bluuebunny/crossref_metadata_2025 huggingface dataset:
The induction of leaf‐roll galls by the apple aphids Dysaphis devecta and D. plantaginea
Authors: FORREST J. M. S. , DIXON A. F. G.
Published: February 2008

Dysaphis devecta causes the leaves of its host plant to roll laterally whereas D. plantaginea causes them to roll longitudinally. Both species of aphid are phloem feeders. D. devecta prefers to feed on the smaller veins in the lamina whereas D.plantaginea chooses the midrib. However, groups of D. devecta or D. plantaginea confined to the stem of an apple seedling induced young leaves several centimetres away to develop leaf rolls characteristic of each species. A single larva of D. devecta or D. plantaginea can induce a leaf‐roll or a stem‐bend on an apple seedling within 24 h. It is suggested that characteristic abnormalities in leaves attacked by D. devecta and D. plantaginea are caused by specific substances in the saliva of each aphid.
The role of the perennial stinging nettle, Urtica dioica, as a reservoir of beneficial natural enemies
Authors: PERRIN R. M.
Published: February 2008

A wide range of natural enemies, including predators, parasites and entomophagous fungi were observed to feed on the stinging nettle aphid, Microlophium carnosum, populations of which increased rapidly in late April and early May. Patches of stinging nettles thus served as an important alternate feeding site for some beneficial natural enemies before pest aphids appeared on cultivated plants. Anthocoridae, Miridae and Coccinellidae were the most abundant specific predators sampled on nettles; only the Coccinellidae appeared to disperse over a defined period to other habitats. The hymenopterous parasites Aphidius ervi and Ephedrus lacertosus parasitized up to 10% of M. carnosum populations in June: two species of the fungus Entomophthora occurred spasmodically.

Cutting patches of nettles in May or June had the most striking effect on the species and numbers of Coccinellidae. Cutting in mid‐June might increase the numbers and impact of natural enemies on nearby pest infestations.
Duration of effects of benomyl on growth and wilt (Verticillium dahliae) development in the strawberry, cv. Cambridge Vigour, in relation to time of inoculation
Authors: TALBOYS P. W. , FRICK E. L. , DAVIES MOIRA K.
Published: February 2008

Single doses of benomyl, 0–4 g/plant in 1972 or 0–04 g in 1973, were applied in 100 ml water to the surface of the soil in 12‐5 cm pots containing Cambridge Vigour strawberry plants, either before inoculation with Verticillium dahliae or at various times up to 56 days afterwards. Pre‐inoculation treatments were terminated by washing the potting medium from the roots at the time of inoculation and their effects on pathogenesis and growth were relatively small. Post‐inoculation treatments with benomyl prevented or suspended pathogenesis for at least as long as fungistatic activity could be detected in petiole segments by bioassay; this was for more than 150 days after the larger dose, 50–60 days after the smaller dose applied 7–28 days after inoculation and 30 days when applied 56 days after inoculation.

There were no consistent differences in the uptake and persistence of benomyl in inoculated and non‐inoculated plants.

Early post‐inoculation treatment caused some retardation of plant growth, but benomyl‐treated inoculated plants were generally comparable in size with similarly treated non‐inoculated ones, and much larger than untreated inoculated plants.

Increasing the dose of benomyl applied to the soil apparently had little influence on the intensity of its effects but greatly increased their duration, probably because of the low solubility of the systemic chemical.
The response of various breeding lines of lettuce to beet western yellows virus
Authors: WATTS L. E.
Published: February 2008

The field occurrence of symptoms of beet western yellows virus (BWYV) disease in breeding lines of summer lettuce was studied in trials conducted from 1971 to 1974. No evidence of immunity was found in seventy cultivars and over 500 lines from ten crosses, but some lines, notably those with Little Gem as one parent, appeared to be less affected by the disease.

When the number of plants showing symptoms was recorded on a weekly basis it was apparent that only minor differences existed in the response to infection. In the earlier maturing lines, 50 % of the plants exhibited symptoms within 16 to 20 days of hearting, and later maturing lines reached the same level of disease incidence within 7 to 16 days after hearting.

The search for resistance should be widened to include wild species; strict selection techniques up to flowering time should also be used to increase field resistance in the present cultivars.
Storage characteristics of some vegetables and soft fruits
Authors: ROBINSON J. E. , BROWNE K. M. , BURTON W. G.
Published: February 2008

Rates of carbon dioxide production, in air and in 3 % 02, over a range of temperatures, were measured for over thirty commodities, and rates of evaporation, under known water vapour pressure deficit, measured for most of them. Optimum storage conditions in air for each commodity were determined. Storage life under these optimum conditions, and under the nearest practical approximation to them, was estimated. In most cases the optimum temperature is ooC, examples of exceptions being runner beans, cucumbers, potatoes, green peppers and tomatoes. The humidity should usually be high, 100 % r.h. often being optimal, particularly for leafy vegetables, provided the temperature is low. Commodities resistant to evaporation, however, such as the onion, may with advantage be stored at lower humidities, thus reducing the microbial hazards.
Screening potato clones for resistance to dry rot (Fusarium solani var coeruleum)
Authors: JELLIS G. J.
Published: February 2008

