bluuebunny/crossref_metadata_2025 huggingface dataset:
STEM INFECTION OF COTTON BY XANTHOMONAS MALVACEARUM (E. F. SM.) DOWSON
Authors: LAST F. T.
Published: February 2008

Varying the position of stem inoculation, the concentration of inoculum and the age of plant affected the reaction of cotton, Gossypium sp., to infection with Xanthomonas malvacearum (E. F. Sm.) Dowson.

The extent of stem discoloration, internal and external, and the probability of disease ocurring in leaves by bacteria moving within the plant increased (a) the nearer the point of stem inoculation was to the apex, and (b) the higher the concentration of inoculum. The leaf symptoms were not the angular spots typical of primary leaf infection. Instead, bacteria seemed to lodge in, discolour and blacken sections of leaf veins. Then tissue next to the affected veins became water‐soaked and leaf sectors dependent upon these veins died and dried. These symptoms usually developed 14 to 55 days after inoculation in the expanding leaves.

The amounts of stem discoloration and the probabilities of leaf symptoms developing were less when hypocotyls of old plants were inoculated than when hypocotyls of young plants were inoculated. The probabilities of leaf symptoms developing were similar, however, when young tissues in young and old plants were inoculated.

American cotton, Gossypium hirsutum, was less affected by stem inoculation than Egyptian cotton, G. barbadense. Of the resistance factors against primary leaf infection only B6m gave appreciable stem resistance.
THE EFFECTS OF GIBBERELLIC ACID AND KINETIN ON THE GROWTH OF MAJESTIC POTATO
Authors: HUMPHRIES E. C.
Published: February 2008

The effects of spraying potato plants (var. Majestic) with gibberellic acid and kinetin were investigated. Gibberellic acid increased both leaf area and dry‐matter production over the short period of the experiment, but there were indications that this would not persist at maturity. Kinetin alone depressed leaf area and dry‐matter production, but this did not occur in the presence of gibberellic acid. The mean net assimilation rate measured over a 2‐week period was not significantly reduced by gibberellic acid.
SOME EFFECTS OF FEEDING BY LYGUS VOSSELERI POPP. (HETEROPTERA, MIRIDAE) ON THE STEM APEX OF THE COTTON PLANT
Authors: DALE J. E. , COAKER T. H.
Published: February 2008

The effects of damage to the main stem apex of the cotton plant caused by feeding of Lygus vosseleri Popp. have been investigated using a cell counting technique. It was found that mechanical damage of the tip due either to feeding of Lygus or to pricking with a glass needle caused an increase in cell division and maturation rates in the stem apex. The significance of this in relation to the possible effects of Lygus damage on plant height is discussed.
STUDIES ON SEED HEALTH
Authors: MUSKETT A. E.
Published: February 2008

An account is given of the survey made in 1940‐55 to determine the incidence of the seed‐borne fungal parasites of flax. It was shown that fibre flax seed produced in eastern and south‐eastern England was relatively free from contamination with Colletotrichum linicola, Polyspora lini and Phoma sp. and that there was no build‐up of infection in seed stocks in these areas. In the wetter and cooler regions west and north of the Pennines, conditions were more favourable for these fungi, and seed contamination tended to increase.

Seed contamination with Botrytis cinerea was general throughout the United Kingdom, with a tendency to be higher in coastal and upland areas. The incidence of Fusarium lini and Alternaria linicola in fibre flax seed produced in the United Kingdom was negligible.

The examination of seed samples from other countries indicated the possible importance of P. lini in Denmark, of B. cinerea and C. linicola in the Netherlands, of A. linicola as a contaminant of oil flax seed in Sweden, and of C. linicola in parts of Canada.

Seed disinfection, using a thiram product, proved useful for the control of flax diseases in general, but should be used as an ancillary to the method of avoiding seed infection by limiting the production of seed flax to areas where the risk of contamination is slight or absent. Where there is any risk of a build‐up of contamination, seed disinfection should be carried out as a routine practice each season.
EXPERIMENTS WITH A VIRUS DISEASE OF THE COTTON BOLLWORM HELIOTHIS ARMIGERA (HBN.)
Authors: COAKER T. H.
Published: February 2008

Laboratory tests with a nuclear polyhedral virus disease of Heliothis armigera indicated that it was more infective and had a shorter incubation period in the younger instars than in the older larvae.

Larvae on cotton plants sprayed with an aqueous suspension of the virus became infected; mortality depended on the number of polyhedra applied to the plant irrespective of the concentration in the suspension. Spraying with the virus seems unlikely to control bollworm in Uganda, but might do so where it is not already endemic and where bollworm numbers fluctuate more during the year.
CHANGES IN THE TRANSMISSIBILITY BY APHIDS OF A STRAIN OF CUCUMBER MOSAIC VIRUS
Authors: BADAMI R. S.
Published: February 2008

A strain of cucumber mosaic virus isolated from a spinach plant in 1946 was readily transmitted by Myzus persicae until 1955 when it lost this property, although it was still being propagated in conditions in which other strains remained transmissible. M. circumflexus also transmitted other strains but not this one. It was transmitted as readily as other strains by Aphis gossypii and Myzus ascalonicus. M. ascalonicus transmitted less frequently than Aphis gossypii. Transmission of the spinach strain by other aphids did not make it transmissible by Myzus persicae; nor did propagation in different plant species or several passages through spinach. In 1955 the spinach strain was occasionally transmitted by M. persicae, but the cultures isolated in this way were no more readily transmissible by the aphid than was the bulk culture maintained by manual inoculation of sap, and after a few weeks all cultures ceased to be transmitted by M. persicae.
CROOK ROOT OF WATERCRESS
Authors: TOMLINSON J. A.
Published: February 2008

The discovery, occurrence and symptoms of crook‐root disease (Spongospora subterranea (Wallr.) Lagerh. f.sp. nasturtii Tomlinson) are described.

