Sample Optimization for Five Plant-Parasitic Nematodes in an Alfalfa Field

A data base representing nematode counts and soil weight from 1,936 individual soil cores taken from a 7-ha alfalfa field was used to investigate sample optimization for five plant-parasitic nematodes: Meloidogyne arenaria, Pratylenchus minyus, Merlinius brevidens, Helicotylenchus digonicus, and Paratrichodorus minor. Sample plans were evaluated by the accuracy and reliability of their estimation of the population and by the cost of collecting, processing, and counting the samples. Interactive FORTRAN programs were constructed to simulate four collecting patterns: random; division of the field into square sub-units (cells); and division of the field into rectangular sub-traits (strips) running in two directions. Depending on the pattern, sample numbers varied from 1 to 25 with each sample representing from 1 to 50 cores. Each pattern, sample, and core combination was replicated 50 times. Strip stratification north/south was the most optimal sampling pattern in this field because it isolated a streak of fine-textured soil. The mathematical optimmn was not found because of data range limitations. When practical economic time constraints (5 hr to collect, process, and count nematode samples) are placed on the optimization process, all species estimates deviate no more than 25 % from the true mean. If accuracy constraints are placed on the process (no more than 15% deviation from true field mean), all species except Merlinius required less than 5 hr to complete the sample process.     

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.     

Vertical distribution of plant-parasitic nematodes in sandy soil under maize

Distribution of plant-parasitic nematode species at soil depths of 0–15 cm, 15–30 cm, and 30–45 cm was examined in two maize fields in Florida during 1987 and 1988. Soil type in both fields was an Arredondo fine sand, consisting of 94–96% sand at all three depths. On most sampling dates, more than 50% of the Belonolaimus longicaudatus collected occurred at the 0–15 cm depth. Only 20–30% of Criconemella sphaerocephala were present at this depth, and the depth distribution of this nematode differed in the two fields. The greatest densities of Pratylenchus brachyurus often occurred at 15–30 cm. Vertical distributions of Meloidogyne incognita and Paratrichodorus minor were erratic and showed marked seasonal variation. For all species examined except B. longicaudatus, a diagnostic soil sample collected 15 cm deep would recover only a minority of the nematode population present in the soil profile.     

Phytoparasitic Nematodes Adjacent to Established Strawberry Plantations

Plant-nematode populations associated with uncultivated vegetation, adjacent strawberry plants, and alternate crop sites were studied at three locations in Minnesota. At one site (Forest Lake), Paratylenchus projectus, Meloidogyne hapla, and Pratylenchus tenuis were frequently associated with the roots of native vegetation. These nematode species were also present in adjacent strawberry beds. Among alternate crops observed, oats and muskmelon usually supported the fewest nematodes although moderate densities of Xiphinema americanum and P. tenuis were found at one location in plots planted to oats. Pratylenchus tenuis was also found on rye at one location.     

Coarse root spatial distribution determined using a ground-penetrating radar technique in a subtropical evergreen broad-leaved forest, China

Coarse roots play a critical role in forest ecosystems and both abiotic and biotic factors affect their spatial distribution. To some extent, coarse root density may reflect the quantity of root biomass and biotic competition in forests. However, using traditional methods (e.g., excavation) to study coarse roots is challenging, because those methods are time-consuming and laborious. Furthermore, these destructive methods cannot be repeated in the same forests. Therefore, the discovery of non-destructive methods for root studies will be very significant. In this study, we used a ground-penetrating radar technique to detect the coarse root density of three habitats (ridge, slope and valley) and the dominant tree species (Castanopsis eyrei and Schima superba) in a subtropical forest. We found that (i) the mean of coarse root density for these three habitats was 88.04 roots m^?2, with roots being mainly distributed at depths of 0–40 cm. Coarse root densities were lower in deeper soils and in areas far from the trunk. (ii) Coarse root densities differed significantly among the three habitats studied here with slope habitat having the lowest coarse root density. Compared with S. superba, C. eyrei had more roots distributed in deeper soils. Furthermore, coarse roots with a diameter >3 cm occurred more frequently in the valleys, compared with root densities in ridge and slope habitats, and most coarse roots occurred at soil depths of 20–40 cm. (iii) The coarse root density correlated negatively with tree species richness at soil depths of 40–60 cm. The abundances of the dominant species, such as C. eyrei, Cyclobalanopsis glauca, Pinus massoniana, had significant impacts on coarse root density. (iv) The soil depth of 0–40 cm was the “basic distribution layer” for coarse roots since the majority of coarse roots were found in this soil layer with an average root density of 84.18 roots m^?2, which had no significant linear relationships with topography, tree species richness, rarefied tree species richness and tree density. Significant relationships between coarse root density and these factors were found at the soil depth of 40–60 cm, which was the “potential distribution layer” for coarse root distribution.     

