COI haplotype groups in Mesocriconema (Nematoda: Criconematidae) and their morphospecies associations

Without applying an a priori bias for species boundaries, specimen identities in the plant-parasitic nematode genus Mesocriconema were evaluated by examining mitochondrial COI nucleotide sequences, morphology, and biogeography. A total of 242 specimens that morphologically conformed to the genus were individually photographed, measured, and amplified by a PCR primer set to preserve the linkage between specimen morphology and a specific DNA barcode sequence. Specimens were extracted from soil samples representing 45 locations across 23 ecoregions in North America. Dendrograms constructed by neighbor-joining, maximum likelihood, and Bayesian Inference using a 721-bp COI barcode were used to group COI haplotypes. Each tree-building approach resulted in 24 major haplotype groups within the dataset. The distinctiveness of these groups was evaluated by node support, genetic distance, absence of intermediates, and several measures of distinctiveness included in software used for the exploration of species boundaries. Five of the 24 COI haplotype groups corresponded to morphologically characterized, Linnaean species. Morphospecies conforming to M. discus, Discocriconemella inarata, M. rusticum, M. onoense, and M. kirjanovae were represented by groups composed of multiple closely related or identical COI haplotypes. In other cases, morphospecies names could be equally applied to multiple haplotype groups that were genetically distant from each other. Identification based on morphology alone resulted in M. curvatum and M. ornatum species designations applied to seven and three groups, respectively. Morphological characters typically used for species level identification were demonstrably variable within haplotype groups, suggesting caution in assigning species names based on published compendia that solely consider morphological characters. Morphospecies classified as M. xenoplax formed a monophyletic group composed of seven genetically distinct COI subgroups. The species Discocriconemella inarata is transferred to Mesocriconema inaratum based on its phylogenetic position on the COI tree as well as previous phylogenetic analyses using 18S, ITS1, and cytochrome b nucleotide sequences. This study indicates that some of the species considered cosmopolitan in their distribution are actually multispecies polyphyletic groupings and an accurate assessment of Mesocriconema species distributions will benefit from molecular determination of haplotype relationships. The groups revealed by COI analysis should provide a useful framework for the evaluation of additional Mesocriconema species and will improve the reliability of designating taxonomic units in studies of nematode biodiversity. 

Nematode assemblages in native plant communities of molokai, hawaii

FOUR NATIVE PLANT COMMUNITY TYPES (IN DECREASING ELEVATION: montane bog, rain forest, wet mesic forest, drier forest) on Molokai were sampled for nematodes. Six samples of 10 cores each were gathered from each community. Nematodes were extracted from 200 cm(3) soil by elutriation. All extracted nematodes were counted and identified to species-level taxa. Sixty-seven species were identified among the four plant communities; only eight species occurred in all four communities. Species diversity and evenness were greater in the rain forest and mesic forest than in the bog and the drier forest, but the drier forest and mesic forest had similar species communities. The bog nematode community was not similar to the other three sites. In a presence/absence cluster analysis, all six bog sample assemblages clustered together. The rain forest samples also clustered together but were associated with the mesic forest sample closest to the rain forest edge. Of 11 nematode orders collected, Tylenchida accounted for 40% to 73% of all individuals, followed by Dorylaimida (5% to 17%). Diplogasterida were absent. No plant-parasitic nematodes of known Hawaiian agricultural importance or occurrence were collected in these native plant communities. Calculated nematode densities (76,000 to 321,300/m(2)) were comparable to those reported for some other Pacific tropical forests.

Filenchus flagellicaudatus n. sp. and Lelenchus schmitti n. sp. (Nemata: Tylenchidae) from Molokai, Hawaii

Filenchus flagellicaudatus n. sp. and Lelenchus schmitti n. sp. are described from Pepe'opae bog on Molokai, Hawaii. Filenchus flagellicaudatus n. sp. is distinguished from all other Filenchus spp. by stylet length (10 microm), robust metacorpus, elongated basal bulb, and extraordinarily long, whip-like tail (c = 2.6, c' = 31.8). Lelenchus schmitti n. sp. differs from other Lelenchus spp. by its shorter body length, weak dorso-ventral compression of the head region, and a more posterior vulva (V = 49-52). The spacious amphid pocket is introduced as a useful character for the differentiation of Lelenchus spp. from other Tylenchidae.

