Single female cuhures of Pratylenchus penetrans were established from soil and root samples collected from 10 geographically isolated locations in North America. The resultant isolates were used to evaluate nematode egression from and multiplication on roots of potato clones to distinguish intraspecific differences among isolates. The 10 nematode isolates were statistically separated into four groups based on percentage of nematodes that egressed from the P. penetrans-resistant potato done L 118-2. The Cornell (CR), Wisconsin (WI), Long Island (LI), and Adirondack (AD) isolates, selected as representative isolates of each of the four groups, exhibited 53%, 39%, 25%, and 10% egression from L118-2, respectively. Reproduction of these four isolates was measured on three potato cultivars (Russet Burbank, Butte, and Hudson) and two breeding lines (NY85 and L118-2). The LI and AD isolates reproduced well on all five potato clones. The CR isolate reproduced well on Russet Burbank and NY85 but significantly less on Butte, Hudson, and L118-2. Reproduction of the WI isolate was less than the LI and AD isolates but more than the CR isolate on all potato clones tested except Russet Burbank. Reproduction of the WI isolate on Russet Burbank was less than the other three isolates. Based on these results, four distinct intraspecific variants of P. penetrans are proposed: Cornell, Wisconsin, Long Island, and Adirondack.
biotype; egression; lesion nematode; pathotype; potato; Pratylenchus penetrans; reproduction; resistance; Solanum tuberosum
Cropping systems in which resistant potato cultivars were grown at different frequencies in rotation with susceptible cultivars and a nonhost (oats) were evaluated at four initial nematode population densities (Pi) for their ability to maintain Globodera rostochiensis at a target level of <0.2 egg/cm³ of soil. At a Pi of 0.1 to 1 egg/cm³ of soil, cropping systems with 2 successive years of a resistant cultivar every 3 years of potato production reduced and maintained G. rostochiensis at <0.2 egg/cm³ of soil. At a Pi of 1 to 4 eggs/cm³ of soil, 2 successive years of a resistant cultivar followed by 1 year of oats for every 4 years of production were necessary to reduce and maintain G. rostochiensis populations at <0.2 egg/cm³ of soil. At a Pi greater than 4 eggs/cm³ of soil, 2 successive years of a resistant cultivar plus 1 year of oats reduced G. rostochiensis densities to <0.2 egg/cm³ of soil, but the population increased above that density after cropping 1 year to a susceptible cultivar. The numbers of cysts and eggs per cyst in the final population (Pf) of G. rostochiensis were influenced by initial density and the frequency of growing a susceptible cultivar in a cropping system. The lowest number of cysts and eggs per cyst in the final G. rostochiensis population occurred with a cropping system consisting of 2 successive years of a resistant cultivar followed by oats with a susceptible cultivar grown the fourth year of production.
cropping system; density; ecology; Globodera rostochiensis; golden nematode; integrated control; potato; potato cyst nematode; rotation
The behavior of two isolates of Pratylenchus penetrans on six potato clones was assessed to test the hypothesis that these nematode isolates from New York were different. Four potato cultivars (Superior, Russet Burbank, Butte, and Hudson) and two breeding lines (NY85 and L118-2) were inoculated with nematode isolates designated Cornell (CR) and Long Island (LI). Population increase and egression of nematodes from roots were used to distinguish resistance and susceptibility of the potato clones. Based on numbers of eggs, juveniles, and adults in their roots 30 days after inoculation, potato clones Butte, Hudson, and L118-2 were designated resistant to the CR isolate and susceptible to the LI isolate. More eggs were found in the roots of all plants inoculated with the LI isolate than with the CR isolate. The clones NY85 and L118-2 were inoculated with the CR and LI isolates in a 2 x 2 factorial experiment to assess differences in nematode egression. Egression was measured, beginning 3 days after inoculation, for 12 days. The rates of egression were similar for the four treatments and fit linear regression models, but differences were detected in numbers of egressed nematodes. More nematodes of the CR isolate than the LI isolate egressed from L118-2. Differences in egression of females was particularly significant and can be used as an alternative or supplement to reproduction tests to assess resistance in potato to P. penetrans and to distinguish variation in virulence.
