Symptoms included vascular and cortical browning, necrosis, and death of seed stalks. Isolations were made from the edge of stalk lesions and the crown. In addition to Fusarium oxysporum, the known cause of stalk blight (2), two isolates of F. solani were identified by morphology. For pathogenicity tests, sugar beet plants (FC606 [4]), grown in pasteurized potting mix and induced to flower by exposure at 4 to 7°C for 90 days (1) were used. Bolting plants were maintained in a greenhouse at 24 to 27°C. A 100-μl drop of a spore suspension (104 spores per ml) of each Fusarium isolate was placed on the surface of the seed stalk. The plant was stabbed through the drop with a sterile 18-gauge needle so that the drop was taken into the plant by hygroscopic pressure. Positive and negative control treatments were a stalk blight isolate of F. oxysporum from an Oregon seed production field and sterile water, respectively. Three plants were inoculated per isolate. Each inoculation site was wrapped loosely in Parafilm for 1 week to maintain a high humidity level around the site of inoculation, and seed stalks were covered in cloth bags (1). After 1 week, the Parafilm was removed and plants were examined weekly for symptoms. At 4 weeks, lesion size was measured. After 5 weeks, sections were taken from the seed stalk around the site of inoculation, surface disinfested with 0.5% NaOCl, and plated on potato dextrose agar to confirm the presence of the pathogen. The experiment was done twice. One of the two isolates of F. solani caused dark brown lesions on all inoculated seed stalks. On one plant, at 4 weeks after inoculation when the bag was being removed for observation, the seed stalk broke at the site of inoculation because of a spreading, brown lesion at the site. No lesions were observed on the water control plants. Brown lesions were observed on seed stalks inoculated with the known stalk blight isolate. Lesions were significantly (P = 0.001) larger with F. oxysporum than with F. solani when measured at 4 weeks (mean of 6.3 cm versus 2.2 cm, respectively). Lesions caused by F. solani showed a dark discoloration through the cortical tissue, as opposed to those caused by F. oxysporum, for which most of the initial discoloration was in the vascular bundles and epidermis. Fusarium isolates recovered from inoculated plants were morphologically similar to the isolates used for inoculation. Fusarium spp. were not isolated from the water control plants. While some F. solani isolates cause seedling or mature root disease in sugar beet (3), to our knowledge, this is the first report of a Fusarium species other than F. oxysporum causing a rot of sugar beet stalks.

Influence of Plant Severing on Movement of <I>Ostrinia nubilalis</I> Larvae in <I>Zea mays</I> Hybrid Seed Production Fields

Genetically engineered corn hybrids that contain a cry gene from the bacterium Bacillus thuringiensis Berliner (Bt) are gaining popularity for controlling the corn pest Ostrinia nubilalis (Hübner). Continuous use of Bt corn, however, could select for O. nubilalis that are resistant to this corn. Monitoring for insect resistance is important, because it could help maintain the Bt technology. A possible monitoring method is to collect larval insects in commercial drying bins after harvest from Bt seed production fields. A drawback to this method is that these collections may be contaminated by insects that moved as later instars from severed non-Bt male rows into the adjacent Bt female rows. These larvae have little to no exposure to Bt toxin, resulting in possible "false positives." The objectives of this study were to first find which combination of planting and severing dates produces the least number of larvae that move from non-Bt male plants to Bt female plants and to assess O. nubilalis larval movement from severed non-Bt male rows to Bt female rows. Field studies in 2002 and 2003 were designed to simulate a hybrid seed production field. Results suggest that movement of O. nubilalis larvae from male corn is minimized when corn is planted early and male plants are severed by 2 wk post-anthesis. This reduces the likelihood of false positives by reducing the number of susceptible larvae moving between Bt and non-Bt plants. Also, larvae moved to all four female rows that were adjacent to the severed rows, but there were significantly more larvae found in the closest row compared with the other three. These results could be used to develop a monitoring program to find O. nubilalis larvae with resistance to Bt corn in field populations of O. nubilalis.