A modification of the Boyd method is described in which cores of potato tissue are used instead of whole tubers. This reduces the space required for incubation, permits good control of the environment and eliminates the need to sacrifice valuable seed material. The method was used for testing the resistance of sixteen cultivars of potato on five occasions over two seasons.
The fumigation of seeds with methyl bromide
Authors: POWELL D. F.
Published: February 2008

Forty varieties of vegetable, cereal, fodder and grass seeds at 10, 13 and 16% moisture content were fumigated with methyl bromide at 10 and 18oC, to determine the maximum safe moisture content required to avoid unacceptable phytotoxicity. Dosages (concentration x time products) of 200 and 400 mg h/1 of technical and commercial methyl bromide were used and treated seeds were compared with controls in germination tests. Results were not consistent, but in c. 30 % of the comparisons lower moisture contents, lower temperature and lower dosage each resulted in better germination than the corresponding higher values. The reductions in germination of treated samples were usually less than 5 % and the overall average reduction was only 2.3%. This work showed that under controlled conditions the treatments are safe for most of the tested varieties of seed, but for some seeds, particularly white clovers, Agrostis and runner beans, the highest moisture content (16%) should be avoided.
Comparison of centrifugal and other methods for standardization of extraction of nematodes from soil
Authors: HARRISON JUDITH M. , GREEN C. D.
Published: February 2008

The extraction of many genera of nematodes from four different soil types by sedimentation, mobility, sieving and centrifuging was compared. All methods were found to extract similar numbers of nematodes. Centrifuging was the most versatile technique and the best for clay soils. Baerman sieving was generally poor and particularly so for sands and for the genus Tylen‐chorhynchus. Rotylenchus was the only genus of those identified that was extracted equally well by all techniques. Centrifugal extraction was selected as the routine method for surveys as it was effective on all soil types, was less likely to be subject to variation and, although poor for Longidorus, extracted a wider spectrum of nematodes.
Effects of variation in ear temperature on growth and yield of spring wheat
Authors: FORD MARGARET A. , PEARMAN I. , THORNE GILLIAN N.
Published: February 2008

Wheat plants were kept in a growth room at 15 oC from 7 days after an‐thesis until maturity and their ears were warmed to 20 or 25 oC for various periods. Continuous warming initially increased the growth rate of the ear and decreased that of the stem, but hastened senescence of the ear and decreased final grain yield by decreasing dry weight per grain. Warming the ears increased the movement of 14C and nitrogen to them from the leaves and stem during the early stages of grain growth but decreased it later. Warming the ears for only the first 10 or 20 days also hastened ear senescence; grain yield decreased progressively with increase in duration of the warm period. All effects were greater at 25 than at 20 oC.

The effects of changing ear temperature from 15 to 20 oC were independent of the temperature of the rest of the plant. Altering the humidity of the air around the ears by 4–7 mb at constant temperature had no effect on ear growth or senescence.

Warming all of the plant except the ears from 15 to 20 oC increased ear growth slightly during early grain growth and decreased it later, irrespective of ear temperature: stem dry weight, leaf area and net photosynthetic rate of flag leaves and green stems were decreased and dark respiration rate of stems was increased.
Cytological techniques for use in apple breeding
Authors: LESPINASSE Y. , ALSTON F. H. , WATKINS R.
Published: February 2008

Details are given of improved cytological squash techniques for mitotic and meiotic counts which are especially useful in apple breeding. The cytological characteristics of scion varieties (including triploids such as the recently named Suntan), apple rootstocks (including tetraploids), and second backcross progenies of the mildew resistant species Malus hupehensis (2n= 51) to the cultivated apple (in which most seedlings were found to be diploid) are discussed with reference to their implications for apple breeders.
The control of peach leaf curl (Taphrina deformans) with Off‐Shoot T
Authors: BURCHILL R. T. , FRICK E. L. , SWAIT A. A. J.
Published: February 2008

Effective control of peach leaf curl disease (Taphrina deformans) was obtained with two winter sprays of a 63 % mixture of fatty alcohols (Off‐Shoot T) applied at 5 % a.i. Phototoxicity was insignificant.
The reaction of wheat genotypes to Septoria tritici
Authors: BROKENSHIRE T.
Published: February 2008

Seedling leaves, flag leaves, culms and heads of wheat genotypes were evaluated under glasshouse and field conditions for reaction to Septoria tritici. Parameters used for resistance screening were the incubation and latent periods, disease and sporulation levels, and 1000 grain weight.

Significant correlations were obtained between reactions of different plant organs and between field and glasshouse tests; significant interspecific and intraspecific differences occurred for all screening parameters. Triticum aestivum varieties showed a wide range of disease reaction ranging from the high resistance of Elite Lepeuple, Maris Dove, Maris Ensign, Chalk and Tommy to the high susceptibility of Rothwell Sprite, Sovereign, Cardinal, Maris Ranger and Maris Templar.
Mildew reinfection in adjacent and separated plots of sprayed barley
Authors: BAINBRIDGE A. , JENKYN J. F.
Published: February 2008

In latin square experiments in 1973 and 1974, reinfection of sprayed barley, by mildew (Erysiphe graminis f.sp. hordei) was decreased by widely spacing the plots. In 1974, when yields differed between plots which were either contiguous or separated, the results suggested different times to spray for best yield increase.
The effect of resistance to Amphorophora rubi in raspberry (Rubus idaeus) on the spread of aphid‐borne viruses
Authors: JONES A. T.
Published: February 2008

The effectiveness of resistance to the aphid Amphorophora rubi in restricting the spread of aphid‐borne viruses was assessed in a field experiment using six genotypes of red raspberry. In one block of the experiment, the genotypes alternated with rows of virus‐infected Mailing Jewel raspberry, and in the other they alternated with virus‐free Mailing Jewel. During 4 years, the numbers of A. rubi and the amount of 52V virus spread in the two blocks were similar, suggesting that this virus was mostly introduced from outside the plots.

