Effects of rice-cultured Paecilomyces lilacinus on Rotylenchulus reniformis were studied in both greenhouse and field microplot tests with 'Rutgers' tomato. Numbers of R. reniformis were reduced (P ≤ 0.05) by P. lilacinus, with suppression in the initial greenhouse test ranging from 46 to 48% for two rice + P. lilacinus treatments; the rice-only treatment caused a nonsignificant reduction of 25%. In the second greenhouse test, total R. reniformis numbers were restricted (P ≤ 0.05) by 41% by the rice + P. lilacinus treatment, whereas the rice-only treatment had a slight negative effect (16% inhibition, NS). Total numbers of R. reniformis were suppressed 59 and 36% at midseason and harvest, respectively, in microplots infested with P. lilacinus. The fungus was recovered from egg masses via isolations in the second greenhouse test. Shoot and fruit growth of Rutgers tomato were restricted by R. reniformis in the initial greenhouse test irrespective of P. lilacinus treatment, but this nematode did not affect fresh shoot weights in the second greenhouse test, The nematode also limited shoot growth of Rutgers tomato in microplots, and P. lilacinus suppressed R. reniformis numbers sufficiently to prevent related impairment of shoot and fruit growth. This study indicated that P. lilacinus has detrimental effects on R. reniformis population development under both greenhouse and field microplot conditions.
biological control; Lycopersicon esculentum; nematode; Paecilomyces lilacinus; reniform nematode; Rotylenchulus reniformis; tomato
A host suitability study of 32 plant species to Meloidogyne konaensis included 54 vegetable cultivars, 12 field crop cultivars, one Gardenia sp., and two weed species. Host suitability was classified according to a M. konaensis reproductive factor: final population density (Pf) (eggs + J2) / initial population density (Pi) (eggs). The number of eggs per gram dry root, and a galling index was also included. Reproductive factor ranges and percentages of plants in the ranges were as follows: Pf/Pi > 5.0, 56.5%; 5.0 ≥ Pf/Pi > 1.0, 24.6%; 1.0 ≥ Pf/Pi > 0, 15.9%; and Pf/Pi = 0, 3%. Peanut and 'Decicco' broccoli were nonhosts. Few or no galls were observed on pepper, corn, ginger, waterchestnut, 'Michihili' chinese and 'Marion' market cabbage, although the reproductive factor of M. konaensis was above 5 on these plants.
field crops; gardenia; Meloidogyne konaensis; nematode; nonhosts; root-knot nematode; vegetable; weed
Alfalfa is a host of Pratylenchus penetrans and P. neglectus, whereas crested wheatgrass is a host of P. neglectus but not of P. penetrans. In a 120-day greenhouse experiment at 24 ñ 3 C, P. neglectus inhibited the growth of 'Lahontan' alfalfa and 'Fairway' crested wheatgrass. There were no differences in persistence and plant growth of alfalfa and crested wheatgrass, or reproduction of P. neglectus, in single plantings of alfalfa (AO) or crested wheatgrass (CWO), or in interplanted alfalfa and crested wheatgrass (ACW) treatments. On alfalfa, P. penetrans inhibited growth and reproduced more than did P. neglectus. Inhibition of plant growth and reproduction of P. penetrans was greater on alfalfa in AO than in ACW treatments. Pratylenchus penetrans did not reproduce on crested wheatgrass, but inhibited growth of crested wheatgrass in interplanted treatments and was avirulent in single planted treatments. Results were similar in a controlled growth chamber experiment at 15, 20, 25, and 30 C. Both nematode species inhibited alfalfa growth at all temperatures, and P. penetrans was more virulent than was P. neglectus to alfalfa at all temperatures and treatments. Plant growth inhibition and reproduction of P. penetrans on alfalfa in single and interplanted treatments were similar at 15-20 C, but were greater in single than in interplanted treatments at 25-30 C. Pratylenchus penetrans was avirulent to crested wheatgrass in the single planted treatments at all temperatures, but inhibited growth of crested wheatgrass in interplanted treatments at 20-30 C. Plant growth and reproduction of P. neglectus on crested wheatgrass was similar in single and interplanted treatments at 20-30 C and 15-30 C, respectively.