Nematode Response to Carbofuran

Higher populations of Meloidogyne incognita larvae and Pratylenchus penetrans were recovered from soil treated with carbofuran 10 and 15 days after treatment, respectively, than were recovered from untreated control soil. The number of P. penetrans, however, was lower 50 days after treatment, and symptoms developed only occasionally on the root systems of host plants. Populations of Tylenchorhynchus claytoni inoculated at different distances from the base of corn seedlings growing in carbofuran-treated soil did not move toward the plant, whereas they were attracted in untreated soil from a distance of 12 cm. P. penetrans moved at random in treated agar medium when inoculations occurred 4 cm away from the root tips of tomato seedlings under aseptic conditions. Those nematodes that reached the roots were never observed feeding during a 20-day observation period. Specimens of P. penetrans placed on the developing roots moved at random and never penetrated. In contrast, numerous P. penetrans penetrated roots of seedlings growing in untreated medium.     

Plant-parasitic nematodes affecting vegetable crops in greenhouses

This work focuses on investigating plant-parasitic nematodes that affect greenhouse vegetables. The study took place in the Rostov region (Russian Federation) between May 2019 and May 2020 and involved 180 samples of soil and roots of 30 different vegetables in the families Cucurbitaceae (6), Solanaceae (8), Umbelliferae (8), Lamiaceae (4) and Allioideae (4) from 20 intensive farming locations. In this study, 11 nematode genera were detected. The most common genus was Meloidogyne, followed by Helicotylenchus, Pratylenchus, and Scutellonema. The highest Meloidogyne densities were detected in cucumbers, green peppers, carrots, eggplants, basil, and celery. Onions were not infected with Meloidogyne at all. Plant diseases caused by Pratylenchus, Scutellonema and Helicotylenchus were present in 29.7%, 51.5% and 81.6% of all crops examined, respectively. Xiphinema were found exclusively in carrots and celery, while Ditylenchus were only present in tomatoes and carrots (for each, the prevalence was 2.1%). The relative abundance of Meloidogyne, Helicotylenchus, and Pratylenchus was 58.3%, 10.4%, and 2.1%, respectively. As regards other genera, the relative abundance was less than 1%. The results show that soil properties are as important for the abundance, distribution and structure of the plant-parasitic nematode communities as the host plant. Findings may be helpful in improving the vegetable pest controls.     

Distribution and Prevalence of Parasitic Nematodes of Cowpea (Vigna unguiculata) in Burkina Faso