Lloyd George and Mailing Jewel raspberry became heavily infested with A. rubi and were rapidly infected with raspberry leaf mottle, raspberry leaf spot and 52V viruses. Glen Clova and Norfolk Giant raspberry, which contain minor genes for resistance to A. rubi, were infested with fewer A. rubi and virus spread more slowly in these cultivars. A. rubi were rare on Mailing Orion and an East Mailing raspberry selection (888/49) which have genes A1 and A10 respectively for resistance to A.rubi, and these plants remained largely free of virus. The role of minor and major gene resistance to A. rubi in restricting virus spread is discussed.

A few Macrosiphum euphorbiae and Myzus ornatus were recorded on several of the raspberry genotypes.
The relative performance of white clover genotypes with rhizobial and mineral nitrogen in agar culture and in soil
Authors: MYTTON L. R.
Published: February 2008

Vegetative propagules of adult plants of white clover grown in agar culture show a better agreement with the performance of adult plants grown in soil than that previously reported of nodulated seedlings. This suggests that, whilst results obtained from the inoculation of seedlings can only be extrapolated to other situations with great caution, laboratory techniques which allow nitrogen fixation assessments to be made on adult plants may be useful in predicting performance under more natural conditions.

The growth of vegetative propagules of mature plants dependent on rhizo‐bium fixed nitrogen was also compared with propagules receiving abundant inorganic nitrogen. In agar culture there were no differences in yield between nitrogen sources, indicating that the symbiotic associations could fix sufficient nitrogen for growth under these relatively restrictive conditions. In soil, however, only the slower genotypes came near to providing sufficient nitrogen from symbiosis to sustain their potential yield as measured from their growth with inorganic nitrogen. The more vigorous the genotype the greater was the short‐fall in nitrogen supplied by the rhizobium association. Joint regression analysis showed that any apparent interactions between plant genotypes and the source of nitrogen was a function of the genotypes' potential growth rate. The importance of quantifying nitrogen fixation in relation to the growth potential of the host genotype is emphasized, and the need, in legume breeding programmes, for simultaneous selection of host and rhizobium is discussed.
Studies on plant growth‐regulating substances. XXIX. The plant growth‐retarding properties of certain quaternary ammonium halides
Authors: CHAMBERLAIN VALERIE K. , CHAMBERLAIN K. , WAIN R. L.
Published: February 2008

The plant growth‐retarding activity of a series of N‐methyl‐N‐chloro‐alkyl‐pyrrolidinium and ‐piperidinium halides has been measured using wheat and barley seedlings and dwarf bean plants. Some of these compounds possess activity comparable to that of 2‐chloroethyl‐trimethyl‐ammonium chloride (CCC).

The activities of twenty‐four quaternary halides of pyridine, N‐methyl‐pyrrolidine and N‐methylpiperidine, each possessing a chlorinated benzyl group, have also been determined in the wheat seedling and dwarf bean tests. Many of these compounds were active and activity could be correlated with the substitution pattern in the benzyl group.
Field and glasshouse experiments on the control of potato mop‐top virus
Authors: COOPER J. I. , JONES R. A. C. , HARRISON B. D.
Published: February 2008

Field observations during 3 yr on a stock of potato cv. Red Craigs Royal partially infected with potato mop‐top virus (PMTV) confirmed that the virus was passed by an infected mother plant to only a proportion of its progeny tubers, and showed that in this cultivar symptomless plants gave rise only to symptomless progeny. The elimination of PMTV from stocks can therefore be greatly accelerated by removing symptom‐bearing plants. Infected potato tubers were not freed from PMTV by treating them at 37 °C for up to 8 wk. Treating ‘seed’ tubers bearing powdery scabs that contain PMTV‐carrying resting spores of Spongospora subterranea with formaldehyde or organo‐mercurial fungicide greatly decreased PMTV establishment when the tubers were planted in previously uninfective soil, but fumigation with 2‐aminobutane was ineffective.

