INVESTIGATIONS ON RESISTANCE OF OATS TO STEM EELWORM, DITYLENCHUS DIPSACI KÜHN

A procedure adopted for testing many varieties of oats and segregating progenies for reaction to attack by stem eelworm ( Ditylenchus dipsaci Kühn) is described, and its merits and limitations discussed in relation to the breeding of resistant varieties.
A study of some 250 forms of oats revealed new sources of resistance in cultivated and wild species. New sources of resistance in the cultivated species Avena sativa were found only in winter types, and in the other hexaploid species in forms belonging to A. byzantina (C) Koch, and the winter wild oat A. ludoviciana Dur.
Segregate progenies in advanced generations could be selected in the field by their reaction in a single drill in the first year followed by a head-row progeny test in the next season. Reaction was sufficiently well defined to identify the truebreeding resistant and susceptible lines.
The inheritance of reaction to stem eelworm in crosses involving Grey Winter and susceptible types depended on a single factor pair with resistance dominant.     

THE SUSCEPTIBILITY OF POTATO VARIETIES TO INFESTATION BY THE EELWORMS DITYLENCHUS DESTRUCTOR AND D. DIPSACI

Twenty-five varieties of potato in common commercial cultivation were found to be susceptible to tuber attack by potato-derived populations of Ditylenchus destructor under field and pot experimental conditions. Stunting and leaf deformation may also be caused by the eelworms but appear less consistently. A race of D. destructor from mushroom spawn had almost no effect on potatoes. Various races of D. dipsaci can reproduce in the shoot tissue of potato, sometimes causing damage. One population of this stem eelworm produced lesions on the tubers.     

ON THE STEM AND BULB EELWORM (ANGUILLULINA DIPSACI KUHN) WITH SPECIAL REFERENCE TO ITS OCCURRENCE ON WEEDS OF ARABLE LAND

The importance of wild hosts of Anguillulina dipsaci Kühn as carriers of infection needs no emphasis. The occurrence of the eelworm in the weeds, cleavers ( Galium aparine ) and duckweed ( Stellaria media ) taken in crops of oats and field beans which were themselves suffering from stem eelworm disease, was recorded by Johnson (1936) and Johnson & Thompson (1937); Walton (1937) confirmed the occurrence of infested cleavers plants in eelworm-infested oats. Walton also stated that experiments indicated that seed oats failed to carry eelworm infection, and from circumstantial evidence similar to that recorded by Johnson (1936) stated that "infestations of oat crops which occur, even after the absence of the crop for more than six years, are in all probability attributable to weeds rather than to infested seed". The present writer failed to obtain living eelworms from oat seed from infested crops in Yorkshire. This paper summarizes the results of field observations and experiments accumulated mainly during the past three years.     

SOME OBSERVATIONS ON THE HATCHING RESPONSES OF THE CABBAGE-ROOT EELWORM, HETERODERA CRUCIFERAE FRANKLIN

Samples of root diffusate from sprouts ( Brassica oleracea var. gemmifera ), swedes ( B. napus var. napobrassica ), rape kale ( B. napus var. arvmsis ), and white mustard ( Sinupis alba ), all stimulated larval emergence from cysts of Heterodera cruciferae. When mustard-root diffusate was added to leachings from the other species tested there was no apparent effect on larval emergence. In half dilution with tap water, mustard leachings were comparable in activity with similar dilutions of leachings from the other species under observation. Leachings from soil were less active than those from the four species of plants tested, but showed significant activity in comparison with tap water.
The form of the hatching curve was studied using diffusates from both sprouts and mustard roots, and in each case when cumulative hatch was plotted against time on a logarithmic scale, the sigmoid curve obtained closely fitted the theoretical sigmoid calculated from a probit analysis of the data.
Estimates were obtained of the log activity values of leachings from the four species of plants tested and from soil, following an examination of the dilution curves for mustard and sprouts root diffusates. These curves were closely parallel with one another, and it was therefore considered justifiable to derive log activity values for these root diffusates, although the cysts used in the hatching tests and the root-diffusate samples were each obtained from a single source. For this reason some caution is perhaps called for in the interpretation of the results presented in this paper.     

OBSERVATIONS ON THE OCCURRENCE OF THE EELWORM, PRATYLENCHUS PRATENSIS FILIPJEV, IN DELPHINIUM ROOTS

Pratylenchus pratensis has been found associated with lesions on delphinium roots: its presence in the tissues is best demonstrated by a modification of the Flemming staining method.
At specific sites, the severity of delphinium root-rot was correlated with the soil population of P. pratensis . After infested soils had been fumigated with methyl bromide, delphiniums grown in the treated soils had more vigorous root systems, containing fewer eelworms per unit weight than those grown in untreated soil. The use of D-D also shows promise as a control measure against P. pratensis .
No pathogenic fungus has been found in the delphinium root lesions.     

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).     

OBSERVATIONS ON THE EFFECTS OF THE PARASITIC NEMATODES DITYLENCHUS MYCELIOPHAGUS, APHELENCHOIDES COMPOSTICOLA AND PARAPHELENCHUS MYCELIOPHTHORUS ON THE GROWTH AND CROPPING OF MUSHROOMS

The parasitic nematodes Ditylenchus myceliophagus, Aphelenchoides composticola and Paraphelenchus myceliophthorus severely damage mushroom mycelium and, in great numbers, reduce or even prevent cropping. The relationships between fluctuation of nematode population, state of the mycelium, duration of cropping and the yield of mushrooms are illustrated in a series of figures.     

FURTHER EXPERIMENTS ON THE ABSORPTION OF IONS BY PLANTS,INCLUDING OBSERVATIONS ON THE EFFECT OF LIGHT

1. The conditions of illumination were found to exert a very significant influence on absorption of ions from dilute solution by Nitella. These conditions were also found to influence the penetration of Br and NO₃ into the cell sap. 2. It is concluded that absorption of ions by plants from dilute solutions involves energy exchanges, with light as the ultimate source of the energy. It is suggested that the absorption is intimately related to growth and metabolism. 3. One ion may affect the removal from solution or penetration into the cell sap of another ion present in the same solution, even in solutions of extremely low concentration. It is probable that all three types of relations may exist—anion to anion, cation to cation, and anion to cation. 4. The sulfate and phosphate ions exerted far less influence on the absorption of nitrate than did chlorine and bromine ions. It is suggested as a possibility that sulfate does not penetrate readily to those surfaces at which chlorine, bromine, nitrate, and other ions may become effective.     

THE INFLUENCE OF THE HOST ON THE DIMENSIONS OF THE PLANT PARASITIC NEMATODE, DITYLENCHUS DESTRUCTOR

Measurement data and body ratios from eleven populations of Ditylenchus destructor are presented. The data for lengths of males and females have been analysed for variance, and many differences between population means are shown to be significant. The essential importance of structural characters and the care with which sizes and dimensional ratios must be used, in the identification of a species, is emphasized.