Population Fluctuations of Three Nematode Genera in Putting Greens in Northern Illinois

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.     

Vertical Distribution of Three Nematode Genera in a Bentgrass Putting Green in Central Illinois

A study was conducted to determine the vertical distribution of Tylenchorhynchus nudus, Criconemella curvata, and Helicotylynchus cornurus in the upper 5 cm of bentgrass (Agrostis palustris cv. Penncross) putting green turf. The effect of fenamiphos on the vertical distribution of these species also was examined. Experimental design was a split-plot in which whole-plots were fenamiphos treated (0.11 kg a.i./100 m²) or untreated, and sub-plots were two strata (depths of 0-2.5 crn and 2.5-5.0 cm). Soil samples were collected during the growing season for 2 years after treatment to determine root weight and number of nematodes. Root weight was greater in the upper stratum on all sampling dates in both years. When differences between strata in population density were observed, T. nudus, C. curvata, and H. cornurus were more concentrated in the upper stratum. Vertical distribution of T. nudus, C. curvata, and H. cornurus was similar to the distribution of root weight. The difference in population density of H. cornurus between upper and lower strata was affected by fenamiphos on some dates, whereas differences between strata were unaffected for T. nudus and C. curvata. Double arcsine transformed proportions of the total populations of T. nudus, C. curvata, and H. cornurus in the upper stratum on each sampling date indicated no differences between fenamiphos treated and untreated plots in 1989 or 1990.     

Population Response to Temperature in the Subfamily Tylenchorhynchinae

The effects of temperature on population development of 11 species of stunt nematodes in the subfamily Tylenchorhynchinae were compared on red clover or Kentucky bluegrass in constant-temperature tanks at 5-degree intervals from 10 to 35 C. The optimum temperature for population increase on red clover in 90 days was 30 C for Tylenchorhynchus agri, T. nudus, T. martini, and T. clarus, 25 C for T. sylvaticus and T. dubius, and 20 C for T. canalis, Merlinius brevidens, and Quinisulcius capitatus. The optimum was 30 C for T. robustoides and 25 C for T. maximus on Kentucky bluegrass. The temperature range for population increase was 20-35 C for T. agri, T. nudus, T. martini, and T. clarus, 20-30 C for T. sylvaticus and T. robustoides, 15-25 C for T. maximus, 10-25 C for T. dubius, and 10-20 C for M. brevidens and Q. capitatus. T. canalis increased only at 20 C. All species were recovered in numbers near their inoculum level at 10 C. There was no survival of T. sylvaticus, T. dubius, T. canalis, T. robustoides, T. maximus, M. brevidens, and Q. capitatus at 35 C, or of the last three of these species at 30 C. Temperature had no effect on sex ratio in final populations. Population increase was greatest in T. martini and least in T. canalis.     

Effect of Tylenchorhynchus nudus on Growth of Kentucky Bluegrass

The effect of Tylenchorhynchus nudus on growth of Kentucky bluegrass was investigated under controlled environmental conditions in both a phytotron and a greenhouse. The nematode significantly reduced weights of clippings, crowns and roots. Pathogenicity was greater in sandy loam soil than in loam and was enhanced by submitting plants to nutrient and/or moisture stresses; soil nutrient level was most critical. The results suggest that T. nudus contributes significantly to summer decline of bluegrass lawns in South Dakota.     

Effects of Nematicides on Nematode Densities in Turf in Connecticut

The plant-parasitic nematodes Criconemoides lobatum, Hoplolaimus tylenchiformis, and Tylenchorhynchus dubius were present in the top 7.5 cm of sod consisting of numerous stolons and fibrous roots. Phenamiphos and 1,2-dibromo-3-chloropropane (DBCP) controlled all three species, whereas ethoprop and oxamyl controlled H. tylenchiformis and T. dubius but not C. lobatum. Benomyl and carbofuran controlled H. tylenchiformis but had poor control of C. lobatum and T. dubius. The effectiveness of carbofuran varied with the type of formulation, being most effective as a quick-release formulation. C. lobatum was the most difficult to control with chemicals. No chemical treatment improved the growth of ''Astoria colonial'' bentgrass (A. tenuis Sibth.) or Kentucky bluegrass (Poa pratensis L.) under the moist condtions prevalent in these tests.     