Meloidogyne haplanaria n. sp. (Nematoda: Meloidogynidae), a Root-knot Nematode Parasitizing Peanut in Texas

Meloidogyne haplanaria n. sp. is described and illustrated from specimens parasitizing peanut in Texas. The perineal pattern of the female is rounded to oval with a dorsal arch that is high and rounded except for striae near the vulva, which are low with rounded shoulders. The striae are distinctly forked in the lateral field, and punctations often occur as a small group near the tail tip and singly within the whole perineal pattern. The female stylet is 13-16 microm long and has broad, distinctly set-off knobs. The excretory pore opens 40-118 microm from the head, approximately halfway between the anterior end and the metacorpus. Males are 1.2-2.4 microm in length and have a high, wide head cap that slopes posteriorly. The labial disc and medial lips are partially fused to form an elongated lip structure. In some specimens the labial disk is distinctly separated from the lips by a groove. The stylet is 17-22 microm long and has wide knobs that are rounded and distinctly set off from the shaft. Mean second-stage juvenile length is 419 microm. The head region is not annulated, and the large labial disc and crescent-shaped medial lips are fused to form a dumbbell-shaped head cap. The stylet is 9-12 microm long and has rounded, posteriorly sloping knobs. The slender tail, 58-74 microm long, has a distinct, inflated rectum and a slightly rounded tip. The hyaline tail terminus is 11-16 microm long. The isozyme phenotypes for esterase and malic dehydrogenase do not correspond to any other recognized Meloidogyne species. Tomato and peanut are good hosts; corn and wheat are very poor hosts; and cotton, tobacco, pepper, and watermelon are nonhosts.

Host Range and Distribution of the Clover Root-knot Nematode, Meloidogyne trifoliophila

The ability of Meloidogyne trifoliophila to gall 230 species and cultivars of plants was determined in a greenhouse. All clovers (Trifolium spp.) were severely galled regardless of species or cultivar. Most soybean cultivars were moderately to severely galled. Among other legumes, broad bean, garden pea, Korean lespedeza, sweetclover, and common vetch were good hosts, but alfalfa, bird's-foot trefoil, peanut, and pole bean were poor or nonhosts. Among other plant families, most Apiaceae (Umbelliferae) and Brassicaceae (Cruciferae) were galled, but Cucurbitaceae, Iridaceae, Malvaceae, Poaceae, and Solanaceae were rarely or never galled. Results for Amaryllidaceae, Asteraceae, Lamiaceae, and Liliaceae were variable. This nematode was not found in a survey of pasture and soybean fields in southwestern Tennessee.

What Every Author and Reviewer Should Know about the Publication Process in the Journal of Nematology

The Journal of Nematology is a publication of the very highest quality for communicating the most recent discoveries in the science of nematology. The authors of this Viewpoint article desire to maintain the status of the journal while lessening the burden placed on the editorial staff. A few simple steps taken by authors during the manuscript preparation phase can greatly improve the quality of their papers. Authors should carefully review the "Author's Publication Handbook and Style Manual" before and during the preparation of a manuscript intended for publication in the Journal of Nematology. In addition, authors should submit a completed "Author's Checklist for Preparation of Papers" with each manuscript submitted to the journal. Reviewers should provide thorough reviews, return mantlscripts in a timely manner, and clearly define statements regarding revisions.

Meloidogyne trifoliophila n. sp. (Nemata: Meloidogynidae), a Parasite of Clover from Tennessee

Meloidogyne trifoliophila n. sp. is described from white clover collected at Ames Plantation, Fayette County, Tennessee. The perineal pattern is rounded, with long, smooth striae and rounded arch, and without distinct lateral lines or perivulval striae. The female stylet is 12.6-15.5 mum long, the excretory pore is level with or up to one stylet length posterior to the stylet knobs, and the vulva is subterminal. The posterior terminus is weakly protuberant. The male lateral field is composed of approximately eight repeatedly broken or forked incisures. The male stylet is 17.0-18.9 mum long, the stylet knobs are rounded and sloping, gradually merging with the shaft, and the head region consists of one large annule. Second-stage juveniles are 357-400 mum long, with a stylet length of 11.9-13.6 mum and one head annule. The tail tapers to a slender tip. This new species is similar to M. graminicola and M. triticoryzae but differs from them in perineal pattern and lateral field morphology, and numerous morphometric characters.

