Occurrence of Aphelenchoides besseyi in Louisiana Rice Seed and Its Interaction with Sclerotium oryzae in Selected Cultivars

Aphelenchoides besseyi, the nematode causal agent of white-tip disease of rice, was recovered from 5.5% of 474 seed samples obtained from rice seed warehouses in Louisiana. Laboratory tests in which A. besseyi-infested rice seed was treated with Phostoxin®, a compound used for control of insects in stored grain, indicate that it also has nematicidal properties. In 18-week-duration greenhouse tests, populations of A. besseyi increased 4-5-fold on the cultivars Saturn and Melrose and 3-fold on Nova ''76. Green weights of Nova ''76 plants inoculated with A. besseyi and Sclerotium oryzae, the causal agent of rice stem rot, were significantly reduced below those of plants inoculated with either organism alone or with distilled water. Weights of Melrose plants were reduced significantly by treatments with A. besseyi alone and A. besseyi plus S. oryzae, but not by S. oryzae alone. Saturn plant weights were not reduced significantly by either organism alone or by the two in combination.     

Characterization of Isolates of Meloidogyne from Rice-Wheat Production Fields in Nepal

Thirty-three isolates of root-knot nematode were recovered from soil samples from rice-wheat fields in Nepal and maintained on rice cv. BR 11. The isolates were characterized using morphology, host range and DNA sequence analyses in order to ascertain their identity. Results indicated phenotypic similarity (juvenile measurements, perennial pattern, host range and gall shape) of the Nepalese isolates with Meloidogyne graminicola, with minor variations. The rice varieties LA 110 and Labelle were susceptible to all of the Nepalese isolates, but differences in the aggressiveness of the isolates were observed. Phylogenetic analyses based on the sequences of partial internal transcribed spacer (ITS) of the rRNA genes indicated that all Nepalese isolates formed a distinct clade with known isolates of M. graminicola with high bootstrap support. Furthermore, two groups were identified within the M. graminicola clade. No correlation between ITS haplotype and aggressiveness or host range was found among the tested isolates.     

An Aphelenchoides sp. nematode Parasitic of Polianthes tuberosa in the Mekong Delta

Polianthes tuberosa is a commercially valuable flower crop in the Mekong Delta of Vietnam that is propagated by the harvesting and planting of bulbs. The cultivation of P. tuberosa is complicated by an endemic nematode infection that damages a high proportion of the plants. Based on morphological criteria and ribosomal RNA gene sequencing, we have determined that the infection is caused by an Aphelenchoides sp. nematode and is most likely Aphelenchoides besseyi. By scoring various parts of harvested plants with flowers for the presence of viable nematodes over a period of six months, we determined that the nematode is an ectoparasite that can survive the intercrop periods, especially in the bulbs that are used to plant new crops. A comparison of farming practices in the Mekong Delta failed to identify useful control methods, but rather indicated that fields that have cultivated P. tuberosa for the longest periods suffer the worst damage from the nematode infection. Finally, we demonstrated that the nematode is capable of infecting 30 rice cultivars but does not cause the white tip disease usually associated with A. besseyi infection.     

Studies on genetic diversity among populations of Persicaria barbata (L.) H. Hara from India based on internal transcribed spacer sequences of nuclear ribosomal DNA

Internal transcribed spacer (ITS) region of nuclear ribosomal DNA from 16 populations of Persicaria barbata (L.) H. Hara (Polygonaceae) belonging to five geographical locations of India (Arunachal Pradesh, Himachal Pradesh, Bihar, Karnataka and Andaman Island) was sequenced. Analysis of nucleotide sequences reveals polymorphism among the populations. UPGMA analysis conducted on the ITS datasets shows that the sampled populations of P. barbata are grouped according to their geographic locations and are supposed to be evolved under reproductive isolation which most probably are due to the long distance distribution and population fragmentation.     

Interactions between Heterodera avenae and Pratylenchus neglectus on Wheat

In a long-term field experiment, differential population densities of Heterodera avenae were produced by frequent cropping with resistant (cv. Panema) or susceptible (cv. Peniarth) oat. The two oat cultivars were equally good hosts of Pratylenchus neglectus in a glass house experiment with field soil. On wheat crops grown after oats in field experiments, P. neglectus population densities in roots were higher in plots where H. avenae had been controlled than in plots with moderate infestations (40 H. avenae eggs/g soil). The field observations indicated that the reduction in population densities of P. neglectus coincided with the development in roots of sedentary stages of the cyst nematode. Evidence for an indirect effect of H. avenae on P. neglectus was found in vitro in a split-root experiment. In the same field, grain yields of two wheat cultivars susceptible or resistant to H. avenae, but both susceptible to P. neglectus, was not reduced by P. neglectus. Alternation of H. avenae resistant and susceptible cultivars is a possible way of exploiting the inverse relationship between these nematodes, whilst controlling cyst nematode -populations in intensive cereal production systems.     

