Genome Announcement: The Draft Genome of the Carrot Cyst Nematode Heterodera Carotae.

Heterodera carotae, the carrot cyst nematode, is a significant pest affecting carrot globally. Here we present the draft genome of H. carotae, which was generated from short read libraries from Illumina HiSeq technology, and the corresponding genome annotation.

Growth, Sporulation, and Pathogenicity of the Raspberry Pathogen Phytophthora rubi Under Different Temperature and Moisture Regimes.

Phytophthora root rot of raspberry, which is mostly caused by Phytophthora rubi, is a significant issue for the Washington State red raspberry industry. Considered a cool weather pathogen, it is often assumed that it is most active and infective during the cool, wet winters of the region when soil temperatures range from 5 to 10°C; however, there are little data to support this view. More recent research has found that symptoms of root disease during late summer were strongly associated with P. rubi. Therefore, experiments were conducted at four temperatures from 5 to 20°C to evaluate the effects of temperature on P. rubi mycelial growth and sporulation and the effects of both temperature and soil moisture on the pathogenicity of P. rubi on red raspberry. At 20°C, P. rubi grew fastest and sporulated the most heavily. However, disease was most severe at both 15 and 20°C. The soil moisture parameters tested did not affect the pathogenicity results. These results show that P. rubi is more likely to infect during the spring and summer months (from May through September), when soil temperatures are consistently in the range of 15 to 20°C.

Short-Term Effects of Sublethal Doses of Nematicides on Meloidogyne incognita.

Meloidogyne species are one of the most important groups of plant-parasitic nematodes globally because of their ability to damage most cultivated plants. Although they are widespread and economically important, there are limited control measures to combat these nematodes. New nonfumigant nematicides have been discovered that have the potential to be widely utilized for the management of plant-parasitic nematodes. Because of the longer half-lives in soil and lower toxicity of new nematicides compared with traditional fumigant and nonfumigant nematicides, understanding how nematodes respond to sublethal doses of nematicides is imperative to understanding whether nematicide resistance has the potential to develop. Characterizing responses of nematodes to sublethal doses will provide the foundation for future work, such as gene expression studies. In this study, the nematicides oxamyl (Vydate), fluazaindolizine (Salibro), fluensulfone (Nimitz), and fluopyram (Velum), were evaluated to understand how sublethal doses affect the fecundity and mobility of Meloidogyne incognita second-stage juveniles (J2). Using a microwell assay system, dose-response curves for each nematicide were established for M. incognita J2. Fluopyram was the most toxic nematicide, with effective doses up to 230 times lower than that of other nematicides. The other nematicides had predicted ED50 values (effective doses that resulted in 50% of the population becoming inactive) of 89.4, 131.7, and 180.6 ppm for oxamyl, fluensulfone, and fluazaindolizine, respectively. The 24-h ED50 of each nematicide was then used in both motility and infectivity assays. The motility and activity of M. incognita J2 exposed to ED50 doses of fluazaindolizine and fluensulfone was significantly reduced, with nematodes initially being motile but eventually becoming inactive. However, the motility of M. incognita J2 exposed to ED50 doses of fluopyram and oxamyl was not different from a water control. In a pot assay, M. incognita J2 exposed to ED50 doses of fluazaindolizine, oxamyl, and fluensulfone were unable to reproduce on tomato, with reproduction factors (RF = final population density/initial population density) of 0 to 0.03. Fluopyram did not reduce reproduction of M. incognita, with a mean RF of 38.7 ± 4.5, which was similar to the RF of 46.3 ± 4.6 for the water control. This study is the first comprehensive evaluation of M. incognita activity, motility, and fecundity after exposure to the traditional nematicide, oxamyl, as well as three new nematicides, fluazaindolizine, fluopyram, and fluensulfone.

Developmental Dynamics of Meloidogyne hapla in Washington Wine Grapes.

