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1.
In experiments on competition between Pratylenchus neglectus and Meloidogyne chitwoodi in barley, the species that parasitized the roots first inhibited penetration by the latter species. Prior presence of P. neglectus impeded the development of M. chitwoodi. Pratylenchus neglectus reduced egg production, final population levels, and reproductive index of M. chitwoodi. The reduction was linearly related to initial population densities of P. neglectus. Initial population densities of M. chitwoodi had no effect on final population levels of P. neglectus. Carbon assimilation by barley plants was reduced when either nematode species was present alone, but not when both were present together. Both nematode species assimilated lower amounts of carbon when present together than when present alone. A split-root experiment demonstrated that translocatable chemicals were not involved in the competition between the two species.  相似文献   

2.
An initial density (Pi) of 1,540 Pratylenchus neglectus/kg soil suppressed shoot growth of potato, Solanum tuberosum cv. Russet Burbank, in a greenhouse test at 3 weeks. After 6 weeks, shoot weights were reduced by Pi of 662 and 1,540 nematodes/kg soil, the final soil densities of P. neglectus were twice the respective Pi, and the numbers of nematodes per gram dry root were 5,363 and 7,981. In 1986-88 field microplot experiments with the Norchip cultivar, neither shoot nor root weight was suppressed by P. neglectus. In 1986 a Pi of 115 nematodes/kg soil suppressed the total number and weight of tubers per plant. In 1987 a Pi of 186 nematodes/kg soil suppressed the marketable and total number of tubers by 19 and 25 %, respectively. In 1988 a Pi of 1,884 nematodes/ kg soil reduced total and marketable weight by 18 and 19%, respectively. In 1986 and 1987 nematode population densities in the soil increased 34-fold and 27-fold, respectively. In 1988 the Pi of 1,884 nematodes/kg soil rose to 21,890/kg at midseason, then dropped to 4,370/kg at harvest. These studies show for the first time that P. neglectus reproduces well on potato and can cause yield losses. Because of its distribution and abundance, P. neglectus may be considered an economically important parasite of potato in Ontario.  相似文献   

3.
Population dynamics of Meloidogyne chitwoodi were studied for 2 years in a commercial potato field and microplots. Annual second-stage juvenile (J2) densities peaked at harvest in mid-fall, declined through the winter, and were lowest in early summer. In the field and in one microplot study, population increase displayed trimodal patterns during the 1984 and 1985 seasons. Overwintering nematodes produced egg masses on roots by 600-800 degree-days base 5 C (DD₅) after planting. Second-generation and third-generation eggs hatched by 950-1,100 DD₅ and 1,500-1,600 DD₅, respectively, and J2 densities rapidly increased in the soil. A fourth generation was observed at 2,150 DD₅ in 1985 microplot studies. Tubers were initiated by 450-500 DD₅, but J2 were not observed in the tubers until after the second generation hatched at 988-1,166 DD₅. A second period of tuber invasion was observed when third generation J2 hatched. The regional variation in M. chitwoodi damage on potato may be explained by degree-day accumulation in different potato production regions of the western United States.  相似文献   

4.
Responses of egg masses, free eggs, and second-stage juveniles (J2) ofMeloidogyne hapla and M. chitwoodi to ethoprop were evaluated. The results indicated that J2 were the most sensitive, followed by free eggs and egg masses. In general, M. chitwoodi was more susceptible to ethoprop than M. hapla. Ethoprop at 7.2 μg a.i./g soil protected tomato roots from upward migrating M. chitwoodi for 5 weeks. The zone of protection was extended to 10 and 20 cm below the root zone when 3.6 and 7.2 cm water were applied over 8 days. Ethoprop at 1.8, 3.6, and 7.2 μg a.i./g soil degraded faster and killed fewer M. chitwoodi J2 in potato field soil previously exposed to ethoprop than in unexposed soil or sterilized exposed soil. The enhanced biodegradation property of the exposed soil lasted 17 months after the last application of ethoprop. The limited downward movement of ethoprop in the soil, migration of M. chitwoodi J2 into the treated zone, presence of resistant life stage(s) at the time of application, and loss of efficacy due to enhanced biodegradation may have a significant effect on the performance of ethoprop.  相似文献   