Interaction of Meloidogyne naasi,Pratylenchus penetrans,and Tylenchorhynchus agri on Creeping Beentgrass

The pathogenicity and interactions of Meloidogyne naasi, Pratylenchus penetrans, and Tylenchorhynchus agri on ''Toronto C-15'' creeping bentgrass, Agrostis palustris, was studied in a long-term greenhouse experiment. Based on dry weights of roots and clippings, M. naasi alone and in all combinations with P. penetrans and T. agri was highly pathogenic to creeping bentgrass. P. penetrans and T. agri alone and in combination inhibited root growth but adversely affected top growth only when the two were co-inoculated. In combination, the effects of each species on top growth were additive, with M. naasi the dominant pathogen. Creeping bentgrass was an excellent host for M. naasi and T. agri, but a poor host for P. penetrans. T. agri inhibited population increase of M. naasi, indicating nematode-nematode competition, but neither T. agr/ nor P. penetrans was affected by any of the combinations.     

Studies on the Host Range,Biology, and Pathogenicity of Punctodera punctata Infecting Turfgrasses

Punctodera punctata completed its life cycle on Poa annua (annual bluegrass), P. pratensis (Merion Kentucky bluegrass), Lolium perenne (perennial ryegrass), and Festuca rubra rubra (spreading fescue). Minimum time for completion of a life cycle from second-stage juvenile to mature brown cyst was 40 days at 22-28 C. Inoculation by single juveniles indicated that reproduction was most likely by amphimixis. Infestation levels of 50 or 500 juveniles/250 cm³ soil did not affect top dry weight, root dry weight, or total dry weight of Poa annua.     

Interrelationships Among Macrophomina phaseolina,Criconemella xenoplax,and Tylenchorhynchus annulatus on Grain Sorghum

Microplot experiments were established in 1992, 1993, and 1994 to investigate the relationships among Macrophomina phaseolina, Criconemella xenoplax, mad Tylenchorhynchus annulatus on grain sorghum in Louisiana. A factorial treatment arrangement of two grain sorghum hybrids (De Kalb DK 50 and Pioneer hybrid 8333), three levels of M. phaseolina (0, 10, and 100 colony-forming units (CFU)/g soil), and three nematode inoculum levels (0, 1x, and 2x) were used. Nematode inocula at 1x levels were 929, 1,139, and 1,445 C. xenoplax and T. annulatus/microplot in 1992, 1993, and 1994, respectively. Plants were harvested after 90-105 days. In all 3 years, grain sorghum root and head dry weights were suppressed as nematode inoculum level increased. These reductions were detected both in the absence and in the presence of M. phaseolina at 10 CFU/g. Reproduction of both nematode species was suppressed by M. phaseolina. Interactions between M. phaseolina and nematodes were antagonistic with regard to plant dry weights, yield, and nematode reproduction, so that combined effects were less than the sum of the effect of each pathogen alone.     

Interaction of Ditylenchus dipsaci and Meloidogyne hapla on Resistant and Susceptible Plant Species

Numbers ofDitylenchus dipsaci or Meloidogyne hapla invading Ranger alfalfa, Tender crop bean, Stone Improved tomato, AH-14 sugarbeet, Yellow sweet clover, and Wasatch wheat from single inoculations were not significantly different from numbers by invasion of combined inoculations. D. dipsaci was recovered only from shoot and M. hapla only from root tissue. Combined inoculations did not affect reproduction of either D. dipsaci or M. hapla. D. dipsaci suppressed shoot growth of all species at 15-30 C, and M. hapla suppressed shoot growth of tomato, sugarbeet, and sweet clover at 20, 25, and 30 C. There was a positive correlation (P < 0.05) between shoot and root growth suppression by D. dipsaci on all cultivars except wheat at 20 C and tomato at 30 C. M. hapla suppressed (P < 0.05) root growth of sugarbeet at 20-50 C and wheat at 30 C. Growth suppression was synergistic in combined inoculations of sweet clover shoot growth at 15 C and root growth at 20-30 C, wheat root growth at 15 and 20 C, and tomato root growth at 15-30 C (P < 0.05) D. dipsaci invasions caused mortality of alfalfa and sweet clover at 15-30 C and sugarbeet at 20-30 C. Mortality rates of alfalfa and sweet clover increased synergistically (P < 0.05) from combined inoculations.     