Meloidogyne hapla is the most prevalent plant-parasitic nematode in Washington state wine grape vineyards. Understanding the developmental dynamics of M. hapla can improve the timing of diagnostic sampling and nematicide application. Three Vitis vinifera vineyards in Washington were sampled March 2015 to March 2017 to determine the developmental dynamics of M. hapla by measuring second-stage juveniles (J2) in soil, eggs and adult females in roots, and fine root tips. A model of M. hapla J2 development based on soil growing degree days using a base temperature (Tb) of 0°C (GDDsoil) and a start date of 1 March was developed. This model was validated at two additional vineyards in Washington and was robust with R2 values > 0.74. M. hapla has one generation per year and overwinters primarily as the J2 infective stage. Juvenile populations declined after 1 March, reaching their lowest density in early July and reaching a maximum density over the winter. M. hapla egg and root tip densities reached a maximum in early August. The number of females per root tip did not vary throughout the year. A single generation with defined peaks in J2 population densities will allow for specific timing of nematicide interventions.

Impact of Globodera ellingtonae on yield of potato (Solanum tuberosum).

Globodera ellingtonae was described from Oregon and Idaho in 2012. Due to the close phylogenetic relationship of this nematode to the potato cyst nematodes G. pallida and G. rostochiensis, and evidence that G. ellingtonae reproduces on potato (Solanum tuberosum), potential damaging effects to potato by this nematode are of great concern. To evaluate the pathogenic effects of G. ellingtonae on potato, five field and two microplot trials were conducted over a four-year period including comparisons of a range of G. ellingtonae initial population densities (Pi) and potato cultivars. In two field trials, potato 'Russet Burbank' was inoculated with Pi of G. ellingtonae ranging from 0 to 80 eggs/g soil; a similar trial was conducted with potato 'Désirée.' In another field trial, potato cultivars varying in maturity lengths were either inoculated (80 eggs/g soil) or not with G. ellingtonae. In a final field trial, 'Ranger Russet' was inoculated with Pi of G. ellingtonae ranging from 0 to 360 eggs/g soil. Additionally, Russet Burbank was inoculated with G. ellingtonae Pi ranging from 0 to 169 eggs/g soil in microplots. In all trials, data on tuber yield, aboveground biomass, final eggs/cyst, final population densities (Pf), and reproduction factor (RF = Pf/Pi) were collected. In only two of six trials conducted with increasing levels of Pi, was there a significant negative correlation between Pi of G. ellingtonae and yield of potato. Based on the linear regression model of tuber yield on logPi for Russet Burbank, 30.5 to 40.9% yield loss was predicted at a Pi of 40 and 80 eggs/g soil, respectively, and for Ranger Russet, 16.5 and 19.7% yield loss was predicted at a Pi of 40 and 80 eggs/g soil, respectively. None of the potato cultivars inoculated with 80 G. ellingtonae eggs/g soil had significantly reduced yields compared to non-inoculated plants. Reproduction factor values across trials ranged from 4.0 to 8.3 when inoculated with Pi of 40 eggs/g soil, demonstrating that the nematode successfully invaded and reproduced on potato in all trials. Care should be taken in extrapolating the results from these experiments conducted in Oregon to probable effects of G. ellingtonae on potato in other environments.KeywordsPotato, Damage, Globodera, Regression.Globodera ellingtonae was described from Oregon and Idaho in 2012. Due to the close phylogenetic relationship of this nematode to the potato cyst nematodes G. pallida and G. rostochiensis, and evidence that G. ellingtonae reproduces on potato (Solanum tuberosum), potential damaging effects to potato by this nematode are of great concern. To evaluate the pathogenic effects of G. ellingtonae on potato, five field and two microplot trials were conducted over a four-year period including comparisons of a range of G. ellingtonae initial population densities (Pi) and potato cultivars. In two field trials, potato 'Russet Burbank' was inoculated with Pi of G. ellingtonae ranging from 0 to 80 eggs/g soil; a similar trial was conducted with potato 'Désirée.' In another field trial, potato cultivars varying in maturity lengths were either inoculated (80 eggs/g soil) or not with G. ellingtonae. In a final field trial, 'Ranger Russet' was inoculated with Pi of G. ellingtonae ranging from 0 to 360 eggs/g soil. Additionally, Russet Burbank was inoculated with G. ellingtonae Pi ranging from 0 to 169 eggs/g soil in microplots. In all trials, data on tuber yield, aboveground biomass, final eggs/cyst, final population densities (Pf), and reproduction factor (RF = Pf/Pi) were collected. In only two of six trials conducted with increasing levels of Pi, was there a significant negative correlation between Pi of G. ellingtonae and yield of potato. Based on the linear regression model of tuber yield on logPi for Russet Burbank, 30.5 to 40.9% yield loss was predicted at a Pi of 40 and 80 eggs/g soil, respectively, and for Ranger Russet, 16.5 and 19.7% yield loss was predicted at a Pi of 40 and 80 eggs/g soil, respectively. None of the potato cultivars inoculated with 80 G. ellingtonae eggs/g soil had significantly reduced yields compared to non-inoculated plants. Reproduction factor values across trials ranged from 4.0 to 8.3 when inoculated with Pi of 40 eggs/g soil, demonstrating that the nematode successfully invaded and reproduced on potato in all trials. Care should be taken in extrapolating the results from these experiments conducted in Oregon to probable effects of G. ellingtonae on potato in other environments.KeywordsPotato, Damage, Globodera, Regression.