Agropyron cristatum; alfalfa; crested wheatgrass; Medicago sativa; nematode; Pratylenchus neglectus; P. penetrans; reproductive index; root lesion nematodes; root weight; shoot weight; survival; virulence
The polymerase chain reaction (PCR) was used to amplify a fragment of the ribosomal DNA (rDNA) from species and undescribed populations of Aphelenchoides and Ditylenchus angustus. The PCR primers used were based on conserved sequences in the 18S and 26S ribosomal RNA genes of Caenorhabditis elegans. In C. elegans, these primers amplify a 1,292 base pair (bp) fragment, which consists of the two internal transcribed spacers and the entire 5.8S gene. Amplification products from crude DNA preparations of 12 species and populations of Aphelenchoides and from D. angustus ranged in size from approximately 860-1,100bp. Southern blots probed with a cloned ribosomal repeat from C. elegans confirmed the identity of these amplified bands as ribosomal fragments. In addition to the differing sizes of the amplified rDNA fragments, the relative intensity of hybridization with the C. elegans probe indicated varying degrees of sequence divergence between species and populations. In some cases, amplified rDNA from the fungal host was evident. Storage of A. composticola at - 45 C for 2 years did not affect the ability to obtain appropriate amplified products from crude DNA preparations. Amplified rDNA fragments were cut with six restriction enzymes, and the restriction fragments produced revealed useful diagnostic differences between species and some undescribed populations. These results were consistent with previous studies based on morphology and isoenzymes. Three undescribed populations of Aphelenchoides were found to be different from all the species examined and from each other.
Aphelenchoides; Ditylenchus; fungi; nematode; PCR; rDNA
In a peach orchard with an initial soil pH of 4.9, preplant application of 0, 13.2, 18.2, 27.3, or 54.2 kg lime/tree site altered soil pH (range after 1 year = 4.8-7.3) but did not affect numbers of Criconemella xenoplax or tree circumference. Liming also failed to reduce the incidence of bacterial canker, which affected 17% of the trees by the sixth year after planting. Four years after planting, numbers of C. xenoplax exceeded 400/100 cm³ soil, regardless of treatment. Trees with higher densities of C. xenoplax had a higher incidence of canker. The nematophagous fungus Hirsutella rhossiliensis was not detected until the fourth year. Thereafter, the incidence of H. rhossiliensis and percentage C. xenoplax parasitized by H. rhossiliensis increased, but the increases lagged behind increases in numbers of nematodes. In an almond orchard with an initial soil pH of 4.6, preplant application of 0, 6.4, 12.8, or 25.0 kg lime/tree site altered soil pH (range after 1 year = 4.7-7.1). Numbers of C. xenoplax remained low (<20/100 cm³ soil), whereas numbers of Paratylenchus sp. increased to high levels (>500/100 cm³ soil), regardless of treatment. Low levels (<20/100 cm³ soil) of H. rhossiliensis -parasitized Paratylenchus sp. were detected. No bacterial canker occurred, but tree circumference was greater after 6 years if soil pH was intermediate (6.0-7.0).
almond; biocontrol; biological control; Criconemella xenoplax; Hirsutella rhossiliensis ; lime; nematode; Paratylenchus sp.; peach; Prunus dulcis; Prunus persica; soil pH
The root-knot nematode Meloidogyne incognita was cultured monoxenically on excised tomato roots. Galls and egg masses were observed daily using a light microscope. Two phases were distinguished in the gelatinous matrix of the egg mass: a translucent, amorphous material on the surface of the egg mass and a denser, layered phase in which nematode eggs were deposited. Egg masses were also cryofixed, fractured, and observed as frozen, hydrated specimens on a cold stage in a scanning electron microscope (SEM). In the SEM, the layered phase appeared as a meshwork of fibrils that became more loosely associated as the gelatinous matrix aged: Small pearl-like bodies were observed along the fibers of gelatinous matrix. The egg shell surface and several stages of embryo development, including the one-cell stage, initial cleavages, blastula, gastrula, tadpole stage, elongation, and molt of the first-stage juvenile within the egg shell, were observed and photographed with this technique. The developmental events observed were consistent with those described in other nematode species with different techniques.