Assessment of crook root in commercial watercress beds indicated that the disease increased with increasing distance from the water source, was more severe from October to April than from May to September, and affected brown more than green watercress.

The healthier condition of plants near the fresh‐water inlets, compared with those growing further down the bed, was associated with the low concentration of zoospores.

Water from the river Dene, Wellesbourne, contained a factor inhibiting crook root, which was shown to be calcium bicarbonate. In laboratory tests, increasing concentrations of calcium bicarbonate from 62 to 540 p.p.m. gave an increasing degree of control of the disease. The same effect was shown in a small field test.

The combined (Ca + Mg) bicarbonate content in eighty‐seven spring and artesian waters supplying diseased watercress beds in various counties varied, with one exception, from 282 to 401 p.p.m. The only bed fed by water with a higher total bicarbonate content (525 p.p.m.) was free from crook root.

It was shown that solutions containing 350–750 p.p.m. calcium bicarbonate had no effect on the germination of zoosporangia or the activity of zoospores.

Certain resemblances are noted between the control of crook root by calcium bicarbonate and the control of club root of brassicas by lime.
OBSERVATIONS ON THE INFECTION OF COX'S ORANGE PIPPIN APPLES BYGLOEOSPORIUM PERENNANSZELLER & CHILDS
Authors: EDNEY K. L.
Published: February 2008

Conidia ofGloeosporium perennansgerminating on the surface of Cox's Orange Pippin apples in the orchard, produce a germ tube which generally swells to form a thick‐walled appressorium. If the underlying tissues are not suberized the appressorium then produces an infection thread which penetrates the wall of the epidermal cell. If the underlying tissue is suberized no infection thread is formed. Subsequent rotting takes place either by penetration via a point of weakness in the suberized layer of cells across the lenticel as in Cox's Orange Pippin or by direct invasion of this layer as in the variety Sunset. Some lenticels have been observed where the suberized layer has not formed.

Fruit infected in August and September rots at a greater rate than fruit infected in June and July of the same year. In years when susceptibility to rotting is high, infections initiated in July may develop more rapidly than those initiated later in the season in a year when susceptibility to rotting is relatively low. The rate of rotting has been found to increase with the size of fruit.
THE ADAPTATION OF FUNGI TO FUNGICIDES: ADAPTATION TO CAPTAN
Authors: PARRY K. E. , WOOD R. K. S.
Published: February 2008

In sucrose‐nitrate liquid media Botrytis cinerea was able to grow from spores when the media contained captan at concentrations up to three‐quarters of the saturation value. Because of this, and the low water solubility of the fungicide (< 1 p.p.m.) all attempts to produce resistant strains were made with agar media.

Spores did not germinate when applied as a suspension in water to the surface of a sucrose‐nitrate agar containing 500 p.p.m. captan; about 1% germinated when the concentration was 250 p.p.m. Similar results were obtained when an agar extracted with water and pyridine was used. There was some growth from spores on agar containing 250 p.p.m. captan; this always started at the edge of the agar.

Resistant strains were produced when disks were transferred from cultures growing on agar containing low concentrations of captan to agar containing higher concentrations. By repeating this process over a period of months a strain was produced eventually which grew slowly but continuously, and sporulated on agar containing 250,000 p.p.m. captan. However, the very low solubility of the fungicide made it difficult to assess quantitatively the degree of adaptation. Although agar disk inocula from resistant strains retained their resistance on transfer to captan agar, inocula consisting of suspensions of spores only, or of hyphae and spores, were no more resistant than the parent strain. The resistant strain retained the first type of resistance after it had been grown on fungicide‐free media for four periods of 2 weeks.

Spores from the resistant strain were more resistant than spores from the parent strain in germination tests with drops on glass slides; a concentration of 0·6 p.p.m. captan prevented germination of parent spores, but one or two spores out of a total of some 4000 spores of the resistant strain germinated at concentrations of 100 p.p.m. This type of resistance, transmissible by spores, was reduced when the resistant strain was grown on fungicide‐free agar.

Spores from resistant strains had a very low viability, although they were produced normally and were normal in size and appearance; when obtained directly from a culture on a captan medium only 2% germinated whereas in similar conditions there was 100% germination of parent spores. Viability was increased to 13% after one transfer on a fungicide‐free medium but was no more than 52% after four transfers.

Preliminary attempts to obtain strains of Venturia inaequalis resistant to captan were unsuccessful.

The significance of the results obtained is discussed.
BROWN ROOT ROT OF TOMATOES: II. THE FUNGAL FLORA OF THE RHIZOSPHERE
Authors: EBBEN M. H.
Published: February 2008

The fungal populations of soil and of the rhizosphere of tomatoes in steamed, fallowed and unsteamed plots were compared. Steaming greatly reduced the numbers of fungi in the soil, but fallowing had little effect. Soil bacteria were greatly reduced by steaming but increased to the level in the unsteamed plots after heavy watering. Outer rhizosphere fungal populations in unsteamed plots in July were larger than in the steamed plots, but by October this difference had disappeared, although roots in the unsteamed soil showed the greater development of disease.