Hybrids between cultivated and wild carrots in natural populations in Denmark

Many cultivated plant species are able to hybridize with related wild plants. However, it is not clear whether their hybrids are able to survive and reproduce outside managed fields, and if cultivar genes introgress into wild populations. In areas where wild carrots co-occur with carrot root-crops, pollen and seeds may flow from two different sources in the fields to the surrounding wild populations: from pure cultivar plants that occasionally flower, and from flowering 'bolters' that originate from hybridizations between wild (male) and cultivated carrots (female) in seed production fields in warmer regions of the world. To test whether hybrids are formed and survive in wild Danish populations, and whether prolonged hybridization has led to introgression of cultivar genes, we collected leaf material from adult individuals growing close to carrot fields and analysed their genotypic composition by AFLP. Four hybrids were identified among the 71 plants analysed, and these were most likely F(2) or backcross individuals, sired by pollen from hybrid bolters. Wild populations close to fields were genetically somewhat more similar to cultivars than wild populations far from fields, suggesting that neutral or beneficial cultivar alleles can introgress into the wild gene pool. Despite generations of improvement and adaptation of cultivar carrots to highly managed field conditions, hybrids can thus sometimes survive in wild populations close to carrot fields, and their genes transfer to wild populations by introgression.

First Report of Onion yellow dwarf virus, Leek yellow stripe virus, and Garlic common latent virus in Garlic in Oregon.

A general mosaic and yellowing of leaves of three cultivars of garlic (Allium sativum L., Late, Early, and Germinador) were observed in two seed-production fields in Morrow County, OR in June 2005. Approximately 50% of plants within the 50-ha fields were symptomatic. With recent findings of Onion yellow dwarf virus (OYDV), Leek yellow stripe virus (LYSV), and Garlic common latent virus (GCLV) in Washington (2), 45 composite samples of 10 leaves each from symptomatic (mosaic and yellowing) and nonsymptomatic plants were analyzed with a GCLV-specific antiserum (Agdia Inc., Elkhart, IN). All samples of 'Germinador' were infected regardless of symptoms, whereas 6.7% of all 'Late' and 'Early' samples were positive. GCLV infection was verified by reverse transcription (RT)-PCR using primers specific to the coat protein gene of GCLV followed by cloning and sequencing of the cloned amplicon. To determine the presence of a potyvirus, all composite samples were also tested with a general potyvirus antiserum (Agdia) and all samples from symptomatic plants were found to be positive. Representative positive samples from each cultivar were then tested by RT-PCR using degenerate, potyvirus group specific primers (3), and an amplicon of the expected size was obtained. To confirm which potyvirus was present, amplicons were cloned and sequenced, and sequence comparisons indicated that the representative samples were infected with OYDV. All symptomatic samples from the three cultivars were positive for OYDV when tested by RT-PCR using primers specific to its coat protein gene (1). Additionally, 53.3 and 6.7% of 'Early' and 'Late' samples, respectively, were also positive when tested with LYSV-specific primers (4). LYSV infection was further verified through cloning and sequencing of the cloned amplicon. Because this garlic is grown for seed, studies are being initiated to determine if current season spread occurs and yields are reduced. To our knowledge, this is the first report of OYDV, LYSV, and GCLV in garlic in Oregon.

ACCase-Inhibitor Herbicide Resistance in Downy Brome (Bromus tectorum) in Oregon

In spring 2005, a downy brome population with possible resistance to fluazifop-P, an acetyl-CoA carboxylase (ACCase) inhibitor (group 1) herbicide was found in a commercial creeping red fescue seed production field, near La Grande, OR, where fluazifop-P had been used to control downy brome repeatedly over 7 yr. Greenhouse experiments were conducted to confirm resistance to a number of group 1 herbicides. The suspected resistant downy brome accession was tested for resistance to fluazifop-P and tested for cross-resistance to other aryloxyphenoxy propionate (APP) and cyclohexanedione (CHD) herbicides, including quizalofop-P, sethoxydim, and clethodim. Data recorded included plant-mortality counts and biomass. Tests revealed that the La Grande downy brome accession was highly resistant to fluazifop-P and sethoxydim at all tested rates. The La Grande accession suffered no mortality from fluazifop-P or sethoxydim treatments up to the maximum tested rate of eight times (8×) the labeled recommendation. The La Grande accession was resistant to quizalofop-P and clethodim at the labeled rate or less but was susceptible to application rates higher than the labeled rate. The control downy brome accession was completely susceptible to fluazifop-P, quizalofop-P, and clethodim at all rates and exhibited increasing susceptibility with increasing sethoxydim rate. This pattern of cross-resistance differs from that of a previously reported case of ACCase resistance in downy brome.