A comprehensive survey of the plant parasitic nematodes associated with cowpea (Vigna unguiculata) production fields was carried out in the three primary agro-climatic zones of Burkina Faso in West Africa. Across the three zones, a total of 109 samples were collected from the farms of 32 villages to provide a representative coverage of the cowpea production areas. Samples of rhizosphere soil and samples of roots from actively growing cowpea plants were collected during mid- to late-season. Twelve plant-parasitic nematode genera were identified, of which six appeared to have significant parasitic potential on cowpea based on their frequency and abundance. These included Helicotylenchus, Meloidogyne, Pratylenchus, Scutellonema, Telotylenchus, and Tylenchorhynchus. Criconemella and Rotylenchulus also had significant levels of abundance and frequency, respectively. Of the primary genera, Meloidogyne, Pratylenchus, and Scutellonema contained species which are known or suspected to cause losses of cowpea yield in other parts of the world. According to the prevalence and distribution of these genera in Burkina Faso, their potential for damage to cowpea increased from the dry Sahelian semi-desert zone in the north (annual rainfall < 600 mm/year), through the north-central Soudanian zone (annual rainfall of 600-800 mm/year), to the wet Soudanian zone (annual rainfall ≥ 1000 mm) in the more humid south-western region of the country. This distribution trend was particularly apparent for the endoparasitic nematode Meloidogyne and the migratory endoparasite Pratylenchus.     

Nematodes in Dryland Field Crops in the Semiarid Pacific Northwest United States

Soils and roots of field crops in low-rainfall regions of the Pacific Northwest were surveyed for populations of plantparasitic and non-plant-parasitic nematodes. Lesion nematodes (Pratylenchus species) were recovered from 123 of 130 non-irrigated and 18 of 18 irrigated fields. Pratylenchus neglectus was more prevalent than P. thornei, but mixed populations were common. Population densities in soil were affected by crop frequency and rotation but not by tillage or soil type (P < 0.05). Many fields (25%) cropped more frequently than 2 of 4 years had potentially damaging populations of lesion nematodes. Pratylenchus neglectus density in winter wheat roots was inversely correlated with grain yield (r² = 0.64, P = 0.002), providing the first field-derived evidence that Pratylenchus is economically important in Pacific Northwest dryland field crops. Stunt nematodes (Tylenchorhynchus clarus and Geocenamus brevidens) were detected in 35% of fields and were occasionally present in high numbers. Few fields were infested with pin (Paratylenchus species) and root-knot (Meloidogyne naasi and M. chitwoodi) nematodes. Nematodes detected previously but not during this survey included cereal cyst (Heterodera avenae), dagger (Xiphinema species), and root-gall (Subanguina radicicola) nematodes.     

Estimating Relative Error in Nematode Numbers from Single Soil Samples Composed of Multiple Cores

Spatial distributions of several species of plant-parasitic nematodes were determined in each of three fallow vegetable fields and in smaller subunits of those fields. Goodness of fit to each of several theoretical distributions was tested hy means of a X² test. Distributions for most species showed good agreement with a negative binomial model. An exception occurred with Crictmemella sp., which showed a better fit to the Neyman Type A distribution. For nematodes distributed according to the negative binomial model, the number of cores per composite sample needed to achieve specified relative errors was calculated. For a given nematode species, such as Quinisulcius actus (Allen) Siddiqi or Meloidogyne incognita (Kofoid &White) Chitwood, the k values for the negative binomial distribution increased as field size decreased, with the result that fewer cores were needed to achieve the same level of precision in a smaller field. Best results were achieved when the single sample was used to estimate populations in fields of 0.25-0.45 ha in size. When using only a single composite sample to estimate mixed populations of the nematodes studied here in a field of that size, approximately 22 cores per composite sample would be needed to estimate all population means within a standard error to mean ratio of 25%. Considerably, more cores were needed to maintain a given level of precision in fields of 1.0 ha or greater, and it may be necessary to subdivide larger unils (ca. 1.5 ha and up) for accurate sampling.     

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

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

Effect of Foliar Application of Carbofuran and a Related Compound on Plant-parasitic Nematodes under Greenhouse and Growth Chamber Conditions

Greenhouse and growth chamber studies were made to investigate the downward systemic nematicidal activity of carbofuran and its analog 2,3-dihydro-2,2-dimethyl-7-benzofuranyl [(di-n-butyl)-4-aminosulfenyl] carbamate against Meloidogyne incognita, Tylenchorhynchus claytoni, and Pratylenchus penetrans. Oxamyl was used as standard in tests with T. claytoni. Both carbofuran and its analog reduced all three plant-parasitic species when plant foliage was sprayed with chemical suspension of 1,200, 2,400 or 4,800 ppm. The studies show that fewer chemical applications were required to reduce populations of P. penetrans than to reduce populations of T. claytoni. Oxamyl was somewhat less active than either carbofuran or its analog.     