Root surface counts indicated that the populations on actively growing roots in July in steamed and unsteamed plots reached similar levels, and there was a slight fall in numbers in both types of plot in October. Fungal infection of roots increased noticeably in unsteamed plots between July and October, although root surface numbers showed a decrease.

Of the fungal species isolated Colletotrichum atramentarium showed a distribution between soil and root surface which suggested that it was a root inhabiting fungus. Cephalosporium spp. were also found on the root surface and in roots, especially those from steamed soil.
SOME PROPERTIES OF THREE VIRUSES ISOLATED FROM A DISEASED PLANT OF SOLANUM JASMINOIDES PAXT. FROM INDIA
Authors: BADAMI R. S. , KASSANIS B.
Published: February 2008

Three mechanically transmissible viruses were isolated from a diseased Solanum jasminoides plant obtained from India. One is a strain of potato virus Y, which in some potato varieties produces symptoms resembling those caused by potato virus C, but unlike potato virus C it is readily transmitted by Myzus persicae. The second, named tobacco wilt virus, is also transmitted by M. persicae but much less readily, whereas the third, named datura necrosis virus, is not. All three have a wide host range, but neither tobacco wilt nor datura necrosis viruses infects potato plants. All three have long flexuous particles and similar general properties.

Simultaneous infection with datura necrosis virus usually decreases the concentration reached by potato virus Y in tobacco plants but not in Nicotiana glutinosa.
SUSCEPTIBILITY OF LARVAE OF THE LARGE WHITE BUTTERFLY (PIERIS BRASSICAE L.) TO TWO VIRUS DISEASES
Authors: SIDOR Ć.
Published: February 2008

A cytoplasmic polyhedral virus ex Phalera bucephala (L.) induces a polyhedrosis in some stocks of Pieris brassicae (L.). Larvae from different localities vary in their susceptibility to their own viruses and the stock of Pieris brassicae larvae most susceptible to its granulosis is also more susceptible to the polyhedrosis.

Polyhedra obtained from Pieris brassicae, infected from Phalera bucephala, did not cause a cytoplasmic polyhedrosis in larvae of Plutella maculipennis (Curtis) and Pseudaletria unipuncta (Haw.), but did do so in the larvae of Lymantria monacha (L.).
MOVEMENT OF EELWORMS.: IV. THE INFLUENCE OF WATER PERCOLATION
Authors: WALLACE H. R.
Published: February 2008

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.
THE EMERGENCE OF LARVAE FROM FREE EGGS OF THE POTATO‐ROOT EELWORM HETERODERA ROSTOCHIENSIS (WOLL.)
Authors: FENWICK D. W. , WIDDOWSON ELIZABETH
Published: February 2008

A technique for conducting hatching experiments on eggs freed from cysts is described. The form of the hatching response was found to be similar to that of eggs contained within cysts, but the response of the free eggs to the hatching stimulus was slightly more rapid. Investigations into factors affecting free egg hatching showed that it was necessary to presoak cysts before extracting the eggs from them for hatching. Eggs taken from dry cysts or from cysts that had been opened or cracked before presoaking did not respond to diffusate. When free eggs and whole cysts were exposed to the same graded series of dilutions of diffusate, the L.A. values (i.e. log concentrations of hatching factor) derived from plotting the hatching curves were in very close agreement.
SPATIAL DISTRIBUTION OF FEEDING ACTIVITY IN THE WILD HOUSE‐MOUSE (MUS MUSCULUS L.)
Authors: CROWCROFT PETER
Published: February 2008

Solitary house mice confined in a large pen were supplied with wheat in wooden trays distributed evenly throughout the area, and the number of grains removed daily from each was counted. A mouse tended to feed sporadically over the whole area, but feeding was more intense at a few trays, not necessarily near the nest, and not the same on successive nights. When new sources of the same food were introduced a mouse tended to patronize them during the first night. At the same time there was a significant drop in the number of the old trays visited. This suggested that new food sources stimulated investigation rather than avoidance.
AN ANALYSIS OF COMPETITION BETWEEN BARLEY AND WHITE PERSICARIA: I. THE EFFECTS ON GROWTH
Authors: ASPINALL D. , MILTHORPE F. L.
Published: February 2008

Barley and white persicaria (Polygonum lapathifolium L.) were grown in pure and mixed populations of varying density in sand culture in a glasshouse. The leaf areas and dry weights of leaves, stems and roots were determined at intervals. During the phase of vegetative growth the addition of dry matter by barley was unaffected, although tillering was reduced, by competition from dense stands of white persicaria, whereas the growth of white persicaria was reduced by low densities of barley. The decline in leaf area and reduction in root growth of barley with the onset of flowering was accompanied by increased growth of white persicaria with the production of branches from the upper axillary buds. These flowered and set abundant seed. This behaviour probably accounts for the persistence of this weed in arable rotations.