egression; lesion nematode; nematode; pathotypes; potato; Pratylenchus penetrans; resistance; Solanum tuberosum
We evaluated the ability of the nematode-pathogenic fungus Hirsutella rhossiliensis (Deuteromycotina: Hyphomycetes) to reduce root penetration and population increase of Pratylenchus penetrans on potato. Experiments were conducted at 24 C in a growth chamber. When nematodes were placed on the soil surface 8 cm from a 14-day-old potato cutting, the fungus decreased the number entering roots by 25%. To determine the effect of the fungus on population increase after the nematodes entered roots, we transplanted potato cuttings infected with P. penetrans into Hirsutella-infested and uninfested soil. After 60 days, the total number of nematodes (roots and soil) was 20 ± 4% lower in Hirsutella-infested than in uninfested soil.
biological control; Hirsutella rhossiliensis; migratory endoparasite; nematode; nematophagous fungus; potato; Pratylenchus penetrans; root lesion nematode; Solanum tuberosum
Potato clones from five different breeding populations were evaluated for their relative resistance and susceptibility to Pratylenchus penetrans. Resistance and susceptibility were distinguished by an index of susceptibility (SI) calculated from the numbers of P. penetrans (including eggs) per g of root of individual clones in relation to that of a susceptible control at 30 or 70 days after inoculation. Evaluations were carried out using 7.5-cm clay pots in a growth chamber at 24 C with 15-hour day length. In the initial evaluation, 70 days after inoculation, the SI of individual clones ranged from 0.01 to 0.75. Clones that supported the least P. penetrans were from a breeding population derived from Solanum tuberosum ssp. andigena that was originally selected for its resistance to the potato cyst nematode, Globodera pallida. In succeeding tests, these clones had a significantly low SI than did susceptible controls or cultivars that were previously reported to possess resistance to P. penetrans, except cv. Hudson. Resistance to P. penetrans from the Pallida-resistant breeding population was incorporated into potato germplasm better adapted to North American growing conditions.
breeding; control; Globodera pallida; nematode; race; Solanum tuberosum
The probability of spreading cysts of Globodera rostochiensis on farming equipment and potato tubers was investigated in naturally infested field plots. The number of cysts recovered from soil that adhered to equipment differed significantly between different pieces of equipment. These differences were related to initial nematode density and, in most cases, to the volume of soil that adhered to the equipment. At an initial density of 0.04 egg/cm³ of soil, significantly more cysts were recovered from a potato digger than from a potato hiller, cultivator, or plow. At an initial density of 0.90 egg/cm³ of soil, significantly more cysts were recovered from the plow than from the other equipment. Although the population density was 22 times greater, only 10 times more cysts adhered 3 to equipment used in soil with a density of 0.90 egg/cm³ of soil than when used in soil infested at 0.04 egg/cm³. The number of potato tuber samples (4.5 kg) that contained cysts with viable eggs was positively correlated with the initial densities of G. rostochiensis in soil in which they were produced. The percentage of tuber samples with cysts containing viable eggs was 10-12% for tubers harvested from soil with densities less than 1 egg/cm³ and 30-76% for tubers harvested from soil with densities greater than 4 eggs/cm³ of soil.
dispersal; distribution; golden nematode; potato cyst nematode; spread
Eleven fungal isolates were tested in agar dishes for pathogenicity to Pratylenchus penetrans. Of the fungi that produce adhesive conidia, Hirsutella rhossiliensis was a virulent pathogen; Verticillium balanoides, Drechmeria coniospora, and Nematoctonus sp. were weak or nonpathogens. The trapping fungi, Arthrobotrys dactyloides, A. oligospora, Monacrosporium dlipsosporum, and M. cionopagum, killed most of the P. penetrans adults and juveniles added to the fungus cultures. An isolate of Nematoctonus that forms adhesive knobs trapped only a small proportion of the nematodes. In 17-cm³ vials, soil moisture influenced survival of P. penetrans in the presence of H. rhossiliensis; nematode survival decreased with diminishing soil moisture. Hirsutella rhossiliensis and M. ellipsosporum were equally effective in reducing numbers of P. penetrans by 24-25% after 4 days in sand. After 25 days in soil artificially infested with H. rhossiliensis, numbers of P. penetrans were reduced by 28-53%.
