bluuebunny/crossref_metadata_2025 huggingface dataset:
The effectiveness of traps used currently for monitoring populations of the cabbage root fly (Delia radicum)
Authors: FINCH S.
Published: February 2008

Six different types of traps were compared for capturing adults of Delia radicum. Cone traps caught so few flies that it seems inadvisable for them to be used for monitoring populations of this pest. All the other traps tested were suitable for monitoring D. radicum populations. When expressed on a trap for trap basis, the large 1800 cm2 Canadian traps caught most flies. When expressed as the numbers of flies caughthnit area of trapping surface, most flies were caught in the water traps. Similar numbers of D. radicum, D. platura, syrphids, blowflies and a tachinid, Eriothrix rufomaculatus were caught per unit area on each of three different vertical sticky traps. Although water traps have the advantage that they catch about 5 times as many females D. radicum/unit area as the most effective vertical sticky traps of a comparable size, their disadvantage is that they catch about 10 times as many beneficial syrphids. The reasons why water traps are so effective against D. radicum are discussed, with details of how to convert water‐trap data to sticky‐trap equivalents, and vice versa.
New approaches for restricting spread of potato leafroll virus by different methods of eradicating infected plants from potato crops
Authors: WOODFORD J. A. T. , GORDON S. C.
Published: February 2008

Experiments were made at Invergowrie in 1984 and 1985 to compare the spread of potato leafroll virus (PLRV) after removing infected plants by three different methods; conventional roguing, desiccation with diquat, or incineration for 45–60s using a propane gas flame. Potato leaf roll ‘infector’ plants, grown in plots of virus‐free Maris Piper seed potatoes, were artificially infested in June with aphids (Myzus persicae) from a laboratory culture, and removed from the plots after 2 or 3 wk. In both years, natural infestations of potato aphids were scarce during this period. There was no significant difference in the proportion of tubers infected with PLRV in adjacent plants after the neighbouring infector plants had been rogued by hand or desiccated with diquat, but the proportion was considerably reduced following incineration of the infector plants. In 1984, the spread of PLRV in conventionally rogued plots was also significantly reduced by a mixture of deltamethrin plus heptenophos, applied four times from 80% crop emergence, and was almost eliminated by a treatment with aldicarb granules, either at planting, or as a side‐dressing 5 wk later. In 1985, delaying infector removal by 8 days in early July significantly increased the spread of PLRV to neighbouring plants from 2.3% (1 July) to 8.3% (9 July). A single application of deltamethrin plus heptenophos to infectors 1 wk before removal did not significantly decrease spread. Although incineration was quick and effective, the value of this method of eradicating infector plants in seed potato crops is limited because it failed to destroy infected tubers.
The effect of heat treatment and meristem‐tip culture on June Yellows in strawberry
Authors: WATKINS C. A. , McNICOL R. J. , YOUNG K. , JONES A. T.
Published: February 2008

Because there is some evidence that June Yellows (JY) of strawberry may be caused by a pathogenic agent, combinations of heat treatment and meristem‐tip culture that are known to eliminate some viruses from tissues were used in attempts to cure affected Cambridge Favourite strawberry plants from JY. None of 397 propagants derived from JY‐affected plants subjected to various combinations of these treatments were freed from JY. Indeed, all propagants showed more obvious JY symptoms than the parent plants from which they were derived, suggesting that such treatments may be useful for detecting incipient JY in symptomless strawberry stocks.
Distribution of velvet tobacco mottle virus in its mirid vector and its relationship to transmissibility
Authors: GIBB KAREN S. , RANDLES J. W.
Published: February 2008

Following acquisition by feeding, velvet tobacco mottle virus (VTMoV) was detected in the gut, haemolymph and faeces of the mirid vector, Cyrtopeltis nicotianae, but not in the salivary glands. Virus antigen was detected in the gut and haemolymph for up to nine days following acquisition. Infective virus was detected in the secretions and excretions of the mirids immediately after acquisition and was also detected in the faeces of nymphs after six days. Insoluble nigrosin dye was eliminated intermittently from the gut up to six days after ingestion, in a manner similar to the loss of virus infectivity. Non‐infective mirids were able to inoculate plants from infectious sap deposits on the upper epidermis. An ingestion‐defecation model of insect transmission in which the salivary glands are not implicated is proposed as one explanation for the persistence of transmission in this mirid‐virus association.
Characterisation of a new strain of tobacco necrosis virus isolated from nutrient feeding solution*
Authors: ADAM G. , WINTER S. , LESEMANN D.‐E.
Published: February 2008