Genome Announcement: The Draft Genomes of Two Radopholus similis populations from Costa Rica.

Radopholus similis is an economically important pest of both banana and citrus in tropical regions. Here we present draft genomes from two populations of R. similis from Costa Rica that were created and assembled using short read libraries from Illumina HiSeq technology.

Resistance of Potato Breeding Clones and Cultivars to Three Species of Potato Cyst Nematode.

In the United States, potato cyst nematodes Globodera rostochiensis and G. pallida are quarantined pests. A new cyst nematode species, Globodera ellingtonae, discovered in Oregon and Idaho, reproduces well on potato but is not currently a quarantine pest. Identifying resistance to all three Globodera spp. would provide a valuable management tool. Thirteen breeding clones and nine cultivars were evaluated in Oregon, Idaho, and New York laboratories where the nematode populations are maintained. Minitubers or tissue culture plants were planted into pots and inoculated with eggs in replicated experiments. Results indicated that five entries were partially resistant or resistant to all three species, while another five were resistant or partially resistant to G. rostochiensis and G. ellingtonae. Resistance to G. rostochiensis pathotypes Ro1 and Ro4 is controlled by the H1 gene and this study suggests that H1 may confer resistance to G. ellingtonae as well. Observed resistance to G. pallida was lower relative to the levels of resistance observed for G. rostochiensis and G. ellingtonae. Germplasm with G. pallida or G. ellingtonae resistance will be used in hybridizations to develop russet-skinned cultivars with long tubers which represent the predominant market class in western U.S. production, and to further explore the basis of potato resistance to Globodera spp.

Late-summer Disease Symptoms in Western Washington Red Raspberry Fields Associated with Co-Occurrence of Phytophthora rubi, Verticillium dahliae, and Pratylenchus penetrans, but not Raspberry bushy dwarf virus.

Sixty percent of the $109 million processed red raspberry industry of the United States occurs in northern Washington State. In 2012, late-summer symptoms of vascular wilt and root disease were observed in many raspberry plantings. These symptoms were initially attributed to Verticillium dahliae. However, diagnostic tests for the pathogen were often contradictory and other soilborne pathogens (Phytophthora rubi and Pratylenchus penetrans) or Raspberry bushy dwarf virus (RBDV) might also have been involved. Therefore, a survey was conducted in 2013 and 2014 to (i) establish the incidence and soil population levels of V. dahliae in red raspberry production fields, (ii) compare among diagnostic methods and laboratories for detecting and quantifying V. dahliae from raspberry field soil, and (iii) assess which pathogens are associated with late-summer disease symptoms of raspberry. Plant and soil samples were collected from 51 disease sites and 20 healthy sites located in 24 production fields. Samples were analyzed for the presence and quantity of each pathogen using traditional plating and extraction methods (V. dahliae, P. rubi, and P. penetrans), quantitative polymerase chain reaction (qPCR) (V. dahliae and P. rubi), and enzyme-linked immunosorbent assay (RBDV). Results showed that V. dahliae was present in 88% of the production fields and that detection of the pathogen differed by method and by laboratory: qPCR detected V. dahliae in the soil from approximately three times as many sites (51 of 71 total sites) as by plating on NP10 semi-selective medium (15 of 71 total sites). Soil populations of V. dahliae were slightly greater at disease sites, but the pathogen was detected with similar frequency from healthy sites and it was rarely isolated from diseased plants (4%). P. rubi, P. penetrans, and RBDV were also common in production fields (79, 91, and 53% of fields, respectively). Both P. rubi (soil and root samples) and P. penetrans (root populations only), but not RBDV, were more frequently found at disease sites than healthy sites, and the amount of P. rubi detected by qPCR was greater from disease sites than healthy sites. In addition, P. rubi was isolated from 27% of the symptomatic plants located at disease sites. Regardless of detection method, V. dahliae, P. rubi, and P. penetrans, either with or without RBDV, were more likely to co-occur at disease sites (73%) than healthy sites (35%), suggesting that a soilborne disease complex is present in raspberry production fields. Results indicate that P. rubi is the primary pathogen most strongly associated with late-summer symptoms of disease, but root populations of P. penetrans and higher soil populations of V. dahliae may also be of concern. Therefore, disease control methods should focus on all three soilborne pathogens.

