Phytophagous Nematodes Research Articles

Population dynamics in the belowground food webs in two different agricultural systems

The biomass of 17 different groups of organisms was established every 6 weeks during 1 year in two arable fields cropped to winter wheat; one field was under conventional management (CONV) and the other under integrated management (INT). Bacteria showed the highest average biomass, followed by earthworms (INT only) and amoebae. Most of the groups of organisms had higher biomasses in INT than in CONV. The difference was statistically significant for protozoans, bacterivorous, fungivorous, and phytophagous nematodes and earthworms. Predatory Collembola, cryptostigmatic and bacterivorous mites, and enchytraeids showed a smaller biomass in INT than in CONV. The annual biomass production for each group was estimated using simulation model calculations. Bacteria showed the highest production followed by amoebae and earthworms (INT only). Most of the groups showed a higher biomass production in INT than in CONV. Exceptions were predatory and nematophagous mites, predatory and omnivorous Collembola, and enchytraeids. The total annual production was approximately 32 kg C ha−1 cm−1 depth in CONV and approximately 57 kg C in INT. The population dynamics were analysed by hierarchical cluster analysis. Four different clusters were found in CONV and INT. Bacteria, fungi, protozoans, bacterivorous nematodes and predatory mites showed the same trend in population dynamics in CONV and INT. All other groups showed different population dynamics in CONV and INT. This observation and the composition of these clusters suggested different conditions in CONV and INT.

Responses of Nematodes to Ungulate Herbivory on Bluebunch Wheatgrass and Idaho Fescue in Yellowstone National Park

Above- and belowground biomass of Idaho fescue Festuca idahoensis and bluebunch wheatgrass Agropyron spicatum and nematode densities under these plant species were sampled during the growing season inside and outside a 2-year old exclosure on Crystal Bench in Yellowstone National Park. Early in the growing season, grazed plants of both species had lower shoot and root biomass than ungrazed plants. Standing biomass of grazed plants was equal to ungrazed plants at the end of the growing season. Densities/g root biomass of phytophagous and bacterial feeding nematodes were higher under grazed than ungrazed plants of both plant species only early in the growing season. Foliar concentrations of nitrogen in grazed plants were higher than ungrazed plants but there was no difference in root nitrogen between grazed and ungrazed plants. The effects of ungulate grazing on the Northern winter range of Yellowstone National Park has recently received considerable attention (Frank 1990, Coughenour 1991, Singer 1992, Wallace submitted). Early interest in this topic centered around the question to cull or not to cull elk in the Park. However, as the concepts of "maintaining ecological processes" (Houston 1982) and "ecosystem management" (Keiter 1991) have gained acceptance in Park management, understanding the dynamics and interactions of a broader array of herbivores inhabiting the Park have become increasingly important. In this paper, we describe the results of a study which focused on the effects of aboveground herbivory on nematode density and trophic structure. Root-feeding nematodes are major herbivores in other grassland systems and may consume twice as much biomass as aboveground consumers (Ingham and Detling 1984, Stanton 1988). Houston (1982) reported that nothing is known about the effects of nematodes on the native grasses of the northern range especially in combination with aboveground grazers. We hypothesized that if spring grazing is intense, grazed plants would initially show a decline in root growth and phytophagous nematodes. Cessation of root growth is a common response of plants to grazing and may occur within the first 2-24 hours (Hodgkinson and Baas Becking 1977). Evidence to date supports the idea that phytophagous nematode densities are highest under moderate levels of grazing and low under heavily grazed and ungrazed plants (Stanton 1983, Stanton et al. 1984, Seastedt 1985, Seastedt et al. 1988). Because senescing roots, subsequent to grazing, provide increased substrates for decomposers, we also hypothesized that microbial activity and nitrogen mineralization should increase (Stanton et al. 1984). As a result, we expected to detect an increase in microbial feeding nematodes. As root regrowth occurred, we expected phytophagous nematodes to increase. However, we predicted that populations would not reach levels found under ungrazed plants because plants in grazed areas experience higher levels of nitrogen mineralization (Holland and Detling 1990) than ungrazed plants and may produce proportionally fewer numbers of root hairs (nutrient absorption organs) which serve as feeding sites for nematodes. Because of reduced densities of phytophagous nematodes and increased mineralization rates under grazed plants, we expected grazed plants to recoup their losses rapidly. The net result we predicted would be no detectable differences in aboveground or belowground biomass during years of normal rainfall. Thus, our study addressed 3 null hypotheses. First, root and shoot biomass of grazed and ungrazed plants will be similar at the end of the growing season. Second, density of phytophagous and microbial feeding nematodes will not differ between grazed and ungrazed plants. Finally, nitrogen concentration of roots and aboveground foliage will not be higher in grazed than in ungrazed plants. We focused our attention on bluebunch wheatgrass Agropyron spicatum and Idaho fescue Festuca idahoensis because of their importance as winter range forages and because Mueggler (1975) reported that bluebunch wheatgrass was more sensitive and recovered more slowly to heavy clipping than Idaho fescue.

