Resistance in Potato to Pratylenchus penetrans

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.     

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.     

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.     

Characterization of Pratylenchus penetrans from Ten Geographically Isolated Populations Based on Their Reaction on Potato

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.     

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.     

The Influence of Pratylenchus penetrans on the Incidence and Severity of Verticillium Wilt of Potato

The influence of Pratylenchus penetrans on the incidence and severity of Verticillium wilt was examined in the potato cultivars ''Kennebec'', ''Katahdin'', and ''Abnaki''. Single-stem plants were grown in soil maintained at a temperature of 22 ± 1 C. Axenically cultured nematodes were suspended in water and introduced to the soil, at a rate of ca 5,000/25.4-cm pot, through holes made around each stem. Ten days after infestation with nematodes, conidial suspensions of Verticillium albo-atrum were introduced into the soil at a rate of ca 1,000,000/pot. Among Katahdin plants, the severity of foliar symptoms was increased in the presence of both pathogens 2 and 3 weeks after soil intestation. During the remaining 5 weeks, severity of foliar symptoms was not different between plants infected by both pathogens and those infected by Verticillium alone. Within the wilt-susceptible cultivar Kennebec and the resistant eultivar Abnaki, no effects on foliar symptom severity were observed. When plant heights, shoot weights, and tuber yields were analyzed, a Pratylenchus-Verticillium interaction was not evident within any of the cultivars tested. Nematode populations in roots and rhizosphere were suppressed in Kennebec and Katahdin plants in the presence of Verticillium.     

Infectivity of Pratylenchus penetrans on Alfalfa

The infectivity of Pratylenchus penetrans on alfalfa seedlings cv. Du Pulls was studied. The dense root-hair zone was the preferred zone of penetration by females, males, and third-stage larvae. A lesion initially appeared as a water-soaked area at the root surface, becoming yellow and elliptical as the nematode entered the cortex, with dark-brown cells later appearing in the centre as the nematode fed. At 20 C, females penetrated roots earlier, faster, and in greater numbers than either males or third-stage larvae. Females penetrated roots at temperatures from 5 to 35 C, with maximum penetration between 10 and 30 C, while males and third-stage larvae penetrated roots only between 10 and 30 C with maximum penetration a t 20 C. Penetration of roots by females, males, and third-stage larvae increased after storage of 5 C for 35 days, but decreased after storage of 140 days or more. Combinations of the three life stages in pairs neither enhanced nor inhibited penetration of roots by individual life stages; males were not attracted to females. Increasing inoculum density up to 20 nematodes/seedling did not affect penetration.     

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.     

Changes in Vertical Distribution of Pratylenchus scribneri under Potato and Corn

The vertical distribution of Pratylenchus scribneri populations was monitored under irrigated corn and potato grown in loamy sand soil. population estimates were based on the number of nematodes recovered from 100-cm³ soil samples and the roots contained therein. Reproduction was assessed by counting the number of second-stage juveniles. An index of population maturity was computed to evaluate the age structure of populations. At no time were nematodes distributed uniformly among five soil depths from 0 to 37.5 cm deep. During the summer (June-September), changes in the total number of P. scribneri and the number of second-stage juveniles recovered were not consistent among the depths sampled. Early (April-June) and late (September-November) in the season, changes in the abundance, reproduction, and maturity of populations were similar among depths. The timing and pattern of increases in numbers of nematodes suggests that variation in the abundance of P. scribneri in the soil profile beneath potato and corn was caused primarily by reproduction rather than the movement of nematodes.     

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.     

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.     

Influence of Edaphic Factors and Previous Crop on Pratylenchus spp. Population Densities in Potato

Root and soil samples from commercial potato fields were assayed for nematodes in 1983 and 1984. Pratylenchus spp. population densities in Suffolk County, New York, were consistently, though not always statistically, higher in potato fields that had been planted to rye or wheat rather than potatoes during the previous growing season. Regardless of the previous crop, population densities in the two potato production areas in Suffolk County differed significantly: population densities on the south fork were 1.9-5.5 times higher than those on the north fork. Species prevalence differed significantly on the two forks but was not related to the previous year''s crop. P. penetrans and P. crenatus were found primarily on the north and south forks, respectively. Differences in species distribution were associated with differences in soil types. P. crenatus was usually found on loams and silt loams, but P. penetrans was found more frequently on sandy soils.     