5.
In a petri-dish study, development of the nematode Pratylenchus neglectus was observed every 4 days, and stage-specific development times were estimated, using a parameter estimation algorithm for a distributed-delay population model. The lower threshold temperature for development of a population of P. neglectus was 7.75 C. Temperatures above 25 C were unfavorable for this population on barley. Total numbers of P. neglectus in barley roots and associated soil in pots were greatest at 25 C and lower at temperatures above and below that level. There was no change in nematode numbers per gram of root as temperature increased between 24 C and 32 C because root weights decreased at higher temperatures. Restricted root mass may contribute to the lower total nematode population levels at higher temperature. Maximum number of nematodes moved through a 2-cm layer of sand on a Baermann funnel at about 20 C; lowest number of nematodes moved at 10 C and 30 C.  相似文献   

6.
    
Soils and roots of field crops in low-rainfall regions of the Pacific Northwest were surveyed for populations of plantparasitic and non-plant-parasitic nematodes. Lesion nematodes (Pratylenchus species) were recovered from 123 of 130 non-irrigated and 18 of 18 irrigated fields. Pratylenchus neglectus was more prevalent than P. thornei, but mixed populations were common. Population densities in soil were affected by crop frequency and rotation but not by tillage or soil type (P < 0.05). Many fields (25%) cropped more frequently than 2 of 4 years had potentially damaging populations of lesion nematodes. Pratylenchus neglectus density in winter wheat roots was inversely correlated with grain yield (r2 = 0.64, P = 0.002), providing the first field-derived evidence that Pratylenchus is economically important in Pacific Northwest dryland field crops. Stunt nematodes (Tylenchorhynchus clarus and Geocenamus brevidens) were detected in 35% of fields and were occasionally present in high numbers. Few fields were infested with pin (Paratylenchus species) and root-knot (Meloidogyne naasi and M. chitwoodi) nematodes. Nematodes detected previously but not during this survey included cereal cyst (Heterodera avenae), dagger (Xiphinema species), and root-gall (Subanguina radicicola) nematodes.  相似文献   

7.
    
Seasonal vertical migration of Meloidogyne chitwoodi through soil and its impact on potato production in Washington and Oregon was studied. Nematode eggs and second-stage juveniles (J2) were placed at various depths (0-180 cm) in tubes filled with soil and buried vertically or in holes dug in potato fields. Tubes were removed at intervals over a 12-month period and soil was bioassayed on tomato roots. Upward migration began in the spring after water had percolated through the tubes. Nematodes were detected in the top 5 cm of tubes within 1-2 months of burial, depending on depth of placement. Potatoes were grown in field plots for 4 or 5 months before the tubers were evaluated for infection. One hundred eggs and J2 per gram soil placed at 60 and 90 cm caused significant tuber damage at the Washington and Oregon sites, respectively. At the Washington site, inoculum placed at 90, 120, and 150 cm caused potato root infection without serious impact on tuber quality, but inoculum diluted 2-8 times and placed at 90 cm did not cause root or tuber infection. Nematode migration was dependent on soil texture; 9 days after placement at the bottoms of tubes, J2 had moved up 55 cm in sandy loam soil (Oregon) but only 15 cm in silt loam (Washington). Thus, the importance of M. chitwoodi which occur deep in a soil profile may depend on soil texture, population density, and length of the growing season.  相似文献   

8.
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.  相似文献   

9.
    
