LABORATORY ERRORS ASSOCIATED WITH THE ESTIMATION OF THE POPULATION DENSITY OF HETERODERA SPECIES IN SOIL

As unexpectedly large sampling errors were obtained in preliminary population studies on Heterodera , an examination was made of the laboratory errors associated with sampling for H. göttingiana and H. schachtii. Soil samples were taken from microplots and appeared to be satisfactory, being without the usual heterogeneity found in sampling from fields. There was little evidence of errors introduced by the technique used for estimating the number of eggs and larvae in a subsample. These errors, when they occurred, were always small, and this standard technique was deemed satisfactory. The logarithmic transformation was suitable for statistical analysis of both cyst and egg counts.
Apart from the residual variation, there were two other important sources of variation when sampling for eggs. There was a large variation between sub-samples, caused by differences in the number of cysts and in the number of eggs per cyst. There was also in some instances a difference between observers counting the same eggs of up to 20%. Where a comparative measure of density is sufficient, this bias is probably unimportant, and to increase accuracy of estimates of eelworm density, most laboratory work should be devoted to the separation of cysts from the soil sample.     

MOVEMENT OF EELWORMS

Tracks were plotted of about 300 individual eelworms comprising six species among water droplets on a glass surface. Measurements of the tracks indicated that the product of length and activity of an eelworm divided by its speed was a constant. This supports the hypothesis that the speed of an eelworm among water droplets is a function of its length and activity. This principle can only be applied to movement in soil where the length of the eelworm is less than about three times the particle diameter. Under such conditions the eelworms move in thin films or water droplets over particles. Among smaller-sized particles the speed of the eelworms is influenced by particle size. With increasing eelworm length there is an increase in soil particle size for maximum mobility.     

SOME OBSERVATIONS ON THE CEREAL-ROOT EELWORM POPULATION OF FIELD PLOTS OF CEREALS WITH DIFFERENT SOWING TIMES AND FERTILIZER TREATMENTS

In the autumn of 1953 an experiment was begun to follow changes in the cereal-root eelworm population of small plots on a field in Shropshire. The plots were cropped with either oats, wheat, barley or rye, sown in the autumn and spring, and some plots had fertilizer. Each plot received the same treatment for 3 years; in the fourth year an indicator crop of spring oats was grown on all the plots.
Under rye and autumn-sown wheat the eelworm population fell to a level which permitted a good oat crop in 1957. Autumn-sown wheat, barley and rye generally produced lower eelworm populations than their spring-sown counterparts, but autumn-sown oats proved to be the most efficient host. The order of host efficiency was oats (best), barley, wheat, rye. The eelworm populations were generally higher on plots receiving fertilizer treatment. In this experiment all oat plots, and spring-sown barley plus fertilizer, produced populations which severely damaged the 1957 oat crop.     

PROVISIONAL LISTS OF HOST PLANTS OF SOME ROOT EELWORMS (HETERODERA SPP.)

In host-range tests carried out at Cambridge, 1951-3, beet eelworm was found to parasitize nearly all Cruciferae tested, while other hosts were found amongst the Amaranthaceae, Caryophyllaceae, Chenopodiaceae, Labiatae, Phytolaccaceae, Polygonaceae, Scrophulariaceae and Tropaeolaceae. Cabbage eelworm parasitized nearly all Cruciferae tested, and a few Labiatae. Hosts of Galeopsis and clover eelworms were found amongst the Caryophyllaceae, Labiatae, Leguminosae, Polygonaceae and Scrophulariaceae. Potato eelworm cysts were found only on Lycopersicum and Solanum ; carrot eelworm only on Daucus ; and hop eelworm only on Urtica (Urticaceae) and Cannabis and Humulus (Cannabinaceae). Pea eelworm appeared to parasitize only the genera Lathyrus, Lens, Pisum and Vicia (Leguminosae), while hosts of oat eelworm appeared to be distributed more or less at random within the Gramineae.     