Decreasing the pH of infective soil to 5‐0 by applying sulphur greatly decreased the infection of potato cv. Arran Pilot with PMTV and S. subterranea in field experiments, but this treatment did not eliminate either; when the pH of treated soil was raised the transmission of PMTV resumed. Treating infective soil with a range of fungicides greatly decreased the infection of Nicotiana debneyi bait seedlings in glasshouse experiments but only calomel at 75 kg/ha controlled spread of PMTV and 5. subterranea to potato in field experiments. In other field experiments, applying zinc frit, zinc sulphate or zinc oxide to infective soil greatly decreased the spread of both to potato. The amount of zinc required increased with increase in clay content of the soil. However, treatment with zinc compounds did not eliminate PMTV‐carrying vectors from soil, and when treated soil was diluted with autoclaved soil many of the bait seedlings planted in the mixture became infected. The zinc frit was phytotoxic because of its boron content but zinc sulphate and zinc oxide caused little or no decrease in tuber yield. The zinc content of potato tubers was increased but not doubled in zinc‐treated plots, and during the first year after treatment the zinc content of topsoil decreased greatly. The zinc content of ryegrass grown after potatoes was greater than of potato tubers but did not reach a level considered dangerous to livestock. Treatment of soil with sulphur, zinc oxide or calomel may be useful for small plots used in the early stages of propagation of virus‐tested potato clones where there is risk of infection with PMTV.
Studies on plant growth‐regulating substances. XLII. Abscisic acid as a genetic character related to drought tolerance
Authors: LARQUÉ‐SAAVEDRA A. , WAIN R. L.
Published: February 2008

Abscisic acid levels were measured in turgid or wilted detached leaves from maize and sorghum seedlings. Lines, cultivars and hybrids known to exhibit different abilities to withstand water stress were compared. The leaves of those tolerant to drought were shown to contain substantially more free abscissic acid. The effect was more clearly shown by sorghum than by maize. The results are discussed in relation to the physiology of drought tolerance.
Agropyron repens ‐ allelopathy?
Authors: Sagar G. R. , Ferdinandez D. E. F.
Published: February 2008

Following the work of Becholtz and Bandeen, a series of glasshouse experiments was made to examine the effects of root‐zone interference between Agropyron repens and wheat. In a solution‐culture experiment the reduction in growth of wheat due to the presence of A. repens could be largely corrected by increasing the nutrient supply in the solution. In similar studies but using soils, the depression of growth of wheat could not be corrected. Foliage applications of nitrogen to wheat plants grown with A. repens had no effect. Using a split‐pot technique it was found that the part of the root system of wheat growing in the same medium as the rhizomes and roots of A. repens was very severely suppressed. These results will be discussed.
Varietal differences in the susceptibility of Brussels sprouts to lepidopterous pests
Authors: DUNN J. A. , KEMPTON D. P. H.
Published: February 2008

The attack by cabbage caterpillars on open‐pollinated cultivars of Brussels sprouts at Wellesbourne was recorded approximately weekly from July to October in 1973 and 1974. The red‐foliaged cv. Rubine was much less attacked by Pieris rapae than any of the twenty‐five green‐foliaged cultivars tested, the least attacked of which were The Aristocrat, Continuity, Evergreen and Pride of the Market. Rubine also showed some resistance to attack by Mamestra brassicae and Evergestis forficialis, as did The Aristocrat. Continuity, though as resistant as any of the cultivars to E. forficialis, was not resistant to M. brassicae. No evidence of antibiosis was found and resistance, based on non‐preference, is considered to result from ovipositing P. rapae adults discriminating against the red colour of Rubine and against the leaf composition (relative volatile content) of the green‐foliaged resistants. This could also apply with M. brassicae and E. forficialis.
Some observations on assessing Phoma betae infection of sugar‐beet seed
Authors: GAMBOGI P. , BYFORD W. J.
Published: February 2008

Near‐ultraviolet or ‘black’ light applied continuously from the start of incubation, facilitates tests for Phoma betae on sugar‐beet seed by stimulating the production of pycnidia and restricting mycelial growth of P. betae and other fungi. Pretreatment of the seed with dilute sodium hypochlorite decreases the number of seeds with P. betae by removing superficial infection, but some of this is of significance in the field. Rubbing beet seed also decreased counts of P. betae in the laboratory and increased field emergence, primarily by removing the fungus.

Griseofulvin sprayed on beet‐seed plants either 2 wk or 2 days before harvest significantly decreased seed infection with P. betae, but not to a level at which further seed treatment could be omitted.
Chemical treatment and inoculation of hardwood stumps for control of Armillaria mellea
Authors: RISHBETH J.
Published: February 2008

The type of chemical treatment used to control regrowth from hardwood stumps affects their colonization by fungi. Since such stumps often act as sources of infection for Armillaria mellea this may have important consequences. Ammonium sulphamate generally favours growth of species causing rapid decay, some of which compete well with A. mellea, whereas 2,4,5‐trichlorophenoxyacetic acid tends to promote growth of Chondro‐stereum purpureum which is replaced by A. mellea. The former treatment is recommended for situations where serious damage from A. mellea seems likely to occur, because the best hope of control is to ensure rapid killing of stump roots.

Prompt colonization of stumps was obtained by inoculating the cut surface with spores of a wood‐rotting fungus and then treating it with 40% ammonium sulphamate. In birch stumps jointly inoculated with Coriolus versicolor and A. mellea the amount of wood occupied by the latter after 4 yr was greatly reduced by comparison with controls inoculated with A. mellea alone. Stump inoculation might be worth developing for use in valuable plantations and other intensively managed areas such as parks and gardens, especially where measures such as stump excavation are impracticable.
Growth and development of soyabean cv. TK5 as affected by tropical daylengths, day/night temperatures and nitrogen nutrition
Authors: HUXLEY P. A. , SUMMERFIELD R. J. , HUGHES A. P.
Published: February 2008

Two experiments were done in Saxcil growth cabinets in order to investigate the effects of climatic factors and nitrogen nutrition on the growth, reproductive development and seed yield of soyabean cv. TK5. In the first, plants were grown to maturity in eight environments comprising all combinations of two short daylengths (11 h 40 min and 13 h 20 min), two day (27 and 33oC) and two night (19 and 24oC) temperatures. In the second, day temperature was kept at 33oC but the night temperature was varied (19 and 24oC) as was the mineral nitrogen supply (20 and 197 ppm N) to plants which were either inoculated or not with an effective single strain of Rhizobium.