Whole Genome Sequences of the Raspberry and Strawberry Pathogens Phytophthora rubi and P. fragariae.

Phytophthora rubi and P. fragariae are two closely related oomycete plant pathogens that exhibit strong morphological and physiological similarities but are specialized to infect different hosts of economic importance, namely, raspberry and strawberry. Here, we report the draft genome sequences of these two Phytophthora species as a first step toward understanding the genomic processes underlying plant host adaptation in these pathogens.

Developmental Dynamics of Globodera ellingtonae in Field-Grown Potato.

Globodera ellingtonae is a recently described nematode parasite of potato, which is closely related to the economically significant potato cyst nematodes G. rostochiensis and G. pallida. Because of the close relationship of G. ellingtonae to the potato cyst nematodes, a greater understanding of its biology is critical. Two experiments were conducted in Oregon to explore the developmental biology of G. ellingtonae in field-grown potato. The first experiment was conducted in 2013 and 2014 to determine the developmental timing of G. ellingtonae life stages and reproduction by inoculating potato with soil containing cysts followed by weekly collection of soil and root samples. Life stages; second-stage juveniles (J2) in soil and roots, third-stage juveniles (J3) and fourth-stage (J4) females and males in roots, males and females or cysts in soil, and egg number and developmental state were quantified. Normalizing across years using accumulated developmental degree days above 6°C (DD6), J2 of G. ellingtonae were found in soil from 41 to 588 DD6; two peaks of J2 invasion of roots were observed. The first adult females were observed at 387 and 449 DD6 in 2013 and 2014, respectively. The next generation of eggs was first observed from 675 to 854 DD6 and 50% egg development (containing a vermiform juvenile) occurred at approximately 920 DD6. A second J2 hatch was observed in both years at 927 to 1,073 DD6. The developmental dynamics of G. ellingtonae observed here are similar to those reported for G. rostochiensis and G. pallida from several geographical locations. In the second experiment, the effect of potato and bare soil on G. ellingtonae egg hatch was evaluated; in 2014 and 2015, packages containing cysts in soil were buried under potato or in bare soil at the time of planting and eggs per cyst determined weekly. Across years, a significant reduction in eggs per cysts under potato (>50%) was observed 35 days after planting (DAP) and, at 63 DAP, eggs per cyst were reduced by 76 to 96% compared with initial egg per cyst densities. In bare soil, the maximum reduction in densities of eggs per cyst was 55 to 73%. This annual reduction in egg numbers of G. ellingtonae in bare soil is similar to that reported for G. pallida and G. rostochiensis.

Annual and Perennial Alleyway Cover Crops Vary in Their Effects on Pratylenchus penetrans in Pacific Northwest Red Raspberry (Rubus idaeus).