Effect of Ditylenchus dipsaci and Pratylenchus penetrans on Verticillium Wilt of Alfalfa

Verticillium albo-atrum wilt symptoms appeared faster and were significantly more severe in the presence of Ditylenchus dipsaci in Vernal, a wilt-susceptible cultivar, than in Marls Kabul, a wilt-resistant cultivar. Winter kill in the field was not affected by the nematode during the first winter, but 50% of plants were killed in the second winter. Forage yield from nematode-infected plants was significantly reduced the second year. Interaction with V. albo-atrum did not significantly reduce forage yields below that of D. dipsaci alone. Pratylenchus penetrans did not increase the severity of wilt symptoms in the presence of V. albo-atrum, nor did it affect forage yield in the greenhouse. It did, however, reduce alfalfa yields in presence of V. albo-atrum under field conditions. D. dipsaci and P. penetrans reproduced faster in Vernal than in Maris Kabul when the fungus was present.     

Globodera rostochiensis Population Density Decline in Relation to Spatial Distribution around Resistant Potato Plants

Golden nematode, Globodera rostochiensis (GN) population decline under resistant potatoes was related to cyst distance from plants 23 cm apart in rows 92 cm apart. GN decline, determined by sampling an infested field planted to the resistant cultivar ''Yankee Chipper'', was 81.8% in cores 11.5 cm from plants within rows. Decline was 27.4% at 23 cm from plants between rows and 36.6% at 46 cm. Population decline of juveniles in cysts added to soil in bags was 90.3% for cysts 11.5 cm from plants within rows planted to the resistant cultivar ''Rosa''. Decline between rows was 83.5, 76.9, and 60.4% at 11.5, 23.0, and 46.0 cm from plants, respectively. Maximum decline within for rows 30.5, 46.0, 61.0, and 92.0 cm apart, respectively. Decline under fallow was 43.5%, signif- which peaked 7 weeks AE. There was no effect of soil depth on population decline at any sampling position. Decreasing row spacing resulted in 79.9, 74.2, 73.4, and 66.1% GN population decline for rows 30.5, 46.0, 61.0, and 92.0 cm apart, respectively. Decline under fallow was 43.5%, significantly less than under potatoes. Potato root weight between rows was negatively correlated with row spacing and positively correlated with GN population decline.     

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.     

Relationship between Root Growth of Potato,Root Diffusate Production,and Hatching of Globodera rostochiensis

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.     

Suppression of Alfalfa Growth by Concommitant Populations of Pratylenchus penetrans and two Fusarium species

Growth of alfalfa (Medicago sativa cv. Vernal) seedlings was compared after inoculation with combinations of either Pratylenchus penetrans and Fusarium soloni or P. penetrans and F. oxysporum f. sp. medicaginis. A synergistic disease interaction occurred in alfalfa when F. oxysporum and P. penetrans were added simultaneously to the soil. Alfalfa growth was suppressed at all inoculum levels of P. penetrans and F. oxysporum, but not with F. solani. Seedlings inoculated with the nematode alone gave lower yields than when inoculated with either Fusarium species alone. Fusarium oxysporum, but not F. solani, was pathogenic to alfalfa under similar experimental conditions. Fusarium oxysporum did not alter the populations of P. penetrans in alfalfa roots, whereas the presence of F. solani was associated with a diminished number of P. penetrans in the roots.     

Control of Meloidogyne spp. on Russet Burbank Potato by Applying Metham Sodium through Center Pivot Irrigation Systems

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.     

Interpreting Upland Rice Yield and Pratylenchus zeae Relationships: Correspondence Analyses

Correspondence analyses were used to explore the relationships between yield and populations of Pratylenchus zeae in an upland rice field and in a greenhouse experiment. Initial soil (Pi) and final root (Pf) population densities of P. zeae, and yield (Y) of rice cv. UPL Ri5 were determined at 490 spots in the field. Very low Y was linked to very high Pf. Low Y was linked to medium or high Pi and medium Pf. Medium to very high Y were clustered with undetectable Pi and very low or high Pf. All yield levels were independent of very high Pi. In the greenhouse experiment where seven nematode inoculum levels and three fertilizer levels were evaluated, low Y was associated with medium or high Pf and high Y with high or low Pf. The analyses indicated that nematode-yield interaction involved a complex, dynamic process, in which the root-carrying capacity probably was a determining factor. Correspondence analysis, which does not require assumptions on the shape of nematode population-yield relationships or on variable distributions, revealed meaningful associations in these complex data sets.