Taller, more branched, later flowering plants were produced in the longer daylength but seed yield was hardly affected because the components of yield did not all respond similarly. In the higher day temperature treatments seed yield per plant was reduced by half because all yield components were adversely affected ‐ pods per plant by 34 %, mean seed dry weight by 24 % and seeds per pod just slightly. There was a marked effect of the higher night temperature which promoted early vegetative growth, induced early flowering and although the number of pods per plant was, overall, reduced by 48 %, seed yield per plant was little affected as mean seed dry weight was increased by 37 % and the number of seeds per pod was also increased slightly.

Prior to flowering, nodulated plants obtained about two thirds of their total nitrogen requirement via direct uptake and one third through the symbiotic system. Vegetative dry weight and plant nitrogen content were increased by the higher mineral nitrogen level and, although height was slightly diminished, more branches were produced. Seed yield, however, was only slightly increased.

These experiments have shown that night temperature is an environmental factor of major importance for the growth of this soyabean cultivar. They have provided, also, a more rational basis for interpreting seasonal variations in growth and seed yield of soyabean in the tropics where, clearly, day and night temperature effects can override those of daylength and nitrogen nutrition.
The spread of Phoma exigua within the potato crop
Authors: LOGAN C.
Published: February 2008

The incidence of gangrene that developed in tuber samples harvested in a systematic way from potato crops planted with surface sterilized gangrene‐free seed surrounding a small plot planted with gangrene‐affected seed showed that in two out of the three years marked outward spread of Phoma exigua var.foveata occurred in an uneven manner to about 4 ft (1–2 m) from the central plot. The occurrence of var. foveata was restricted to the immediate area in and around the gangrene infection locus whilst P. exigua var. exigua was more widely and evenly distributed throughout the experimental area.

The incidence of infection in and around the central plot varied from year to year and it is suggested that the main method of spread of var. foveata inoculum is by rain splash. Infection by both fungi appeared to be influenced in a similar manner in all three seasons.
Influence of crop background on natural enemies of aphids on Brussels sprouts
Authors: SMITH JUDITH G.
Published: February 2008

The most abundant natural enemies of aphids on Brussels sprout crops were Syrphidae, different species being attracted differentially to weedy or weed‐free plots according to whether they were more host‐plant‐orientated (e.g. Melanostoma spp., Platycheirus spp.) and thus affected directly by the background, or more aphid‐orientated (e.g. Syrphus balteatus) and so less affected by background than by aphid numbers. Oviposition by Melanostoma spp. was usually much greater in weedy sprout crops than on sprouts in bare soil, and their eggs were also very abundant on weeds. Eggs of other syrphid species were scarcer on weeds. In contrast to Melanostoma, Platycheirus spp. usually oviposted preferentially on sprouts growing in bare soil. Oviposition by S. balteatus was in response to aphid abundance and thus tended to become greater on sprouts in bare soil. Notably more adults of non‐aphido‐phagous Syrphidae were caught over weedy than over non‐weedy Brussels sprout plants.

Anthocoris nemorum nymphs and adults were very common on sprout plants and weeds in the weedy crop but were scarce on sprouts in bare soil; A. nemorum oviposited on white and yellow charlock (Raphanus raphanistrum and Sinapis arvensis) occasionally.

Parasitism of Brevicoryne brassicae by Diaeretiella rapae appeared to be related to aphid numbers and was only indirectly influenced by the crop background.

Field experiments with green and brown cloth backgrounds showed that some syrphids were attracted to green; A. nemorum was relatively scarce over both artificial backgrounds.

It is concluded that decreased natural enemy action is partly responsible for the initially greater abundance of B. brassicae in a weed‐free crop of Brussels sprouts than in a weedy crop.
New virulence gene combinations in British isolates of Bremia lactucae
Authors: CRUTE I. R. , DAVIS ANNE A.
Published: February 2008

Isolates of Bremia lactucae made in 1974 from new Dutch‐bred lettuce cultivars carrying the R gene combinations 3, 4, 7 or 3, 4, 7, 8 proved to have the V gene combination 1, 3, 4, 5, 6, 7, 8 predominant. An isolate obtained from cv. Larganda (R2, 7) was found to overcome all ten R genes identified in lettuce cultivars to date and could be designated V 1, 2, 3, 4, 5, 6, 7, 8, 9, 10. The virulence combinations 3, 7, and 2, 3, 7 have not previously been reported in British B. lactucae collections although the former has been found in Holland and both occur in Sweden. The practical implications of these findings are discussed.
Ultrastructural changes in leaf cells of poplar naturally infected with poplar mosaic virus
Authors: ATKINSON M. A. , COOPER J. I.
Published: February 2008

In poplar (Populus x euramericana cv. Robusta) infected with poplar mosaic virus, rod‐shaped, virus‐like particles (c. 13 nm in diameter) occurred singly or in loose bundles in the cytoplasm of cells in palisade and mesophyll tissue and in vascular parenchyma. The cell walls had local overgrowths consisting of membranous elements (vesicles and/or tubules) in a loosely fibrillar matrix. Accumulations of endoplasmic reticulum with enlarged cisternae occurred near cell nuclei.