Effects of Temperature,Plant Age,Soil Texture,and Meloidogyne incognita on Early Growth of Soybean

A digitizer-microcomputer combination was utilized to determine soybean seedling response to population densities of M. incognita (Mi) under varied environmental conditions. Plant age, temperature, soil texture, and initial Mi inoculum (Pi) influenced the pattern of shoot and root growth. Effects of Mi on plant top growth were evident on plants inoculated 2 days after seeding, but generally were not noticeable on those receiving Mi after 4, 6, or 8 days (observations limited to 6 days after inoculation). The greatest Pi of Mi (16,700 juveniles/plant) suppressed root growth on plants inoculated at 2 or 4 days after seeding. Mi had no impact on root growth at 22 C on plants inoculated 6 or 8 days after seeding at any temperature used (22, 26, 30 C). New root initiation was inhibited on soybeans inoculated 2 days after seeding at the highest Pi at all three temperatures, but only at 30 C for a Pi of 1,670 juveniles/plant. Growth of first order lateral roots and general root length were suppressed by Mi on the youngest (2-day) plants. However, a low Pi (167 juveniles/ plant) resulted in root proliferation on 4-day-old plants at 26 C. Mi was most damaging in a low clay-content soil mixture.     

Competition Between Tylenchorhynchus annulatus and Mesocriconema xenoplax on Grain Sorghum as Influenced by Macrophomina phaseolina

Greenhouse experiments were conducted to examine competition between Tylenchorhynchus annulatus and Mesocriconema xenoplax on grain sorghum roots that were colonized by the fungus Macrophomina phaseolina or free from fungus colonization. An incomplete factorial treatment design consisted of two levels of M. phaseolina (0 or 10 colony-forming units/g soil) and 12 T. annulatus:M. xenoplax ratios: 1,000:0; 750:0; 500:0; 250:0; 0:0; 0:250; 0:500; 0:750; 0:1,000; 750:250; 500:500; and 250:750. Plants were harvested after 105 days. Despite similar feeding habits, competition between these ectoparasitic nematode species was limited. Tylenchorhynchus annulatus was more susceptible to antagonism by M. xenoplax than the reverse, but susceptibility depended on initial inoculum ratio. Root colonization by M. phaseolina reduced competitive effects of T. annulatus on M. xenoplax but not the reverse. Both nematode species reduced shoot dry weight but only T. annulatus reduced root dry weight. Both plant weight parameters were reduced by M. phaseolina.     

Relationship between Cultural Factors and Nematodes on Merion Kentucky Bluegrass

A 2-year study was conducted on Merion Kentucky bluegrass turf (Poa pratensis) to identify potential relationships among seasonal population dynamics of nematodes, chemical applications, thatch, tillering, dollar spot caused by Sclerotinia homoeocarpa, clipping weight, and other factors. Numbers of Tylenchorhynchus maximus determined during June were inversely related to the wet weight of grass from May. One or more monthly counts of Paratylenchus hamatus, Criconemella rusium, and T. maximus negatively correlated with the numbers of spring tillers. Applications of benomyl, used for dollar spot control, decreased numbers of T. maximus and free-living nematodes, and this chemical was associated with acidification of the thatch. Hoplolaimus galeatus levels were associated with an estimated 8% increase in the severity of dollar spot.     

Descriptions of Two New Species of Tylenchorhynchus Cobb, 1913 (Nematoda: Tylenchida), with Details on Morphology and Variation of T. claytoni

Two new species of plant parasitic nematodes (Tylenchorhynchus quaidi n. sp. and T. tritici n. sp.) from Pakistan are described and illustrated. Tylenchorhynchus quaidi n. sp., from soil around roots of potato (Solanum tuberosum) from an experimental field of NNRC, Karachi, Pakistan, is distinguishable from other species by its peculiar sunken dome-shaped head. Although similar to T. goffarti, it differs by head shape, areolation of lateral field, ratios a (23-28 vs. 29-37) and c (11-14 vs. 13-20), and a vagina that is half sclerotized and half unsclerotized. Tylenchorhynchus tritici n. sp., from soil around roots of wheat (Triticum aestivum) from Campbellpur, Pakistan, is similar to T. ventrosignatus and T. nordiensis. It differs from T. ventrosignatus by a continuous lip region, number of head annules (2-3 vs. 4), coarse body annulation, absence of a wave-like structure near the vulva, and by tail shape and number of tail annules (15-23 vs. 28-32). It differs from T. nordiensis by stylet length (12.4-14.6 vs. 11-13 μm), shape of stylet knobs, number of head annules (2-3 vs. 4), non-areolated lateral field in region of phasmids, and not fusing in posterior third of tail. Morphometrics of Tylenchorhynchus claytoni from soil around stunted maize (Zea mays L.), in Muscatine County, Iowa, and several other populations are given. Detailed morphometric data on T. claytoni based on topotypes collected from type locality and several other populations revealed that this species shows variations in the shape of tail in females, number of tail annules (and sometimes annules extending further back on the terminus, almost being an annulated terminus), position of phasmid, and shape of lip region. The subgenus Bitylenchus is proposed as a new synonym of Tylenchorhynchus and its species referred to the latter genus.     