Yield-loss models were developed for potato early dying, caused by an interaction between Verticillium dahliae and Pratylenchus penetrans. Yield data were collected over 5 years (1985-1989) from potato plants grown in microplots infested with V. dahliae and (or) P. penetrans. The model y = b₀ + (1 - b₀)/(1 + [VD/36.7]), where y was the relative yield (with uninfested controls = 1.0) and VD was the preplant density of V. dahliae microsclerotia per cm³ soil, was fitted to the data set. When P. penetrans = 0, b₀ = 0.55 (SE = 0.099), and when P. penetrans > 0, b₀ = 0.23 (SE = 0.035). This model assumed that yield loss was proportional to the concentration of preplant microsclerotia of V. dahliae, and only qualitatively related to presence or absence of P. penetrans. This study contrasts with previous reports that predict yield loss being proportional to preplant population densities of both P. penetrans and V. dahliae.  相似文献   

10.
    
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.  相似文献   

11.
The effect of the Mi gene on the reproductive factor of Meloidogyne chitwoodi and M. hapla, major nematode pests of potato, was measured on nearly isogenic tomato lines differing in presence or absence of the Mi gene. The Mi allele controlled resistance to reproduction of race 1 of M. chitwoodi and to one of two isolates of race 2. No resistance to race 3 of M. chitwoodi or to M. hapla was found. Variability in response to isolates of race 2 may reflect diversity of virulence genotypes heretofore undetected. Resistance to race 1 of M. chitwoodi could be useful in potato if the Mi gene were functional following transferral by gene insertion technology into potato. Since the Mi gene is not superior to RMc₁ derived from Solarium bulbocastanum, the transferral by protoplast fusion appears to offer no advantage.  相似文献   

12.
    
An accession of Solanum hougasii, a wild tuber-bearing potato species native to Mexico, was found to be resistant to races 1 and 2 of Meloidogyne chitwoodi. A resistant selection was selfed and its progeny possessed the same combined resistance uniformly. A selected resistant seedling from the selfed progeny was crossed to cultivated tetraploid potato (S. tuberosum) to form an F₁ hybrid, and was backcrossed to cultivated tetraploid potato to form a BC₁ population in which resistance to the two races segregated. Progeny of the BC₁ were tested in inoculation experiments with four replicates for each progeny genotype for each race of nematode. Resistance was evaluated on the basis of extracted egg counts from the entire root system of pot-grown plants. Considering resistance to each race separately, for race 1, non-host (Rf ≤ 0.1) status was exhibited by approximately half of the BC₁. About one-third of the progeny showed non-host status to race 2. Egg production among progeny that showed non-host status for both races was higher with race 2 than with race 1. Analysis of co-segregation established that genetic control for the two races appears to be independently segregating. Although genes for resistance to race 1 derived from S. bulbocastanum and S. fendleri were previously described, this report is the first analysis showing independent genetic control in Solanum spp. for resistance to race 2 of M. chitwoodi only.  相似文献   

13.
The objective of this experiment was to determine the effects of fenamiphos 15G and short-cycle potato (PO)-sweet potato (SP) grown continuously and in rotation with peanut (PE)-grain sorghum (GS) on yield, crop quality, and mixed nematode population densities of Meloidogyne arenaria, M. hapla, M. incognita, and Mesocriconema ornatum. Greater root-gall indices and damage by M. hapla and M. incognita occurred on potato than other crops. Most crop yields were higher and root-gall indices lower from fenamiphos-treated plots than untreated plots. The total yield of potato in the PO-SP and PO-SP-PE-GS sequences increased from 1983 to 1985 in plots infested with M. hapla or M. arenaria and M. incognita in combination and decreased in 1986 to 1987 when root-knot nematode populations shifted to M. incognita. The total yields of sweet potato in the PO-SP-PE-GS sequence were similar in 1983 and 1985, and declined each year in the PO-SP sequence as a consequence of M. incognita population density increase in the soil. Yield of peanut from soil infested with M. hapla increased 82% in fenamiphos-treated plots compared to untreated plots. Fenamiphos treatment increased yield of grain sorghum from 5% to 45% over untreated controls. The declining yields of potato and sweet potato observed with both the PO-SP and PO-SP-PE-GS sequences indicate that these crop systems should not be used longer than 3 years in soil infested with M. incognita, M. arenaria, or M. hapla. Under these conditions, these two cropping systems promote a population shift in favor of M. incognita, which is more damaging to potato and sweet potato than M. arenaria and M. hapla.  相似文献   