Cover crops can provide many benefits to agroecosystems, such as lessening soil erosion and increasing water infiltration. However, cover crop use is not common in established red raspberry (Rubus idaeus) fields in the Pacific Northwest. Raspberry growers are concerned about resource competition between the cover crop and raspberry crop, as well as increasing population densities of the plant-parasitic nematode Pratylenchus penetrans, which has a wide host range and has been shown to reduce raspberry plant vigor and yield. A 2-yr study was conducted in an established 'Meeker' raspberry field in northwest Washington to evaluate the effects of nine alleyway cover crops, mowed weed cover, and the industry standard of bare cultivated soil on P. penetrans population dynamics, raspberry yield, and fruit quality. The host status for P. penetrans of cover crops included in the field experiment, as well as Brassica juncea 'Pacific Gold' and Sinapis alba 'Ida Gold', was also evaluated in greenhouse experiments. In the field experiment, P. penetrans population densities did not increase in alleyway cover crop roots over time or in alleyway soil surrounding cover crop roots (means range from 0 to 116 P. penetrans/100 g of soil) compared with the bare cultivated control (means range from 2 to 55 P. penetrans/100 g of soil). Pratylenchus penetrans populations did not increase over time in raspberry grown adjacent to alleyways with cover crops (means range from 1,081 to 6,120 P. penetrans/g of root) compared with those grown adjacent to bare cultivated soil alleyways (means range from 2,391 to 5,536 P. penetrans/g of root). Raspberry grown adjacent to bare cultivated soil did not have significantly higher yield or fruit quality than raspberry grown adjacent to cover crops in either year of the experiment. In the greenhouse assays, 'Norwest 553' wheat and a perennial ryegrass mix were poor hosts for P. penetrans, whereas 'Nora' and 'TAM 606' oat and 'Pacific Gold' and 'Ida Gold' mustard were good hosts. These results support the idea that the potential benefits of alleyway cover crops outweigh the potential risk of increasing P. penetrans population densities and do not compromise raspberry yield or fruit quality.

Draft Transcriptome of Globodera ellingtonae.

Globodera ellingtonae is a newly described cyst nematode found in Idaho, Oregon, and Argentina. Here we present the first transcriptome assembly of G. ellingtonae, providing a valuable resource for comparing the evolution of expressed genes between potato cyst nematode species.

Control of Globodera spp. Using Brassica juncea Seed Meal and Seed Meal Extract.

The eradication program for the potato cyst nematode (PCN), Globodera pallida, in the Northwest of the United States revolves around the use of soil fumigation. Alternative, integrated strategies are needed to continue to battle this invasive nematode. Laboratory, greenhouse, and field experiments were conducted with G. pallida and another cyst nematode found in the United States, Globodera ellingtonae, to evaluate the efficacy of a new formulated Brassica juncea seed meal extract, as well as a traditional B. juncea seed meal, as alternate eradication strategies. This is the first report on the efficacy of B. juncea seed meal extract against plant-parasitic nematodes. Rates of B. juncea seed meal greater than 2.2 t/ha and 4.5 t/ha for G. pallida and G. ellingtonae, respectively, were required for egg hatch suppression, as determined by a potato root diffusate (PRD) bioassay. Reproduction of G. pallida on potato after exposure to B. juncea seed meal at a rate of 2.2 t/ha was also significantly reduced. In the field, 8.9 t/ha B. juncea seed meal almost eliminated egg hatch of G. ellingtonae. Rates needed for Globodera spp. suppression were greatly reduced when using the B. juncea seed meal extract. When compared side-by-side, half as much B. juncea seed meal extract, 1.1 t/ha, was required to suppress G. ellingtonae egg hatch to the same extent as B. juncea seed meal. Exposure of G. pallida to B. juncea seed meal extract at 4.5 t/ha reduced egg hatch by 90% compared with a nonamended control. The ability to reduce the amount of material being applied to soil by using an extract has the potential for integration into a G. pallida eradication program.

The Draft Genome of Globodera ellingtonae.

Globodera ellingtonae is a newly described potato cyst nematode (PCN) found in Idaho, Oregon, and Argentina. Here, we present a genome assembly for G. ellingtonae, a relative of the quarantine nematodes G. pallida and G. rostochiensis, produced using data from Illumina and Pacific Biosciences DNA sequencing technologies.

The mitochondrial genome of Globodera ellingtonae is composed of two circles with segregated gene content and differential copy numbers.

