Evaluation of an antibiotic-producing strain of Pseudomonas fluorescens for suppression of plant-parasitic nematodes

The antibiotic 2,4-diacetylphloroglucinol (DAPG), produced by some strains of Pseudomonas spp., is involved in suppression of several fungal root pathogens as well as plant-parasitic nematodes. The primary objective of this study was to determine whether Wood1R, a D-genotype strain of DAPG-producing P. fluorescens, suppresses numbers of both sedentary and migratory plant-parasitic nematodes. An experiment was conducted in steam-heated soil and included two seed treatments (with Wood1R and a control without the bacterium) and six plant-nematode combinations which were Meloidogyne incognita on cotton, corn, and soybean; M. arenaria on peanut; Heterodera glycines on soybean; and Paratrichodorus minor on corn. Wood 1R had no effect on final numbers of M. arenaria, P. minor, or H. glycines; however, final numbers of M. incognita were lower when seeds were treated with Wood1R than left untreated, and this reduction was consistent among host plants. Population densities of Wood1R were greater on the roots of corn than on the other crops, and the bacterium was most effective in suppressing M. incognita on corn, with an average reduction of 41%. Despite high population densities of Wood1R on corn, the bacterium was not able to suppress numbers of P. minor. When comparing the suppression of M. incognita on corn in natural and steam-heated soil, egg production by the nematode was suppressed in natural compared to steamed soil, but the presence of Wood1R did not result in additional suppression of the nematodes in the natural soil. These data indicate that P. fluorescens strain Wood1R has the capacity to inhibit some populations of plant-parasitic nematodes. However, consistent suppression of nematodes in natural soils seems unlikely.

Control of Paratrichodorus allius and Corky Ringspot Disease in Potato with Shank-injected Metam Sodium

Corky ringspot disease (CRS) of potato produces necrotic areas in tubers that are considered quality defects that can lead to crop rejection. CRS is caused by tobacco rattle virus that is vectored by stubby-root nematodes (Paratrichodorus spp., Trichodorus spp.) at very low population densities, making disease management difficult and expensive. Fumigation with metam sodium (MS) is a common practice to control soil-borne fungi and increase potato yield. MS is generally applied in water via chemigation (water-run, WR) but is ineffective at controlling CRS when WR-applied, even at high rates. Therefore, WR MS is often used in combination with 1,3-dichloropropene (1,3-D), aldicarb or oxamyl to attain adequate CRS control. Between 1996 and 2000, fields with a history of CRS were treated with WR MS, shank-injected MS, and/or 1,3-D, and tubers were evaluated for symptoms of CRS. Shank injection of MS (SH MS) at depths of 41 cm, 15 and 30 cm, or 15, 30 and 45 cm controlled CRS over 3 years of testing. All rates of 280 liters/ha or greater were effective. Shank injection of metam potassium (MP) at rates of 448 liters/ha was also effective. 1,3-D controlled CRS alone or in combination with WR or SH MS. Proper shank application of MS or MP may adequately control CRS without the additional cost of other nematicides at low (<10 P. allius/250 g soil) to moderate (10 to 30 P. allius/250 g soil) populations of the nematode vector. Although SH MS was superior to WR MS, additional research is necessary to determine if this practice would be sufficient at higher CRS disease pressure or if addition of other nematicides would be necessary.

Entomopathogenic nematodes are not an alternative to fenamiphos for management of plant-parasitic nematodes on golf courses in Florida

With the cancellation of fenamiphos in the near future, alternative nematode management tactics for plant-parasitic nematodes (PPN) on golf courses need to be identified. The use of entomopathogenic nematodes (EPN) has been suggested as one possible alternative. This paper presents the results of 10 experiments evaluating the efficacy of EPN at managing PPN on turfgrasses and improving turf performance. These experiments were conducted at various locations throughout Florida over the course of a decade. In different experiments, different EPN species were tested against different species of PPN. Separate experiments evaluated multiple rates and applications of EPN, compared different EPN species, and compared single EPN species against multiple species of PPN. In a few trials, EPN were associated with reductions in certain plant-parasite species, but in other trials were associated with increases. In most trials, EPN had no effect on plant parasites. Because EPN were so inconsistent in their results, we conclude that EPN are not acceptable alternatives to fenamiphos by most turf managers in Florida at this time.