THE HATCHING RESPONSES OF SOME ROOT EELWORMS OF THE GENUS HETERODERA

An account is given of investigations on the hatching responses, under laboratory conditions, of nine species or varieties of Heterodera , namely, the beet, cabbage, clover, Galeopsis , carrot, hop, potato, oat and pea eelworms. In the first seven of these, marked differences occurred in hatching responses from cysts incubated in root leachings from various plants, these differences being virtually diagnostic for the eelworm species concerned. In general, good responses to leachings from host plants occurred, whereas there was little or no response in non-host leachings; but cases of response to non-hosts and of failure to respond to hosts were encountered. Promising results were obtained in the analysis, by bio-assay, of mixtures of some of these eelworm species. No appreciable response occurred from cysts of oat and pea eelworms incubated in host leachings, but there was some evidence that such a response did occur from pea eelworm cysts under field conditions. Curves for rate of hatching of seven species and for hatching in diluted leachings in five species were found to be of the form described by Fenwick for potato eelworm. Results are given of some experiments on the effect of age of plant on potency of the root leachings, and on the loss of potency during storage.     

EFFECTS OF REPEATED FIELD INJECTIONS OF D-D MIXTURE AGAINST POTATO-ROOT EEL-WORM

Autumn injections of D-D mixture have been annually repeated for three years on a silt soil at Moulton (Holland, Lincolnshire) and a black fen soil at Prickwillow (Ely, Cambridgeshire), with different results. At Moulton there was an increased yield of tubers each time D-D was used, with no significant residual effects after the first year, and no marked long-term effect on the eelworm population. At Prick-willow D-D gave an increased yield in the first season only, with no positive residual effects on yield, and an apparent stimulating effect on the eelworm population. At Moulton in 1948 and 1950 (but not in 1949) the cost of the D-D treatment was heavily outweighed by the value of the resultant increase in crop. However, on the organic soil at Prickwillow D-D treatment was ineffective in 1949 and 1950 and the eelworm population, initially higher than at Moulton, remained at a level inducing failure of the potato crops.     

Field trials with D-D mixture against potato-root eelworm

A D-D mixture has been tested against Heterodera rostochiensis at seven 2-acre sites on sands, silts and blackland soils. Apart from a pilot trial where soil was injected in spring, injections were carried out in the autumn, and potatoes were grown the following year. Factors investigated were rate of application (0, 200, 400 and 800 lb. D-D/acre), depth of injection (4 or 8 in.) and the effect of rolling after injection. At the most responsive of the sites (Wainfleet), increases in yield, kill, and the post-crop eelworm population were all roughly proportional to the rate of application. Under favourable circumstances a 50% increase in yield and something like a 50% reduction in eelworm population 4 weeks after injection can be expected from 800 lb./acre, but the reduction is more than made good during the growth of the subsequent crop; accelerated multiplication of eelworm on the treated plots leads to their having a larger population than the untreated controls at lifting time. Of the sites tested, the blackland soils gave a lower eelworm kill and a much lower yield increase from D-D than silts or sands. After autumn injection the nematocidal, and probably the phytocidal, effects of D-D persist in the soil for many weeks. The hypochlorite method of 'hatching' eelworm larvae for counting has proved unreliable.     

CALCIUM CHLOROACETATE AS A SOIL DRESSING AGAINST BEET EELWORM: HETERODERA SCHACHTH SCHMIDT, WITH CERTAIN ADDITIONAL OBSERVATIONS

Calcium chloroacetate at 3 and 6 cwt./acre produced significant increases in the yields of sugar beet (both washed beet and total sugar) in a trial on fen soil of the 'skirt' type infested with beet eelworm, Heterodera schachtii Schmidt. However, the material had no effect on the eelworm content of the soil whether measured by cysts, viable cysts or eggs and larvae. An instance is recorded of a significant drop in the level of the beet eelworm infestation in the presence of sugar beet.     