development; egg; egg mass; embryogenesis; gelatinous matrix; low-temperature scanning electron microscopy; Meloidogyne incognita; root gall; nematode; root-knot nematode; scanning electron microscopy; ultrastructure
Fine structure of developing sperm of the monospecific genus, Ekphymatodera, was compared with other Heteroderinae as part of a study to recognize diversity and phylogenetically informative characters within the subfamily. Sperm of Ekphymatodera originate from germ cells connected to a central rachis, a character which is shared with Globodera, but not with other Heteoderinae. In Ekphymatodera, and cyst-forming genera, a layer of cortical microtubules lies just beneath the surface of the plasma membrane. Sperm of Ekphymatodera are unique among Heteroderinae examined by the presence of spiral surface elevations on the filopodia, a character that may prove to be a synapomorphy for Sarisoderini. Fibrous bodies are abundant in spermatids; however, they do not persist in sperm of Ekphymatodera as they do in Meloidodera and Verutus. The male gonad of Ekphymatodera is lined by epithelial cells, which are greatly enlarged near the ejaculatory canal. These enlarged cells contain vesicles with concentric lamellar inclusions, not observed in other genera of the subfamily. Sperm of Heteroderinae are rich in diversity, and examination of additional representative species may indicate new phylogenetically informative characters.
Ekphymatodera thomasoni; filopodia; fine structure; Heteroderinae; lamellar inclusion; male gonad; nematode; ontogeny; phylogeny; pseudopodia; sperm; systematics; ultrastructure
Reproduction of Meloidogyne javanica on Crotalaria juncea PI 207657 and cv. Tropic Sun, Sesamum indicum, Dolichos lablab, and Elymus glaucus was assessed using a root-gall index, a reproductive index obtained by dividing the final population of juveniles (J2) in soil by the initial J2 population (Pf/Pi), and the number of J2 per gram of root recovered from roots by mist chamber extraction. Lycopersicon esculentum (cv. UC 204 C) was included as a susceptible host. The root-gall index and soil reproductive index were poor indicators of the host status of our test plants as compared with mist chamber extraction of J2 from roots. Lycopersicon esculentum had a mean root-gall index of 7.8. Some plants of S. indicum and E. glaucus had a few galls and other plants had none, with mean root-gall indices of 1.6 and 0.8, respectively. No galls were observed in C. juncea and D. lablab. Lycopersicon esculentum had the highest mean soil Pf/Pi value (mean = 1.93), while in C. juncea and some replicates of S. indicum no soil J2 were found. Even though some replicates had no galls, all replicates supported nematode reproduction. The mean numbers of J2 per gram root after 5 days of mist extraction were 447.7, 223.3, 165.5, 96.9, 42.3, and 41.9 for D. lablab, L. esculentum, E. glaucus, S. indicum, and C. juncea PI 207657 and cv. Tropic Sun, respectively. Accurate assessment of nematode resistance was influenced by sampling time and the nematode extraction technique used. Individual plants of both C. juncea and S. indicum supported nematode reproduction to some extent; however, both C. juncea and S. indicum have potential as cover crops to reduce M. javanica numbers.