Alternatives to fenamiphos for management of plant-parasitic nematodes on bermudagrass

Plant-parasitic nematodes can be very damaging to turfgrasses. The projected cancellation of the registration for fenamiphos in the near future has generated a great deal of interest in identifying acceptable alternative nematode management tactics for use on turfgrasses. Two field experiments were conducted to evaluate the effectiveness of repeated applications of several commercially available nematicides and root biostimulants for reducing population densities of plant-parasitic nematodes and (or) promoting health of bermudagrass in nematode-infested soil. One experimental site was infested with Hoplolaimus galeatus and Trichodorus obtusus, the second with Belonolaimus longicaudatus. In both trials, none of the experimental treatments reduced population densities (P </= 0.1) of plant-parasitic nematodes, or consistently promoted turf visual performance or turf root production. Nematologists with responsibility to advise turf managers regarding nematode management should thoroughly investigate the validity of product claims before advising clientele in their use.

Reproduction of Belonolaimus longicaudatus, Meloidogyne javanica, Paratrichodorus minor, and Pratylenchus brachyurus on Pearl Millet (Pennisetum glaucum)

Pearl millet (Pennisetum glaucum) has potential as a grain crop for dryland crop production in the southeastern United States. Whether or not pearl millet will be compatible in rotation with cotton (Gossypium hirsutum), corn (Zea mays), and peanut (Arachis hypogaea) will depend, in part, on its host status for important plant-parasitic nematodes of these crops. The pearl millet hybrid 'TifGrain 102' is resistant to both Meloidogyne incognita race 3 and M. arenaria race 1; however, its host status for other plant-parasitic nematodes was unknown. In this study, the reproduction of Belonolaimus longicaudatus, Paratrichodorus minor, Pratylenchus brachyurus, and Meloidogyne javanica race 3 on pearl millet ('HGM-100' and TifGrain 102) was compared relative to cotton, corn, and peanut. Separate greenhouse experiments were conducted for each nematode species. Reproduction of B. longicaudatus was lower on peanut and the two millet hybrids than on cotton and corn. Reproduction of P. minor was lower on peanut and TifGrain 102 than on cotton, corn, and HGM-100. Reproduction of P. brachyurus was lower on both millet hybrids than on cotton, corn, and peanut. Reproduction of M. javanica race 3 was greater on peanut than on the two millet hybrids and corn. Cotton was a nonhost. TifGrain 102 was more resistant than HGM-100 to reproduction of B. longicaudatus, P. minor, and M. javanica. Our results demonstrated that TifGrain 102 was a poor host for B. longicaudatus and P. brachyurus (Rf < 1) and, relative to other crops tested, was less likely to increase densities of P. minor and M. javanica.

Evaluation of Pearl Millet Grain Hybrids for Resistance to Meloidogyne spp. and Leaf Blight Caused by Pyricularia grisea

Pearl millet, Pennisetum glaucum, has potential as a grain crop in the southeastern United States. Our objectives were to (i) determine the resistance and/or tolerance of pearl millet hybrids to Meloidogyne incognita race 3 and M. arenaria race 1; (ii) compare reproduction of Meloidogyne spp. on pearl millet and corn; and (iii) determine the disease severity of leaf blight caused primarily by Pyricularia grisea. In a field naturally infested with M. incognita, experimental pearl millet hybrids with inbreds 114 and 117 as the pollinators had fewer numbers of second-stage juveniles and more severe leaf blight than did HGM-100, a nematode-susceptible hybrid; hybrids with inbred 115 as the pollinator were similar to HGM-100 in both nematode numbers and foliar disease severity. Grain yields in pearl millet were greater in plots treated with 1,3-dichloropropene than in control plots and were negatively correlated with leaf blight severity. In a greenhouse experiment, both M. incognita and M. arenaria produced fewer eggs on pearl millet hybrids with pollinators 114, 117, 101, 102, and 103 than on hybrid HGM-100. Reproduction of M. incognita was less on the resistant pearl millet hybrids than on corn. Because both M. incognita and P. grisea can reduce grain yield of pearl millet, hybrids developed for the southeastern United States should be resistant to both pathogens.