MOVEMENT OF EELWORMS

Experiments on vertical migration through saturated soil fractions, horizontal migration through soil fractions at different pressure deficiencies and migration in single layers of particles showed that the beet eelworm, Heterodera schachtii Schmidt, attained maximum speed when the pore diameters were between 30–60 μ. Speed of the eelworms increased as lateral displacement of the body was restricted by external resistances acting perpendicularly to the body axis; at the maximum speed there was no lateral movement, each part of the body following the part immediately in front of it. The speed of beet eelworm larvae in water films of various thickness was measured; maximum speed occurred in a film 2–5 μ thick. Four arbitrarily classified types of progression were observed in the pore spaces. It is suggested that the 'moisture characteristic' supplies most of the information required about the physical properties of the soil in relation to eelworm movement. By examining such a curve the pore size distribution can be ascertained and the probable behaviour of beet eelworm larvae in the medium predicted.     

The effects on a population of potato-root eelworm (Heterodera rostochiensis) of growing potatoes resistant to pathotype B

The effects on a potato-root eelworm (Heterodera rostochiensis Woll.) population of growing potatoes resistant to pathotype B of the eelworm were investigated. The eelworm population, which was originally nearly entirely pathotype A, had been changed into a mixture of pathotypes A, B and C before 1961, when the experiments described in this paper began, by growing potatoes resistant only to pathotype A. The resistant potatoes grown in the years 1961 and 1962 were certain clones of the hybrid triploid species Solarium xjuzepczukii Buk., clones bred from S. multidissectum Hawkes with the gene H₂ and clones bred from S. vernei Bitt. et Wittm. In the years 1963-65 the clone used was D 40 which has both the gene H₂ from Andigena and the gene H₂ from 5. multidissectum and is resistant to both pathotypes A and B of the eelworm. The only potatoes which caused a reduction in the egg population were those bred from S. vernei. The clone D 40, although it had little effect on the egg population, appeared to have more resistance than could be accounted for from possessing genes H₁ and H₂.     

PÓT TESTS OF NEMATICIDES AGAINST POTATO-ROOT EELWORM

Details are given of nematicidal tests, directed against the potato-root eelworm, in 81. glazed pots of infested soil. The soil was sampled a few weeks after injection to secure data on the kill achieved, by counting the eelworm larvae hatching in root diffusate. A potato tuber was then planted in each pot and yielded information on phytotoxic or soil-amendment effects. A second soil sample at the end of the season showed the degree to which the eelworm population had recovered after treatment. With only duplicate pots, and single batches of 100 cysts from each pot, clear-cut results were achieved with D–D mixture and ethylene dibromide. In the present pilot test, the data were handled by ordinary analysis of variance methods, by which the lowest significant percentage kill was 73%, but the methods could be adapted for purposes of probit analysis.     

The resistance of potato varieties to Heterodera schachtii Schmidt, the potato-root eelworm

The potato varieties Epicure and Doon Star permitted the production of fewer and smaller cysts of Heterodera schachtii on their roots than the varieties Golden Wonder and Majestic, when all were grown under standard conditions. Under the stimulus of potato-root excretion the number of larvae which emerged from Epicure and Doon Star cysts was less than that from Majestic or Golden Wonder cysts of the same volume. Accepting Lapage's (1938) criteria of resistance to nematode infestation in animals and applying them to plants, it is concluded that this deleterious effect of the variety on the eelworm is probably of the nature of a degree of resistance to eelworm attack specific to each variety and is physiological and not anatomical in action. Of the varieties tested, Epicure is judged the most resistant, closely followed by Doon Star. Majestic is fairly susceptible but not so much so as Golden Wonder on which the eelworm forms large cysts that are extremely productive of larvae.     