Crotalaria; Dolichos; Elymus; host status; Meloidogyne javanica; nematode; nematode reproduction; Pf/Pi; reproductive index; resistance evaluation; root-gall index; Sesamum
The closely related soybean (Glycine max) cultivars Centennial and Pickett 71 were confirmed to be resistant and susceptible, respectively, to the root-knot nematode Meloidogryne incognita. Increases in superoxide dismutase (SOD) activity were detected in roots of both soybean cultivars 48 hours following inoculation. Superoxide dismutase activity increased in roots of the susceptible cultivar overall, but declined after 96 hours in roots of the resistant cultivar. The isoelectric points of SOD isolated from preparasitic and parasitic developmental stages of the nematode appeared to differ. The SOD activity increased dramatically as nematodes matured and enlarged. Plant and nematode SOD were present as ca. 40-kDa cuprozinc dimers. Initial increases in SOD activity in infected tissue appeared to involve nematode regulation of plant gene expression. However, as the nematode enlarged, SOD activity could be detected within the female body only.
enzyme; Glycine max; host-parasite interaction; Meloidogyne incognita; nematode; resistance; root; soybean; superoxide dismutase
Field experiments were conducted in 1989 and 1990 to examine the population fluctuation patterns of Tylenchorhynchus nudus, Criconemella curvata, and Helicotylenchus cornurus in mixed bentgrass and annual bluegrass putting greens on two golf courses near Chicago, Illinois, to determine if fluctuation patterns could be extrapolated to unsampled greens. Fenamiphos-treated and untreated plots were established on seven putting greens on two golf courses. Greens were sampled intensively five times during the growing season, and statistical comparisons of population levels per gram of root were made among dates for each green. Population levels per gram of root changed significantly on all greens in both years for each of the three nematode populations. Within a putting green in either year, population fluctuation patterns in fenamiphos-treated and untreated plots were similar. Population fluctuation patterns were different between years, however. Within a year, population fluctuation patterns among greens showed similarities indicating that carefully monitoring a few locations may allow extrapolation of population fluctuation data to other locations within that year.
Agrostis palustris; annual bluegrass; bentgrass; Criconemella curvata; golf course; Helicotylenchus cornurus; nematode; Poa annua; population dynamics; population fluctuation; putting green; turfgrass; Tylenchorhynchus nudus
Two new species of Epsilonema are described from coral sand from Polynesia and New Caledonia. Epsilonema exoticum, with ca. 131 annules, is characterized by heterogeneous vacuolar ornamentation, small amphid, and male with small field of tiny copulatory thorns. Epsilonema enigmaticum, with ca. 168 annules and small vacuoles and ridges on the cuticle, differs from all other species of the genus by the number (10-16) of subcephalic setae.
Epsilonema; marine nematode; nematode; taxonomy
One grower trial and two experiment station tests were conducted to evaluate a new nematicide, fosthiazate, for management of Meloidogyne javanica in Florida flue-cured tobacco. Fosthiazate was applied broadcast and incorporated at rates ranging from 21 to 84 g/100 m² and compared with 1,3-dichloropropene at 240 and 460 ml/100 m² and fenamiphos at 67 g/100 m². All fosthiazate treatments increased tobacco yields and reduced root galling. Application of 1,3-D provided the highest tobacco yields and greatest reductions in root galling. The fenamiphos treatment outperformed all fosthiazate treatments in tobacco yield and root gall reduction. Fosthiazate may therefore have limited utility compared with 1,3-D and fenamiphos as a nematicide for tobacco in peninsular Florida.