Control of Paratrichodorus allius and Corky Ringspot Disease of Potato in the Columbia Basin of Oregon

Corky ringspot disease (CRS) of potato, caused by tobacco rattle virus that is vectored by stubby-root nematodes (Paratrichodorus spp.), is often controlled by aldicarb. When use of aldicarb on potato was suspended in 1989, an increase in crops rejected due to CRS in the Columbia Basin of the U.S. Pacific Northwest occurred. During 1992-94, several fumigant and nonfumigant nematicides were tested alone and in combination for control of P. allius and CRS. Aldicarb alone significantly reduced CRS but not to acceptable levels. Metam sodium or ethoprop alone did not control CRS, but metam sodium plus ethoprop provided adequate control under light disease pressure. Two or three postemergence applications of oxamyl, either with or without metham sodium, appeared to control CRS at low pressure. Fosthiazate reduced CRS incidence when used alone but not in combination with metam sodium. At low P. allius population densities, 1,3 dichloropropene (1,3-D) controlled CRS at 94 liters/ha, and rates of 140 liters/ha or greater were adequate at higher population densities. Treatment with 1,3-D plus chloropicrin was no better than 1,3-D alone and did not always control CRS. Combinations of 1,3-D at 94 liters/ha or greater plus metam sodium at 374 liters/ha or greater controlled CRS. Paratrichodorus allius numbers were higher and severity of CRS greater after wheat than after field corn, but P. allius declined rapidly after potato was planted and remained at low levels until harvest.

Distribution of plant-parasitic nematodes on sugarcane in louisiana and efficacy of nematicides

A survey conducted from May 1995 through August 1998 revealed diverse nematode communities in Louisiana sugarcane fields. High populations of Mesocriconema, Paratrichodorus, Pratylenchus, and Tylenchorhynchus were widespread in nine sugarcane production parishes. Comparisons of plant cane and ratoon sugarcane crops indicated that nematode community levels increase significantly in successive ratoon crops. Nematicide trials evaluated the efficacy of aldicarb, ethoprop, and phorate against indigenous nematode populations. Aldicarb consistently increased the number of millable stalks, cane tonnage, and yield of sucrose in soils with a high sand content. Yield increases were concomitant with reductions in the density of the nematode community shortly after planting and at harvest. In soils with a higher clay content, the chemicals were less effective in controlling nematode populations and, as a result, yield increases were minimal.

Immunogold Localization of Tobacco Rattle Virus Particles within Paratrichodorus anemones

Unequivocal evidence of the viral nature of virus-like particles observed at the specific site of retention of tobacco rattle virus (TRV) in Paratrichodorus and Trichodorus nematodes has not previously been available. A new staining technique using safranin-O, which does not affect viral antigenicity, was used with an antiserum raised against the coat protein of TRV and prepared for use with immunogold labelling. Application of this method enabled the occurrence and localization of particles of TRV to be confirmed in the pharynx of the natural vector of the virus, Paratrichodorus anemones, and provided unequivocal evidence that the particles observed were TRV particles. The TRV particles were observed attached only to the cuticle lining the posterior tract of the pharyngeal lumen of the vector. Therefore, the specific site of retention of TRV particles in P. anemones is apparently more localized than reported to occur in other vector trichodorid species.

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.

Effects of soil fumigants and aldicarb on corky ringspot disease and trichodorid nematodes in potato

In 1982 and 1983 the soil fumigants ethylene dibromide (EDB), EDB + chloropicrin, and 1,3-dichloropropene (1,3-D) applied with one or three chisels per row were evaluated singly and in combination with aldicarb on potato, Solanum tuberosum cvs. Atlantic and Sebago, for control of trichodorid nematodes and potato corky ringspot disease (CRS). In 1982 dosages per chisel for EDB, EDB + chloropicrin, and 1,3-D were 16.8, 23.9, and 56.1 liters/ha, respectively. EDB was applied at 12.6 liters per chisel per ha in 1983. Aldicarb was applied at 3.4 kg a.i./ha in-the-row. Differences (P </= 0.05) in the percentages of tubers having CRS and in mean trichodorid population densities were recorded between methods of fumigant application and among fumigants. The reductions in CRS associated with triple-chisel applications compared with single-chisel applications of the fumigants were insufficient to justify their commercial use solely for CRS control. Addition of aldicarb to all fumigation treatments, regardless of the fumigant application method, resulted in highly effective control of CRS. The disease was less severe in Atlantic; however, CRS was sufficiently severe to justify use of aldicarb on either cultivar.

Trichodorus philipi n. sp. from South Africa, with Notes on Paratrichodorus lobatus and P. acutus

A new species in the family Trichodoridae, from the rhizosphere of native plants of the Cape Fynbos in the western Cape, Republic of South Africa, is described and illustrated. Trichodorus philipi n. sp. resembles T. cottieri Clark, 1963 and T. degans Allen, 1957, from which both sexes are distinguished by a shorter body and onchiostyle. The females differ by the more posterior position of excretory pore, presence of two pairs of lateral body pores, and shape and sclerotization of vulval-vaginal region in lateral view. Males differ by the more posterior position of excretory pore and ventromedian cervical papilla and length and shape of the spicules. Additional morphological details and morphometrics are given for Paratrichodorus lobatus (Colbran, 1965) Siddiqi, 1974 and P. acutus (Bird, 1967) Siddiqi, 1974.