Occurrence of Pasteuria-like Organisms on Selected Plant-Pamsitic Nematodes of Pineapple in the Hawaiian Islands

Soils from 320 sites representing diverse undisturbed habitats from five Hawaiian Islands were assessed for occurrence of Pasteuria-like organisms. Mean annual rainfall at sites ranged from 125-350 cm, elevation from 69-2,286 m, and annual mean temperature from 12-24 C. Seven different natural communities were represented: wet lowland, mesic lowland, wet montane, mesk montane, dry montane, mesic subalpine, and dry alpine. Pasteuria spp. in a soil sample was detected by baiting with infective stages of Helicotylenchus dihystera, Meloidogyne javanica, Pratylenchus brachyurus, and Rotylenchulus reniformis, followed by cultivation of the nematodes on pineapple plants for 10-11 months. All nematode baits except R. reniformis were readily recovered from the soil samples. A sample was considered Pasteuria-positive if at least 5 % of the nematode specimens showed endospore attachment. Thirteen percent of all samples were positive for Pasteuria-like organisms. The frequencies of association between Pasteuria spp. and Meloidogyne, Helicotylenchus, or Pratylenchus species were 52%, 24%, and 24%, respectively. Positive samples were more prevalent on the older islands of Kauai and Oahu (75%), in lowland communities (61%), and in areas with introduced vegetation (60%). More than 27% of the positive samples were associated with plant species in a few selected families that included Meliaceae and Myrtaceae. Occurrence of Pasteuria spp. seemed to be positively associated with mean annual rainfall or temperature, but negatively associated with elevation.

Description of the Kona Coffee Root-knot Nematode, Meloidogyne konaensis n. sp

Meloidogyne konaensis n. sp. is described from coffee from Kona on the island of Hawaii. The perineal pattern of the female is variable in morphology, the medial lips of the female are divided into distinct lip pairs, and the excretory pore is 2-3 stylet lengths from the base of the stylet. Mean stylet length is 16.0 mum, and the knobs gradually merge with the shaft. The knobs are indented anteriorly and rounded posteriorly and the dorsal esophageal gland orifice (DEGO) is long, 3.5-7 mum. The morphology of the stylet of the male is the most useful diagnostic character, with 6-12 large projections protruding from the shaft. One medial lip may be divided into distinct lip pairs. A large intestinal caecum often extends nearly to the level of the DEGO. Mean juvenile length is 502 mum, mean stylet length is 13.4 mum, and mean tail length is 58 mum. The tail may be distinctly curved ventrally and the phasmids are located in the ventral incisure about one anal body width posterior to the anus.

Association of nematodes and dogwood cankers

Dogwood canker is a serious production problem of unknown etiology. From May 1985 through April 1989, cankers from 290 flowering dogwood trees in 15 separate nurseries were sampled for nematodes. Seventy-three percent (213) of the cankers contained nematodes. Panagrolaimus rigidus (Schneider) Thorne (115/290) and Aphelenchoides spp. (91/290) were the most frequently collected taxa. Panagrolaimus rigidus was reared on 2% water agar with unidentified bacteria as the food source. Aphelenchoides spp. were reared in antibiotic-amended agar culture with the fungus Glomerella cingulata (Stoneman) Spauld. &Schrenk as a food source. Repeated attempts to culture Aphelenchoides spp. on dogwood callus tissue were unsuccessful. Artificially created stem wounds inoculated with combinations of Aphelenchoides spp. and P. rigidus callused completely in 60 days with no indication of canker development. Very low numbers of nematodes were recovered from inoculated trees, but P. rigidus and one Aphelenchoides sp. were efficient dispersers and occurred in treatments other than those in which they were inoculated.

Reproduction of Plant-parasitic Nematodes on Winter Rapeseed (Brassica napus ssp. oleiferas)

The reproduction of isolates of five plant-parasitic nematode species on the winter rapeseed cultivars Bridger, Gorzanski, H-47, Lindora, and Viking was evaluated. Each cultivar was a good host for Helicotylenchus pseudorobustus, Meloidogyne hapla, and M. incognita, All rapeseed cultivars were poor hosts for Pratylenchus scribneri, in comparison with a susceptible reference host. Heterodera glycines females rarely developed on any cultivar, but low numbers of juveniles invaded roots and males occasionally reached maturity.

Trichodorus elefjohnsoni n. sp. (Nemata: Trichodoridae) from Undisturbed Appalachian Forest

A new species of Trichodoridae, Trichodorus elefjohnsoni, is described from undisturbed regions of Great Smoky Mountains National Park, United States. It resembles T. orientalis De Waele &Hashim, 1984, T. persicus De Waele &Sturhan, 1987, and T. taylori De Waele, Mancini, Roca, ' Lamberti, 1982 in arrangement of ventromedian cervical papillae and posterior preanal supplements, but differs by combinations of the following characteristics: body length 516-731 mum; spicule length 33-50 mum, spicules densely striated, constricted medially; vaginal sclerotizations ovate; one pair of lateral body pores near vulva.