biological control; Hirsutella rhossiliensis; migratory endoparasite; Monacrosporium ellipsosporum; nematode; nematophagous fungi; Pratylenchus penetrans; root lesion nematode
The establishment of Globodera rostochiensis Rol populations was examined under greenhouse conditions. The probability of G. rostochiensis population establishment was calculated from the number of plants that produced new cysts with viable eggs following inoculation with various numbers of eggs of different ages. Probability of population establishment was positively correlated with inoculum density but was not affected by the age of eggs used in these experiments. The probability of G. rostochiensis establishment ranged from 5% at densities of 2 eggs/pot to 100% at densities of 25 eggs/pot or greater. At densities of 3 eggs/pot and beyond, there was no correlation between inoculum density and the number of viable eggs/new cyst. Also, the number of plants that produced new cysts was a function of inoculum density and not age of eggs. Juveniles from eggs 1 year old or older were equally as infective as were those from eggs in newly developed cysts (4 months old).
Globodera rostochiensis; golden nematode; nematode spread; population establishment; potato; Solanum tuberosum
Potato cultivars Katahdin (susceptible) and Rosa (resistant) were exposed to infective second-stage juveniles (J2) of Globodera rostochiensis for varying periods of time, after which root systems were washed and plants were placed in Hoagland's solution to assess J2 egression and male emergence. After transfer to liquid culture, many J2 egressed from both cultivars, but significantly more egressed from the resistant Rosa than from Katahdin. Juveniles that egressed from Rosa invaded a second host, resistant or susceptible, in significantly fewer numbers than did juveniles that egressed from Katahdin. Also, significantly fewer males developed in and emerged from resistant host roots, relative to susceptible ones. These effects of resistance may be an important component of the tolerance to invasion by G. rostochiensis exhibited by Rosa.
Globodera rostochiensis; host resistance; male development; juvenile invasion; potato; Solanum tuberosum
The fecundity of Globodera rostochiensis (R₁A) females that developed on resistant Rosa and susceptible Katahdin potato cultivars were compared. Cysts collected from each cultivar were bulked, separated into four sizes (> 500 μm, 355-500 μm, 250-355 μm, and < 250 μm), and crushed to determine fecundity as measured by viable egg content (VEC). Fewer and generally smaller cysts developed on Rosa than on Katahdin. Although cyst size significantly (P = 0.01) influenced VEC, cyst age (8 or 13 weeks) had no effect. Regardless of size, cysts produced on Rosa contained significantly fewer viable eggs than did cysts produced on Katahdin. The fecundity of progeny from cysts produced on Rosa was significantly reduced compared with that of progeny from cysts produced on Katahdin. After two generations on Katahdin, the VEC of cysts from a population originating from Rosa was significantly less than that of cysts from a population originating from Katahdin, indicating that in the presence of a pure population of G. rostochiensis R₁A, the females that develop on the resistant cultivar Rosa represent a diminished rather than a superior selected population.
female fecundity; Globodera rostochiensis; host resistance; potato; Solanum tuberosum
One susceptible (D6) and two resistant (E2 and N4) clones of Solanum sparsipilum × (S. phureja × haploid of S. tuberosum) were used to study the responses of potato roots and tubers to race 1 of Meloidogyne incognita (Kofoid &White) Chitwood. The compatible response was characterized by rapid penetration of large numbers of second-stage juveniles (J2) into roots, cessation of root growth, and occasional curving of root tips. The life cycle of M. incognita in the susceptible clone was completed in 25 days at 23-28 C. The incompatible response was characterized by penetration of fewer J2 into roots, necrosis of feeding sites within 2-7 days, and lack of nematode development. There were no differences in response of tubers from resistant and susceptible clones to nematode infection. Small numbers of J2 were detected in tubers, but they did not develop.