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.     

Effects of Storage Temperature and Extraction Procedure on Recovery of Plant-parasitic Nematodes from Field Soils

Storage of nematodes in soil at -15 C for 1 to 16 weeks greatly increased nematode recovery by a sugar-flotation-sieving procedure. One week of exposure to -15 C killed all nematodes except Pratylenchus zeae and Tylenchorhynchus claytoni which were recoverable in decreasing numbers up to 10 weeks by the Baermann funnel method. Optimum storage temperature for survival of most nematode species was 13 C. The numbers of Meloidogyne incognita, T. claytoni, Belonolaimus Iongicaudatus, and P. zeae recoverable by either extraction method remained constant or increased when stored at 13-24 C for 16 weeks. This was also true for Helicotylenchtts dihystera and Xiphinema americanum extracted by the Baermann funnel technique, whereas the numbers retrieved by the sugar-flotation-sieving method decreased slightly. All species except T. claytoni decreased appreciably in soil stored at 36 C.     

Factors Affecting Population Trends of Plant-Parasitic Nematodes on Rangeland Grasses

The effects of environmental conditions on population trends of plant-parasitic nematodes were studied in experimental plots of five wheatgrasses in the western Utah desert. In a 3-year (1984-86) field study, soil water and temperature affected the population trends of the ectoparasites, Tylenchorhynchus acutoides and Xiphinema americanum, and the migratory endoparasite, Pratylenchus neglectus, on Fairway crested wheatgrass, Agropyron cristatum; ''Hycrest'' crested wheatgrass, A. cristatum X A. desertorura; ''Rosana'' western wheatgrass, Pascopyrum smithii; ''Oahe'' intermediate wheatgrass, Thinopyrum intermedium; and RS-1 hybrid (Elytrigia repens X Pseudoroegneria spicata). The largest soil populations of these nematode species were collected in 1984 under good plant-growth conditions. A reduction in nematode populations occurred in 1985 and 1986, possibly because of low soil-water conditions. There was a positive relationship between high soil water and maximum population densities of T. acutoides in the spring and fall of 1984, and between low soil water and minimum population densities of the nematode in 1985 and 1986. Pratylenchus neglectus populations were affected by soil water, although to a lesser degree than the ectoparasitic nematodes. Population densities of the three nematode species were significantly lower in the drier years of 1985 and 1986 than in 1984. Nematode populations were greater at the lower soil depths in the fall than in the spring or summer.     

古尔班通古特沙漠西部梭梭种群退化原因的对比分析

古尔班通古特沙漠植被的建群种梭梭在沙漠的低平地和小沙丘(高度<5 m)区域发生大面积退化死亡,而在大沙丘(高度>10 m)生境中梭梭却长势良好。对此分析了梭梭林枯死植株的空间分布、活株和死株的年龄结构,研究了地下水埋深以及对比低平地、小沙丘和大沙丘3种生境土壤理化性质对梭梭生存的影响。发现梭梭死亡植株在观测的19个样点中的15个呈显著的集群分布,表明梭梭植株死亡并非是种内自疏。梭梭各年龄级植株均在死亡,说明死亡与植株年龄关系不大。退化区地下水埋深过浅或过深均对梭梭生长不利,表明地下水埋深对梭梭生长产生显著影响。低平地和小沙丘区土壤电导率高,土壤水分入渗速率慢,且0-90 cm深度范围梭梭侧根数和成活的梭梭幼苗幼株数较少,与梭梭正常生长的大沙丘区明显不同。综合分析认为梭梭退化主要是由自身的根系分布特性,以及地下水位、土壤盐分、土壤水分入渗变化等综合作用,实质是梭梭水分利用受限和种群更新不良引起的。     

