Interaction of Pratylenchus penetrans and Rhizoctonia fragariae in Strawberry Black Root Rot

A split-root technique was used to examine the interaction between Pratylenchus penetrans and the cortical root-rotting pathogen Rhizoctonia fragariae in strawberry black root rot. Plants inoculated with both pathogens on the same half of a split-root crown had greater levels of root rot than plants inoculated separately or with either pathogen alone. Isolation of R. fragariae from field-grown roots differed with root type and time of sampling. Fungal infection of structural roots was low until fruiting, whereas perennial root colonization was high. Isolation of R. fragariae from feeder roots was variable, but was greater from feeder roots on perennial than from structural roots. Isolation of the fungus was greater from structural roots with nematode lesions than from non-symptomatic roots. Rhizoctonia fragariae was a common resident on the sloughed cortex of healthy perennial roots. From this source, the fungus may infect additional roots. The direct effects of lesion nematode feeding and movement are cortical cell damage and death. Indirect effects include discoloration of the endodermis and early polyderm formation. Perhaps weakened or dying cells caused directly or indirectly by P. penetrans are more susceptible to R. fragariae, leading to increased disease.     

Seasonal Populations of Pratylenchus penetrans and Meloidogyne hapla in Strawberry Roots

Strawberry roots were sampled through the year to determine the populations and distribution of Pratylenchus penetrans and Meloidogyne hapla. Three strawberry root types were sampled—structural roots; feeder roots without secondary tissues; and suberized, black perennial roots. Both lesion and root-knot nematodes primarily infected feeder roots from structural roots or healthy perennial roots. Few nematodes were recovered from soil, diseased roots, or suberized roots. Lesion nematode recovery was correlated with healthy roots. In both 1997 and 1998, P. penetrans populations peaked about day 150 (end of May) and then declined. The decline in numbers corresponded to changes in total strawberry root weight and root type distribution. The loss of nematode habitat resulted from loss of roots due to disease and the transition from structural to suberized perennial roots. Meloidogyne hapla juvenile recovery peaked around 170 days (mid June) in 1997 and at 85, 147, 229, and 308 days (late March, late May, mid August, and early November, respectively) in 1998. There appear to be at least four generations per year of M. hapla in Connecticut. Diagnostic samples from an established strawberry bed may be most reliable and useful when they include feeder roots taken in late May.     

Comparison of Pratylenchus penetrans Infection and Maladera castanea Feeding on Strawberry Root Rot

The interaction of lesion nematodes, black root rot disease caused by Rhizoctonia fragariae, and root damage caused by feeding of the scarab larva, Maladera castanea, was determined in greenhouse studies. Averaged over all experiments after 12 weeks, root weight was reduced 13% by R. fragariae and 20% by M. castanea. The percentage of the root system affected by root rot was increased by inoculation with either R. fragariae (35% more disease) or P. penetrans (50% more disease) but was unaffected by M. castanea. Rhizoctonia fragariae was isolated from 9.2% of the root segments from plants not inoculated with R. fragariae. The percentage of R. fragariae-infected root segments was increased 3.6-fold by inoculation with R. fragariae on rye seeds. The presence of P. penetrans also increased R. fragariae root infection. The type of injury to root systems was important in determining whether roots were invaded by R. fragariae and increased the severity of black root rot. Pratylenchus penetrans increased R. fragariae infection and the severity of black root rot. Traumatic cutting action by Asiatic garden beetle did not increase root infection or root disease by R. fragariae. Both insects and diseases need to be managed to extend the productive life of perennial strawberry plantings.     

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.     

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.     

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.     

Infection of Pratylenchus penetrans by Nematode-pathogenic fungi

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%.     

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.     

Impact of Plant Nutrition on Pratylenchus penetrans Infection of Prunus avium Rootstocks

A hypothesis that cherry rootstocks grown under optimal nutrient conditions are affected less by Pratylenchus penetrans infection than those grown under deficient nutrient conditions was tested by growing four Prunus avium L. rootstocks (''Mazzard'', ''Mahaleb'', ''GI148-1'', and ''GI148-8'') at a soil pH of 7.0 over a period of 3 months under greenhouse conditions (25 ñ 2 °C). Pratylenchus penetrans was inoculated at 0 (control) or 1,500 nematodes per g fresh root weight for a total of 3,600, 4,200, 10,500, and 11,400 per plant on Mazzard, Mahaleb, GI148-1, and GI148-8, respectively, with nutrients (commercial fertilizer) applied once at planting (deficient) or twice weekly (optimal). The experiment was repeated once. The optimum nutrient regime resulted in greater soil nutrient levels and plant growth; higher leaf concentrations of N, P, K, and Mg; and fewer P. penetrans than under the deficient nutrient regime. The addition of fertilizer either may increase nematode mortality in the soil or improve rootstock resistance to nematode infection. Increases in Ca in leaves from the nutrient-deficient and nematode-infected treatments suggested the plants were physiologically stressed. The Pf/Pi ratios indicated that these rootstocks may have had resistance to P. penetrans; however, because of the dominant role of nutrition in the experimental design, the question of resistance could not be properly addressed.     