Terrestrial nematodes of alaska I. Trichodoridae (nemata)

Four species of Trichodoridae, two of them new and belonging to the T. aequalis complex, are reported from Alaska. Trichodorus carlingi n. sp. differs from all other species of the genus in having conspicuously hamate spicules. Vaginal sclerotizations are trapezoidal to rectangular. Trichodorus paucisetosus n. sp., which resembles T. sparsus Szczygiel, 1968 and T. nanjingensis Liu & Cheng, 1990, has sparsely setose, noncephalated spicules partially striated in one or two zones, oval to round vaginal sclerotizations, sperm in discrete spermathecae, and onchiostyle 57-72 mum long. Trichodorus californicus Alien, 1957 is reported from many sites in Alaska, and T. aequalis Allen, 1957 is reported from one site. Trichodorus californicus was collected almost exclusively from glacial refugial regions north of the Alaska Range.

Development, Distribution, and Host Studies of the Fungus Macrobiotophthoira vermicola (Entomophthorales)

The life cycle and host range of Macrobiotophthora vermicola were studied. Secondary spores produced from forcibly ejected primary spores adhered to the cuticle of Cruznema tripartitum, germinated, and penetrated the cuticle within 30 minutes. New primary spores were produced within 24 hours of initial spore adhesion. In a host range study, species of Rhabditidae, Diplogasteridae, and Aphelenchoidea were hosts, but not species of Bunonematidae, Tripylidae, Cephalobida, or Tylenchina. Numbers of second-stage Meloidogyne incognita juveniles were not decreased when added to soil seeded with infected C. tripartitum. In six Tennessee soybean fields, Macrobiotophthora vermicola was the most commonly encountered nematode-destroying fungus, followed by a sterile, nonseptate fungus and Arthrobotrys conoides. Nematophagous fungi were isolated more frequently from silt loam soils than from clay soils. Addition of C. tripartitum to soil extract plates as a bait nematode did not increase isolations of nematophagous fungi.

Four New Species of Heteroderidae Including Ekphymatodera n. gen. from California

Four new species and a new genus of Heteroderidae from California are described, and their significance for phylogenetic analysis of the family is discussed. The new genus with type species, Ekphymatodera thomasoni n. gen., n. sp., shares many characteristics with Hylonema Luc, Taylor, &Cadet, 1978, but it is distinguished by its much greater vulva-anus distance and unique cuticular pattern. Hypotheses of relationships of Ekphymatodera and Hylonema with Sarisodera Wouts and Sher, 1971 versus Heterodera Schmidt, 1871 are discussed. Verutus californicus n. sp. is larger than the type species, Verutus volvingentis Esser, 1981, differing in females particularly by the greater distance of its excretory pore from the anterior end. Monophyly of Verutus, which may be an outgroup of all other Heteroderidae, is strengthened by description of V. californicus. Atalodera trilineata n. sp. differs from other ataloderines by having second-stage juveniles with three lateral lines and from the type, Atalodera ucri Wouts and Sher, 1971, by the more subtle cuticular pattern of females and longer juveniles with much longer tails. Atalodera festucae n. sp., with four lateral lines in juveniles, has smaller females than A. trilineata and has a protruding dorsal vulval lip. A unique common ancestor for Atalodera-Sherodera-Thecavermiculatus is supported, and monophyly with Thecavermieulatus andinus Golden, Franco, Jatala, &Astocaza, 1973 is considered.

Parasitism of Woody Ornamentals by Meloidogyne hapla

Meloidogyne hapla is the dominant root-knot nematode found in Tennessee woody ornamental nurseries. In greenhouse tests, M. hapla produced galls and formed egg masses on roots of Abelia x grandiflora, Comus florida, Hydrangea paniculata grandiflora, Photinia x fraseri, Spiraea x bumalda, Spiraea x vanhouttei, and Viburnum carlesii. Galls on H. grandiflora and V. carlesii were mostly large and fusiform. Galls on C. florida were spherical and usually terminal, whereas those on the other species were minute. Lateral roots grew from galls on all susceptible plants. Two Acer spp., two Buxus spp., three llex spp., five Prunus spp., three Rhododendron spp., Euonymus alata, Ligustrum sinense, Magnolia x soulangiana, Nandina domestica, and nine conifer species were nonhosts or very poor hosts.