The greater competitive ability of barley may be attributed to its larger embryo, giving much larger plants at emergence. The intrinsic relative growth rate of white persicaria is as high as, or higher than, that of barley and falls more slowly with time. This advantage is not sufficient to offset the initial differences in size while barley is vegetative. The larger embryo size of barley also determines the more intense competition that exists between plants of this species than between plants of white persicaria at similar densities and times from germination. With equal weights of produce per pot (or unit area) the intensity of competition within each species appears to be similar.

It is emphasized that the course of growth with time, rather than weight‐density relationships at given points of time, must be followed in order to understand the influence of density. Two functions of the relative growth rate with time are examined.
STUDIES ON PLANT GROWTH‐REGULATING SUBSTANCES. XIII CHLORO‐ AND METHYL‐SUBSTITUTED PHENOXYACETIC AND BENZOIC ACIDS
Authors: PYBUS MARY B. , SMITH MARGARET S. , WAIN R. L. , WIGHTMAN F.
Published: February 2008

The physiological activity of complete series of mono‐ and di‐substituted chloro‐and methyl‐phenoxyacetic and benzoic acids have been investigated using the wheat cylinder, pea segment and pea curvature tests. In the phenoxyacetic acids, high activity was associated with substitution in the 3‐, 4‐, 2:4‐, 2:5‐ and 3:4‐positions and in general, chlorine had a greater effect than methyl in conferring activity.

With the benzoic acids, 2:3‐, 2:5‐ and 2:6‐, disubstitution gave active compounds, the chloro‐derivatives again being the more active. The 2:5‐compound was the most active in the dichloro‐ series, all members of which were less active than the 2:3:6‐trichloro‐ and 2:3:5:6‐tetrachloro‐acids. Benzoic acids substituted in the 4‐ position were either inactive or exhibited only weak growth‐promoting activity.

The results are discussed in relation to recent theories which attempt to relate growth‐promoting activity with the position of substituents in the aromatic ring.
STUDIES IN THE BACTERIAL DISEASES OF SUDAN CROPS: III. ON THE OCCURRENCE, HOST RANGE AND TAXONOMY OF THE BACTERIA CAUSING LEAF BLIGHT DISEASES OF CERTAIN LEGUMINOUS PLANTS
Authors: SABET K. A.
Published: February 2008

The bacterial leaf blights of dolichos bean (Dolichos lablab L.), soybean (Glycine soja Sieb. and Zucc.), catjang cowpea (Vigna unguiculata (L.) Walp.), lucerne (Medicago sativa L.) and three species of senna (Cassia L.) were investigated and found to be caused by Xanthomonas phaseoli (Smith) Dowson, X. phaseoli var. sojense (Hedges) Starr & Burkholder, X. vignicola Burkholder, X. alfalfae Riker, Jones & Davis and X. cassiae Kulkarni, Patel & Dhande, respectively. None of these diseases has been investigated before in the Sudan and the lucerne disease had not been previously reported from this country.

A comparative study which included several strains of the above bacteria as well as X. phaseoli var. fuscans (Burkholder) Starr & Burkholder, X. cajani Kulkarni, Patel & Abhyankar, and X. tamarindi Patel, Bhatt & Kulkarni, showed that the organisms were indistinguishable by the usual bacteriological procedures and the minute differences in certain biochemical characters were considered of little or no diagnostic value. Cross‐inoculations revealed that the host ranges of these pathogens, with the exception of X. cajani and X. tamarindi overlapped. The latter two organisms infected only their original hosts, viz. Cajanus cajan (L.) Millsp. and Tamarindus indica L., respectively. Where a particular host was infected by more than one pathogen, the symptoms and effects they produced on that host were similar in every respect except in the case of X. vignicola when infecting Phaseolus vulgaris L. and Dolichos lablab. In this exceptional case the mature spots were dry and white, not conforming to the usual russet or dark‐brown, haloed spots produced by other bacteria. Infection in most cases first appeared as minute dark‐green more or less watersoaked spots which generally developed on all parts of the plants including the stems, leaves and pods.

The systematic position of the pathogens under investigation was reconsidered and for the reasons discussed below all the bacteria included in the study were reduced to special forms of X. phaseoli with the exception of X. phaseoli var. fuscans, the varietal rank of which has been maintained.
MOVEMENT OF EELWORMS: V. OBSERVATIONS ON APHELENCHOIDES RITZEMA‐BOSI (SCHWARTZ, 1912) STEINER, 1932 ON FLORISTS‘ CHRYSANTHEMUMS
Authors: WALLACE H. R.
Published: February 2008

Adults of Aphelenchoides ritzema‐bosi tend to migrate up the stems of chrysanthemum plants in stationary water films possibly by a negatively geotropic response. A current of water down the stem opposes such an upward movement. Greatest mobility occurred in thick films of water in places with a high concentration of epidermal hairs as at the top of the stem and on the undersurface of leaves. Ciné films of movement in thick and thin films showed that there were fundamental differences in the type of locomotion in these two environments. Invasion of leaves via stomata was observed and the method of movement is described. The presence of A. ritzema‐bosi in leaves appears to render the epidermis permeable to water. During dry weather there is little movement inside the leaf, but after rainfall activity increases as water enters the leaf. Spread of eelworm infestation in the leaf occurs in the mesophyll and across veins although initially these act as barriers. Emergence occurs via the stomata, chiefly on the undersurface. When the leaf is wet, about 50% of the eelworms emerge in the first hour. During wet weather many eelworms were recovered from the surfaces of leaves and it is suggested that eelworms spread mostly under these conditions.
STUDIES IN THE BACTERIAL DISEASES OF SUDAN CROPS
Authors: SABET K. A.
Published: February 2008