Occurrence of Ustilago striiformis in Dactylis glomerata Seed Production Fields in Oregon

Stripe smut, caused by Ustilago striiformis, is a common disease of grasses grown for turf, but quantitative information concerning its occurrence in grass seed production fields is lacking. In 2004, 2005, and 2006, stripe smut was detected in 16, 17, and 3 out of 51, 42, and 33 Dactylis glomerata (orchardgrass) seed production fields surveyed in western Oregon, respectively. Stripe smut was not previously known to occur in these fields. The percentage of plants per transect with stripe smut in 2004, 2005, and 2006 ranged from 0 to 12, 0 to 4, and 0 to 1, respectively. In additional surveys during 2004-2006, to determine whether stripe smut was also occurring in seed production fields of other grasses in western Oregon, stripe smut was found in one field of Agrostis stolonifera, but was not detected in fields of Agrostis castellana, A. capillaries, Festuca arundinacea, F. longifolia, F. ovina, F. rubra subsp. commutata, F. rubra subsp. rubra, or Lolium perenne. Accepted for publication 9 July 2007. Published 23 October 2007.

Quantitative and Molecular Epidemiology of Bacterial Blight of Onion in Seed Production Fields

ABSTRACT Onion, a biennial plant species, is threatened by the emerging, seed-borne, and seed-transmitted Xanthomonas axonopodis pv. allii. Bacterial blight epidemics were monitored in seed production fields over two seasons. Temporal disease progress was different between the two seasons, with final incidence ranging from 0.04 to 0.06 in 2003 and from 0.44 to 0.61 in 2004. The number of hours with temperatures above 24 degrees C was the best descriptor for predicting the number of days after inoculation for bacterial blight development on inoculated plants. Fitting the beta-binomial distribution and binary power law analysis indicated aggregated patterns of disease incidence data. The beta-binomial distribution was superior to the binomial distribution for 97% of the examined data sets. Spatial dependency ranged from 5.9 to 15.2 m, as determined by semivariance analysis. Based on amplified fragment length polymorphism (AFLP) analysis, it was concluded that plots predominantly were infected by the inoculated haplotype. A single other haplotype was identified by AFLP in all plots over the 2 years, and its detection in the field always followed wind-driven rains. X. axonopodis pv. allii-contaminated seed were detected by semiselective isolation and a nested polymerase chain reaction assay at levels up to 0.05% when final disease incidence was 0.61. Contaminated seed originated from both diseased and asymptomatic plants.

Shattercane,Sorghum Bicolor(L.) Moench Ssp.Drummondii(Nees ex Steud.) De Wet ex Davidse—Black Sheep of the Family

Look at a field of almost any grain and the top of the crop will be almost as tabletop flat as the ground below. Modern genetics produce almost perfectly uniform crop varieties and hybrids with identical, “cookie-cutter” individual plants. But one crop stubbornly refuses to cooperate with breeders. Look at a field of mature hybrid grain sorghum [Sorghum bicolor(L.) Moench ssp.bicolor] and you will see rugged individualists sticking up above the fruited plain of sameness like grain elevators towering over a small Midwestern town. These “off type” sorghum plants can be mutants, or the result of the random outcrossing of parent plants in seed production fields from the pollen of volunteer plants from a previous year's crop, nearby grain, or forage sorghums. They may also come from crosses with weedy types growing nearby such as johnsongrass [Sorghum halepense(L.) Pers.] or the dreaded shattercane [Sorghum bicolor(L.) Moench ssp.drummondii(Nees ex Steud.) de Wet ex Davidse] (Clark and Rosenow 1992). Just what is shattercane? Where did this “black sheep” of theSorghumclan come from? And why is it such a widespread weed today?