STUDIES IN THE RELATIONSHIP OF EELWORMS AND BACTERIA TO CERTAIN PLANT DISEASES

Two types of organism are known to be present in strawberry plants suffering from cauliflower disease, namely, eelworms, Aphelenchoides ritzema-bosi and/or Aphelenchoides fragariae , and a bacterium, Corynebacterium fascians. Neither type, inoculated separately, has consistently reproduced the disease.
An experimental investigation of a possible obligate etiological relationship between the eelworm and the bacterium is described, in which Aphelenchoides ritzema-bosi and several strains of Corynebacterium fascians were inoculated together and separately.
No abnormalities appeared in the absence of the eelworm. Typical cauliflower symptoms were reproduced only by a combination of the eelworm and strains of C. fascians originally isolated from cauliflower strawberries. Small alaminate leaves and enations appeared in all treatments where the eelworm was introduced, including those where no bacteria were co-inoculated. Subsequent isolations, however, demonstrated the presence of contaminant strains of C. fascians in the latter plants. The severity of the enation symptom was related to the presence of a particular strain of C. fascians , but the alaminate leaves showed no such correlation. Evidence on the source of the contaminant strains found in the experimental plants is discussed.
In parallel field investigations it was established that eelworm-infested strawberries showing no cauliflower symptom frequently bore alaminate leaves, with which C. fascians was consistently associated. It is suggested therefore that cauliflower is simply the least frequent of a range of symptoms of a bacterial disease endemic in strawberry plants infested with Aphelenchoides spp.     

Field studies of potato-root eelworm, Heterodera rostochiensis Wollenweber, 1938-40

Field studies of potato crops under different soil and fertility conditions and exposed to attack by diverse concentrations of potato-root eelworm led to the following conclusions:
In the north-western agricultural advisory province potato-root eelworm is not a major cause of failure or partial failure of potato crops on land where the viable cyst concentration is low (under 10/10 c.c. of soil). On such land increased yields can be obtained by improving conditions for plant growth, widening the rotation and increasing the fertility of the soil.
The production of satisfactory crops on land with a low eelworm population is likely to be accompanied by considerable increases in the numbers of root eelworms in the soil.
Crops free from signs of 'potato sickness' or 'potato-root eelworm disease' can be grown on land heavily infested with root eelworms (viable cyst concentration exceeding 25/10 c.c.), if no other adverse condition, such as unsuitable weather, lack of available food or incidence of fungus disease, affects the growth of the crop, but yields from heavily infested land are not likely to be more than moderate.
The treatments used against eelworms in the trials described here did not give results commensurate with their cost.
The practical difficulties of incorporating lethal substances with soil in the field are considerable, and this may have contributed to the disappointing results obtained.
The study of the influence of host variety on cyst production suggests that varietal differences in the host plants may influence the numbers of cysts formed on the crop, but the evidence is not conclusive.     

THE STIMULATORY PROPERTIES OF SOME ORGANIC SUBSTANCES ON CYSTS OF THE BEET EELWORM, HETERODERA SCHACHTII SCHMIDT

Techniques for determining the influence of various substances on the rate of larval emergence from cysts of the beet eelworm are described. There is no significant difference between the rates of larval emergence in glutamic acid, galactinol, inositol and water; the rate of larval emergence in beet diffusate, on the other hand, was significantly higher. Studies of larval emergence in carbohydrates suggest that the cyst population used in the experiments was heterogeneous, consisting of two types of cyst which have different reactions to stimulation at different concentrations. The significance of root exudates in relation to beet eelworm is discussed.     