We are indebted to Mr A. G. Mackay, Bryant and May (Forestry Ltd) for supplying the poplar material and we acknowledge technical assistance from Mrs D. McCall. The work was supported financially by the Natural Environment Research Council.
Observations of life‐cycle, population development and vertical distribution of Longidorus macrosoma on raspberry and other crops
Authors: COTTON J.
Published: February 2008

High population densities of Longidorus macrosoma were recorded in the field under raspberry, blackcurrant and cherry, and low densities under grass and alternating spring barley and fallow. Comparison of population development in the field within and between the rows of raspberry and under fallow, suggested that multiplication and development of the nematode was related to the availability of growing host roots, but the nematode was unable to complete its life‐cycle within 1 yr. The nematode was distributed to at least 60 cm depth in association with raspberry. In glasshouse pot tests, the nematode took at least 1 yr to complete its life‐cycle on raspberry and was unable to do so during the period of the experiment on ryegrass and in fallow soil.
Some effects of leaf posture on photosynthesis and yield in wheat
Authors: AUSTIN R. B. , FORD M. A. , EDRICH J. A. , HOOPER B. E.
Published: February 2008

Canopy enclosures were used to study the photosynthesis of two winter wheat genotypes with contrasting leaf posture (E, erect; L, lax). Over the grain filling period, the net carbon dioxide fixation during the daytime was nearly always greater in E than in L. In general, a greater proportion of the fixation took place in the lower leaves of E than L.

Because of the slower senescence of its lower leaves, the leaf area index of E was slightly but consistently higher than that of L and this appeared to account, in part, for the difference between the genotypes in canopy photosynthesis. However, during June and early July, when the leaf area indices were above three, the more uniform distribution of light in the canopy of E than in that of L appeared to be a cause of its higher rate of photosynthesis.

Over the grain filling period, more dry matter was lost from the stems of L than from those of E. It is suggested that the shortfall of assimilate for grain filling was met, at least in part, by translocation of materials from the stems and that their greater depletion in L made up for the lower contribution from current assimilation in this genotype.
Studies on plant growth‐regulating substances. XLIII. 2 ‐Chloro ‐3 ‐phenoxypropionitriles
Authors: KEMP M. S. , RIUS‐ALONSO C. , WAIN R. L.
Published: February 2008

A number of ring substituted 2‐chloro‐3‐phenoxypropionitriles have been prepared and their plant growth‐regulating activity has been assessed in the wheat coleoptile, pea segment and pea curvature tests, and also by spray treatments on tomato and dwarf French bean plants. The activities of these compounds are compared with those of previously studied 2‐chloro‐3‐phenylpropionitriles and the results are discussed in terms of chemical structure/biological activity relationships and mode of action.
Infection of ryegrass plants with ryegrass mosaic virus decreases numbers of the mite vector
Authors: GIBSON R. W.
Published: February 2008

Fewer of the eriophyid mite Abacarus hystrix, vector of ryegrass mosaic virus (RMV), were found on RMV‐infected field plants of Italian ryegrass (Lolium multiflorum cv. S. 22) than on healthy plants. In glasshouse experiments, mites multiplied similarly on healthy and infected plants until disease symptoms developed; afterwards, they did not multiply as rapidly on infected plants and appeared to disperse from them more than from healthy ones, thus encouraging disease spread.
A comparative study of the infection of perennial ryegrass by Fusarium nivale and F. culmorum in sterilized soil
Authors: HOLMES S. J. I.
Published: February 2008

Fusarium nivale and F. culmorum were frequently found in association with damaged perennial ryegrass.

In glasshouse experiments using sterilized soil the pathogenicity of F. nivale isolates varied greatly, but those which were pathogenic reduced seedling emergence and damaged established young plants.

All the F. culmorum isolates tested significantly reduced the emergence of S321 perennial ryegrass seedlings, but none had any effect on the growth of established seedlings.

Combined inoculations with both Fusarium species further reduced seedling emergence but resulted in less damage to established seedlings than was obtained with F. nivale alone.
Chemical suppression of the symptoms of two virus diseases
Authors: TOMLINSON J. A. , FAITHFULL E. M. , WARD C. M.
Published: February 2008

Carbendazim applied at the rate of 2 g per plant to the roots of tobacco (Nicotiana tabacum cv. White Burley) plants before infection with tobacco mosaic virus (TMV) caused very considerable reduction in the severity of disease symptoms in systemically infected leaves but did not affect their virus content. Leaves of untreated, infected plants had a greatly reduced chlorophyll content 100 days after infection whereas the chlorophyll content of leaves of infected plants treated with carbendazim was similar to that of normal uninfected leaves. Carbendazim had no effect on the infectivity of TMV in vitro or on the local lesion reaction of N. glutinosa plants when inoculated with TMV.

