Influence of Pratylenchus vulnus and Meloidogyne hapla on the Growth of Rootstocks of Rose

Pratylenchus vulnus is involved in a desease of Rosa noisettiana ''Manetti'' rose rootstock characterized by darkening of roots, death of feeder roots, and stunting of entire plants. The disease is more severe when plants are grown in silt loam soil than when they are grown in sandy loam soil. The nematodes reproduce best in silt loam soil at 20 C. Meloidogyne hapla did not affect the growh of Manetti. Rosa sp. ''Dr. Huey'', Manetti, and R. odorata rose rootstocks were found to be goos hosts for P. vulnus whereas R. multiflora was less suitable. M. hapla reproduced well on R. odorata, Dr. Huey, and R. multiflora, but not on Manetti.     

Behavioral Effects of Carbofuran and Phenamiphos on Pratylenchus vulnus. III. Penetration and Development

Penetration of bean roots by Pratylenchus vulnus was inhibited by continuous exposure of the nematode to carbofuran and phenamiphos and by drenches of higher concentrations of these chemicals. The inhibition was explicable by inhibition of motility, dispersion, and attraction. If incubated in aerated distilled water, nematodes treated with carbofuran and phenamiphos recovered and reproduced as well as untreated nematodes. Foliar treatments were ineffective. Apparently, no basipetal transport of carbofuran and phenamiphos occurs in beans. Both nematicides arrested nematode development by interfering with egg production and transitions between life stages.     

Behavioral Effects of Carbofuran and Phenamiphos on Pratylenchus vulnus. I. Motility and Dispersion

The motility and dispersion of Pratylenchus vulnus was affected by lower concentrations of phenanliphos (an organophosphate) than of carbofuran (a carbamate). At the higher concentrations in the active ranges, somatic musculature activity was inhibited while the activity of internal-organ muscnlature persisted. Treated nematodes recovered when placed in aerated distilled water, but recovery decreased as treatment concentrations increased. Second-stage larvae dispersed more slowly than later stages or adults. Dispersion from a point source followed a natural log pattern under ideal conditions, similar to a diffusion pattern.     

The long-term effects of four monocultural regimes on two field populations of the nematodes Xiphinema diversicaudatum and Longidorus spp.

Population density changes of Xiphinema diversicaudatum and several Longidorus spp. were observed under four cultural regimes in long-term field experiments. Numbers of X. diversicaudatum increased under strawberry and, to a lesser extent, ryegrass, but remained more or less unchanged in hop and fallow plots. A mixture of four Longidorus spp. increased in numbers under grass but stayed static, or declined slowly under the other cultural regimes. All changes in population density were slow to occur, taking 3 or 4 yr for differences to become statistically significant. Fluctuations in larval numbers were mainly responsible for overall population changes; numbers of adults showed little difference over 5 yr.     

Behavioral Effects of Carbofuran and Phenamiphos on Pratylenchus vulnus. II. Attraction to Bean Roots

Pratylenchus vulnus (L₃, L₄, adults) are attracted to the roots of growing bean seedlings. The attraction is inhibited by treating the nematodes with solutions of carbofuran or phenamiphos at concentrations below those necessary to inhibit motility and dispersion. Nematicide treatments of plants without treatment of nematodes are ineffectual because nematodes are attracted equally well to treated and untreated seedlings.     

Effects of Temperature on Rate of Feeding of the Plant Parasitic Nematodes Rotylenchus robustus,Xiphinema diversicaudatum,and Hemicycliophora conida

Rotylenchus robustus, Xiphinema diversicaudatum, and Hemicycgiophora conida were observed feeding over a range of temperatures on perennial rye-grass (Lolium perenne) seedlings grown on agar plates. R. robustus fed between 0.5 and 42.5 C, X. diversicaudatum between 5.0 and 37.0 C and H. conida between 5.0 and 34.0 C. Between 10 and 25 C there was a direct relationship between temperature and rate of esophageal bulb contractions. Above 25 C the number of esophageal contractions/min did not increase at the same rate and eventually decreased. At the extremes of temperature range, abnormal feeding behaviour was observed. Rates of esophageal bulb contraction did not differ in the different nematode life stages and sexes, or at different feeding sites on the roots.     