Inheritance of Resistance to Pratylenchus penetrans in Alfalfa

Fifty-two alfalfa (Medicago sativa L.) clones, randomly selected from the cultivar Baker and the experimental line MNGRN-4, were evaluated for resistance (based on nematode reproduction) to Pratylenchus penetrans in growth chamber tests (25 C). Twenty-five clones, representing the range of nematodes and eggs per plant, were selected and retested. Four moderately resistant and two susceptible alfalfa clones were identified. Inheritance of resistance to P. penetrans was studied in these six clones using a diallel mating design. The S₁, Fl, and reciprocal progenies differed for numbers of nematodes and eggs per g dry root and for shoot and root weights (P < 0.05). Resistance, measured as numbers of nematodes in roots, was correlated between parental clones and their S₁ families (r = 0.94), parental clones and their half-sib families (r = 0.81), and S₁ and half-sib families (r = 0.88). General combining ability (GCA) effects were significant for nematode resistance traits. Both GCA and specific combining ability (SCA) effects were significant for plant size traits, but SCA was more important than GCA in predicting progeny plant size. Reciprocal effects were significant for both nematode resistance and plant size traits, which may slow selection progress in long-term selection programs. However, the GCA effects are large enough that breeding procedures that capitalize on additive effects should be effective in developing alfalfa cultivars with resistance to P. penetrans.     

Observations on the Invasion and Endoparasitic Behavior of the Root Lesion Nematode Pratylenchus penetrans

The endoparasitic behavior of Pratylenchus penetrans was examined using video-enhanced contrast microscopy to observe living nematodes inside root tissue. Feeding behavior could be separated into phases of probing, cell penetration by the stytet, salivation, and food ingestion for brief and extended periods. After cell penetration, a small "salivation zone" was formed around the stylet tip. No feeding tubes were observed. Feeding and migration were interrupted by rest phases when a nematode became characteristically coiled inside a cell. Tissue damage was caused primarily by migration and extended feeding periods. Aspects of egg laying and molting are also described.     

Penetration of Celery and Alfalfa Roots by Pratylenchus penetrans as Affected by Temperature

A greater percentage of females than juveniles or males of P. penetrans penetrated celery roots grown in infested soil at 5, 18, or 30 C; the difference was greatest at 5 C. The time of initial penetration of alfalfa seedlings inoculated with single nematodes on water agar varied with temperature. Females penetrated the seedlings earlier and over a wider range of temperatures than did males or juveniles. The rate of penetration was highest for females. After initial penetration, the penetration rate decreased with time. At 13-28 C, approximately 80% of roots were penetrated by females and only 25-30% by males and juveniles by the end of the experiment.     

Pathogenicity of Pratylenchus penetrans,Heterodera glycines,and Meloidogyne incognita on Soybean Genotypes

The pathogenicity of Heterodera glycines, Meloidogyne incognita, and Pratylenchus penetrans on H. glycines-resistant ''Bryan,'' tolerant-susceptible ''G88-20092,'' and intolerant-susceptible ''Tracy M'' soybean cultivars was tested using plants grown in 800 cm³ of soil in 15-cm-diam. clay pots in three greenhouse experiments. Plants were inoculated with 0, 1,000, 3,000, or 9,000 H. glycines race 3 or M. incognita eggs, or vermiform stages of P. penetrans/pot. Forty days after inoculation, nmnbers of all three nematodes, except H. glycines on Bryan, generally increased with increasing inoculum levels in Experiment I. Heterodera glycines and M. incognita significantly decreased growth only of Tracy M. At 45 and 57 days after inoculation with 6,000 individuals/pot in experiments II and III, respectively, significantly more P. penetrans and M. incognita than H. glycines were found on Bryan. However, H. glycines and M. incognita population densities were greater than P. penetrans on G88-20092 and Tracy M. Growth of Tracy M infected by H. glycines and M. incognita and growth of G88-20092 infected by M. incognita decreased in Experiment III. Pratylenchus penetrans did not affect plant growth. Reduction in plant growth differed according to the particular nematode species and cultivar, indicating that nematodes other than the species for which resistance is targeted can have different effects on cultivars of the same crop species.     

Differentiation of Two New York Isolates of Pratylenchus penetrans Based on Their Reaction on Potato

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.     

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.     

Effect of Initial Nematode Population Density on the Interaction of Pratylenchus penetrans and Verticillium dahliae on 'Russet Burbank' Potato

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.     

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.     

Comparative Response of Alfalfa to Pratylenchus penetrans Populations

Four populations of Pratylenchus penetrans did not differ (P > 0.05) in their virulence or reproductive capability on Lahontan alfalfa. There was a negative relationship (r = -0 .7 9 ) between plant survival and nematode inocula densities at 26 ± 3 C in the greenhouse. All plants survived at an inoculum level (Pi) of 1 nematode/cm³ soil, whereas survival rates were 50 to 55% at 20 nematodes/cm³ soil. Alfalfa shoot and root weights were negatively correlated (r = - 0.87; P < 0.05) with nematode inoculum densities. Plant shoot weight reductions ranged from 13 % at Pi 1 nematode/cm³ soil to 69% for Pi 20 nematodes/cm³ soil, whereas root weight reductions ranged from 17% for Pi 1 nematode/cm³ soil to 75% for Pi 20 nematodes/cm³ soil. Maximum and minimum nematode reproduction (Pf/Pi) for the P. penetrans populations were 26.7 and 6.2 for Pi 1 and 20 nematodes/cm³ soil, respectively. There were negative correlations between nematode inoculum densities and plant survival (r = 0.84), and soil temperature and plant survival (r = -0 .7 8 ). Nematode reproduction was positively correlated to root weight (r = 0.89).     

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.     

Soil Temperature Effects on Onion Seedling Injury by Pratylenchus penetrans

The effect of soil temperatures 7-25 C upon injury to seedling onions by Pratylenchus penetrans was investigated. At 7-13 C < 100 nematodes/g of root caused significant reduction in onion root weights by the fifth week. More than 400 nematodes/g were required to produce comparable injury at 16-25 C.