A bacterial disease of mahogany (Khaya senegalensis and K. grandifoliola) is reported for the first time. The disease causes rough or scabby leaf spots and small knob‐like cankers on the branches, which may die back as a result of infection. The symptoms of the disease differ to some extent with locality and host species. The causal organism is readily isolated from the leaves and young branches. Infection of the leaves takes place through the stomata at any time of the year. Several methods of inoculation into green shoots and woody branches were attempted but typical shoot infections were produced only when young green shoots were rubbed with the pathogen; the resulting blisters change to the typical knob‐like cankers when the shoots become woody.

The disease is attributed to a new species of Xanthomonas, namely, X. khayae sp. nov., a description of which is given.
ANTIBACTERIAL SUBSTANCES IN SEED COATS AND THEIR ROLE IN THE INFECTION OF SWEET PEAS BY CORYNEBACTERIUM FASCIANS (TILFORD) DOWSON
Authors: JACOBS S. E. , DADD A. H.
Published: February 2008

Antibacterial substances active against Corynebacterium fascians have been shown to be present in the coats of various seeds. There were considerable differences in activity between the seeds of different genera and species and between individual seeds of a single species.

C. fascians also showed strain variation in sensitivity to the antibacterial substances of the seeds of any one species. An inverse relationship was demonstrated between the sensitivity of a strain to the sweet‐pea seed substances and its ability to infect sweet‐pea seedlings under laboratory conditions.
WILT OF LUCERNE CAUSED BY SPECIES OF VERTICILLIUM
Authors: ISAAC IVOR , LLOYD A. T. E.
Published: February 2008

The incidence and symptoms of a disease of lucerne induced by Verticillium spp. are much less severe immediately after the crop has been first cut than later when the crop has matured. Infection becomes more marked as the season advances and the age of the ley increases, and cuts taken in the third harvest year are proving unprofitable.

In cross‐inoculation studies the causal organisms of lucerne wilt, V. albo‐atrum and V. dahliae prove to be only mild pathogens to hop, potato, tomato and antirrhinum, and are not pathogenic to sainfoin and clover. The last two may therefore be cultivated as fodder crops in those areas most severely affected by lucerne wilt, but the cultivation of potatoes after lucerne should be discouraged, particularly if lucerne is to be sown in future years, since the potatoes might build up a reservoir of inoculum of the lucerne pathogen. In studies of host‐parasite relations it is shown that V. albo‐atrum and V. dahliae from lucerne, V. albo‐atrum from hop, V. tricorpus from tomato and V. nigrescens and V. nubilum from potato vary in their effects upon lucerne seedlings growing on agar media, V. albo‐atrum from lucerne being, as in the field, the most virulent and the only one to reach the xylem vessels under the conditions of the experiments.

The dressings Agrosan‐GN (containing mercury) and Fernasan (containing thiram) are toxic both to spores of Verticillium on lucerne seed coats and to infected plant material carried with seed, and although they are also toxic in vitro to Rhizobium mellelotus this did not prevent dressed seeds which had been inoculated with the bacterium from developing into healthy seedlings bearing normal root‐nodules.
EXPERIMENTS ON THE CONTROL OF BOTRYTIS DISEASE OF LETTUCE
Authors: WAY J. M. , KEYWORTH W. G.
Published: February 2008

Experiments were made during 1955‐57 on the fungicidal control of Botrytis attack on lettuce, cv. May Queen, matured in frames from November to April, and cv. Trocadero Improved, grown as seedlings in frames from November to March and then matured in the field from March to June. The frame lettuce were treated during their whole period of growth and the field lettuce in the seedling stage only.

On both types, 0.33% thiram sprays applied on up to five occasions gave the best control of disease: 5% tecnazene dust was effective on the frame crop, in 2 out of 3 years when applied to the plants and also when incorporated in the top soil at the rate of 15 g. per sq.yd. Tecnazene applications did not give a good control of the disease on the field crop. Sprays with 0.25% captan were almost as effective as the thiram treatments on the field lettuce but not on the frame crop.
FURTHER STUDIES OF TOBACCO ANTHRACNOSE IN SOUTHERN RHODESIA*
Authors: COLE J. S.
Published: February 2008

Results of laboratory tests in Southern Rhodesia indicate that Colletotrichum tabacum, Böning, the causal organism of tobacco anthracnose, could survive in dry soil for 13–17 weeks and therefore might survive from one season to the next in dry soil in the absence of tobacco‐plant residue. The most favourable conditions for survival arose when soils of high organic content dried out fairly soon after being infected; soils which remained moist were the least favourable.

Chemical control of soil infection with methyl bromide gas at 1 lb./100 sq.ft. was effective and not phytotoxic. Of the wettable powders used as soil disinfectants, thiram was more effective than zineb or maneb, but all were phytotoxic at certain concentrations. Phytotoxicity to tobacco, which took the form of stunting and poor root growth, varied with different commercial preparations of thiram and zineb.
METHODS OF CONTROLLING BLACK‐POD DISEASE (CAUSED BY PHYTOPHTHORA PALMIVORA) OF THEOBROMA CACAO IN NIGERIA
Authors: THOROLD C. A.
Published: February 2008

Supplementary methods of controlling black‐pod disease (Phytophthora palmivora) of cocoa in Nigeria are considered, because fungicide application is not always economic.