THE POTATO TUBER NEMATODE, DITYLENCHUS DESTRUCTOR THORNE, 1945; THE CAUSE OF EELWORM DISEASE IN BULBOUS IRIS

For about twenty-five years a fairly widespread disease of bulbous iris has been known, the cause of which has always been attributed to a biologic race of the stem eelworm Ditylenchus dipsaci (Kühn, 1857), Filipjev, 1936.
Thorne (1945) showed that the nematode causing rot in potato tubers is different from D. dipsaci and named it D. destructor. This nematode has since been reported from Mentha arvensis L. by Hurst (1948) and from Sonchus arvensis L. by Goodey & Goodey (1949).
Examination of nematodes from diseased iris bulbs showed them to possess rounded tail tips and six incisures on each lateral field; characters by which Ditylenchus destructor is distinguished from D. dipsaci.
Cross-inoculation experiments showed that the eelworm causing disease in potato tubers would invade and set up characteristic symptoms in iris bulbs and, in the opposite direction, the eelworm responsible for disease in iris bulbs would give rise to characteristic symptoms in potato tubers. Transfer was also effected from potato and iris to Mentha arvensis and from iris to Sonchus arvensis.
The history of the disease in bulbous iris is briefly reviewed and the biology of Ditylenchus destructor discussed and compared with that of D. dipsaci.
The conclusion that D. destructor is the nematode causing eelworm disease of bulbous iris has been reported earlier (Goodey, J. B. 1950).     

Paternity testing using the poisonous sting in captive white‐spotted eagle rays Aetobatus narinari: a non‐invasive tool for captive sustainability programmes

A group of captive white‐spotted eagle rays Aetobatus narinari produced 20 offspring, with an unknown father. Part of the poisonous sting was removed from each fish and DNA was extracted from the epidermis for paternity research using eight microsatellite markers of which four were from another species Aetobatus flagellum. This non‐invasive sampling technique can be applied on all members of Myliobatiformes.     

EXPERIMENTS ON THE CONTROL OF CHRYSANTHEMUM EELWORM(APHELENCHOIDES RITZEMA-BOSI, SCHWARTZ) HOT WATER TREATMENT

The minimum times required for killing the chrysanthemum eelworm ( Aphelenchoides ritzema-bosi , Schwartz) in water, over a range of temperatures have been determined and the technique employed is described. A temperature of 115° F. for 5 min. is preferable to the usual standard treatment of 110° F. for 20–30 min. and enables stools to be treated with less retardation of cuttings or death of stools, with a consequent great increase in the number of cuttings obtained. The results are of special value in connexion with varieties susceptible to damage by the hot water treatment.     

MOVEMENT OF EELWORMS.: IV. THE INFLUENCE OF WATER PERCOLATION

A study was made of the relationship between rate of flow of water through sands of different particle size and the downward velocity of eelworms of various lengths and activities. The relationship between rate of flow of water and velocity of eelworms is not linear. For rates of flow less than about 500 cm./hr. the velocity of the eelworms relative to the velocity of water is greater than for flow rates greater than about 500 cm./hr. For rates of flow greater than 500 cm./hr. an equation is derived which relates velocity of eelworms, rate of water flow, length of eelworms and pore diameter in the sand. The following facts were established: the velocity of the eelworms increases as pore diameter increases; the velocity approaches zero when the eelworms' length exceeds four times the pore diameter; the relationship between velocity of eelworm and velocity of water is independent of the eelworms' own activity; the equation of eelworm movement is valid for both continuous and discontinuous saturated flow. With flow rates less than about 500 cm./hr., the velocity of the eelworms increases as the eelworms' activity increases and eelworms appear to pass through smaller pores than at high flow rates. Dead or inactive eelworms do not progress very far in sand even at high flow rates and observations suggest that slight flexing movements of the eelworm body is essential for passage.     

A Two One-Sided Parametric Tolerance Interval Test for Control of Delivered Dose Uniformity—Part 2—Effect of Changing Parameters

This article examines the effects of changing parameters in the test which was proposed by the FDA at the October 2005 Advisory Committee meeting for confirming delivered dose uniformity in orally inhaled and nasal drug products. This article is an extension of the characterization study presented in an accompanying article (Part 1). The goal of this study is to understand how parameters of the test affect the test performance. The effects of changing test parameters such as target interval, maximum allowable proportion in the tail area, and sample size are examined. The results show that changing the maximum allowable tail area and/or the target interval have the largest impact on the test outcomes, i.e., probability of acceptance for a given batch mean and standard deviation. The presented information may provide potential users of the test with a set of tools for optimizing the test characteristics for a particular product.