BACKGROUND: The evolution of animal mitochondrial (mt) genomes has resulted in a highly conserved structure: a single compact circular chromosome approximately 14 to 20 kb long. Within the last two decades exceptions to this conserved structure, such as the division of the genome into multiple chromosomes, have been reported in a diverse set of metazoans. We report on the two circle multipartite mt genome of a newly described cyst nematode, Globodera ellingtonae. RESULTS: The G. ellingtonae mt genome was found to be comprised of two circles, each larger than any other multipartite circular mt chromosome yet reported, and both were larger than the single mt circle of the model nematode Caenorhabditis elegans. The genetic content of the genome was disproportionately divided between the two circles, although they shared a ~6.5 kb non-coding region. The 17.8 kb circle (mtDNA-I) contained ten protein-coding genes and two tRNA genes, whereas the 14.4 kb circle (mtDNA-II) contained two protein-coding genes, 20 tRNA genes and both rRNA genes. Perhaps correlated with this division of genetic content, the copy number of mtDNA-II was more than four-fold that of mtDNA-I in individual nematodes. The difference in copy number increased between second-stage and fourth-stage juveniles. CONCLUSIONS: The segregation of gene types to different mt circles in G. ellingtonae could provide benefit by localizing gene functional types to independent transcriptional units. This is the first report of both two-circle and several-circle mt genomes within a single genus. The differential copy number associated with this multipartite mt organization could provide a model system for deconstructing mechanisms regulating mtDNA copy number both in somatic cells and during germline development.

Effect of Application Timing of Oxamyl in Nonbearing Raspberry for Pratylenchus penetrans Management.

In 2012, the Washington raspberry (Rubus idaeus) industry received a special local needs (SLN) 24(c) label to apply Vydate L® (active ingredient oxamyl) to nonbearing raspberry for the management of Pratylenchus penetrans. This is a new use pattern of this nematicide for raspberry growers; therefore, research was conducted to identify the optimum spring application timing of oxamyl for the suppression of P. penetrans. Three on-farm trials in each of 2012 and 2013 were established in Washington in newly planted raspberry trials on a range of varieties. Oxamyl was applied twice in April (2013 only), May, and June, and these treatments were compared to each other as well as a nontreated control. Population densities of P. penetrans were determined in the fall and spring postoxamyl applications for at least 1.5 years. Plant vigor was also evaluated in the trials. Combined results from 2012 and 2013 trials indicated that application timing in the spring was not critical. Oxamyl application reduced root P. penetrans population densities in all six trials. Reductions in P. penetrans population densities in roots of oxamyl-treated plants, regardless of application timing, ranged from 62% to 99% of densities in nontreated controls. Phytotoxicity to newly planted raspberry was never observed in any of the trials. A nonbearing application of oxamyl is an important addition to current control methods used to manage P. penetrans in raspberry in Washington.

Distribution and Longevity of Pratylenchus penetrans in the Red Raspberry Production System.

One of the major constraints on the production of red raspberries in the Pacific Northwest is the presence of the root-lesion nematode Pratylenchus penetrans. Current management of this nematode relies heavily on preplant soil fumigation; however, regulations have made the practice more difficult and expensive. Additional issues with soil fumigation include lack of efficacy at deeper soil depths and potential inability to penetrate raspberry root material that remains in the field during fumigation which may harbor P. penetrans. To address these issues, two field experiments were conducted in northwestern Washington. In the first experiment, the residency time of P. penetrans in root material from the previous raspberry crop, which was terminated with or without the use of herbicides, was monitored over time. Pratylenchus penetrans was found in root material from 6 to 8 mon after the crop was terminated, and herbicide application did not reduce P. penetrans residency time compared to untreated root material. In a second experiment, the vertical distribution of P. penetrans at three different times during the field establishment process (pre- and postfumigation, and at planting) was determined at two locations. Both locations had detectable prefumigation P. penetrans populations at all depths. However, postfumigation populations showed a different distribution pattern between locations. The location with coarser soil had populations located mainly at shallower depths with a maximum of 44 P. penetrans/100 g soil at 16 to 30 cm deep, whereas the location with finer soil had populations located mainly at deeper depths with a maximum of 8 P. penetrans/100 g soil at 76 to 90 cm deep. At planting, distribution tended to equilibrate among depths at both locations, but the overall population pattern across depth at each location was similar to that observed at postfumigation. Understanding more about the residency time and distribution of this nematode may provide growers with information that can be used to more effectively target P. penetrans.

Impact of Pratylenchus penetrans on Establishment of Red Raspberry.