14.
A somatic hybrid, CBP-233, between resistant Solanum bulbocastanum (SB-22) and susceptible S. tuberosum (R4) was tested for resistance to Meloidogyne chitwoodi race 1. One week after inoculation, only 0.04-0.4% of the initial inoculum (Pi, 5,000 eggs) as second stage-juveniles infected SB-22 and CBP-233 root systems, compared to 2% in R4. After 8 weeks, the number of M. chitwoodi in SB-22 and CBP-233 roots remained lower (0.3-1.5% of Pi) compared to R4, which increased from 2% to ca. 27%. Development of M. chitwoodi was delayed on SB-22 and CBP-233 by at least 2 weeks, and only half of the infective nematodes established feeding sites and matured in resistant clones compared to 99% in susceptible R4. Necrotic tissue surrounded nematodes that failed to develop in SB-22 and CBP-233. The reproductive factor (ratio of final number of eggs recovered from roots to Pi) was <0.01 for both SB-22 and CBP-233 and 46.8 for R4. Delaying inoculation of CBP-233 from 1 to 3 months after planting did not increase the chance or rate of tuber infection. Only a few M. chitwoodi developed to maturity on CBP-233 tubers and deposited a small number of eggs. SB-22 rarely produced tubers in these experiments, and like CBP-233 were resistant to M. chitwoodi. It appeared that the mechanisms of resistance to M. chitwoodi in roots and tubers of CBP-233 are similar.  相似文献   

15.
Metham sodium applied in October through center pivot irrigation systems was evaluated for control of Meloidogyne hapla at 374, 468, and 701 liters/ha and for control of M. chitwoodi at 468 liters/ha on potato. Metham sodium at the high rates effectively controlled M. hapla. No females were detected in the tubers at the high rates of nematicide application, whereas a mean of 19 and 69% of the tubers were infected at the low rate and in the nontreated controls, respectively. In the M. chitwoodi trial only 1.5% of the tubers in the treated plots were infected compared with 82% in the nontreated plots. Metham sodium effectively controlled M. chitwoodi to soil depths of 30, 61, and 91 cm.  相似文献   

16.
    
Four similar growth chamber experiments were conducted to test the hypothesis that the initial population density (Pi) of Pratylenchus penetrans influences the severity of interactive effects of P. penetrans and Verticillium dahliae on shoot growth, photosynthesis, and tuber yield of Russet Burbank potato. In each experiment, three population densities of P. penetrans with and without concomitant inoculation with V. dahliae were compared with nematode-free controls. The three specific Pi of JR penetrans tested varied from experiment to experiment but fell in the ranges 0.8-2.5, 1.8-3.9, 2.1-8.8, and 7.5-32.4 nematodes/cm³ soil. Inoculum of V. dahliaewas mixed into soil, and the assayed density was 5.4 propagules/gram dry soil. Plants were grown 60 to 80 days in a controlled environment. Plant growth parameters in two experiments indicated significant interactions between P. penetrans and V. dahliae. In the absence of V. dahliae, P. penetrans did not reduce plant growth and tuber yield below that of the nematode-free control or did so only at the highest one or two population densities tested. In the presence of K dahliae, the lowest population density significantly reduced shoot weight and photosynthesis in three and four experiments, respectively. Higher densities had no additional effect on shoot weight and caused additional reductions in photosynthesis in only one experiment. Population densities of 0.8 and 7.5 nematodes/cm³ soil reduced tuber yield by 51% and 45%, whereas higher densities had no effect or a 15% additional effect, respectively. These data indicate that interactive effects between P. penetrans and V. dahliae on Russet Burbank potato are manifested at P. penetrans population densities less than 1 nematode/cm³ soil and that the nematode population density must be substantially higher before additional effects are apparent.  相似文献   

17.
    