Population Growth of Pratylenchus penetrans on Winter Cover Crops Grown in the Pacific Northwest

Population growth of Pratylenchus penetrans on 13 fall and winter cover crops was studied in the greenhouse and field. All crops except oat cv. Saia supported population growth of P. penetrans in greenhouse experiments, although the response of P. penetrans to oat cv. Saia varied considerably between experiments. The mean ratio of the final population density/initial population density (Pf/Pi) after 16 weeks for P. penetrans added to a greenhouse soil mix was 0.09, whereas Pf/Pi values after 10 weeks for two experiments with naturally infested soil were 0.95 and 2.3. Although P. penetrans increased on sudangrass cv. Trudan 8 and sudangrass × sorghum hybrid cv. SS 222, subsequent incorporation of sudangrass vegetation into soil reduced P. penetrans populations to preplant levels. Field experiments were inconclusive but suggested that oat cv. Saia or rye cv. Wheeler may be better choices for winter cover than weed-contaminated fallow or other crops on P. penetrans-infested sites in the Pacific Northwest.     

Use of Green Manure Crops in Control of Hirschmanniella mucronata and H. oryzae in Irrigated Rice

Four field experiments were conducted to study the effect of Sesbania rostrata and Aeschynomene afraspera as rotational and green manure crops on the population dynamics of Hirschmanniella mucronata and H. oryzae, and subsequent rice yields. The sequential cropping of the legumes with rice controlled both nematode species. In two experiments, yield of rice was related to the nematode population denisites at planting and harvesting of the second rice crop (R² = 0.391, P < 0.001, and R² = 0.57, P < 0.001), regardless of the treatments. Rice yield increases were attributed to nutritional effect of the green manure and the reduction of the nematode populations or the modification of a factor(s) linked to the nematode populations induced by their cropping. As the two leguminous crops do not generate direct return, using them to control the rice-root nematodes was not economical, despite the significant yield increase obtained.     

Morphological and Molecular Identification of Globodera pallida Associated with Potato in Idaho

The identity of a newly discovered population of pale potato cyst nematode Globodera pallida associated with potato in eastern Idaho was established by morphological and molecular methods. Morphometrics of cysts and second-stage juveniles were generally within the expected ranges for G. pallida with some variations noted. The Idaho population and paratype material from Epworth, Lincolnshire, England, both showed variations in tail shape, with bluntly rounded to finely pointed tail termini. Compared to literature values for the paratypes, second-stage juveniles of the Idaho population had a somewhat shorter mean body length, and cysts had a slightly higher mean distance from the anus to the nearest edge of the fenestra. PCR-RFLP of the rDNA ITS region, sequence-specific multiplex PCR and DNA sequence comparisons all confirmed the identity of the Idaho population as G. pallida. The ITS rDNA sequence of the Idaho isolate was identical to those from York, England, and the Netherlands. Species-specific primers that can positively identify the tobacco cyst nematode Globodera tabacum were also developed, providing a new assay for distinguishing this species from G. pallida and the golden potato cyst nematode Globodera rostochiensis.     

Conventional and PCR Detection of Aphelenchoides fragariae in Diverse Ornamental Host Plant Species

A PCR-based diagnostic assay was developed for early detection and identification of Aphelenchoides fragariae directly in host plant tissues using the species-specific primers AFragFl and AFragRl that amplify a 169-bp fragment in the internal transcribed spacer (ITS1) region of ribosomal DNA. These species-specific primers did not amplify DNA from Aphelenchoides besseyi or Aphelenchoides ritzemabosi. The PCR assay was sensitive, detecting a single nematode in a background of plant tissue extract. The assay accurately detected A. fragariae in more than 100 naturally infected, ornamental plant samples collected in North Carolina nurseries, garden centers and landscapes, including 50 plant species not previously reported as hosts of Aphelenchoides spp. The detection sensitivity of the PCR-based assay was higher for infected yet asymptomatic plants when compared to the traditional, water extraction method for Aphelenchoides spp. detection. The utility of using NaOH extraction for rapid preparation of total DNA from plant samples infected with A. fragariae was demonstrated.     