There is no evidence that resistance occurs within the local population of Amelonado‐type trees.

Although the percentage of diseased pods was greater with trees closely spaced (5 times 5 ft. to 8 times 8 ft.), than with widely spaced trees (10 times 10 ft. to 15 times 15 ft.), the closer spacings often gave more healthy pods per acre.

Loss of pods from black‐pod was decreased when trees were inspected frequently (alternate days) and infected pods were removed when showing the earliest symptoms. However, this procedure may not be economic, except when potential yields are relatively small (fewer than twelve pods per tree).

Satisfactory control of black‐pod was obtained with copper fungicides, applied with either hand‐sprayers or a power‐sprayer. The monetary return depends on yield level, rather than on disease incidence or on spraying costs. It is recommended that spraying should be practised when the potential yield is twelve or more pods per tree.
GROWTH AND NUTRITION OF TIMOTHY (PHLEUM PRATENSE L.)
Authors: LANGER R. H. M.
Published: February 2008

During the first year of growth of timothy, variations in nitrogen supply affected the number of tillers and leaves, leaf area and dry weight, but had little influence on relative growth and net assimilation rates, except at very low levels of nitrogen. Differentiation and ear emergence occurred slightly earlier at high nitrogen and ear length was increased; there was also an increase in the proportion of fertile tillers among the total number produced after the first few weeks of tillering. The effect of nitrogen supply on the number, dry weight and ear length of early primary tillers was small but became larger in later tillers. Irrespective of the level of nitrogen supply, tillers had particularly high net assimilation rates during the first few weeks following their appearance.
THE EFFECT OF TEMPERATURE ON REPRODUCTION BY THE ALATAE OF PEMPHIGUS BURSARIUS (L.)
Authors: DUNN J. A.
Published: February 2008

The reproductive rate of the winged forms of Pemphigus bursarius was studied at temperatures between 38 and 82° F. The fundatrigeniae gave the greatest total reproduction at about 60° F. but the highest reproductive rate at 70–81° F. Corresponding temperatures for the sexuparae were 55 and 67° F. approximately. The average outdoor air temperatures prevailing at the time when the respective winged forms are most abundant correspond closely to the temperatures required by the alatae for maximum reproduction. On a basis of temperature, adult sexuparae trapped underground can expect to survive about 12 days in early September and about 30 days at the end of October.
THE BIOLOGY OF LETTUCE ROOT APHID
Authors: DUNN J. A.
Published: February 2008

Lettuce root aphid, Pemphigus bursarius L., is a pest which sometimes causes considerable and widespread damage to crops of summer lettuce.

Its favourite primary host is Lombardy poplar. On hatching in spring, from eggs that have overwintered on this host, the fundatrices cause the development of hollow, flask‐shaped galls on the leaf petioles. A fundatrix becomes enclosed within a gall, where it matures, and gives rise to between 100 and 250 young. These fundatrigeniae are all potential alatae and on developing wings leave the gall and migrate to lettuce and other secondary hosts; they reproduce rapidly.

Lettuce sown between mid‐April and the end of May is most severely attacked, while lettuce sown in July escapes attack. The alternative secondary hosts belong to the Compositae, subfam. Liguliflorae, and although lettuce is preferred by the fundatrigeniae, Lapsana communis L. and Sonchus asper (L.) Hill often have big colonies of Pemphigus bursarius on their roots. The size of the mature apterae varies between hosts and is largest on lettuce and Sonchus asper.

All winged alienicolae are sexuparae and fly back to poplar. Thus alternative secondary hosts are not reservoirs for lettuce‐infesting alatae.

The sexuparae begin appearing on lettuce from about the last week in August. They generally come up to the soil surface and settle around the ‘collar’ of the host plant, to mature and develop wings. Having flown back to the primary host, the sexuparae seek out crevices in the bark where they produce arostrate sexuales. The ovipara contains one egg, and after mating she crawls as far into the bark crevice as possible and oviposits.
STUDIES ON THE PROPERTIES OF SOIL‐BORNE VIRUSES OF THE TOBACCO‐RATTLE TYPE OCCURRING IN SCOTLAND
Authors: CADMAN C. H. , HARRISON B. D.
Published: February 2008

Soil‐borne viruses of the tobacco‐rattle type occur in sandy and peaty soils in many parts of Scotland, and infect many species of crop and weed plants, often only in the roots. They also occur in potato plants that have diseases of the stem‐mottle type. The viruses can be distinguished from other soil‐borne viruses occurring in Britain by the symptoms they cause in tobacco, Chenopodium amaranticolor and French bean.