The plant-parasitic nematode, Pratylenchus penetrans, is a major constraint to red raspberry (Rubus idaeus) production. To determine the impact of P. penetrans on the establishment and productivity of eight raspberry cultivars, R. niveus, and R. leucodermis, plants were grown in fumigated and nonfumigated soil. Then, soil and root populations of P. penetrans and plant productivity (vigor, cane height, biomass, and yield) were monitored over 2 years. In a separate experiment, the role that soil type plays in mediating P. penetrans populations and raspberry establishment was investigated. At 6 and 12 months after planting, population densities of P. penetrans were lower in fumigated than in nonfumigated soil; this trend continued 18 months after planting. All cultivars and R. leucodermis were found to be extremely susceptible to damage caused by P. penetrans. By the end of the experiment, yield was the most sensitive indicator of plant productivity among cultivars, with losses in nonfumigated soil ranging from 63 to 100% of those observed in fumigated soil. However, there was no difference in the productivity of R. niveus plants grown in nonfumigated versus fumigated soils. Results also indicated that the damage potential of P. penetrans was greater on sandy loam versus silt loam soils. The total plant biomass of 'Meeker' raspberry was 46% lower in a sandy loam soil containing P. penetrans compared with soil without P. penetrans; this trend was not observed consistently in a silt loam soil. Despite the fact that soil fumigation is increasingly more limited by regulations, this study shows the utility of fumigation in reducing P. penetrans populations for a sufficient period of time to ensure that newly planted raspberry seedlings can become successfully established.

The Relationship between Temperature and Development in Globodera ellingtonae.

A new cyst nematode species, Globodera ellingtonae, was recently described from populations in Oregon and Idaho. This nematode has been shown to reproduce on potato. Because of this nematode's close relationship to the potato cyst nematodes, G. rostochiensis and G. pallida, an understanding of the risk of its potential spread, including prediction of potential geographical distribution, is required. To determine the development of G. ellingtonae under different temperatures, we conducted growth chamber experiments over a range of temperatures (10.0°C to 26.5°C) and tracked length of time to various developmental stages, including adult females bearing the next generation of eggs. Both the time to peak population densities of G. ellingtonae life stages and their duration in roots generally increased with decreasing temperature. Regression of growth rate to second-stage (J2) and third-stage (J3) juveniles on temperature yielded different base temperatures: 6.3°C and 4.4°C for J2 and J3, respectively. Setting a base temperature of 6°C allowed calculation of the degree-days (DD6) over which different life stages occurred. The largest population densities of J2 were found in roots between 50 and 200 DD6. Population densities of J3 peaked between 200 and 300 DD6. Adult males were detected in soil starting at 300 to 400 DD6 and remained detectable for approximately 500 DD6. By 784 to 884 DD6, half of the eggs in adult females contained vermiform juveniles. Given the similarity in temperature ranges for successful development between G. ellingtonae and G. rostochiensis, G. ellingtonae populations likely could survive in the same geographic range in which G. rostochiensis now occurs.

Effect of Storage Environment on Hatching of the Cyst Nematode Globodera ellingtonae.

Globodera spp. eggs go through a diapause, which remains dormant until favorable hatching conditions are reached. Because of the regulatory concerns with cyst nematodes, it is often only possible to rear eggs for research in the greenhouse. However, hatch is often lower for greenhouse-produced eggs than for eggs obtained from the field. The goal of this research was to determine storage conditions for Globodera ellingtonae eggs produced in the greenhouse that would increase percentage hatch. Over 3 yr, G. ellingtonae greenhouse-produced eggs were stored in different environments (-20°C, 4°C, room temperature, and the field) in either dry or moist soil. Percentage hatch after exposure to the different environments was determined in potato root diffusate. Across two experiments, field-produced eggs had higher hatch rates (65.2%) than greenhouse-produced eggs (10.4%). Temperature did not have an appreciable influence on hatch of eggs stored dry in two experiments (2.8% to 8.4% and 3.8% to 8.6%), but hatch of eggs stored in moist soil was significantly higher than in dry soil at all temperatures except -20°C (26.8% and 28.7%). However, the ability of G. ellingtonae greenhouse-, microplot-, and field-produced eggs to reproduce on potato in field microplots was not different. Although it may not be possible to produce G. ellingtonae eggs in the greenhouse that have the magnitude of hatch as those produced in the field, hatching can be greatly increased by storing eggs in moist soil at either 4°C or room temperature.