Transgenic Brassica napus fields and Brassica rapa weeds in Quebec: sympatry and weed-crop in situ hybridization

Hybridization between the herbicide-resistant transgenic crop Brassica napus L. (canola) and its weedy relative Brassica rapa L. (bird rape) has been documented in Quebec. Our goal was to evaluate the actual hybridization potential based on range overlap and actual in situ hybridization rates. This was done by mapping B. napus canola fields, comparing them with the sampling locations of B. rapa herbarium specimens from Quebec, gathering information on the presence of B. rapa in certified canola seed production fields, and surveying for B. rapa populations located in, or close to B. napus field margins. Progeny from these populations were screened for herbicide resistance (HR) and for the presence of the HR transgene. Two fields were also selected to evaluate B. rapa density effects on hybridization rates. Significant sympatry was observed in several areas of the province; hybridization occurred in all eight populations (1.1% to 17.5% hybrid seed) located in field margins and in one (1.1%) out of three populations located less than 10 m from a B. napus field. Hybridization rates decreased exponentially as B. rapa density increased, but interplant rates (0% to 68%) were highly variable. Environmental problems could be generated by the release of B. napus crops with traits conferring fitness benefits in nonmanaged areas.

Regional Development of Orchardgrass Choke and Estimation of Seed Yield Loss.

A survey for choke, caused by Epichloë typhina, in orchardgrass seed-production fields in Oregon was conducted annually from 1998 to 2003. In all, 99 fields were inspected, 57 in more than 1 year, to produce a set of 217 observations on disease incidence. There was a significant increase in disease incidence in 38% of the revisited fields, and a significant reduction of incidence in 3%. Yearly increases in disease incidence were as high as 29% in individual fields, but the average yearly increase from 1999 to 2003 was 5 to 8%. In 1998, 60% of all surveyed fields were infested with choke and, by 2003, 90% were infested. Average disease incidence in fields in their first year of production was <2%, and average disease incidence in older fields was approximately 10%, in 2003. Seed yield loss was equal to disease incidence (percentage of tillers diseased), and we found no significant yield compensation in diseased stands. An observed correlation of disease incidence with disease prevalence (proportion of sampled sites infested w ithin a field) may permit simple estimation of incidence and, thus, of potential economic loss in an affected field. We estimate regional loss to the 2004 orchardgrass seed crop due to choke o be approximately $0.8 million.

Novel Analysis of Hyperspectral Reflectance Data for Detecting Onset of Pollen Shed in Maize

Knowledge of pollen shed dynamics in and around seed production fields is critical for ensuring a high yield of genetically pure corn seed. Recently, changes in canopy reflectance using hyperspectral reflectance have been associated with tassel emergence, which is known to precede pollen shed in a predictable manner. Practical application of this remote sensing technology, however, requires a simple and reliable method to evaluate changes in spectral images associated with the onset of tassel emergence and pollen shed. In this study, several numerical methods were investigated for estimating percentage of plants with visible tassels (VT) and percentage of plants that initiated pollen shed (IPS) from remotely sensed hyperspectral reflectance data (397 to 902 nm). Correlation analysis identified regions of the spectra that were associated with tassel emergence and anthesis (i.e., 50% of plants shedding pollen). No single band, however, generated correlations greater than 0.40 for either VT or IPS. Classification using an artificial neural network (ANN) was predictive, correctly classifying 83.5% and 88.3% of the VT and IPS data, respectively. The extensive preprocessing necessary and the black box nature of ANNs, however, rendered analysis of spectral regions difficult using this method. Partial least squares (PLS) analysis yielded models with high predictive capability (R2 of 0.80 for VT and 0.79 for IPS). The PLS coefficients, however, did not exhibit a spectrally consistent pattern. A novel range operator-enabled genetic algorithm (ROE-GA), designed to consider the shape of the spectra, had similar predictive capabilities to the ANN and PLS, but provided the added advantage of allowing information transfer for increased domain knowledge. The ROE-GA analysis is the preferred method to evaluate hyperspectral reflectance data and associate spectral changes to tassel emergence and the onset of pollen shed in corn on a field scale.