Plant-parasitic nematode communities in dogwood, maple, and peach nurseries in tennessee

Nursery blocks (48 dogwood, 27 red maple, and 17 peach) distributed among 20 Tennessee nurseries were sampled for nematodes in March, July, and October 1981. Plant-parasitic nematodes were extracted from soil, counted by genera, and identified to species after fixation. A total of 57 species in 24 genera were found, with 1-16 species occurring in a site. The species most commonly detected were Paratylenchus projectus and Xiphinema americanum, which were found in 88% and 78% of the sites, respectively. Relationships existed between distribution and densities of some species present in more than 10% of the sites and certain soil factors (pH, bulk density, texture, and organic matter content). Plant-parasitic nematode community diversity was related to tree age, percentage of weed ground cover, and number of weed species. Site similarities in community ordinations were dependent on the individual nurseries sampled, tree age, and soil type, but clusters of sites of similar tree ages and soil types were not exclusive.

Nematode community structure in dogwood, maple, and peach nurseries in tennessee

Nursery blocks (48 dogwood, 27 maple, 17 peach) in 20 middle Tennessee nurseries were sampled for nematodes in March,July, and October 1981. Dogwoods and maples were grouped in three age classes: 1-2, 3-5, and 10+ years. Nematodes were extracted from soil samples, counted, and assigned to trophic groups as follows: plant parasites, microbivores, fungivores, predators, and omnivores (= Dorylaimida). Total nematode numbers per 200 cm s soil ranged from 52 to 9,166 (mean = 1,785 +/- 1,420). Nematodes were more abundant in dogwood and maple than in peach blocks, and their numbers were significantly correlated with percentage of weed ground cover and number of weed species. Nematode numbers in dogwood sites were also correlated with dogwood age. Microbivores were the most abundant trophic group in all sites, followed by plant parasites, fungivores, omnivores, and predators. Nematode communities in nursery sites shared characteristics of both undisturbed and agricultural habitats. Degree and diversity of plant ground cover appeared to be the most important factors determining nematode community structure.

Nematode population and community dynamics in soybean-wheat cropping and tillage regimes

The nematode community structures of various soybean-wheat regimes and of a single-cropped, conventionally tilled soybean regime were studied at two sites in Tennessee. Each of the 100 nematode species identified in the study was placed in one of five trophic groups, the most diverse being plant parasites (31 species), followed by Dorylaimida (26 species), bacterivores (23 species), fungivores (15 species), and predators (5 species). No significant differences in overall diversity and dominance among treatments and trophic groups were found. Densities of Heterodera glycines Ichinohe infective juveniles were significantly higher in single-cropped, conventionally tilled soybeans in July. When data were subjected to ordination analysis, it was shown that plant-parasitic nematode communities produced an aggregation of conventionally tilled, single-cropped soybean plots when compared to all double-cropped treatments. Ordination of overall nematode communities yielded similar results.

Hoplolaimoidea (nematoda: tylenchida) from the aleutian islands with descriptions of four new species

Four new species of hoplolaimoid nematodes (Merlinius adakensis, Pratylenchoides megalobatus, Pratylenchus pratensisobrinus, and Pratylenchus ventroprojectus) are described from Adak Island in the Aleutian chain. M. adakensis n. sp. is separated from other species by body length (0.96-1.3 mm), stylet length (32-36 mum), number of tail annules (49-68), and c' (3.1-4.1). P. megalobatus n. sp. differs from all known Pratylenchoides spp. by having a very long esophageal gland lobe (b' = 2.4-3.3, overlap 3-6 times the body width). P. pratensisobrinus n. sp. closely resembles P. pratensis (de Man) Filipjev, but has a longer stylet (15-17 mum), a longer tail (c = 12-15; c' = 2.8-3.7), and more tail annules (23-37). P. ventroprojectus n. sp. is distinguished by body length (392-475 mum), three lip annules, low and flattened cephalic capsule, and presence of terminal subventral projection. Pratylenchoides variabilis Sher, Helicotylenchus amplius Anderson &Eveleigh, and H. spitsbergensis Loof are also reported from Adak and Amchitka Islands.