Meloidogyne incognita; Solanum sparsipilum; Solanum phureja; Solanum tuberosum; potato; root-knot; resistance; susceptibility; compatibility
Decline of Globodera rostochiensis populations occurring naturally in soil and those added to potato hills and furrow centers in nylon bags was correlated with root weight of Hudson, Rosa, and Katahdin potatoes at two locations in New York. Cysts in bags were added to soil at planting and at 1, 3, 5, 7, and 9 weeks after emergence (AE). Fallow decline required only 2-4 weeks in soil and did not increase with time. Decline due to growing potatoes was greater in hills than in furrow centers, and resistant Hudson potatoes stimulated greater nematode hatch for longer times in both hills and furrows than did resistant Rosa and susceptible Katahdin. Potato root diffusate (PRD) was produced in highest concentration early in the season; decreased egg hatch with time was probably the result of declining PRD production and inactivation of PRD in soil. Decreasing potato row spacing from 92 cm to 46 and 23 cm between rows increased G. rostochiensis decline in furrow centers, with the majority of decline occurring within 1-3 weeks AE. Replanting potatoes after 1 week of trap crop growth failed to favor population reduction over a single full season crop.
Globodera rostochiensis; golden nematode; Solanum tuberosum; potato; resistance; root exudate; population dynamics; trap crop
The reliability of morphological characters and host differential plants for distinguishing between two populations of Meloidogyne incognita was studied. Population A (originally from North Carolina) had incognita-type perineal patterns. A single egg mass subpopulation of population A had a mixture of incognita and acrita perineal patterns with 33% of the patterns atypical for either species. Population B (from Georgia) had predominantly acrita-type patterns with only about 5% atypical patterns. The head shapes of males from both populations were mainly M. incognita. On the basis of stylet length, both populations conformed to M. incognita acrita. Both populations were identified as M. incognita race 1 by reaction on the North Carolina differential hosts. Reactions on azalea and pepper gave no clear identification of the populations. We concluded that there is no relation between perineal pattern, male head shape, and parasitism of host differentials with the two populations studied.
Meloidogyne incognita; races; morphology; taxonomy; parasitism
The effects of extraction technique, sample size, soil moisture level, and overflow rate on recovery of Globodera rostochiensis and (or) Heterodera schachtii cysts from organic soils were investigated. A modified Fenwick can (MFC) and an underflow elutriator (UE) described in this paper were evaluated and compared for cyst recovery efficiency and amount of organic flotsam collected. The MFC and UE extracted similar numbers of cysts, but the UE collected 50% less flotsam than the MFC. Sample size was negatively correlated with cyst recovery and positively correlated with amount of flotsam. The amount of flotsam recovered with the MFC was correlated with overflow speed. Presoaking air dried samples for 30 minutes halved the amount of flotsam without affecting cyst recovery. Extracting cysts from wet soil without prior drying resulted in negligible recovery with both extraction techniques. There were no significant differences in cyst recovery of the two genera tested.
elutriation; extraction; Globodera rostochiensis; potato cyst nematode; Heterodera schachtii; sugarbeet cyst nematode
Movement of potato root diffusate (PRD) through soil was examined by using the hatch of eggs from Globodera rostochiensis cysts as an indicator. Porous bags containing cysts were placed at increasing distances and depths from potato roots, whose growth was restricted by nylon mesh. Significantly greater hatch was observed up to 50 cm laterally away from potato roots, compared with hatch in fallow soil. Eight weeks after plant emergence, we detected a concentration gradient of PRD, as measured by egg hatch, that decreased with increasing lateral and vertical distance from the root zone. Egg hatch beyond 5 weeks after plant emergence was not attributed to PRD.
