Ultrastructural Pathology of Cells Affected by Pratylenchus penetrans in Alfalfa Roots

Cortical parenchyma cells penetrated and fed upon by Pratylenchus penetrans for 48 hours contained only cytoplasmic debris. Proximal cells had an increase in tannin deposits, degenerated mitochondria, increased numbers of ribosomes, and no internal membrane structure. Often the endodermis was collapsed and contained massive tannin deposits on the inner cell wall and cell lumen. Similar observations were made in the stele, except tannin deposits were not as prominent. Multivesicnlate structures were observed both in the endodermis and in the stele.     

Temporal Changes in the Vertical Distribution of Pratylenchus penetrans under Raspberry

Population densities of Pratylenchus penetrans and the biomass of fine roots of raspberry at depths of 0-5, 5-10, 10-20, and 20-30 cm were determined every 2 weeks for 2 years. The vertical distribution of P. penetrans varied from season to season, but the seasonal changes were not similar for the 2 years. In most seasons, the greatest population density was in the 5 to 10-cm-depth interval. Population densities of P. penetrans were not consistently correlated with the vertical distribution of raspberry roots in any season.     

Control of Pratylenchus penetrans and Meloidogyne hapla and Yield Response of Alfalfa Due to Oxamyl Seed Treatments

Alfalfa (Medicago sativa L. cv. Saranac) seed were soaked for 20 minutes in water, acetone, or methanol containing 10 or 50 mg/ml of oxamyl (Vydate L) or coated with a 2% aqueous cellulose solution containing the same amounts of oxamyl. Seed were analyzed for oxamyl by HPLC immediately after treatment and after 9 and 26 months of storage. Oxamyl content of alfalfa seed did not decline after 26 months of storage. The effects of seed treatment on growth of alfalfa and nematode control were examined using soils infested with Pratylenchus penetrans and Meloidogyne hapla. Germination was not affected by any of the seed treatments. Twenty-one days after sowing, the total growth of alfalfa seedlings grown from seed treated with 50 mg/ml of oxamyl in P. penetrans-infested soils had increased by 62% over controls. Nodulation per pot increased by as much as 267%, and the densities of P. penetrans per gram of root were reduced by as much as 73% compared to control plants. In M. hapla-infested soils, increases in plant growth (32%) and nodulation (71%) also occurred with oxamyl-treated seeds. Root gall reduction (86%) was also substantial due to oxamyl seed treatment.     

Morphological Observations of Pratylenchus penetrans from Celery and Strawberry in Southern Ontario

Pratylenchus penetrans was obtained from Premier strawberry in Norfolk County and the Niagara Peninsula and from celery in the latter area. Host affected the dimensions of P. penetrans to a greater extent than geographical area in Ontario. Adults of P. penetrans from southern Ontario tended to be smaller than those reported elsewhere. The presence of three lip annules was consistent in the seven populations studied, although in some specimens one of the annules did not entirely encompass the head. Crenations around the tail tip of females of P. penetrans was common in the populations studied. Not all of the morphological characters were proportional in size to length of the females of P. penetrans.     

Diagnostic Probes Targeting the Major Sperm Protein Gene That May Be Useful in the Molecular Identification of Nematodes

Discrimination of closely related nematode species is typically problematic when traditional identification characteristics are prone to intraspecific variation. In this study, a molecular approach that can distinguish Pratylenchus penetrans and P. scribneri is described. The approach uses universal primers in conjunction with polymerase chain reaction (PCR) to amplify equivalent fragments of the major sperm protein (msp) gene from any nematode. This gene fragment typically includes an intron of variable sequence. The presence of this highly variable segment in an otherwise conserved gene sequence allows P. penetrans and P. scribneri to be distinguished by either a species-specific amplification or by dot-blot hybridization. The approach is potentially of general utility in species-specific identification of nematodes.     

Effect of Hirsutella rhossiliensis on Infection of Potato by Pratylenchus penetrans

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.     

Management Options for Pratylenchus penetrans in Easter Lily

Alternatives to reduce or modify nematicide use for minimizing groundwater contamination in Easter lily were explored in two field trials. Alternatives to standard 1,3-dichloropropene (1,3-D) plus phorate injection in the first trial were: (i) delaying applications until after winter rains, (ii) removing roots from planting stock, (iii) 1,3-D via drip irrigation, (iv) a chitin-urea soil amendment, (v) the registered insecticide disulfoton, and (vi) several nonregistered nematicides. None of the treatments equaled the standard treatment. In the second trial, potential benefits of adding a systemic nematicide, oxamyl (OX), or a fungicide, metalaxyl (MX), to the standard treatment were explored. Preplant drip irrigation applications of metam sodium (MS), sodium tetrathiocarbonate (ST), and emulsifiable 1,3-D were evaluated alone and in combination with postplant applications of OX and MX. Several drip-applied treatments performed comparably to the standard treatment with respect to the most important criteria of crop quality, bulb circumference. Metam-sodium in combination with either or both OX and MX, 1,3-D plus OX and MX, and ST plus OX and MX provided the best results.     