Criconematina (nematoda: tylenchida) from the aleutian islands

A new genus (Cerchnotocriconenta) and three new species (C. psephinum, Hemicycliophora amchitkaensis, and Paratylenchns amundseni) are described from Adak and Amchitka Islands in the Aleutian chain. The new genus differs from all other criconematid genera in having irregular, convex sculpturing consisting of small, oval plates on the anterior and posterior regions of each annule, with the mid-annular region minutely punctate or dentate. H. arnchitkaensis n. sp. resembles H. similis Thorne and H. zuckermani Brzeski, but has only one head annule, instead of two. P. antundseni n. sp., which has a stylet 17-19 mum long, is similar to P. tateae Wu &Townshend and P. labiosus Anderson &Kimpinski, but differs by the presence of males and the possession of conoid-truncate lip region, functional spermatheca, and long male tail (c = 8.5-9.5). Seriespinula seymouri Wu (Mehta &Raski), Nothocrieonema longulum (Gunhold) De Grisse &Loof, and Macroposthonia xenoplax (Raski) De Grisse &Loof are also reported from the islands.

Three new species of heteroderoidea (nematoda) from the aleutian islands

Three new species of Heteroderoidea are described from Adak and Amchitka Islands in the Aleutian chain. Second-stage juveniles of Thecavermiculatus crassicrustata, n. sp., differ from those of T. gracililancea Robbins by having longer stylets (40-45 mum vs 19-22 mum). The female of T. crassicrustata has a longer neck, a more posterior excretory pore, and lacks a posterior protuberance. Meloidodera eurytyla, n. sp., differs from other Meloidodera spp. in that second-stage juveniles have longer stylets (32-35 mum) and much more massive stylet knobs, while males have a longitudinally striated basal head annule. Meloidogyne subarctica, n. sp., can be separated from other Meloidogyne spp. by combinations of the following characteristics: perineal pattern with large oval areas in the tail region devoid of striae, arch with few unbroken striae; female excretory pore 1.5-2.5 x the stylet length from the anterior end; haploid chromosome number = 18; the spermatheca filled with sperm; stylet length of second-stage juveniles 13.5-15.4 mum.

New species of bunonematoidea (rhabditida) from georgia and tennessee

Three new species of Bunonematidae (Bunonema husseyi, Rhodolaimus dimorphus, R. stephaniae) and one of Plerygorhabditidae (Pterygorhabditis panoplus) are described from Georgia and Tennessee. The juvenile external morphology of P. panoplus is described and illustrated. A lectotype of P. pakistanensis is designated and the two species compared, and the dissimilar nature of cuticular tubercles in Bunonema and Rhodolaimus is discussed.

Movement and Persistence of 1,2-dibromo-3-chloropropane in a Soil with a Plow-pan

Movement and persistence of 1,2-dibrotno-3-chloropropane (DBCP) in a Coastal Plain soil containing a sandy plow-pan were enhanced in each of 2 years by subsoiling, increased depth of application, and increased rate of application. DBCP was extracted from the soil with hexane and analyzed by gas chromatography. Subsoiling at a 35-cm depth gave the greatest increase in lateral movement and downward penetration of DBCP in 1975 (a wet year), but bad less effect in 1976 (a dry year). An increased application rate (10 kg/ha vs. 13.5) improved coverage moderately in 1975 by increasing lateral movement, but had little effect in 1976. Increased application depth (18 vs. 35 cm) improved coverage in both years though more in 1976. Deep placement extended DBCP retention time. Rainfall in 1975 probably decreased the number and size of air-filled pores, slowing loss of DBCP to the atmosphere. Because of reduced porosity, the plow-pan was impervious to the passage of DBCP unless disrupted by subsoiling.

Relative susceptibility of selected cultivars, of potato to Pratylenchus penetrans

Pratylenchus penetrans suppressed the tuber yields of potato cultivars 'Katahdin', 'Kennebec', and 'Superior', but did not affect yields of 'Russet Burbank'. In comparison with noninfested controls, all initial nematode densities (P(i)) of P. penetrans (P(i) = 38, 81, 164, 211/ 100 cm(3) of soil) suppressed yields of Superior; a moderate P(i) (81/100 cm(3) soil) suppressed yields of Kennebec; and on Katahdin, a moderate P(i) enhanced yields, but higher P(i)'s caused a marked loss. In general, yields were related to the tolerance of the cultivars to nematode colonization. Highest nematode densities were found in the roots of Russet Burbank; the next highest, in succeeding order, were found in roots of Kennebec, Katahdin, and Superior. Symptoms of nematode invasion were confined to losses of tuber yield and root weight.