fenamiphos; fosthiazate; 1,3-D; Meloidogyne arenaria; Meloidogyne javanica; nematicides; nematode; nematode management; Nicotiana tabacum; root-knot nematode; tobacco
Effects of winter cover crop management on nematode densities associated with a subsequent corn (Zea mays) crop were examined in five sites in north Florida. Two sites had received winter cover crops of lupine (Lupinus angustifolius), and one site each had rye (Secale cereale), hairy vetch (Vicia villosa), and crimson clover (Trifolium incarnatum). In each site, five different management regimes were compared: 1) conventional tillage after the cover crop was removed for forage; 2) conventional tillage with the cover crop retained as green manure; 3) no-till with the cover crop mowed and used as a mulch; 4) no-till with the cover crop removed as forage; and 5) fallow. Sites were sampled at corn planting and harvest for estimates of initial (Pi) and final (Pf) nematode population densities, respectively. Whether the cover crop was removed as forage or retained as green manure or mulch had no effect (P > 0.10) on population densities of any plant-parasitic nematode before or after corn at any site. Differences between conventional-till and no-till treatments were significant (P ≤ 0.10) only in one experiment for Paratrichodorus minor and two experiments for Pratylenchus spp. Compared with other treatments, fallow reduced (P ≤ 0.05) Pi of P. minor in two of three cases and Pf of Meloidogyne incognita in one of five sites, but enhanced soil Pf of Pratylenchus spp. in three of five sites. Tillage practices and management of cover crop residues had little consistent effect on nematodes, and these practices should be considered based on agronomic benefits rather than for nematode management.
corn; Criconemella spp.; cover crop; cropping system; green manure; Meloidogyne incognita; nematode; organic amendment; Paratrichodorus minor; Pratylenchus spp.; sustainable agriculture; tillage; Zea mays
In 1992, a detection survey for Heterodera glycines (soybean cyst nematode) was conducted in 16 counties in Michigan. The nematode was detected in 12 counties, with absolute frequencies ranging from 6 to 100%. A total of 149 samples was collected, and 53% were infested with H. glycines. Eighty-four growers participated in the survey, and 38 had samples collected from more than one field. Of the 38 growers, 42% had all samples positive for H. glycines, 18% had some positive and negative fields, and 39% had all negative. A risk index was developed to quantify three types of risks: short-term, long-term, and border risk from neighboring counties. Soybean yield was regressed on H. glycines population density and number of years of soybean. Thirty-one percent of the variability in soybean yields was explained by H. glycines cyst population densities. Total number of years in soybean over the last 20 year period explained 19% of the variability in yields. In addition, H. glycines frequencies and population densities were inversely related to Pratylenchus spp. frequencies and population densities.
community ecology; distribution; Heterodera glycines; Glycine max; Michigan; nematode; Pratylenchus spp.; risk assessment; soybean; soybean cyst nematode
The application of geostatistics to plant nematology was made by evaluating soil and nematode data acquired from 200 soil samples collected from the Ap horizon of a reed canary-grass field in northern Minnesota. Geostatistical concepts relevant to nematology include semi-variogram modelling, kriging, and change of support calculations. Soil and nematode data generally followed a spherical semi-variogram model, with little random variability associated with soil data and large inherent variability for nematode data. Block kriging of soil and nematode data provided useful contour maps of the data. Change of snpport calculations indicated that most of the random variation in nematode data was due to short-range spatial variability in the nematode population densities.
change of support; contour mapping; geostatistics; kriging; nematode; plant-parasitic nematode; semi-variogram
A nematicide (fenamiphos) and a herbicide (EPTC) were injected into a sprinkler irrigation system separately and as tank mixtures and applied in 25.4 kl water/ha for nematode and weed control on snapbean. There were no differences (P = 0.05) between methods of injection of fenamiphos + EPTC on efficacy or crop response. The root-gall indices of cultivars Eagle and GV 50 were lower in fenamiphos-treated plots than those treated with EPTC alone and untreated plots. The yield and crop value were greater (P = 0.05) for cultivars Eagle and Nemasnap than GV 50. Fenamiphos 4.48 kg a.i./ha + EPTC 3.36 kg a.i./ha controlled root-knot nematodes, Meloidogyne incognita, ring nematodes, Criconemella ornata, and weeds, and resulted in greater plant growth, yield, and crop value than those from untreated plots. No benefits (P = 0.05) resulted from treatment with fenamiphos at 6.72 kg a.i./ha + EPTC treatment compared with fenamiphos at 4.48 kg a.i. + EPTC.