A virus, isolated from the nutrient feeding solution of a bell pepper culture in a glasshouse, was characterised as a new serotype of tobacco necrosis necrovirus (TNV) and named TNV‐nft. The virus was monopartite and contained a single RNA species and a single coat protein with molecular weights of 1.45± 106 and 2.9 ± 104 daltons, respectively. The particle had an apparent sedimentation coefficient of 110 S and a density of 1.37 g/cm3 in cesium chloride. In decoration tests antiserum prepared against TNV‐nft reacted most strongly with the TNV strains Kassanis A and B, but at lower dilutions it also reacted with all other TNV‐serotypes available. In Ouchterlony tests spur formation occurred with TNV strains Kassanis A and B, indicating that the TNV‐nft strain was serologically distinct. The isolate was not associated with a satellite virus. Cloned cDNA prepared against viral RNA reacted exclusively with the viral RNA band in Northern blots.
Sources of variation in firmness and ester content of ‘Cox’ apples stored in 2% oxygen
Authors: KNEE M. , HATFIELD S. G. S. , FARMAN D.
Published: February 2008

The contribution of various factors to variation in the quality of ‘Cox’ apples after storage in 2% oxygen at 3.3°C was investigated. Within one season variation in the firmness of fruits from different orchards could be largely accounted for by correlations with firmness at harvest and the position of the fruit on the climacteric at the time of harvest. However, different relationships were found between these variables in different seasons. The butyl and hexyl acetate contents of fruit were influenced by season and source of fruit, but little affected by maturity at harvest. Ester content was inversely correlated with fruit firmness after storage. Other factors which were expected to influence the ripening of fruit during storage were found to be unrelated to firmness and ester content. These included the respiration rate of fruit during storage, the resistance of the fruit to gaseous diffusion and its specific gravity. Carbon dioxide production was nearly constant at about 2.3 ml kg‐1h‐1 across seasons, sources and harvest dates. Specific gravity seemed to be particularly affected by season, whereas diffusive resistance decreased with maturity.
Screening for fire blight resistance in apple (Malus pumila) using excised leaf assays from in vitro and in vivo grown material
Authors: DONOVAN ANNE
Published: February 2008

The apple cultivars Greensleeves and Novole and somaclones derived from Greensleeves were tested for resistance to fire blight (Erwinia amylovora) using excised leaf bioassays. Cv. Greensleeves was consistently susceptible to fire blight in in vitro, and in glasshouse and excised leaf bioassays whilst cv. Novole was resistant. Greensleeves somaclones, identified as having intermediate levels of fire blight resistance in glasshouse and in vitro screening tests, also showed intermediate levels of resistance in excised leaf bioassays. The length of leaves and the inoculum concentration employed affected the severity of symptoms observed. Excised leaf bioassays were unsuitable as tests for fire blight resistance using field grown material.
Effects of rotation length, fungicide treatment of seed tubers and nematicide on diseases and the quality of potato tubers
Authors: HIDE G. A. , READ P. J.
Published: February 2008

In 1982 – 88, potatoes were grown in 2‐, 4‐ and 6‐course rotations with spring barley on a field infested with Globodera rostochiensis. Severity of stem canker and black scurf increased with increasing frequency of previous potato crops, and seed tuber treatment with tolclofos‐methyl became less effective in controlling diseases. This suggested that previous crops had increased the amounts of soil‐borne inoculum of Rhizoctonia solani. Oxamyl soil treatment increased stem canker in one year and decreased black scurf in four years.

Seed tuber treatment with imazalil or prochloraz decreased stem base infection by Polyscytalum pustulans and skin spot and silver scurf on tubers. Black dot was prevalent on tubers in all years and was not affected by seed tuber treatment or previous cropping. Oxamyl increased black dot and common scab in five years and decreased % tuber dry matter in six years.