Vertical distribution of Pratylenchus neglectus, P. crenatus and Tylenchorynchus dubius associated with maize roots and the effect of aldicarb residues

Depth samples on a field trial on forage maize revealed consistent differences in the numbers of Pratylenchus neglectus, P. crenatus and Tylenchorynchus dubius at different depths after treatment with aldicarb the previous year. Pratylenchus was more numerous lower down in residual-treated soils but more evenly distributed in untreated soils. T. dubius, although less numerous after aldicarb, was more numerous in the upper layers of the soil. Aldicarb and benomyl applied the previous year had no residual effects on yields.     

Effects of the root-lesion nematode Pratylenchus vulnus and the mycorrhizal fungus Glomus mosseae on the growth of EMLA-26 apple rootstock

The interaction between Pratylenchus vulnus and the endomycorrhizal fungus Glomus mosseae on the growth of EMLA 26 apple rootstock was studied under shadehouse conditions in the field during the first 6 months of growth. Fresh top weights, fresh root weights, and shoot lengths of mycorrhizal plants with and without P. vulnus were significantly higher than those of nonmycorrhizal plants. Addition of P to non-mycorrhizal controls had little overall effect. Mycorrhizal treatments with the nematode showed a significantly lower amount of nematodes per gram of root than nonmycorrhizal treatments with P. vulnus. Root colonization by G. mosseae was not affected by the presence of the nematode. No nutrient deficiencies were detected in foliar analyses, although low levels of K, A1, and Fe were detected in nematode treatments. The highest levels of S, Mg, Mn and Zn were detected in P. vulnus inoculated plants. Mycorrhizal plants had the highest levels of N, Na, P, K, and Fe. The importance of early mycorrhizal infection of EMLA 26 apple root-stock in the presence of the nematode is discussed.     

Effect of annual and perennial cropping regimes in microplots on the population density and vertical distribution of Xiphinema diversicaudatum and on soil porosity

Long-term trends in populations of Xiphinema diversicaudatum were measured in two microplot experiments in which annual and perennial crops of seven plant families were grown in monoculture. Numbers of X. diversicaudatum increased under perennial ryegrass, raspberry and strawberry but decreased under hop, spring barley, potato, sugar beet, cabbage, winter wheat and winter beans; these effects probably reflected differences in the inherent host status of the crops. There were fewer X. diversicaudatum at 40–60 cm below annual crops than below perennial crops, and there were differences between perennial crops in nematode vertical distribution. Soil pore space did not limit nematode population density; total pore space was uniformly large under all crops and there was no detectable instability to water slaking. Under ryegrass a greater proportion of soil volume was occupied by pores too small to accommodate X. diversicaudatum, but since ryegrass supported the second largest nematode population, it seems unlikely that this was seriously limiting.     

Oogenesis and Embryology of Two Plant-parasitic Nematodes,Pratylenchus penetrans and P. zeae

The process of oogenesis was studied in the bisexual species, Pratylenchus penetrans, and the monosexual species, P. zeae. The nucleus of the oocyte of P. penetrans underwent two divisions after sperm penetration. The chromosome number of P. penetrans observed at metaphase of the first maturation division was 2n = 10 and the reduced chromosome number observed at anaphase of the first maturation division was n = 5. Two polar bodies were found within the egg, indicating that this species reproduces by amphimixis. The nucleus o f the oocyte of P. zeae underwent one mitotic division and the chromosome number was 2n = 26. The presence of only 1 polar body indicates that this species reproduces by mitotic parthenogenesis. The development of the embryo was similar in P. penetrans and P. zeae. Unsegmented eggs were usually deposited by females. Following the 9-celled stage, the number of cells increased rapidly until a blastula was formed. Cell differentiation immediately followed, as evidenced by the formation of darker and larger inner endodermal cells and smaller ectodermal cells. Six to 7 days after egg deposition, the first stage larva was coiled three to f o u r times within the egg shell. During the first molt, the styler apex was formed first, then the larva moved frequently and vigorously and the styler was repeatedly thrust into the egg shell. Finally, the shell was broken and the second stage larva emerged. It took 10 days from the unsegmented egg to hatching at 23 C.     

Effects of Pratylenchus brachyurus and P. coffeae on Seedlings of Coffea arabica

Two experiments were carried out to evaluate the effects of Pratylenchus brachyurus and P. coffeae on Coffea arabica. The first experiment was conducted in a greenhouse to determine the effects of Pratylenchus brachyurus and P. coffeae on seedlings of Coffea arabica cv. Mundo Novo. Both Pratylenchus spp. reduced the growth of coffee seedlings. Higher contents of soluble sugars were detected in the leaves of infected plants. The reproduction rate of P. brachyurus was very low on cv. Mundo Novo, indicating an intolerance to this nematode. In a second experiment, C. arabica cultivars Mundo Novo and Catuaf both were intolerant hosts of P. brachyurus.     