Effects of Pratylenchus penetrans on the Infection of Strawberry Roots by Gnomonia comari

The fungus Gnomonia comari, causal agent of strawberry leaf blotch, was inoculated at the crown of young axenized strawberry plants growing in sterilized sand. Only the roots were colonized, and the infection was symptomless. When the fungus colonized the roots in the presence of the root lesion nematode Pratylenchus penetrans, the plants were extremely stunted and their root system was necrotic. Fungal conidiospores were found attached to the cuticle of nematodes extracted from soil inoculated with the two pathogens. These findings indicate that P. penetrans could transport conidiospores through soil.     

Response of Peach Seedlings to Infection by the Root Lesion Nematode Pratylenchus penetrans under Controlled Conditions

Twenty-one open pollinated populations of peach rootstock seedlings were evaluated for their response to infection by the root lesion nematode, Pratylenchus penetrans, over a period of 98 days. Nematode-infected peach seedling populations were shorter in plant height and had less shoot weight but more dry root weight than nematode-free controls. Rootstock differences were demonstrated for nematode increase over the 98-day period, and average total numbers of nematodes in soil and roots. Rootstocks were classified into three groups differing in total nematode population levels, ratio of nematode increase, and the number of nematodes per root. The heritable nature of rootstock response to nematodes was evident. Rootstocks showing the lowest response to nematode infection included Tzim Pee Tao, Rutgers Red Leaf, and two progenies of a cross of these two rootstocks.     

Reproduction of Pratylenchus penetrans on 24 Common Weeds in Potato Fields in Qu��bec

Twenty-four weeds commonly found in commercial potato fields in Quebec were evaluated for their host suitability to the root-lesion nematode, Pratylenchus penetrans, under greenhouse conditions. Brown mustard (Brassica juncea) and rye (Secale cereale) were included as susceptible controls and forage pearl millet hyb. CFPM 101 (Pennisetum glaucum) as a poor host. Pratylenchus penetrans multiplied well on 22 of the 24 weed species tested (Pf/Pi ≥ rye or brown mustard). Cirsium arvense, Leucanthemum vulgare and Matricaria discoida were classified as very good hosts with a Pf/Pi ranging from 1.60 to 2.54, while Ambrosia artemisiifolia and Cyperus esculentus were classified as poor hosts with a Pf/Pi from 0.01 to 0.15. Amaranthus powellii, A. retrqflexus, Raphanus raphanistrum, Rorippa palustris, Cerastium fontanum, Spergula arvensis, Stellaria media, Chenopodium album, Vicia cracca, Elytrigia repens, Digitaria ischaemum, Echinochloa crusgalli, Panicum capillare, Setaria faberii, S. pumila, S. viridis, Polygonum convolvulus, P. scabrum and P. persicaria were intermediate hosts with Pf/Pi values ranging from 0.33 to 2.01. The plant species and the botanical family had a significant impact on nematode reproduction. The Brassicaceae family resulted in the greatest reproduction of P. penetrans, and the Cyperaceae resulted in the least. The plant life-cycle (annual vs. perennial) had no impact on nematode population.     

Plant Pathogen Population Dynamics in Potato Fields

Modern technologies incorporating Geographic Information Systems (GIS), Global Positioning Systems (GPS), remote sensing, and geostatistics provide unique opportunities to advance ecological understanding of pests across a landscape. Increased knowledge of the population dynamics of plant pathogens will promote management strategies, such as site-specific management, and cultural practices minimizing the introduction and impact of plant pathogens. The population dynamics of Alternaria solani, Verticillium dahliae, and Pratylenchus penetrans were investigated in commercial potato fields. A 0.5-ha diamond grid-sampling scheme was georeferenced, and all disease ratings and nematode samples were taken at these grid points. Percent disease severity was rated weekly, and P. penetrans densities were quantified 4 weeks after potato emergence. Spatial statistics and interpolation methods were used to identify the spatial distribution and population dynamics of each pathogen. Interpolated maps and aerial imagery identified A. solani intra-season progression across the fields as the potato crop matured. Late-season nitrogen application reduced A. solani severity. The spatial distributions of V. dahliae and P. penetrans were spatially correlated.     

Competition between Heterodera glycines and Meloidogyne incognita or Pratylenchus penetrans: Independent Infection Rate Measurements

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.     

Reproduction and Parasitism of Pratylenchus neglectus on Potato

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.