Cysts of G. rostochiensis were found attached to Désirée but not to Maris Piper tubers in August. At harvest tubers of both cultivars were affected by superficial pitting and its severity was related to soil populations of G. rostochiensis at planting. This damage was controlled by oxamyl. It is suggested that the pitting developed from holes made in the tuber skin at larval invasion.

In 1989, Désirée seed tubers and healthy mini tubers were planted in all plots and severity of stem canker and black scurf increased with increasing proximity of previous potato crops and with the number of previous crops. Black dot on stems and tubers was not affected by previous cropping but was much less severe in a plot that had not grown potatoes during the seven years of the experiment. The severity of common scab generally decreased as the number of preceding potato crops increased.
The use of antibiotics to eliminate latent bacterial contamination in potato tissue cultures
Authors: GILBERT JULIE E. , SHOHET S. , CALIGARI P. D. S.
Published: February 2008

A simple leaf bioassay was developed to screen for slow‐growing latent bacteria found in potato nodal cuttings. The potato cultures were established to provide a source of sterile leaf tissue for protoplast isolation and the bacteria were only detected after numerous generations in culture. In an attempt to solve this problem cultures were screened before and after various treatments. Two antibiotic mixtures were tested for their efficacy in eliminating bacteria: ABM1 contained penicillin, streptomycin, amphotericin and NaCl while ABM2 contained erythromycin, streptomycin and carbenicillin at various concentrations. Both cocktails, when added to the micropropagation medium, reduced plant growth, induced chlorosis at higher levels and did not eliminate contamination. In terms of protoplast isolation, the only effective treatment was when ABM1 was incorporated into the plasmolysis and enzyme media. It removed contamination at all levels tested and had a differential effect on cell division such that, at low levels of ABM1, protoplasts regenerated successfully.
Study on the factors affecting storage of edible aroids
Authors: AGBOR‐EGBE TOM , RICKARD JUNE E.
Published: February 2008

The effects of temperature (15 °C, 25 °C, 30°C and 24–29°C), relative humidity (45%, 85% and 86–98%) and harvest maturity on the storage behaviour of cormels of the edible aroid species Colocasia esculenta and Xanthosoma sagittifolium were studied. The changes monitored were respiration rates, weight losses, incidence of decay and sprouting. Post‐harvest losses that occurred during storage were influenced by the storage conditions, the state of maturity at harvest and the morphological characteristics of the cormels. When stored under high temperature and humidity more sprouting and decay occurred with C. esculenta cormels than with X. sagittifolium cormels. Less sprouting and decay occurred with Colocasia cormels at high temperature and low humidity than at high temperature and high humidity but higher weight losses were recorded. Wound pathogens were the major cause of post‐harvest deterioration in Colocasia cormels and the causal pathogen of cormel decay was Sclerotium rolfsii.

Under conditions of low temperature (15 °C) and high humidity (85%), cormels of both C. esculenta and X. sagittifolium were successfully stored for periods of 5–6 weeks. Similar storage periods were also possible under tropical ambient conditions with the Xanthosoma cultivars used in these experiments. Under the same storage conditions up to 60% decay occurred in the Colocasia cormels indicating the need for post‐harvest fungicide treatment.
Impact of the field slug Deroceras reticulatum on establishment of ryegrass and white clover in mixed swards
Authors: GLEN D. M. , CUERDEN R. , BUTLER R. C.
Published: February 2008

The relationship between numbers of Deroceras reticulatum and the establishment of ryegrass cv. Melle and white clover cv. Milkanova was studied on a mini‐plot experiment. Assessments 12 and 33 days after sowing showed that Deroceras reticulatum had a proportionally greater impact on survival and growth of clover than on ryegrass. Slugs had no apparent effect on numbers or growth of three species of broad‐leaved weeds (Senecio vulgaris, Cardamine hirsuta and Epilobium sp.) which occurred in the field experiment. In pot experiments where seedlings of ryegrass together with one of three clover cultivars, with or without chickweed (Stellaria media), were exposed to Deroceras reticulatum, seedlings of white clover cv. Aran were less affected by slug grazing than cvs S184 or Milkanova. The presence of different clover cultivars did not significantly influence the impact of slugs on growth of ryegrass or chickweed, nor did the presence or absence of chickweed influence the effect of slugs on ryegrass and clover seedlings. Slugs had less impact on the growth of chickweed than on ryegrass or clover. Thus slug grazing would make clover less able to compete with chickweed as well as the other weeds found in the mini‐plot experiment.
A non‐destructive determination of leaf chlorophyll in Vitis vinifera
Authors: FANIZZA G. , GATTA C. DELLA , BAGNULO C.
Published: February 2008