Criconemella ornata; EPTC; fenamiphos; Meloidogyne incognita; nemagation; nematode; Phaseolus vulgaris; root-knot nematode; snapbean; weeds
The effects of culture filtrates of Rhizoctonia solani and root exudates of R. solani-infected cotton (Gossypium hirsutum) seedlings on hatching of eggs and infectivity of females of Rotylenchulus reniformis were evaluated in an attempt to account for the enhanced nematode reproduction observed in the presence of this fungus. Crude filtrates of R. solani cultures growing over sterile, deionized distilled water did not affect egg hatching. Exudates from roots of cotton seedlings increased hatching of R. reniformis eggs over that observed in water controls. Exudates from cotton seedling roots not infected or infected with R. solani did not differ in their effect on egg hatching. However, infection of cotton seedlings by reniform females was increased in the presence of R. solani, resulting in the augmented egg production and juvenile population densities in soil observed in greenhouse studies.
cotton; culture filtrate; egg hatching; Gossypium hirsutum; infectivity; nematode; reniform nematode; Rhizoctonia solani; root exudate; Rotylenchulus reniformis
Research and commercial blueberry plantings were sampled in October 1991 to determine the population densities and species of phytoparasitic nematodes associated with rabbiteye (Vaccinium ashei), southern highbush (Vaccinium sp.), and highbusb (V. corymbosum) blueberry cultivars and the sod middles between the blueberry rows. In the research planting at Clarksville, Arkansas, samples from the highbush cv. Bluecrop, the southern highbush cv. Cooper and Gulf Coast, and the sod middles had similar numbers of total vermiform phytoparasitic nematodes (125-451/250 cm³ soil), whereas the samples from rabbiteye cv. Climax and Tifblue had significantly lower numbers (4/250 cm³). The major nematode species associated with blueberries and sod was Xiphinema americanum. In a research planting at Bald Knob, Arkansas, which contained Bluecrop and rabbiteye cultivars only, samples from Bluecrop and the sod had similar numbers (288 and 334/250 cm³), and the rabbiteye samples had significantly lower numbers (6-14/250 cm³). Xiphinema americanum was the major species found in the blueberry samples, whereas Mesocriconema ornata was the major species in the sod. Nematode population densities and species distribution in commercial rabbiteye plantings in nine counties in central and southwestern Arkansas varied greatly. The average population density for rabbiteye samples was 129/250 cm³ and for sod was 577/250 cm³. Weed infestations in the blueberry rows in the commercial plantings probably increased the population size and species distribution.
Arkansas; Aorolaimus christiei; blueberry; Criconemella ornata; Gracilacus acicula; Hoplolaimus magnistylus; Helicotylenchus dihystera; Hemicycliophora zuckermani; Meloidogyne sp.; Mesocriconema ornata; Paratylenchus sp.; Paratrichodorus minor; Paratrichodorus sp.; Paratrichodorus christiei; Pratylenchus sp.; nematode; nematode survey; Tetylenchus sp.; Tylenchorhynchus ewingi; Tylenchorhynchus sp.; Vaccinium ashei; Vaccinium corymbosum; Vaccinium sp.; Xiphinema americanum
The response of a mixed population of Meloidogyne incognita and M. javanica to three cultural practices, tobacco cultivars (two cultivars, differing in resistance to M. incognita), cover treatments (three treatments), and inorganic nitrogen fertilizer (two treatments), Pasteuria penetrans, and soil-borne fungi was investigated in a tobacco field in 1991. On all sampling dates, higher densities of root-knot nematodes were observed on tobacco cv. Coker 371 Gold than on K-326. Initially, forage sorghum decreased the number of Meloidogyne spp. on tobacco, compared with weeds and hairy indigo, but had little effect on the density of second-stage juveniles (J2) in soil at mid-season or final harvest. The density of P. penetrans endospores also decreased in soil in forage sorghum plots. On one of four sampling dates, high levels of inorganic nitrogen fertilizer increased the number of P. penetrans endospores produced per nematode female, and decreased the density of Meloidogyne spp. on tobacco. The density of P. penetrans endospores increased in these high-N plots after harvest, especially in the plots planted with K-326. The density of J2 in soil was negatively correlated with both the numbers of endospores attached per J2 and the proportion of J2 with attached endospores in midseason soil samples. No correlation was observed between the nematode density and frequency of fungi colonizing the egg masses of Meloidogyne spp.