Carbendazim was applied to lettuce cv. Cobham Green at a total rate of o‐i g per plant before and after they were infected with beet western yellows virus and the plants were then grown on in the field. At harvest time (50 days after infection) almost all the treated virus‐infected plants were of a normal green appearance, whereas the untreated controls were almost all very severely yellowed and unmarketable.
Studies on the mechanisms of barley seed deterioration
Authors: HARRISON J. G. , PERKT D. A.
Published: February 2008

Decline in vigour and viability of barley seeds during storage at room temperature depended on elapsed time and on seed moisture content and was associated with an increase in fungal contamination. Aspergillus repens, Penicillium cyclopium and Fusarium culmorum each became dominant within certain moisture ranges but other evidence indicated that they were not the primary causes of deterioration.

Respiration rate, dehydrogenase and diastase activities of germinating deteriorated seeds were less than those of non‐deteriorated controls, and the integrity of cell membranes was affected. The principal site of deterioration which affected seedling growth lay in the embryo.
Weed competition in drilled summer cabbage
Authors: ROBERTS H. A. , BOND W. , HEWSON R. T.
Published: February 2008

In four field experiments in different years with summer cabbage drilled in May, naturally‐occurring weed populations of 50–540 plants per m2 reduced the yield of marketable cabbage by 47–100% from that of weed‐free crops. Species composition of the weed population and the rate of emergence and early growth relative to that of the crop were important factors in determining the extent of yield loss. If weeds were removed no later than about 3 wk after 50 % crop emergence and the crop was subsequently kept clean there was no yield loss. If the crop was kept clean without soil disturbance for the first 2 wk or longer, weeds that established after this did not affect yield. There was thus no ‘critical period of weed competition’ and a single weeding 3 wk after 50% crop emergence gave yields similar to those of crops kept weed‐free throughout.
Estimating sib percentages from small samples of F1 hybrid populations
Authors: FREEMAN G. H. , JOHNSON A. G.
Published: February 2008

Plant breeders raising Fx hybrid populations cannot usually grow more than about 300 plants from one seed lot. If not more than k sibs are observed in a random sample of size N, they then need to estimate the probability that the proportion of sibs in the population is at most p. For sample sizes of not more than 300 this note describes the required statistical procedure which, though not new, may be unfamiliar to plant breeders.
South American leaf blight of Hevea brasiliensis: spore dispersal of Microcyclus ulei
Authors: CHEE K. H.
Published: February 2008

Trapping of ascospores and conidia of Microcyclus ulei among young trees of Hevea brasiliensis in Trinidad from May 1973 to May 1975 snowed that ascospores occurred throughout the year whilst conidia were present only during the wet season. Peak ascospore concentrations occurred in August and November during the wet season, the latter peak being more marked and the former coinciding with the period of maximum conidium liberation.

In dry weather the number of ascospores increased during the night to a maximum at 06.00 h, and decreased to a low level during the day. On rainy days heavy ascospore discharge also occurred during the day. Ascospore concentration decreased significantly after dawn on sunny days whilst on overcast days the concentration remained high most of the day. Conidium production was highest around 10.00 h and decreased towards the evening to a low level during the night, reaching a minimum at 07.00 h.
The influence of leaf surface roughness on the spreading of oil spray drops
Authors: BOIZE L. , GUDIN C. , PURDUE G.
Published: February 2008

The effect of surface roughness of leaves on the retention and spreading of oil drops is considered. Three types of roughness have been recognized. Leaf hairs and protruding or recessed veins underlying the cuticle constitute a macroscopic roughness. Microscopic roughness is determined by epidermal cell size and arrangement, which influence the geometry of the grooves between these cells. Ultra‐microscopic roughness is determined by the size, shape and organization of the epicuticular wax system. The effect of environmental conditions on surface roughness is also considered and the significance of the spreading of spray drops is discussed in relation to the application of pesticides.
Ear and flag leaf photosynthesis of awned and awnless Triticum species
Authors: OLUGBEMI L. B. , BINGHAM J. , AUSTIN R. B.
Published: February 2008

The net photosynthetic rates of ears and flag leaves of awned and awnless wheats were measured by infra‐red gas analysis in a controlled environment experiment. At 107 W m‐2 the rates of net photosynthesis of the ears of two awned Triticum aestivum lines were two to three times greater than those of their isogenic awnless counterparts. The net rates of photosynthesis of the flag leaves of all four lines were, however, similar. Net photosynthetic rates of ears of T. durum and T. turgidum, which have much larger awns, were considerably higher than those of T. aestivum. Between 70 and 90% of carbon‐14 assimilated by the flag leaves and by the ears of T. aestivum was translocated to the grains, with no effect of awns in this respect.

In a glasshouse experiment with detached shoots the contributions of the component organs to gross photosynthesis were determined by carbon‐14 labelling. Ears of awnless lines of T. aestivum contributed about 10% to the photosynthesis of the organs above the node of the penultimate leaf and awns increased this to about 18%. Fixation by awned ears of T. durum and T. turgidum was 21–29% and of this 78–86% was contributed by the awns. In both experiments the contribution of the flag leaf to shoot photosynthesis was greater in T. aestivum than in the other species.
The influence of climate on the incidence and severity of some tropical crop diseases
Authors: Waller J. M.
Published: February 2008

Agriculture in tropical countries produces many of the world's most valuable crops, but productivity is limited by a multiplicity of different diseases, many of which have been inadequately studied. Certain characteristics of tropical climates have a fundamental influence on the incidence and severity of many of these diseases. The main seasonal variations which control crop growth and disease epidemiology depend on differences in moisture availability rather than daylength and temperature differences. Marked dry seasons hinder the survival of many pathogens outside hosts unless they can produce drought‐resistant spores. In many tropical areas continuous cropping throughout the year is possible, enabling disease epidemics to continue without interruption over long periods.