A portable leaf greenness meter (SPAD‐501) has been used to provide a rapid and non‐destructive measurement of leaf chlorophyll in Vitis vinifera. Leaf extracted chlorophyll was related linearly to SPAD readings. It is suggested that separate linear equations should be developed for each cultivar so as to maximise the accuracy of estimating leaf chlorophyll content as a function of SPAD readings.
The influence of intercropping with Allium on some insect populations in potato (Solatium tuberosum)
Authors: POTTS MICHAEL J. , GUNADI NIKARDI
Published: February 2008

Two field experiments were conducted in West Java, Indonesia to investigate the effects on insect populations in a potato crop of intercropping with Allium cepa or A. sativum. Intercropping reduced populations of Myzus persicae, Aphis gossypii and Empoasca spp. when less than 0.75 m separated the potato plants and Allium spp. Leaf damage to potato by Henosepilachna sparsa was also reduced at this spacing; but populations of Thrips palmi or T. parvispinus were increased. The implications of these trends are noted.
Effects of Aphis fabae and Uromyces viciae‐favae on the growth of a susceptible and an aphid resistant cultivar of Vicia faba
Authors: PRÜTER C. , ZEBITZ C. P. W.
Published: February 2008

Damaging effects of either black bean aphid (Aphis fabae), broad bean rust (Uromyces viciae‐fabae), or the combination of both were investigated on a susceptible (cv. Diana) and an aphid resistant (cv. Bolero) cultivar of Vicia faba. When compared with rust, aphids caused greater reductions of root dry weight, shoot dry weight, leaf area, and mean relative growth rate. The mean unit leaf rate was also reduced whereas the leaf area ratio was not affected. The damage caused per aphid was highest on the susceptible cultivar. Rust induced damage did not differ between the cultivars. Concomitant infestation with both pests only resulted in additive damage. The population development of aphids was delayed on partially resistant plants. High temperature and rust infection reduced the total number of aphids the plants were able to support but not the level of resistance. Thus the specific damaging effect per aphid was increased.
Losses in productivity of subterranean clover swards caused by sowing cucumber mosaic virus‐infected seed
Authors: JONES R. A. C.
Published: February 2008

Field trials were done in 1988 ‐ 89 at two sites to examine the effects of sowing seed stocks in which a low proportion (1.6–7.0%) of the seed was carrying cucumber mosaic virus (CMV) infection (= infected seed) and the subsequent CM V spread that results, on the productivity of swards of subterranean clover cvs Esperance, Green Range and Karridale. Except in irrigated plots of cv. Green Range, a variable proportion of the CMV‐infected seedlings always failed to establish, so sowing infected seed normally resulted in plots containing fewer or far fewer seed‐infected plants than expected. The rate of virus spread by aphids was faster and resulted in more extensive infection at maturity when the plots contained more seed‐infected source plants. In two irrigated trials at South Perth, in which healthy and infected seed of cvs Esperance and Green Range was sown, CMV spread was extensive. When the plots were left undefoliated, herbage dry wt yields were decreased by 12 – 30% and seed yields by 53 – 64% due to infection. When they were mown, the herbage dry wt losses recorded were 17 – 24%. In three trials at Mt Barker sown with healthy and infected seed, extensive spread of CMV occurred with cv. Green Range but not with cvs Esperance and Karridale. With cv. Green Range, losses of 25 – 28% in herbage dry wt were recorded inside CMV‐affected patches in mown or grazed plots, while losses were up to 13% when herbage was sampled at random. Seed yield losses were 40–42% and 53% in infected mown and undefoliated cv. Green Range plots, respectively. In the mown or grazed plots of cvs Esperance and Karridale, herbage dry wt losses recorded were up to 7% while seed yield losses were 9 – 16% in mown and 9% in undefoliated plots.