biological control; fungi; Meloidogyne incognita; M. javanica; nematode; Nicotiana tabacum; nitrogen fertilizer; Paecilomyces lilacinus; Pasteuria penetrans; population; root-knot nematode; tobacco; tobacco cultivar
Thirty-two cultivars of 10 commonly-grown bedding plants, representing eight families, were evaluated for their response to infection by the root-knot nematode, Meloidogyne incognita race 3, under greenhouse conditions. Four ageratum cultivars, two marigold, and two salvia cultivars were rated resistant after exposure for 8 weeks. Four begonia, four celosia, one dianthus, one verbena, one vinca, and three pansy cultivars were susceptible. Three salvia, one begonia, one gerber, one verbena, and three vinca cultivars were slightly susceptible with an average of ≤ 1 gall per plant. Nematodes, at two initial population densities, affected the dry weights of only a few cultivars. The diversity of annual bedding plant germplasm available may provide adequate sources of resistance to this race of root-knot nematode.
Ageratum houstonianum; Begonia x florens; Catharanthus roseus; Celosia plumosa; Dianthus chinensis; Gerbera jamesonii; nematode; ornamental; resistance; Salvia splendens; Tagetes erecta; Tagetes patula; Verbena × hybrida; Viola wittrockiana
The responses of 20 species of ornamental palms and one cycad (Cycas revoluta) to two populations of the reniform nematode, Rotylenchulus reniformis, from southern Florida were studied in two greenhouse experiments conducted in 1989-1991 and 1991-92. Ornamental palms in pots were exposed to initial population densities of 400 and 1,500 R. reniformis/l00 cm³ soil for 16 and 15 months, respectively. Nematode reproduction occurred on Acoelorrhaphe wrightii and Washingtonia robusta, but not on the other palms or the cycad. In both experiments, nematode numbers on A. wrightii and W. robusta were significantly smaller than those on cowpea (Vigna unguiculata), a susceptible host of the nematode used as a control in these experiments. Nematodes surviving in pots containing nonhost palms for 16 months retained infectivity and were able to reproduce on susceptible cowpea in a bioassay. Sections from Washingtonia robusta roots infected by R. reniformis females showed the nematode feeding on syncytia formed by endodermal, pericyclic, and vascular parenchyma cells in a manner similar to that reported for other monocot hosts of the reniform nematode.
Acoelorrhaphe wrightii; Archontophoenix alexandrae; Bismarckia nobilis; Carpenteria acuminata; Caryota mitis; Chamaedorea cataractarum; Chamaerops humilis; Coccothrinax sp.; Cycas revoluta; Florida; histopathology; infectivity; Meloidogyne incognita; nematode; Neodypsis decaryi; N. lastelliana; Phoenix roebelenii; Ptychosperma elegans; Ravenea rivularis; regulatory nematology; reniform nematode; Rhapis excelsa; root-knot nematode; Rotylenchulus reniformis; Sabal palmetto; survival; Syagrus romanzoffiana; Thrinax morrisii; Trachycarpus fortunei; Washingtonia robusta; Wodeyetia bifurcata; Vigna unguiculata
Four bean genotypes (IPA-1, A-107, A-211, and Calima), representing all possible combinations of resistance and susceptibility to Fusarium oxysporum f. sp. phaseoli (Fop) and Meloidogyne incognita, were each inoculated with three population densities of these pathogens. Calima and A-107 were resistant to Fop; A-107 and A-211 were resistant to M. incognita; and IPA-1 was susceptible to both pathogens. In Fop-susceptible lines (IPA-1 and A-211), the presence of M. incognita contributed to an earlier onset and increased severity of Fusarium wilt symptoms and plant stunting. However, the Fop-resistant Calima developed symptoms of Fusarium wilt only in the presence of M. incognita. Genotype A-107 (resistant to both M. incognita and Fop) exhibited Fusarium wilt symptoms and a moderately susceptible reaction to Fop only after the breakdown of its M. incognita resistance by elevated incubation temperatures (27 C). Root galling and reproduction of M. incognita was generally increased as inoculum density of M. incognita was increased on the M. incognita susceptible cultivars. However, these factors were decreased as the inoculum density of Fop was increased. It was concluded that severe infections of bean roots by M. incognita increase the severity of Fusarium wilt on Fop-susceptible genotypes and may modify the resistant reaction to Fop.