Some virus cultures (M types) multiplied readily and were easily transmitted by mechanical inoculation, whereas others (NM types) were transmitted mechanically only with difficulty. The behaviour of NM types remained constant during twenty successive subcultures. Only slight differences were noted between the symptoms caused by M and by NM types. A proportion of the single‐lesion isolates made from cultures of the M type behaved in every way like NM types: this proportion differed with different parent cultures. Single‐lesion isolates that were of the M type mostly caused somewhat different symptoms from their parent culture. All M types that were tested, including one from the Netherlands, were serologically related: however, different cultures, and different samples of the same culture propagated on different occasions, varied in antigenic constitution. Belladonna mosaic virus, described by Smith (1943) from England, was serologically related to tobacco rattle virus. Infection with each of several M types (including the Dutch culture), protected Nicotiana sylvestris plants from the effects of each of the others. NM types also protected N. sylvestris from the effects of the Dutch culture, but the latter was subsequently isolated from the tip leaves of such plants. Sap from plants infected with cultures of the M type contained characteristic rod‐shaped particles, but none was seen in sap from plants infected with NM types.

In tobacco sap, M types had the following properties: thermal inactivation point, 80–85°C.; dilution end‐point, 10‐5‐10‐6; longevity in vitro, over 6 weeks; infectivity survived freezing and precipitation by ammonium sulphate, but not exposure to pH 3. In many of its properties, including the unusual one of failing to show photoreactivation after ultra‐violet irradiation, tobacco rattle virus resembles tobacco mosaic virus.

Soil‐borne viruses occurring in Britain are classified into three groups, exemplified by tobacco necrosis, tomato black ring and tobacco rattle viruses.
THE PATTERN OF FIELD INFECTION OF POTATO BY THE BEET RINGSPOT STRAIN OF TOMATO BLACK‐RING, A SOIL‐BORNE VIRUS
Authors: HARRISON B. D.
Published: February 2008

The potential importance of the beet ringspot strain of tomato black‐ring, a soil‐borne virus, was assessed by growing stocks of Kerr's Pink potato for 1 year on infested land and subsequently on uninfested land. The incidence of infection in two stocks was 39 and 8% in the first year on uninfested land, and 29 and 5% after 2 years.

The virus was usually restricted to the roots of plants in the first year of infection, but a few plants showed black rings and spots in their leaves. In the second year, 20–55% of the plants grown from tubers set by symptomless, but infected, mother plants were infected: many of these showed leaf necrosis, others had stunted shoots, and cupped and distorted leaves; some were symptomless although systemically infected. In the third and fourth years, most of the progeny from plants which had symptoms or which were symptomless but systemically infected, contained the virus: nearly all such infected plants were stunted and distorted or were symptomless. Infection decreased the weight of tubers produced by plants with severe necrotic spotting but not the yield of plants with less necrosis. The number and weight of tubers per plant were decreased by 15 and 20% respectively, in symptomless systemically infected plants, and by 20 and 30% in stunted plants.
STUDIES ON PLANT CUTICLE: THE CUTIN COMPONENT OF THE CUTICLES OF LEAVES
Authors: ROBERTS MARGARET F. , BATT R. F. , MARTIN J. T.
Published: February 2008

Methods are described for the chemical separation from leaf material of the ventral and dorsal surface cuticular membranes and for the determination of cutin in the membranes and leaf tissues.

The cutin contents of the cuticular membranes separated from leaves of laurel, rhododendron, and Euonymus, and of leaf tissues of cauliflower, red beet, banana, tomato, strawberry and blackcurrant are reported. The relationship between the cutin and waxy components of the leaf cuticle is discussed, and earlier work on the development, structure and chemistry of the cuticle is reviewed.
STUDIES ON PLANT GROWTH‐REGULATING SUBSTANCES: CHLORO‐SUBSTITUTED PHENYLACETIC ACIDS
Authors: PYBUS MARY B. , WAIN R. L. , WIGHTMAN F.
Published: February 2008

The plant growth‐regulating activity of all the mono‐ and di‐ chloro‐substituted phenylacetic acids, together with the 2:3:6‐trichloro‐ derivative, has been determined in the wheat cylinder, pea segment and pea curvature tests. Each of these compounds showed activity, the 2:3‐dichloro‐ and the 2:3:6‐trichloro‐ derivatives being extremely active. The 3:5‐dichloro‐ acid was inactive in the wheat test but showed moderate activity in the pea tests.

All these findings are discussed in relation to the plant growth‐regulating activity of corresponding benzoic and phenoxyacetic acids.
THE INCIDENCE OF CERTAIN SEED‐BORNE DISEASES IN COMMERCIAL SEED SAMPLES
Authors: MARSHALL GILLIAN M.
Published: February 2008

Commercial samples of celery seed have been submitted to the Official Seed Testing Station, Cambridge, from 1926 to 1958, for tests to determine the percentage infection by Septoria leaf spot (Septoria apii‐graveolentis and S. apii). The disease test and a method for estimating the viability of Septoria spores is described. The percentage of samples with less than 1% infection increased from 6.1% in 1926‐31 to 46.2% in 1953‐8 and the percentage of heavily infected samples decreased. But celery samples submitted since 1949 for purity and germination only were more heavily infected (in 1953‐8 only 26.3% had less than 1% infection). In 1957‐8, 78.8% of all celery seed samples tested showed evidence of infection with Septoria spp.

No effect of variety or season on the incidence of disease was found during the survey.

Six out of thirty samples were found to carry viable Septoria as estimated by germination of pycnidiospores.