The mean wt/seed of seed harvested from mown plots of cvs Green Range and Karridale sown with infected seed was 8–12% less than that of seed from mown control plots. CMV was detected in seed harvested from undefoliated cv. Green Range plots and mown plots of cvs Green Range and Karridale sown with infected seed but levels of seed infection with the mown plots were 3–5 times less than in the seed sown.

Field trials were done at two sites in 1987 – 90 to examine the persistence of CMV in subterranean clover swards. CMV infection was established in 1987 and the plots were grazed in subsequent years. At Badgingarra, infection gradually decreased with little CMV being recovered by 1990. At Mt Barker, recovery of CMV was relatively poor in 1988 and even poorer in 1989, but there was some resurgence of CMV infection in 1990.
The use of monoclonal antibodies to detect beet mild yellowing virus and beet western yellows virus in aphids
Authors: SMITH H. G. , STEVENS M. , HALLSWORTH P. B.
Published: February 2008

Information on infectivity of the aphids which invade sugar beet root crops each Spring is required for forecasting incidence and providing advice on control of virus yellows. Monoclonal antibodies, produced in the USA to barley yellow dwarf virus (BYDV) and in Canada to beet western yellows virus (BWYV), were used to distinguish between sugar‐beet‐infecting strains of the luteovirus beet mild yellowing virus (BMYV), and the non‐beet‐infecting strains of the closely‐related BWYV in plant and aphid tissue. Totals of 773 immigrant winged Myzuspersicae and 124 Macrosiphum euphorbiae were caught in water traps in a crop of sugar beet between 25 April and 5 August 1990. Using the monoclonal antibodies and an amplified ELISA, 67%M. persicae and 19%M. euphorbiae were shown to contain BWYV; 8%M. persicae and 7%M. euphorbiae contained BMYV. In studies with live winged aphids collected from the same sugar beet field during May, 25 of 60 M. persicae and two of 13 M. euphorbiae transmitted BWYV to the indicator host plant Montia perfoliata; two M. persicae and two M. euphorbiae transmitted BMYV. In another study three of 65 M. persicae and one of three M. euphorbiae in which only BWYV was detected, transmitted this virus to sugar beet.
A screening technique to evaluate pigeonpea for resistance to Rotylenchulus reniformis*
Authors: SHARMA S. B. , ASHOKKUMAR P.
Published: February 2008

Rotylenchulus reniformis is one of the most important nematode pests of pigeonpea. A simple greenhouse technique has been developed to aid evaluation of pigeonpea genotypes for resistance to R. reniformis. In greenhouse pot experiments, eggsacs of R. reniformis in pigeonpea (cv. ICPL 87) roots were counted by eye and with the aid of a stereoscopic microscope at 15, 30 and 45 days after seedling emergence in soils infested with various numbers of vermiform R. reniformis. Seedlings were rated for the number of eggsacs per root system on a one (no eggsacs) to nine (more than 50 eggsacs) scale. Eggsac ratings were more uniform when roots were evaluated at 30 – 45 days than at 15 days and an inoculum of 15 to 30 individuals/cm3 soil also helped reduce variability. Eggsacs were not easily visible without the aid of a stereoscopic microscope. Of the 14 stains tested, exposure of nematode‐infected roots to 0.25% trypan blue for three min was effective in staining the eggsacs blue without staining the roots. Using the stain, the assessment of infestation by R. reniformis was equally accurate with or without the aid of a stereoscopic microscope. Exposure of eggsacs to trypan blue enhanced the emergence of juveniles from the eggsacs.
The hybridisation of somatically chromosome‐doubled dihaploid potatoes with tetraploid cultivars and the use of doubled dihaploids in genetic analysis of Solatium tuberosum
Authors: De M. J. , FLEMING M. L. M. H.
Published: February 2008

Three doubled dihaploid potatoes were hybridised with six tetraploid cultivars and the offspring examined for commercially important characters. Doubled dihaploids used as parents did not reduce the within progeny phenotypic variation for most characters below that found in material produced by intercrossing heterozygous tetraploids. They could however prove useful for improving some characters in a breeding programme.