Observations on the pathogenicity of Pasteuria penetrans, a parasite of root-knot nematodes

A simple test was used to determine whether or not Pasteuria penetrans spores would attach to 17 species of nematodes. All susceptible individuals had spores attached to their cuticles after 24 h of gentle agitation in suspensions containing 10⁵spores/ml. Spores of P. penetrans from six populations of Meloidogyne only adhered to species of Meloidogyne and they adhered in greatest numbers to the species from which they had been originally isolated. Sonication of spores from infected females increased attachment but the effect was dependent on pH and whether the test was conducted in tap or distilled water. Invasion of tomato roots was reduced by up to 86% when, rather than using healthy juveniles, second-stage juveniles bearing 15 or more spores were added to soil at high densities (1000 or 3000/plant); at low densities (500/plant) invasion was not significantly affected. The rate of development of M. incognita juveniles infected with P. penetrans was slower than that of healthy juveniles. The numbers of second-generation of M. incognita were reduced by 82–93% when juveniles encumbered with 1–15 spores were added to soil instead of those bearing no spores. Pasteuria penetrans populations differed in their aggressiveness and when juveniles encumbered with the same number of spores from two populations were added to soil there were differences in the numbers of females that became infected. The implications of these results for the development of P. penetrans as a biological control agent are discussed.     

The Effects of Temperature on Pratylenchus scribneri and P. alleni Populations on Soybeans and Tomatoes

In soil temperature tests, rates of Pratylenchus scribneri and P. alleni reproduction were measured at various lemperatures on ''Clark 63'' and ''Cutler 71'' soybeans and ''Rutgers'' tomatoes. Recovered P. scribneri equaled or exceeded initial inoculum levels at temperatures of 27.5 C or higher on soybeans, and at 20 C or higher on tomatoes. Population increases were greatest at 3.5 C on both hosts. Populations increased on soybeans, but not on tomatoes, when soil temperature was raised from 25 to 35 C for either 3 or 9 days. Recovered P. alleni were less than the initial inoculum at 27.5 C but higher at 32 and 37.5 C and at 27.5 C on tomatoes, the lowest temperature tested for this nematode. In the field, soil temperatures 10 cm deep in eastern Kansas soybean growing areas reach 27.5 C only occasionally and for relatively short periods, which probably explains the relatively low and variable populations of P. scribneri and P. alleni on soybeans there.     

Fusarium spp. associated with rice Bakanae: ecology,genetic diversity,pathogenicity and toxigenicity

African and Asian populations of Fusarium spp. (Gibberella fujikuroi species complex) associated with Bakanae of rice (Oryzae sativa L.) were isolated from seeds and characterized with respect to ecology, phylogenetics, pathogenicity and mycotoxin production. Independent of the origin, Fusarium spp. were detected in the different rice seed samples with infection rate ranges that varied from 0.25% to 9%. Four Fusaria (F. andiyazi, F. fujikuroi, F. proliferatum and F. verticillioides) were found associated with Bakanae of rice. While three of the Fusaria were found in both African and Asian seed samples, F. fujikuroi was only detected in seed samples from Asia. Phylogenetic studies showed a broad genetic variation among the strains that were distributed into four different genetic clades. Pathogenicity tests showed that all strains reduced seed germination and possessed varying ability to cause symptoms of Bakanae on rice, some species (i.e. F. fujikuroi) being more pathogenic than others. The ability to produce fumonisins (FB₁ and FB₂) and gibberellin A3 in vitro also differed according to the Fusarium species. While fumonisins were produced by most of the strains of F. verticillioides and F. proliferatum, gibberellin A3 was only produced by F. fujikuroi. Neither fumonisin nor gibberellin was synthesized by most of the strains of F. andiyazi. These findings provide new information on the variation within the G. fujikuroi species complex associated with rice seed and Bakanae disease.     