The similarity between the percentage germination of healthy seeds and those bearing Septoria pycnidia confirmed the general belief that Septoria spp. do not affect germination.
THE COLIFORM BACTERIA ASSOCIATED WITH POTATO BLACK‐LEG AND OTHER SOFT ROTS
Authors: GRAHAM D. C. , DOWSON W. J.
Published: February 2008

Twelve glasshouse trials using twenty‐five isolates of coliform soft‐rot bacteria obtained from various countries showed that all the isolates produced typical black‐leg of potato at temperatures of 76° F. (24.5° C.) or over, while some of them could also produce the disease at temperatures below 66° F. (19° C.).

Thus the isolates fall into two main groups of which the high‐temperature group originates mostly from tropical or subtropical countries or from plants grown in heated glasshouses, whereas the low‐temperature group is indigenous in the north temperate regions. The high‐temperature group comprises Pectobacterium carotovorum (Erwinia carotovora), P. carotovorum var. chrysanthemi (E. chrysanthemi) and P. carotovorum var. aroideae (E. aroideae). The low‐temperature group consists of one variety, P. carotovorum var. atrosepticum (E. atroseptica).

This temperature relation provides a possible means of discovering the origin of the black‐leg pathogen in crops grown from Scottish seed in certain tropical or subtropical countries.

As a result of this investigation it is considered that all soft‐rot coliform bacteria are varieties of a single species, P. carotovorum (Jones) Waldee.
COPPICING EXPERIMENTS ON THE SPREAD AND CONTROL OF CACAO SWOLLEN‐SHOOT DISEASE IN NIGERIA
Authors: THRESH J. M. , LISTER R. M.
Published: February 2008

A coppicing technique was used to determine the incidence and distribution of latent and unrecognized infection around naturally occurring outbreaks of cacao swollen‐shoot virus disease in Western Nigeria. All the apparently healthy trees within 30 yards of eighty outbreaks of various sizes were coppiced and most of the infected stumps which regenerated showed symptoms within a year.

The distribution of the infected stumps around thirty‐five outbreaks studied in detail is expressed by the equation log10I=a+bx. I is the estimated intensity of infection in the coppiced stumps at distance x from the nearest infected tree removed at the time of coppicing. The constant a determines the height of the peak of the infection gradient and increases with outbreak size, whereas the slope of the gradient, determined by the negative constant b, is similar around all outbreaks.

The results are consistent with information on the movement of the mealybugs and spread of cacao swollen‐shoot virus in outbreaks. Moreover, they indicate that outbreaks are controlled most economically by removing all obviously infected trees and adjacent apparently healthy ones. Control does not require the destruction of all the trees around outbreaks up to a distance of 30 yards as done previously, but can be achieved by felling fewer trees, the actual number depending on the size of the outbreak.
THE EFFECT ON WOOD‐PIGEON BREEDING OF SYSTEMATIC NEST DESTRUCTION
Authors: MURTON R. K.
Published: February 2008

Wood‐pigeon nests were destroyed in various localities scattered throughout East Anglia during the breeding season of 1956. Nests were destroyed at three periods: 23 July‐7 August; 14–30 September and 29 October‐12 November.

Four nesting habitats were studied—hedgerow, deciduous thicket, mature deciduous woodland and coniferous woodland—amounting to approximately 100 acres of each habitat.

The density of occupied nests varied between different habitats. Hedgerow supported the highest number per acre, deciduous woodland the lowest. The average time required to clear 1 acre of occupied nests during the three trials was 2.7, 2.2, 1.4 hr., respectively. During the first two trials the average expenditure per occupied nest was 0.4 man‐hours; for the third period it was 3.2 man‐hours.

In 1957 nests were destroyed at two separate periods in sites in various counties in East Anglia. Control sites where no nests were destroyed were examined at fortnightly intervals throughout the breeding season and of the total number of young expected to leave their nests in the experimental sites only 37% did so. Nest destruction prevented the other 63% from being fledged.
THE EFFECT OF GIBBERELLIC ACID ON LEAF AREA AND DRY‐MATTER PRODUCTION IN MAJESTIC POTATO
Authors: HUMPHRIES E. C. , FRENCH S. A. W.
Published: February 2008

When gibberellic acid (50 p.p.m. in aqueous solution) was sprayed twice or six times at weekly intervals on potato plants (var. Majestic) with a low or high nitrogen supply it did not affect rate of leaf production on the main axis, but caused earlier senescence of leaves, especially with the more frequent spraying, and inhibited leaf production and growth on laterals of the high‐nitrogen plants at nodes 10 and 11 but not at other nodes. This central region of the stem appears to have a low growth potential, probably because it lies midway between two zones of active growth, viz. the basal branches and the younger leaves on the main stem. Competition between these is increased by gibberellic acid. Gibberellic acid increased leaf area even when lack of nitrogen was restricting growth but this did not produce extra dry matter. Tuber weight was increased more in high‐nitrogen plants by two sprayings than by six sprayings. The net assimilation rate of low‐nitrogen plants was halved by spraying but was not changed in high‐nitrogen plants where the value was similar to that of low‐nitrogen control plants. The high‐nitrogen plants had absorbed nearly all the available nitrogen between the second and third harvests, but plants treated with gibberellic acid, nevertheless, had more total dry weight and tuber dry weight than the controls. The nitrogen content of the leaves expressed on an area basis was lower in sprayed plants and, with continued spraying, fell at the third harvest to equal that of low‐nitrogen plants. Evidently, the effect of gibberellic acid depended on the interaction between the rate of application and the nitrogen supply, but further work is necessary to define the conditions that give the maximal effect on dry‐matter production.