Sugar-cane weed community interactions with arthropods and pathogens

Polyculture can help stabilize agroecosystems against frequent and severe pest outbreaks. An overview of the published data highlights ecological relationships among weeds, nematodes, arthropods, sugar-cane mosaic virus (SCMV), and the sugar-cane crop itself. Whereas individual studies commonly depict weeds as being either “good” or “bad”, this review is a synthesis of the variable roles and interactions of weeds in sugar-cane in order to provide a realistic perspective on the possibilities of weed interactions in sugar-cane agroecosystems. Conservation of weeds in Louisiana sugar-cane has resulted in more diversified arthropod fauna, higher natural enemy populations, and reduced damage by the sugar-cane borer, Diatraea saccharalis (F.). Weed competition and SCMV infection have each been associated with altered sugar-cane free amino acid accumulations that appeared to play a role in reducing populations of selected phytophagous nematodes. The combination of both weed and SCMV stress factors, however, have been shown to favour higher sugar-cane nematode populations. Although some weeds are alternate hosts for SCMV and its aphid vectors, and ratoon stunting disease (RSD), weed growth has not been linked with higher phytophagous nematode infestations or incidence of RSD. Weeds, if kept below economically competitive densities, may be ecologically and financially sound assets to sugar-cane pest management tactics.

Descripción de cuatro poblaciones de Pratylenchus (Nematoda: Tylenchida), provenientes de la Provincia de Córdoba , Argentina

Four populations of phytophagous nematodes belonging to the genus Pratylenchus Filipjev, 1936 (P. hexincisus Taylor & Jenkins, 1957; P. scribneri Steiner, 1943; P. thornei Sher & Allen, 1953; and P. vulnus Allen & Jensen, 1951) from cultivated areas in the Province of Córdoba are described.

ZOOFITOFAGOS EN NOTHOFAGUS CHILENOS

Nematodes and insects have been the only zoophytophagous groups that have been reported in the literature living on Nothofagus in Chile. According to the area covered by Nothofagus and the type of plant that it represents, (apparent) the number of phytophagous insects living on this genus was estimated in 125. A total of 34 phytophagous species were reported as pests. The importance that the infestation to different parts of the plant, would have in tree performance is indicated. The close relationship of sap suckers fauna living on Nothofagus in Australia, New Zealand and Chile is reported. Two genero and two species of phytophagous nematodes is indicated.

The Effect of Clipping and Phytophagous Nematodes on Net Primary Production of Blue Grama, Bouteloua gracilis

Pots of non-mycorrhizal blue grama in an environmental chamber were subjected to three levels of both above ground (0, moderate and heavy clipping) and below ground (0, 50 or 500 phytophagous nematodes per pot) herbivory. Net primary production (NPP), including shoots and crowns, decreased significantly with clipping and nematode infection. Roots also declined with clipping, but moderate nematode infection (50) on unclipped plants significantly increased root weight although NPP was still less. Phytophagous nematode densities decreased with heavy clipping but increased with moderate clipping to over three times the control (unclipped) level. Bacterial feeding nematode densities were depressed both by heavy clipping and by moderate clipping combined with high phytophagous nematode numbers.

The Effect of the Pesticide Carbofuran on Soil Organisms and Root and Shoot Production in Shortgrass Prairie

To test the hypothesis that ectoparasitic phytophagous nematodes are a major consumer of primary production in arid grasslands, carbofuran was applied once in each of two successive years at 12 lb active ingredient/acre to plots of undisturbed prairie in northeastern Colorado. Bacterial feeding and phytophagous nematodes were reduced to 10% of the density on untreated plots but microand macro-arthropods were apparently unaffected. Species composition of the fungal flora of the treated soil was greatly changed and colony counts reduced but incidence of mycorrhizae was unaffected. Although root weight measured in the autumn was significantly greater under treated plots (by 130-150 g m-2 and about 25% of NPP) shoot production was not, possibly due to below average summer rainfall in both years. Nevertheless, our results suggest that nematodes may be the most significant consumer in shortgrass prairies.

Nematodes in relation to plant growth. I. The nematode distribution pattern of typical farms and nurseries.

The distribution of nematodes in fields on ten farms was influenced by soil type, cropping and manuring. The total number of active nematodes per 100 ml. of soil ranged from 1, 005 to 16, 105 with an average of 3, 004. Known and suspected phytophagous nematodes ranged from 120 to 3, 510 per 100 ml. of soil with an average of 909. The prevalent phytophagous genera were Heterodera, Paratylenchus, Pratylenchus, Rotylenchus, Tylenchorhynchus and Meloidogyne. The authors suggest that such surveys are a starting point for further research into several obscure crop husbandry problems. H. R. Wallace. (Abstract retrieved from CAB Abstracts by CABI’s permission)