potato root diffusate; Globodera rostochiensis; hatch
Globodera rostochiensis population densities and potato root growth were measured in field plots of one susceptible and two resistant potato cultivars. Root growth and nematode densities were estimated from soil samples taken at three depths between plants within the rows, three depths 22.5 cm from the rows, and at two depths midway between rows (furrows). Four weeks after plant emergence (AE), nematode densities in the rows had declined 68% in plots of the susceptible cultivar and up to 75% in plots of both resistant cultivars. Significant decline in nematode densities in the furrows 4 weeks AE occurred only in plots of the susceptible cultivar. Total decline in nematode density in fallow soil was 50%, whereas in plots of the resistant cultivars, decline was more than 70% in the rows and more than 50% in the furrows. Nematode densities increased in the rows of the susceptible cultivar but declined in the furrows. We conclude that G. rostochiensis decline or increase is correlated with host resistance and the amount of roots present at any particular site.
potato root growth; population decline; Globodera rostochiensis; root diffusate; Solanum tuberosum
Hatching response of Globodera rostochiensis in potato root diffusate (PRD) collected by soaking individual potato, Solanum tuberosum, root systems in water for 2 hours was used to assess the relationship between root growth and PRD production. Resistant potato cultivars Hudson and Rosa were used as test plants. Maximum hatch occurred in PRD collected 3 weeks after plant emergence (AE) in the greenhouse, and declined after this time. Hatch was positively correlated with increased root weight only during the first 3 weeks AE. Hudson PRD was consistently more active than Rosa PRD in stimulating hatch, except when adjusted for root weight. Although the results indicated that cells at the root tip produced a more active PRD than cells located elsewhere, PRD appeared to be produced along the entire root. Differences in time length of the vegetative growth phase, extent of root growth, and volume of roots, rather than the production of a more active PRD per se, may explain why Hudson is more effective than Rosa in reducing G. rostochiensis population densities in soil.
hatch; Globodera rostochiensis; golden nematode; potato root growth; root diffusate; Solanum tuberosum; potato
cyst nematodes; Globodera rostochiensis; golden nematode; Solanum tuberosum ssp. tuberosum; potato; techniques; viability determination; vintage cysts
The influence of resistant and susceptible potato cultivars on Globodera rostochiensis population density changes was studied at different nematode inoculum levels (Pi) in the greenhouse and field. Soil in which one susceptible and two resistant cultivars were grown and fallow soil in pots was infested with cysts to result in densities of 0.04-75 eggs/cm³ soil. A resistant cultivar was grown in an infested field with Pi of 0.7-16.7 eggs/cm³ soil. Pi was positively correlated with decline of soil population densities due to hatch where resistant potatoes were grown in the greenhouse and in the field but not in fallow soil. However, Pi was not correlated with in vitro hatch of G. rostochiensis cysts in water or potato root diffusate. Under continuous culture o f a resistant cultivar, viable eggs per cyst declined 60-90% per plant growth cycle (4 weeks) and the number of cysts containing viable eggs had decreased by 77% after five cycles. The rate of G. rostochiensis reproduction on both resistant and susceptible cultivars was negatively correlated with Pi. These data were used to predict the effect of resistant and susceptible potato cultivars on G. rostochiensis soil population dynamics.
Globodera rostochiensis; golden nematode; modeling; plant resistance; population dynamics; Solarium tuberosum; potato
The effects of aldicarb, oxamyl, 1,3-D, and plastic mulch (solarization) on soil population densities of the golden nematode (GN) Globodera rostochiensis was assessed in field and microplot experiments with different soil types. Oxamyl was evaluated in both soil and foliar treatments, whereas aldicarb, 1,3-D, and solarization were applied only to soil. Soil applications of aldicarb and oxamyl resulted in reduced nematode populations after GN-susceptible potatoes in plots with initial population densities (Pi) of > 20 and 7.5 eggs/cm³ soil, respectively, but nematode populations increased in treated soil when Pi were less than 20 and 7.5 eggs/cm³soil. In clay loam field plots with Pi of 19-76 eggs/cm³ soil, nematode densities increased even with repeated foliar applications of oxamyl, whereas nematode populations at Pi greater than 76 eggs/cm³ soil were reduced by foliar oxamyl. Treatment with 1,3-D or solarization, singly or in combination, reduced GN soil population densities regardless of soil type or Pi. Temperatures lethal to GN were achieved 5 cm deep under clear plastic but not 10 or 15 cm deep.