Vertical Distribution of Plant-parasitic Nematodes in Sandy Soil under Soybean

Vertical distribution of five plant-parasitic nematodes was examined in two north Florida soybean fields in 1987 and 1988. Soil samples were collected from 0-15 cm, 15-30 cm, and 30-45 cm deep at each site. Soil at the three depths consisted of approximately 96% sand. More than 50% of Belonolaimus longicaudatus population densities occurred in the upper 15-cm soil layer at planting, but the species became more evenly distributed through the other depths as the season progressed. Criconemella sphaerocephala was evenly distributed among the three depths in one field but was low (< 20% of the total density) in the upper 15 cm at a second site. Maximum population densities of Pratylenchus brachyurus were observed at 15-30 cm on most sampling dates. Vertical distributions of Meloidogyne incognita and Paratrichodorus minor were erratic and showed seasonal variation. A diagnostic sample from the upper 0-15 cm of these soybean fields revealed only a minority of the populations of most of the phytoparasitic species present.

Tillage and multiple cropping systems and population dynamics of phytoparasitic nematodes

The effect of two cropping and tillage systems on the population dynamics of four nematode species was evaluated on a loamy sand. Hairy vetch succeeded by corn or grain sorghum was seeded in split plots randomized within whole plots of no-tillage versus conventional tillage over four growing seasons (1980-83). The vetch-corn cropping system increased the density of Meloidogyne incognita 2.9 x more than the vetch-grain sorghum cropping system. In contrast, the vetch-grain sorghum cropping system increased the density of Criconemella ornata 0.7 x more than the vetch-corn cropping system. Meloidogyne incognita and C. ornata were affected more by these cropping systems than were Pratylenchus brachyurus or Paratrichodorus minor. Multiple cropping systems, vetch varieties, and crop host preference affected nematode population densities, whereas tillage treatments, conventional or no-tillage, had little effect on them.

Effects of Several Phytoparasitic Nematodes on the Growth of Basil, Ocimum basilicum

Greenhouse experiments were conducted in 15-cm-d pots of steamed Myakka fine sand to determine the host status and tolerance of common basil (Ocimum basilicum) to several important phytoparasitic nematodes in Florida. Populations of Meloidogyne incognita, Belonolaimus longicaudatus, and Pratylenchus scribneri increased and caused significant suppression of foliage and root growth during a 10-month period. The population of Paratrichodorus christiei increased and caused a significant reduction in foliage yield but did not reduce root growth. Dolichodorus heterocephalus also increased in number without affecting foliage yield or root growth. Basil was a poor host for Hoplolaimus galeatus and was not damaged by this nematode.

Trichodorus petrusalberti n. sp. (Nematoda: Trichodoridae) from Rice with Additional Notes on the Morphology of T. sanniae and T. rinae

A new species in the family Trichodoridae, from the rhizosphere of rice (Oryza sativa L.) in Northern Natal, South Africa, is described and illustrated. Trichodorus petrusalberti n. sp. resembles T. taylori De Waele, Mancini, Roca, and Lamberti, 1982, T. hooperi Loof, 1973, and T. complexus Rahman, Jairajpuri, and Ahmad, 1985, from which it is distinguished by the shape of the spicules. It is distinguished from the former two species by the nonthickened terminal cuticle in the males and by the shape and sclerotization of the vulval-vaginal region in lateral view in the females. Additional morphological details are given for T. sanniae Vermeulen and Heyns, 1985 and T. rinae Vermeulen and Heyns, 1985.

Effect of two nonfumigant nematicides on corn grown in two adjacent fields infested with different nematodes

The organo-phosphate experimental nematicide, O-ethyl S,S-di-sec-butyl phosphorodithioate (FMC 67825), provided yield increases of corn comparable to carbofuran. Both the emulsifiable concentrate and granular formulations of FMC 67825 were equally effective. The evaluations, duplicated in two adjacent fields, clearly demonstrated the importance of the type of plant pathogenic nematodes infesting the sites. Where Belonolaimus longicaudatus occurred, yield increases ranged from 73% to 80%, whereas in the adjacent field (without B. longicaudatus) yields increases ranged from - 14% to 28%.