Improving Corn Grain Purity by Using Color-Sorting Technology

Color sorting is often used to remove unwanted off-colored contaminants. The objectives of this study were to determine the usefulness of color sorting in removing adventitious corn from a seed lot and to evaluate the impact of contaminant color on efficacy. Seed lots of two contrasting colors were used in the experiments: yellow corn in a white lot and purple corn in a yellow lot. Samples were collected from three experimental sites: two white corn seed production fields surrounding a yellow pollen source, and a yellow corn seed production field surrounding a purple popcorn pollen source. Collected samples were color sorted in three successive passes. Outcross levels in the original nonsorted samples ranged from 0.10 to 38.55% in the yellow and white samples and from 0.61 to 45.78% in the purple and yellow samples. Color sorting reduced the percentage of outcross of yellow and purple kernels in the sample. The percentage of yellow seeds in white-seeded corn was reduced to 6.22% in samples collected at 3 ft and 0.01% at 820 ft from the source. The percentage of blue seeds in yellow-seeded corn samples was reduced to 0.58 at 0 ft and 0% at 270 ft from the source. These results indicate that color sorting is very effective at removing outcross seeds.

Quantitative Assessment of Anguina sp. and Rathayibacter rathayi in Dactylis glomerata Seed Production Fields in Oregon and Estimates of Yield Loss.

Anguina sp. is a nematode that infests the inflorescence of orchardgrass and forms galls that replace the seed. Anguina sp. is also a vector of the bacterial pathogen Rathayibacter rathayi, which causes galls or gummosis in orchardgrass (Dactylis glomerata) panicles. The percentage of orchardgrass panicles infected or percentage of seed loss from Anguina sp. or R. rathayi in five commercial orchardgrass seed-production fields in Oregon during 2003 and 2004 was determined. The percentage of panicles with Anguina sp. ranged from 9 to 24%, although the percentage of seed replaced by Anguina sp. was less than 0.2%. The number of galls per panicle ranged from 1 to 29. However, more than 50% of Anguina-infested panicles contained only a single Anguina gall and few panicles had eight or more galls. The percentage of panicles with R. rathayi ranged from 3 to 27%. Percentage of seed loss from R. rathayi ranged from 0.1 to 7.3%. Seed loss in orchardgrass seed-production fields assessed for both Anguina sp. and R. rathayi was found to be as great as 8%. The number of Anguinagalls remaining in fields following harvest ranged from 0 to 40 per square meter.

Tobacco Rattle Virus (TRV) Transmission by Sugar Beet Seeds

ABSTRACTThe study involves tobacco rattle virus (TRV) detection in racemes of two-year beet plants, seedlings, grown from seeds of these plants and seedlings from commercially available sugar beet seeds. Parts of sugar beet roots with a history of TRV were used for growing of two-year floriferous plants. Since plants had symptoms of yellow mosaic on leaves and raceme stipules, we tested each raceme separately with antiserum to TRV and broad beans wilt virus (BBWV) by ELISA. BBWV also causes yellow mosaic on leaves and raceme stipules and is usually combined with TRV infection in beet lately. Of 13 flowering plants, 8 were diagnosed with TRV and 2—with BBWV. TRV virus concentration in racemes was more than 0.3 to more than 0.5 optical units. BBWV showed lower concentration—more than 0.25 optical units in a limited number of plants (only 2), which did not interfere with TRV detection in racemes of flowering beet plants. Artificial vegetative propagation of beet has led to TRV transmission with racemes of two-year beet plants of up to 62%. Seedlings, originating from seeds of two-year beet plant, with extinction value of 0.550 optical units for the sample of its raceme, accounts for 20% of TRV transmission. The results of testing seedlings, grown from commercially available seeds, showed 15% TRV transmission for one batch and 20% for the other. TRV infection of racemes was investigated in samples, collected from a seed-production field. We detected 5% TRV infection in racemes of this field. The progeny of such racemes may transmit TRV to commercial fields, let alone nematode transmission of the virus.