The products of the hybridisations were used to examine the genetic control of discrete variables such as tuber skin pigmentation, tuber flesh colour, and skin russetting. Doubled dihaploids were found to be useful for such studies because they have only three out of the five possible tetraploid genotypes. Presence or absence of red tuber skin in the progenies of cv. Désirée was concluded to be due to the segregation of a dominant major gene which was simplex in the parental cultivar. The yellow flesh of Desiree was found to be recessive. On the hypothesis that russet skin was due to three complementary dominant genes, possible genotypes of the doubled dihaploids and cultivars could also be deduced.
Development of carrot inbreds with resistance to carrot fly using a single seed descent programme
Authors: ELLIS P. R. , SAW PAMELA L. , CROWTHER T. C.
Published: February 2008

Two carrot cultivars, ‘Sytan’ and ‘Long Chantenay’, representing commercially important carrot types and selected for their partial resistance to the carrot fly (Psila rosae) were crossed as the basis for a single seed descent programme. The resulting F1 progeny were mass pollinated to produce an F2 generation and approximately 2000 plants were raised from this segregating family in the glasshouse in 1981. By careful choice of sowing date and glasshouse temperatures it was possible to stimulate the plants to flower within 10 months. Individual king umbels were enclosed within bags and pollinated with blowflies. Resulting seed was sown in pots in the following August and the process of seed production repeated in a 12 month cycle. Each inbred line was selfed in this way over three generations until the F5 stage. Stocks of seed were then multiplied. A total of 753 inbreds were produced by 1987. The vigour of each inbred was evaluated in glasshouse tests and the level of chlorogenic acid was determined by a fluorescence technique. The most vigorous lines with the lowest levels of chlorogenic acid were tested in field experiments against carrot fly at Wellesbourne. Nine inbreds with promising agronomic quality and moderate resistance to carrot fly were selected and seeded. These nine lines were submitted to seed companies with the aim of developing new cultivars of carrot.
Effects of straw disposal and tillage on spread of barley yellow dwarf virus in winter barley
Authors: KENDALL D. A. , CHINN N. E. , SMITH B. D. , TIDBOALD C. , WINSTONE L. , WESTERN N. M.
Published: February 2008

The effects of straw baling or incorporation, combined with ploughing, non‐inversion tillage, or direct drilling on the incidence of barley yellow dwarf virus (BYDV), were investigated in plots of winter barley. Virus infection was more prevalent after ploughing (> 40% of the plot area damaged) than after non‐inversion tillage (9 – 24%) or direct drilling (< 3%). For each cultivation method, more infection was associated with straw baling than with straw incorporation. There was a strong negative correlation between plot yields and the incidence of BYDV(r= ‐0.87).

Monthly pitfall sampling of non‐specific aphid predators showed that the population activity of several taxa (e.g. Linyphiidae, and the larger species of adult and larval Carabidae and Staphylinidae) declined for a short period in autumn‐winter following cultivation. The overall treatment‐ranking for numbers of predators in autumn (direct drilled > non‐inversion > ploughed) was the opposite of subsequent virus infection. The possible roles of aphid predators and other biological mechanisms in determining the observed effects on BYDV, are briefly discussed.
The effects of nitrogen and fungicide on cereal aphid population development and the consequences for the aphid‐yield relationship in winter wheat
Authors: ZHOU X. , CARTER NICK
Published: February 2008

In a field trial, done over two seasons, nitrogen and fungicide inputs to winter wheat were varied to obtain a range of yields to study the effects on aphid population development and the aphid‐yield loss relationship. In the first year, the maximum density of Metopolophium dirhodum and total aphid index were significantly higher in the plots receiving the largest amount of nitrogen but there were few other consistent effects on aphid population development. In the second year there were no significant effects of either nitrogen or fungicide on aphid population development. Mean yields were high in 1987 and 1988 (7.0 and 8.5 t/ha respectively) with less than a 2 t/ha range in either year. There were no significant effects of aphids on yield in the first year but in the second, aphids caused a significant reduction. Damage per aphid unit did not change with increase in yield. The use of this approach in determining pest‐yield loss relationships is discussed.
Further evidence that resistance in raspberry to the virus vector aphid, Amphorophora idaei, is related to the chemical composition of the leaf surface
Authors: ROBERTSON G. W. , GRIFFITHS D. W. , BIRCH A. N. E. , JONES A. T. , McNICOL J. W. , HALL JOANNE E.
Published: February 2008