Effect of Tillage System and Irrigation on Population Densities of Plant Nematodes in Field Corn

Soil populations of plant-parasitic nematodes were monitored bimonthly for 18 months in irrigated and nonirrigated corn plantings using four production systems: conventional and minimum tillage with crop residue returned and minimum tillage with 60% or 90% of previous corn crop residue removed. Populations of Meloidogyne incognita, Scutellonema brachyurum, Pratylenchus scribneri, and Paratrichodorus christiei varied among the tillage, nematicide, and irrigation treatments. Meloidogyne incognita and P. christiei populations were not significantly affected by tillage method, but S. brachyurum populations were highest during April 1981 and 1982 in minimum tillage treatments where crop debris was not removed. In contrast, S. brachyurum populations were lowest during the same period in minimum tillage plots where 90% of previous crop debris had been removed or where residues were incorporated with conventional tillage. Populations of P. scribneri were lowest in minimum tillage during August 1981 and April 1982. Regardless of tillage system, corn yields in all nonirrigated plots were increased during 1982 by application of carbofuran (2.24 kg a.i./ha). No yield increases were observed following nematicide application in 1981.     

Nematodes Parasitic on Forest Trees: III. Reproduction on Selected Hardwoods

The host-parasite relationships of 13 species of plant parasitic nematodes and five species of hardwoods native to the southeastern United States were tested on greenhouse-grown tree seedlings for 6-10 months. Criteria for parasitism were completion o f life cycle and population increase of nematodes. Belonolaimus longicaudatus, Helicotylenchus dihystera, Scutellonema brachyurum and Tylenchorhynchus claytoni parasitized and reproduced on three or more of the species tested. Hoplolaimus galeatus and Pratylenchus brachyurus parasitized two species, Trichodorus christiei and Criconemoides xenoplax parasitized only red maple. Meloidogyne javanica/Liriodendron tulipifera combination was the only positive root-knot nematode/hardwood host-parasite relationship. Hemicycliophora silvestris, Meloidogyne arenaria, M. incognita, and M. hapla were not parasites of the tree species tested.     

Dispersion and Distribution of Pratylenchus scribneri and Hoplolaimus galeatus in Soybean Fields

Examination of dispersional characteristics of Pratylenchus scribneri and Hoplolaimus galeatus indicated that there were patches within soybean fields in which both survival and reproduction wexe enhanced in spite of apparent homogeneity of soil type and topography. Treatment with carbofuran reduced the patchiness (or increased the dispersion) for H. galeatus while it had the opposite effect for P. scribneri. P. scribneri was less highly dispersed in conventional tillage plots than in the zero tillage plots. Populations from quadrats contained entirely within the patches could be described by the normal distribution (in the case of P. scribneri) or by the Poisson distribution (in the case of H. galeatus), while populations from quadrats contained entirely outside the patches could be described by the Poisson distribution for both nematodes. None of the distributions tested (Poisson, normal, negative binomial, Neyman''s) gave an adequate fit when populations from both inside and outside the patches were considered together. In all instances, log₁₀ and ln transformations reduced the goodness of fit of the data to all of the distributions tested. Even with logarithmic transformations, parametric statistics were not appropriate for analysis of data in most instances.     

Seasonal Fluctuations in the Spatial Distribution of Nematode Populations in a California Vineyard

Distribution of Xiphinema americanum and four Meloidogyne spp, was studied in a vineyard over a 13-mo. period. The X. arnericanum population was concd in the upper 60-cm of undisturbed soil in the vine row, whereas the Meloidogyne species were distributed both in and between rows and to greater depths, similar to the distribution of the root system. Samples for assessment of X. americanum densities had least variation when taken in the vine row from the upper 60-cm of soil. Sampling error is reduced in Meloidogyne populations by sampling within 40 cm of the vine both within and/or between rows.