Much agriculture in the tropics is at fairly high altitudes enabling temperate crops to be grown, but low temperatures may present special disease hazards. Violent storms are a feature of many tropical climates and have been implicated in the spread of many bacterial diseases. Drought is a factor which influences the severity of many root diseases. The various effects which moisture, as rain or dew, temperature and cropping cycle can have are illustrated by discussion of sigatoka disease of bananas (Mycosphaerella musicola Leach), South American leaf blight of rubber (Microcyclus ulei (R. Henn.) Arx) and coffee berry disease (Colletotrichum coffeanum Noack).
Sources and inheritance of resistance to downy mildew of the pea, Peronospora pisi
Authors: Matthews P. , Dow K. P.
Published: February 2008

Six hundred and one lines from the John Innes Pisum germplasm collection were surveyed for resistance to downy mildew (Peronospora pisi). Potential sources of resistance were identified in forty‐seven lines. Using the inoculation methods described resistant varieties/lines showed no evidence of infection.

Isolates from recent outbreaks in the United Kingdom when screened against a representative test array of resistant and susceptible lines showed no evidence for a race structure in Peronospora pisi, although differences were found in overall virulence.

The inheritance of resistance was studied in F2 and F3 families. Under the test conditions adopted the results obtained suggest that resistance may either be determined by a single dominant gene or by two recessive genes, but the lack of concordance between F2 and F3 segregation patterns was a disturbing feature despite careful control of experimental conditions. This, coupled with difficulties in obtaining large F3 families presents considerable problems in interpretation.

It is proposed that inbred lines of JI 411 Cobri and JI 399 Cennia be adopted as standards.
Distribution of trichodorid nematodes in Great Britain
Authors: ALPHEY T. J. W. , BOAG B.
Published: February 2008

This survey describes the distribution of trichodorid nematodes in Great Britain. Twelve species were recorded, including the newly described species Trichodorus hooperi Loof, 1973 and the first British record of T. sparsus Szczygiel, 1968. In the survey 3614 samples and records were analysed using the Statistical Package for Social Sciences computer programme. Seven hundred and ninety‐two positive sites, containing 971 trichodorid populations, were located. Outline maps show the geographical distribution of each species. T. primitivus de Man, 1880 was the most commonly found species and had a cosmopolitan distribution. Paratrichodorus pachy‐dermus Seinhorst, 1954 was the next most prevalent and occurred mostly in eastern England and Scotland. Populations of the other ten species were more restricted in both number and distribution. The distribution of trichodorid spp. with respect to altitude, soil type, pH and primary vegetation was tested using chi‐squared contingency tests. A significant relationship between nematodes and environmental factors was found in all cases examined. However, interactions were found between several environmental factors and further tests were applied to study the independence of the species distributions with respect to these interactions.
Synchronization of germination of celery seeds
Authors: SALTER P. J. , DARBY R. J.
Published: February 2008

The effects of osmotic pre‐treatments on the germination response of celery seeds were studied in a series of experiments designed to optimize that treatment. The experimental variables were different osmotica (polyethylene glycol (PEG) or a mixture of potassium nitrate and tri‐potassium orthophosphate), levels of osmotic potential, temperature and duration of treatment. The rate and synchronization of germination were very significantly improved by many of these pre‐treatments but the maximum effects on cv. Lathom Blanching were obtained by treating the seeds with a solution of the salt mixture of c.–10 bars potential at 15 °C for 21 days. This treatment resulted in 50 % germination of the viable seeds within 1–4 days at a temperature of 20 °C compared with 13‐7 days from the untreated seeds. There were indications that the optimum pre‐treatment may vary somewhat between varieties and seed stocks. The results showed that the effects of the two osmotica on germination response were similar, thus enabling a technique to be developed for treating, with the salt solution, larger quantities of seed and germinating them prior to fluid drilling in the field.
Selection of perennial and Italian ryegrass plants resistant to ryegrass mosaic virus
Authors: GIBSON R. W. , HEARD A. J.
Published: February 2008

Perennial ryegrass plants collected from fields and Italian ryegrass plants grown from seed were selected for resistance to infection by ryegrass mosaic virus (RMV) by repeated manual inoculation. Two of 108 perennial ryegrass plants and one of 150 Italian ryegrass plants were symptomless after seven and nine inoculations respectively. These three plants were propagated vegetatively. Plants of the two perennial ryegrass clones showed no symptoms after further manual inoculations with the initial isolate of RMV, or with an inoculum from infected plants collected from several fields, or after inoculation by viruliferous mites. Electron microscopy and back tests indicated that the plants were virus free.

Some plants of the selected Italian ryegrass clone became infected after a further inoculation with mites or sap, but fewer than similarly inoculated unselected plants.