Reproduction of Heterodera schachtii Schmidt on Resistant Mustard,Radish, and Sugar Beet Cultivars

The reproduction of a Wyoming population of Heterodera schachtii was determined for resistant trap crop radish (Raphanus sativus) and mustard (Sinapis alba) cultivars, and resistant and susceptible sugar beet (Beta vulgaris) cultivars in a greenhouse (21 °C/16 °C) and a growth chamber study (25 °C). Oil radish cultivars also were field tested in 2000 and 2001. In the greenhouse study, reproduction was suppressed similarly by the resistant sugar beet cultivar Nematop and all trap crop cultivars (P ≤ 0.05). In the growth chamber study, the radish cultivars were superior to most of the mustard cultivars in reducing nematode populations. All trap crops showed less reproduction than Nematop (P ≤ 0.05). In both studies, Nematop and all trap crops had lower Pf than susceptible sugar beet cultivars HH50 and HM9155 (P ≤ 0.05). In field studies, Rf values of radish cultivars decreased with increasing Pi of H. schachtii (r² = 0.59 in 2000 and r² = 0.26 in 2001). In 2000, trap crop radish cv. Colonel (Rf = 0.89) reduced nematode populations more than cv. Adagio (Rf = 4.67) and cv. Rimbo (Rf = 13.23) (P ≤ 0.05) when Pi was lower than 2.5 H. schachtii eggs and J2/cm³ soil. There were no differences in reproductive factors for radish cultivars in 2001 (P ≤ 0.05); Rf ranged from 0.23 for Adagio to 1.31 for Commodore for all Pi.     

Interpreting Upland Rice Yield and Pratylenchus zeae Relationships: Correspondence Analyses

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

Infection,Reproduction Potential,and Root Galling by Root-knot Nematode Species and Concomitant Populations on Peanut and Tobacco

Single populations of Meloidogyne arenaria races 1 (MA1) and 2 (MA2) and M. hapla (MH), and mixed populations of MA1 + MA2 and MA1 + MH with four inoculum levels of eggs were tested on peanut cv. ''Florigiant'' and M. incognita-resistant tobacco cv. ''McNair 373'' in a greenhouse experiment. Root infection, female development, and reproduction of MA2 on peanut and MA1 on resistant tobacco were limited at 2 and 6 weeks. MA1, MH, and MA1 + MH on peanut had similar root infection (total parasitic forms per root unit) at both 2 and 6 weeks, and similar female development and reproduction potentials at 6 weeks. MA2 tended to depress root infection, female development, and reproduction of MA1 on peanut. MH had little effect on MA1 on this crop. On tobacco, MA2 population had greater incidence of root infection than did MH at 2 weeks. The two nematode species had similar development in roots at 6 weeks. All of these processes were restricted when either MA2 or MH was present together with MA1. As initial inoculum level of parasitically fit populations increased, relative infection ratio on both peanut and tobacco, and reproduction factor on peanut decreased. Populations that had high infection incidence and reproduction rates induced greater root galling than did other populations. Root galling was suppressed in the presence of antagonistic response between nematode populations.     

Identification of Cyst Nematodes of Agronomic and Regulatory Concern with PCR-RFLP of ITS1

The first internally transcribed spacer region (ITS1) from cyst nematode species (Heteroderidae) was compared by nucleotide sequencing and PCR-RFLP. European, Asian, and North American isolates of five heterodefid species were examined to assess intraspecific variation. PCR-RFLP patterns of amplified ITS1 DNA from pea cyst nematode, Heterodera goettingiana, from Northern Ireland were identical with patterns from Washington State. Sequencing demonstrated that ITS1 heterogeneity existed within individuals and between isolates, but did not result in different restriction patterns. Three Indian and two U.S. isolates of the corn cyst nematode, Heterodera zeae, were compared. Sequencing detected variation among ITS1 clones from the same individual, between individuals, and between isolates. PCR-RFLP detected several restriction site differences between Indian and U.S. isolates. The basis for the restriction site differences between isolates from India and the U.S. appeared to be the result of additional, variant ITS1 regions amplified from the U.S. isolates, which were not found in the three India isolates. PCR-RFLP from individuals of the U.S. isolates created a composite pattern derived from several ITS1 types. A second primer set was specifically designed to permit discrimination between soybean (H. glycines) and sugar beet (H. schachtii) cyst nematodes. Fok I digestion of amplified product from soybean cyst nematode isolates displayed a uniform pattern, readily discernible from the pattern of sugar beet and clover cyst nematode (H. trifolii).     