bean; Fusarium oxysporum f. sp. phaseoli; fusarium wilt; host resistance; interaction; Meloidogyne incognita; nematode; Phaseolus vulgaris; root galling; temperature
The efficacy of coastal bermudagrass (Cynodon dactylon) as a rotation crop for controt of root-knot nematode (Meloidogyne arenaria) in 'Florunner' peanut (Arachis hypogoea) was evaluated in a 3-year field trial. Coastal bermudagrass-peanut rotation (CBP) was compared with peanut monoculture without nematicide (P - ) and peanut monoculture with aldicarb (P + ). The performance of CBP was also compared with 'Pensacola' bahiagrass (Paspalum notatum)-peanut (BP), and 'Deltapine 90' cotton (Gossypium hirsutum)-peanut (CP) rotations. Each rotation crop was grown for 2 years (1991, 1992) and peanut was planted without nematicide the third year (1993). In contrast with peanut, the alternate crops of bahiagrass, bermudagrass, and cotton did not support M. arenaria populations. In 1993, the lowest numbers of M. arenaria second-stage juveniles (J2) in soil were in plots with CP and BP; these rotations resulted in the highest peanut yields. CBP failed to increase peanut yield and resulted in the highest population densities of M. arenaria J2. In 1993, aldicarb reduced J2 densities in the soil but did not increase peanut yields. Rotations of BP and CP reduced incidence of southern blight (Sclerotium rolfsii) in peanut, but neither CBP nor aldicarb affected the disease.
aldicarb; Arachis hypogaea; bahiagrass; bermudagrass; cotton; crop rotation; cultural practice; Cynodon dactylon; forage; Gossypium hirsutum; grasses; Meloidogyne arenaria; nematode; nematode control; Paspalum notatum; peanut; Sclerotium rolfsii; root-knot; southern blight; sustainable agriculture
Isolates from a race 5 field population of Heterodera glycines were cultured separately on soybean cultivars 'Bedford' (resistance derived from Peking and plant introduction [PI] 88788) and 'Cordell' (resistance derived from 'Peking', PI 88788, and PI 90763) for 10, 12, and 14 generations. Reproduction was measured of the 10th, 12th, and 14th generations on Bedford and Cordell and on Peking, 'Pickett', PI 88788, PI 90763, and 'Lee' (the soybean lines that are used to determine H. glycines race). The isolate cultured on Bedford remained race 5, whereas the isolate cultured on Cordell changed to race 14, to which Bedford is moderately resistant. Cordell probably derived its race 5 resistance from either Peking or PI 90763 because the isolate resulting from culture on Cordell reproduced on the H. glycines race differentials in a pattern similar to those of other isolates selected on PI 90763 in previous studies. Rotation of cultivars with pedigrees similar to Bedford and Cordell may be effective in managing H. glycines to prevent yield suppression in soybean and the development of new races.
Glycine max; Heterodera glycines; nematode; race; resistance; selection; soybean; soybean cyst nematode