Interactions Among Pratylenchus penetrans,P. scribneri,and Verticillium dahliae in the Potato Early Dying Disease Complex

Microplots were infested with combinations of the fungus Verticillium dahliae and Pratylenchus penetrans and P. scribneri to test for individual and combined effects of these organisms on potato yield and nematode reproduction. Verticillium dahliae alone caused yield losses in all 3 years of the experiment, and the interaction between P. penetrans and V. dahliae was significant (P ≤ 0.05) in 2 years. Pratylenchus penetrans alone caused yield losses in 2 years and P. scribneri alone caused yield losses in 1 year. No two-way or three-way interaction was found involving P. scribneri. In 1987, reproduction for low densities of P. penetrans was 5 times higher when P. scribneri was also present than when it was absent, and 3.5 times higher in 1988. In nematode species mixtures, reproduction of P. scribneri was decreased by V. dahliae in 1987-88. The final population density of P. scribneri was negatively affected by V. dahliae and positively related to the initial proportion of P. scribneri to P. penetrans. In species mixtures with proportions of P. penetrans ranging from 0.1 to 0.5, reproduction of P. penetrans was negatively affected by V. dahliae and decreased linearly in relation to the increase in the initial proportion of P. penetrans in both years. The final population density of P. penetrans was affected only by V. dahliae.     

Germination and effect of reduced humidity on expression of pathogenicity in Verticillium lecanii against the glasshouse whitefly Trialeurodes vaporariorum

Fifteen isolates of the entomopathogenic fungus Verticillium lecanii, from various hosts and locations, were bioassayed in the laboratory at 19 ± 1°C and > 95% r.h. against fourth instar scales of Trialeurodes vaporariorum. Highly pathogenic isolates generally originated from whitefly; however, there was no correlation between conidiospore size or germination rate on agar, and pathogenicity. LT₅₀ values ranged from 5.7 to > 9 days and LC₅₀ (7 days) from 1.3 × 10⁵ to 4.2 × 10⁷ spores/ml. The effect of periods in low humidity (70% r.h.) following 16 or 96 h at > 95% r.h. after immersion of whitefly scales on tomato leaf discs in a suspension of 1 × 10⁶ spores/ml, was compared for five isolates. Progressively longer periods at 70% r.h. following 16 h at > 95% r.h., reduced significantly (P < 0.001) the pathogenicity of all isolates. In these conditions isolate A was least affected by low-humidity transfer. The high pathogenicity of isolate A was associated with its more rapid development on the host cuticle during the first 16 h in high humidity. When inoculated whitefly scales were transferred to 70% r.h. after a preliminary 96 h incubation in high humidity, all five isolates achieved a higher level of pathogenicity compared with their transfer to low humidity after 16 h high humidity. Thus the screening of V. lecanii isolates in limiting humidity conditions provided a more critical assessment of their pathogenicity and of their potential success in whitefly control relevant to the glasshouse environment.     

Influence of Soil Temperature and pH on Pratylenchus Penetrans and P. crenatus in Alfalfa and Timothy

Numbers of Pratylenchus penetrans in alfalfa and timothy, and to a lesser extent P. crenatus in timothy, increased substantially as temperature increased from about l0 C to 30 C. However, P. crenatus in alfalfa decreased in number as temperature increased. Mobility of P. crenatus in vertical soil columns decreased as temperature increased from 9.5 C to 28.5 C. Raising the soil pH from 5.0 to 6.9 in which alfalfa was grown increased the numbers of P. penetrans and greatly reduced the numbers of P. crenatus. The numbers of both nematode species in timothy were reduced significantly as soil pH was increased. The optimum soil pH for movement of P. penetrans was 6.0. Pratylenchus crenatus moved equally well over a range of pH 5.0 to 7.0.     

Observations on the occurrence of Phalaris paradoxa in England and Wales

A study of the occurrence of Phalaris paradoxa in England and Wales was made during summer 1984. Visits were made to 73 farms reported to be infested with this species. The presence of P. paradoxa was confirmed on 68 of them. Three other Phalaris species were also recorded as weeds on five farms. Infested farms were located over a wide area of southern England, with a majority in Essex. Most infestations were apparently less than 10 years old. Many infested fields had P. paradoxa only in the headlands. Varying degrees of control had been achieved with herbicides, hand roguing, cutting down and planting fields to grass. Counts of the densest area in 24 fields gave a median density of 167 and a maximum density of 1289 heads m^-2. With a mean of 96 caryopses per head these densities represent a potential seed production of 16 000 and 120 000 caryopses m^-2 respectively. It is concluded that further spread of the weed could be limited by suitable publicity about its occurrence and the best methods of control.