golden nematode; chemical management; nonchemical management; initial densities; potato; Solanum tuberosum
Soaking potato tuber pieces for 15 min in 8,000 μg/ml of oxamyl just before planting reduced the number of Globodera rostochiensis cysts that developed on potato roots, but this treatment was phytotoxic. Five foliar applications of 1.12 kg a.i./ha of oxamyl or carbofuran at 10-day intervals beginning when 90% of the plants had emerged suppressed increase in G. rostochiensis densities. Similar foliar applications of phenamiphos were ineffective in controlling G. rostochiensis. Soil applications (in the row at planting) of aldicarb, carbofuran, phenamiphos, ethoprop, and oxamyl at 5.6 kg a.i./ha reduced the numbers of white females that developed on potato roots, but only those treatments involving aldicarb and oxamyl suppressed G. rostochiensis population increase. Combined soil and foliar treatments did not provide any advantage over soil treatment alone, as soil applications of 5.6 kg a.i./ha alone were equal to, or better than, combined soil (3.4 kg a.i./ha) and foliar (2.2 kg a.i./ha) applications in controlling G. rostochiensis.
chemical control; Globodera rostochiensis; seed treatments; soil treatments; foliar treatments
Rate of passage through the digestive systems and effects of ingestion on viability of contents of cysts of Heterodera rostochiensis were determined in feeding trials with pigeons, thrushes, starlings, cowbirds, sparrows, and quails. Depending upon species of birds, 12-82% of the cysts ingested passed through the digestive system within 0.5 h. Pigeons required 6 h for complete evacuation. All other birds cmnpletely evacuated ingested cysts from their digestive systems within 3 h. Contents of cysts were nonviable if they were retained in the digestive system of starlings for more than 1.5 h, pigeons more than 1 h, or other birds more than 0.5 h. Cyst contents were nonviable if they remained in contact with excreta from cowbirds or quails for 4 h, thrushes for 96 h, or other species for 72 h after passage. Viability of contents of cysts was inversely related to exposure to excreta-filtrate concentration. Larvae failed to emerge from cysts that were exposed to a 25% concentration of excreta filtrate from starlings, 50% concentration from pigeons or thrushes, or 100% concentration of excreta filtrates from each of the other species. Cysts that were subjected to 44 C (avg. body temperature of cowbirds) for more than 3.5 h were nonviable. Cysts that passed through birds and collected with excrement on polyethylene or soil produced no infective larvae on potato.
Spread of nematodes; pigeons; thrushes; starlings; cowbirds; sparrows; quails
Population densities of Belonolaimus longicaudatus, Pratylenchus brachyurus, and Trichodorus christiei were determined from soil samples taken weekly in Tifton, Georgia during a 14-month period (except for April and May) at 15-cm increments to a depth of 105 cm. Belonolaimus longicaudatus predominately inhabited the top 30 cm of soil that was 87-88% sand, 6-7% silt, and 5-7% clay. No specimens were found below 60 cm where the soil was 76-79% sand, 5-6% silt, and 15-19% clay. Highest population densities occurred during June through September when temperature in the top 30 cm of soil was 22-25 C and soil moisture was from 9 to 20% by volume. Pratylenchus brachyurus was found at all depths, but population densities were greatest 45-75 cm deep where the soil was 78-79% sand, 6% silt, and 15-16% clay. In the months monitored, highest population densities occurred during March, June, and December when the soil temperature 45-75 cm deep was 14-17 C and soil moisture was 22-42%. Trichodorus christiei was found at all depths, but population densities were highest 30 cm deep where the soil was 83% sand, 5% silt, and 12% clay. Highest population densities occurred during December through March when the soil temperature 30 cm deep was 11-17 C and soil moisture was 18-23%.
seasonal fluctttations; Belonolairnus longicaudatus; Pratylenchus brachyurus; Trichodorus christiei