Growth of Isolates of Paecilomyces lilacinus and Their Efficacy in Biocontrol of Meloidogyne incognita on Tomato

The potential of 13 Paecilomyces lilacinus isolates from various geographic regions as biocontrol agents against Meloidogyne incognita, the effects of temperature on their growth, and the characterization of the impact of soil temperature on their efficacy for controlling this nematode were investigated. Maximum fungal growth, as determined by dry weight of the mycelium, occurred from 24 to 30 C; least growth was at 12 and 36 C. The best control of M. incognita was provided by an isolate from Peru or a mixture of isolates of P. lilacinus. As soil temperatures increased from 16 to 28 C, both root-knot damage caused by M. incognita and percentage of egg masses infected by P. lilacinus increased. The greatest residual P. lilacinus activity on M. incognita was attained with a mixture of fungal isolates. These isolates effected lower root-galling and necrosis, egg development, and enhanced shoot growth compared with plants inoculated with M. incognita alone.     

The Influence of Temperature on Meloidogyne incognita on Soybean

The effects of temperature and initial inoculum density of Meloidogyne incognita on soybean growth and nematode reproduction were investigated in greenhouse temperature tanks and in controlled-growth chambers. The interactions of initial inoculum density (P_i) and soil temperature in effects on shoot growth were adequately described by multiple-regression models. At the highest temperatures (30 or 32/28 C), moderate to high inoculum killed many plants. A P_i of 27,000 eggs/15-cm-diam pot retarded shoot growth at 26 C. Only the greatest P_i (81,000 eggs/15-cm pot) suppressed shoot growth at 18, 22, or 20/16 C. Inoculation with 3,000 or 9,000 eggs/plant resulted in heavier root systems at all temperatures except 30 C. At that temperature, 9,000 eggs suppressed root growth. At 18 and 26 C, a Pi of 81,000 eggs was required to retard root growth. Nematode reproduction was related directly to temperature and P_i except at a density of 81,000 eggs/15-cm pot.     

Pathogenic Potential of Tylenchorhynchus dubius on Selected Turfgrass

Tylenchorhynchus dubius was observed to feed on ''Toronto'' creeping bentgrass and ''Merion'' Kentucky bluegrass, and was a key participant in reducing the vegetative growth of both grass species. The severity of foliar and root macrosymptoms incited by T. dubius to ''Toronto'' bentgrass was greater on plants grown at 16 C than on plants maintained at 21, 27 and 32 C. These parasitized plants exhibited a suppression of secondary stolon formation, shortened internodes and premature inflorescence initiation. Initial inoculum densities of 500 and 1000 nematodes/test pot produced similar pathogenic effects on the host. Feeding was primarily on root hairs and epidermal cells immediately behind the meristematic region. No necrotic lesions or other diagnostic symptoms were visible at the feeding sites. Nematodes were not observed inside the roots.     

Importance of Temperature in the Pathology of Meloidogyne hapla and M. chitwoodi on Legumes

Effects of temperatures on the host-parasite relationships were studied for three legume species and four populations of root-knot nematodes from the western United States. The nematode populations were Meloidogyne hapla from California (MHCA), Utah (MHUT), and Wyoming (MHWY), and a population of M. chitwoodi from Utah (MCUT). The legumes were milkvetch (Astragalus cicer), alfalfa (Medicago sativa), and yellow sweet clover (Melilotus officinalis). All milkvetch plants survived inoculation with all nematode populations, while alfalfa and yellow sweet clover were more susceptible. On yellow sweet clover, MHCA was most pathogenic at 30 °C based on suppression of shoot growth while MHUT, MHWY, and MCUT were most pathogenic at 25 °C. All nematode populations suppressed growth of yellow sweet clover more than growth of milkvetch and alfalfa. The reproductive factor (Rf = final nematode population/initial nematode population) of MHCA was positively correlated (r = 0.83) with temperature between 15 °C and 30 °C. The greatest Rf occurred on alfalfa inoculated with MHCA at 30 °C. The Rf of MHUT, MHWY, and MCUT were positively correlated (r= 0.76, r= 0.78, and r= 0.73, respectively) with temperature between 15 °C and 25 °C. The Rf values of MHUT and MHWY were similar on all species and exceeded the Rf of MCUT at all temperatures (P < 0.05).     