Host Status of Crotalaria juncea,Sesamum indicum,Dolichos lablab,and Elymus glaucus to Meloidogyne javanica

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.     

Suitability of Zucchini and Cucumber Genotypes to Populations of Meloidogyne arenaria,M. incognita,and M. javanica

The host suitability of five zucchini and three cucumber genotypes to Meloidogyne incognita (MiPM26) and M. javanica (Mj05) was determined in pot experiments in a greenhouse. The number of egg masses (EM) did not differ among the genotypes of zucchini or cucumber, but the eggs/plant and reproduction factor (Rf) did slightly. M. incognita MiPM26 showed lower EM, eggs/plant, and Rf than M. javanica Mj05. Examination of the zucchini galls for nematode postinfection development revealed unsuitable conditions for M. incognita MiPM26 as only 22% of the females produced EM compared to 95% of the M. javanica females. As far as cucumber was concerned, 86% of the M. incognita and 99% of the M. javanica females produced EM, respectively. In a second type of experiments, several populations of M. arenaria, M. incognita, and M. javanica were tested on zucchini cv. Amalthee and cucumber cv. Dasher II to assess the parasitic variation among species and populations of Meloidogyne. A greater parasitic variation was observed in zucchini than cucumber. Zucchini responded as a poor host for M. incognita MiPM26, MiAL09, and MiAL48, but as a good host for MiAL10 and MiAL15. Intraspecific variation was not observed among the M. javanica or M. arenaria populations. Cucumber was a good host for all the tested populations. Overall, both cucurbits were suitable hosts for Meloidogyne but zucchini was a poorer host than the cucumber.     

Effect of Crop Rotation on Meloidogyne spp. and Pratylenchus spp. Populations in Strawberry Fields in Taiwan

Changes in population levels of Meloidogyne hapla, M. incognita, Pratylenchus coffeae, and P. penetrans were studied in 12 strawberry fields in the Dahu region of Taiwan. Ten potential rotation crops and two cultural practices were evaluated for their effect on nematode populations and influence on strawberry yield. Rotation with rice or taro and the cultural practice of flooding and bare fallowing for four months were found to reduce nematode soil populations to two or fewer nematodes per 100 ml soil. Average strawberry yields increased between 2.4% to 6.3% following taro compared to the bare fallow treatment. Corn suppressed M. incognita and M. hapla populations and resulted in an increased in strawberry yield compared to bare fallow. Other phytopathogens also present in these fields limited taro as the rotation choice for nematode management. Results of this research and economic analysis of the input requirements for various rotation crops, corn and bare fallow were recommended as the most appropriate rotation strategies for nematode management in strawberry in this region.     

Aggressiveness and Damage Potential of Central American and Caribbean Populations of Radopholus spp. in Banana

Monoxenic cultures of burrowing nematode populations extracted from banana roots from Belize, Guatemala, Honduras, and Costa Rica were established on carrot discs. Cultures of Radopholus spp. were also obtained from Florida, Puerto Rico, Dominican Republic, and Ivory Coast. The aggressiveness (defined as reproductive fitness and root necrosis) of these populations was evaluated by inoculating banana plants (Musa AAA, cv. Grande Naine) with 200 nematodes/plant. Banana plants produced by tissue culture were grown in 0.4-liter styrofoam cups, containing a 1:1 mix of a coarse and a fine sand, at ca. 27 °C and 80% RH. Banana plants were acclimated and allowed to grow for 4 weeks prior to inoculation. Plant height, fresh shoot and root weights, root necrosis, and nematode population densities were determined 8 weeks after inoculation. Burrowing-nematode populations varied in aggressiveness, and their reproductive fitness was generally related to damage reported in the field. Plant height and fresh shoot and root weight did not reflect damage caused by nematodes under our experimental conditions. Necrosis of primary roots was closely related to the reproductive fitness of the nematode populations. Variation in aggressiveness among nematode populations followed a similar trend in the two susceptible hosts tested, Grande Naine and Pisang mas. All nematode populations had a low reproductive factor (Rf ≤2.5) in the resistant host except for the Ivory Coast population which had a moderate reproductive factor (Rf ≤ 5) on Pisang Jari Buaya. This is the first report of a burrowing nematode population parasitizing this important source of resistance to R. similis.     