From September 1980 to June 1981, a survey was conducted in the major potato growing regions of northern California, Idaho, Nevada, Oregon. and Washington to determine the distribution of Meloidogyne chitwoodi and other Meloidogyne spp. Meloidogyne chitwoodi and M. hapla were the only root-knot nematode species detected parasitizing potato in all the states surveyed. Meloidogyne chitwoodi occurred alone in 83% of the samples and M. hapla in 11%, with 6% of all samples containing both species. The greater incidence of M. chitwoodi, as compared to M. hapla, may be due to the cool growing season encountered in 1980 (which favored M. chitwoodi but not M. hapla) and to the increased acreage of small grains (which are good hosts for M. chitwoodi but not M. hapla) planted in rotation with potato. Differentiation between these two species can be determined by a differential host test, perineal patterns of mature females, and shape of the tail tip amt of the tail hypodermal terminus of L₂ juveniles.  相似文献   

18.
Competition on soybean between Heterodera glycines (race 3) and Meloidogyne incognita or H. glycines and Pratylenchus penetrans were investigated in greenhouse experiments. Each pair of nematode species was mixed in 3-ml suspensions at ratios of 1,000:0, 750:250, 500:500, 250:750, and 0:1,000 second-stage juveniles or mixed stages for P. penetrans. Nematodes from a whole root system were counted and infection rates standardized per 1,000 nematodes (per replication) prior to testing the null hypothesis through a lack-of-fit F-test. Although the effect of increasing H. glycines proportions on the infection rate of M. incognita was generally adverse, the rate deviated significantly from a trend of linear decline at the 75% H. glycines level in one of two experiments. All lack-of-fit F-tests for the H. glycines and P. penetrans mix were significant, indicating that infection rates for both nematodes varied considerably across inocula. The infection rate of H. glycines decreased with increasing P. penetrans proportions. The rate of P. penetrans infection increased with increasing H. glycines proportions up to the 50% level, but declined at the 75% level. Competition had no effect on nematode development. The general adverse relationships between M. incognita and H. glycines and those between P. penetrans and H. glycines showed a linear trend. The relationship between H. glycines and P. penetrans indicates that the former may be competitive when present at higher proportions than the latter. In this study we have evaluated nematode competition under controlled conditions and provide results that can form a basis for understanding the physical and physiological trends of multiple nematode interactions. Methods critical to data analyses also are outlined.  相似文献   

19.
The Columbia root-knot nematode Meloidogyne chitwoodi parasitizes several plant species, including grasses that have been developed for semiarid environments, and substantially reduces the productivity of cereals and the longevity of perennial grasses growing under semiarid conditions throughout the intermountain region. Thirty-two auto- and allotetraploid (2n = 28) taxa in the perennial Triticeae were evaluated as possible sources of resistance to M. chitwoodi. Low levels of root galling were observed on roots of all accessions; root-gall indices ranged from 0 (no galls) to 1.95 in the grasses compared to 4.67 for the susceptible ''Ranger'' alfalfa check on a scale of 1 to 6. Even though the gall ratings were low, significant (P < 0.01) differences among accessions of the same species, among species, and among genera with different genomes were observed. Within the reproductive indices, which ranged from 0.01 to 1.20 in the grasses compared to 65.38 for the alfalfa check, there was no difference among genera with different genomes and accessions within the same species and genome; however, there was a significant (P < 0.05) difference among species with the same genomes. This variation can be traced to Thinopyrum nodosum (Jaaska-19), which was the only accession with a reproductive factor greater than 1.00. Based on the data, all auto- and allotetraploids are considered resistant to M. chitwoodi.  相似文献   

20.
    
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).  相似文献   

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