Influence of Four Nematodes on Root and Shoot Growth Parameters in Grape

Two grape cultivars, susceptible French Colombard and tolerant Rubired, and four nematodes, Meloidogyne incognita, Pratylenchus vulnus, Tylenchulus semipenetrans, and Xiphinema index, were used to quantify the equilibrium between root (R) and shoot (S) growth. Root and shoot growth of French Colombard was retarded by M. incognita, P. vulnus, and X. index but not by T. semipenetrans. Although the root growth of Rubired was limited by all the nematodes, the shoot growth was limited only by X. index. The R:S ratios of Rubired were higher than those of French Colombard. The reduced R:S ratios of Rubired were primarily an expression of reduction in root systems without an equal reduction in shoot growth, whereas in French Colombard the reduced R:S ratios were due to a reduction in both shoot growth and root growth and to a greater reduction in root growth than shoot growth. All nematodes reproduced equally well on both cultivars. Both foliage and root growth of French Colombard were significantly reduced by M. incognita and P. vulnus. Nematodes reduced the shoot length by reducing the internode length. Accumulative R:S ratios in inoculated plants were significantly smaller than those in controls in all nematode treatments but not at individual harvest dates. Bud break was delayed by X. index and was initiated earlier by P. vulnus and M. incognita. All buds in nematode treatments were less vigorous than in controls.     

Modification of Resistance Expression of Phaseolus vulgaris to Meloidogyne incognita by Elevated Soil Temperatures

The effect of temperature on the reaction of susceptible (Canario Divex) and resistant (A 211) bean pure lines to Meloidogyne incognita was studied with soil temperature tanks housed in a growth chamber at 22 or 24 C. Soil temperature remained constant at 16, 22, 24, 26, 30, or 32 C in several trials. Bean line A 211 was resistant at 16 and 22 C but was susceptible at 24 C and above. Resistance to root-knot nematode reproduction was affected by a lower temperature (24 C) than was resistance to root galling (26 C) in A 211. Incubation of A 211 at 30 C for 3 and 16 days after inoculation with M. incognita resulted in a significant increase in nematode reproduction and root galling, respectively. The resistant reactions of A 211 to nematode reproduction and root galling were retained when inoculated plants were incubated at 21 C for a minimum of 16 and 23 days, respectively, prior to high temperature treatment.     

Differential Effects of Pratylenchus neglectus Populations on Single and Interplantings of Alfalfa Grasses

The invasion by three different Utah populations of Pratylenchus neglectus (UTI, UT2, UT3) was similar in single and interplantings of ''Lahontan'' alfalfa and ''Fairway'' crested wheatgrass at 24 ñ 3 °C. Population UT3 was more pathogenic than UT1 and UT2 on both alfalfa and crested wheatgrass. Inoculum density was positively correlated with an invasion by P. neglectus. Invasions by UT3 at all initial populations (Pi) exceeded that of UT1 and UT2 for both single and interplanted treatments. The greatest reductions in shoot and root weights of alfalfa and crested wheatgrass were at a Pi of 8 P. neglectus/cm³ soil. Pi was negatively correlated with alfalfa and crested wheatgrass shoot and root growth and nematode reproduction. The reproductive factor (Rf) for UT3 exceeded that of UT1 and UT2 in single and interplantings at all inoculum levels. There were no differences in Rfin the Utah populations in single or interplantings. A nematode invasion increased with temperature and was greatest at 30 °C. Population UT3 was more pathogenic than UT1 and UT2 and reduced shoot and root growth at all soil temperatures. Populations UT1 and UT2 reduced shoot and root growth at 20-30 °C. Soil temperature was negatively correlated with shoot and root growth and positively correlated with nematode reproduction. Reproduction of UT3 exceeded that of UT1 and UT2 at all soil temperatures.