Interaction Between Meloidogyne arenaria and Glomus fascicuqlatus in Grape

Root zones of grape (Fitis vinifera cv Thompson Seedless) cuttings were infested with chlamydospores of Glomus fasciculatus or eggs of Meloidogyne arenaria or both. Growth of grapevines was greatest in mycorrhizal (G. fasciculatus) plants. Mycorrhizal development and growth of mycorrhizal and nonmycorrhizal plants were reduced in the presence of M. arenaria. At low initial nematode inoculum (PI) levels (approx. 200 eggs/plant), the presence of mycorrhizae enhanced plant growth during 1 yr, but no significant benefit was achieved by mycorrhizae where PI was high (approx. 2,000 eggs/plant). Final nematode populations were highest in mycorrhizal plants.     

A New Root-Knot Nematode Parasitizing Sea Rocket from Spanish Mediterranean Coastal Dunes: Meloidogyne dunensis n. sp. (Nematoda: Meloidogynidae)

High infection rates of European sea rocket feeder roots by an unknown root-knot nematode were found in a coastal dune soil at Cullera (Valencia) in central eastern Spain. Morphometry, esterase and malate dehydrogenase electrophoretic phenotypes and phylogenetic trees demonstrated that this nematode species differs clearly from other previously described root-knot nematodes. Studies of host-parasite relationships showed a typical susceptible reaction in naturally infected European sea rocket plants and in artificially inoculated tomato (cv. Roma) and chickpea (cv. UC 27) plants. The species is herein described and illustrated and named as Meloidogyne dunensis n. sp. The new root-knot nematode can be distinguished from other Meloidogyne spp. by: (i) perineal pattern rounded-oval, formed of numerous fine dorsal and ventral cuticle striae and ridges, lateral fields clearly visible; (ii) female excretory pore at the level of stylet knobs, EP/ST ratio 1.6; (iii) second-stage juveniles with hemizonid located 1 to 2 annuli anteriorly to excretory pore and long, narrow, tapering tail; and (iv) males with lateral fields composed of four incisures anteriorly and posteriorly, while six distinct incisures are observed for large part at mid-body. Phylogenetic trees derived from distance and maximum parsimony analyses based on 18S, ITS1–5.8S-ITS2 and D2-D3 of 28S rDNA showed that M. dunensis n. sp. can be differentiated from all described root-knot nematode species, and it is clearly separated from other species with resemblance in morphology, such as M. duytsi, M. maritima, M. mayaguensis and M. minor.     

Molecular and Morphological Characterization of the Corn Cyst Nematode,Heterodera zeae,from Greece

The corn cyst nematode Heterodera zeae was detected in soil from an organic maize field in northern Greece. In greenhouse studies, reproduction of H. zeae was detected on maize plants (Zeae mays) using soil high in organic matter; the field was under winter fallow at the time of sampling. Maize plants were grown in a greenhouse with soil from the affected field used as inoculum. Females appeared after six weeks incubation, and abundant cysts were present after 12 weeks. Morphological and molecular diagnosis confirmed the presence of H. zeae in the field. Cysts were identified on the basis of cyst shape and characteristics of the cyst terminal cone, including nature of fenestration, presence of bullae, cyst wall pattern, and fenestral diameter. Second-stage juveniles were identified by body and stylet length, the shape of stylet knobs, shape and length of the tail and hyaline tail terminus, and by the number of lateral lines. Molecular analysis included amplification of the ribosomal internal transcribed spacer regions (ITS 1&2 rDNA) 28S large ribosomal subunit (LSU) D2-D3 expansion segment, and partial 18S small ribosomal subunit (SSU). Restriction fragment length polymorphism (RFLP) of ITS rDNA exhibited several unique enzyme patterns that may be diagnostically useful for H. zeae. These findings are in agreement with prior analysis of H. zeae populations from the U.S. and India. Phylogenetic relationships inferred from ITS rDNA are congruent with previous analyses that placed H. zeae in a clade with H. turcomanica, H. salixophila and species of the Humuli group. Phylogenetic trees based upon heat shock protein (Hsp90) coding sequence were in general agreement with a prior study using the same marker. This study represents the first record of H. zeae in Greece and the second report of this nematode in Europe.