In an approach to understand the mechanism(s) of resistance in raspberry to infestation by the aphid Amphorophora idaei, progeny plants segregating for the A. idaei resistance gene, A10, were bioassayed and dichloromethane extracts from the leaf surface were examined by capillary column gas chromatography (GC). No single GC peak was detected that was present in only the resistant progeny plants. Nevertheless, thirteen compounds present in all samples were quantified and identified by mass spectrometry. They were of four major classes; straight chain hydrocarbons, acetic acid esters of long chain alcohols, tocopherols and triterpenoid compounds, including α and β amyrin. Several of these compounds were not recorded previously in raspberry leaves. Linear discriminant analysis, applied to the standardised chromatographic data in an attempt to relate chemical composition to resistance, successfully partitioned 24 of the 26 plants into resistant and susceptible types as determined by bioassay. These data provide further evidence that resistance in raspberry to A. idaei is related to the chemical composition of the leaf surface.
Selection for resistance to clubroot (Plasmodiophora brassicae) in marrowstem kale (Brassica oleracea var. acephala L.)
Authors: BRADSHAW J.E. , WILLIAMSON CYNTHIA J.
Published: February 2008

Ninety‐six cultivars of Brassica oleracea were screened for clubroot resistance in a seedling test using two populations of Plasmodiophora brassicae. The most resistant cultivars were kales. Sixteen resistant marrowstem kale cultivars of diverse geographical origin were used to start a selection programme for clubroot resistance. Four generations of selection, involving single plants, half‐sib and full‐sib families, reduced a disease index averaged over six clubroot populations from 41.2 to 12.5. This was lower than the most resistant cultivar in the original population, cv. Mixti 28.8, and as good as a German landrace of cabbage noted for its resistance, Bohmerwaldkohl 10.5. In comparison, the mean of five kale controls, cvs Bittern, Canson, Condor, Kestrel and Merlin, was 61.1 and the value for the most susceptible control, cabbage cv. Septa, was 89.3.

In the final assessment, there were no clubroot population x B. oleracea genotype interactions and in the initial assessment of cultivars there were only small interactions which could be removed by an angular transformation of the data. It was concluded that a high level of non‐differential resistance had been achieved and that it may prove durable. It was also concluded from a small field trial that this level of resistance would prevent serious yield losses in practice.
Thermal time assessment of suitable areas for navy bean (Phaseolus vulgaris) production in the UK
Authors: DODD M.
Published: February 2008

In field trials at eight sites throughout the UK the mean thermal time requirement for navy beans from sowing to harvest for a standard cultivar, Marcus, was 2069 Ontario Heat Units (OHU). Low level plastic covers increased the range of warm environments at one site and gave a mean thermal time required of 2098 OHU.

Analysis of daily air temperatures from six weather stations throughout the UK over a 29 year period, showed a 14 day possible planting period on the south coast of England, but gave a high probability of crop failure in Scotland.

Maps of England and Wales indicating the probability of achieving 2000 OHU were produced from 5 km grid point temperatures. Less than 2% of the land had more than a 60% chance of receiving 2000 OHU under the present climate, however this area increased to 70% with a mean temperature rise of 1.5°C. Although 2000 OHU is often used as the thermal time requirement of navy beans, these trials showed that it may be more accurate to use the higher figure of 2087 OHU from sowing to harvest, and restrict the use of 2000 OHU to the period between emergence and harvest. When the map was redrawn using 2087 OHU and current climate, no parts of England and Wales showed a reasonable chance of growing the present cultivars of navy beans.
Studies on the patterns of nitrogen uptake and translocation to the grain of winter barley intended for malting
Authors: CARRECK N. L. , CHRISTIAN D. G.
Published: February 2008

In five experiments carried out between 1987 and 1989, crops of winter barley were grown under a range of agronomic treatments to study the way the treatments influenced the patterns of nitrogen uptake, dry matter production, translocation of assimilates and malting quality.

Rate and timing of nitrogen fertiliser had large effects. Increased and late applications invariably increased nitrogen concentration in the grain by affecting the partitioning of nitrogen between the vegetative and reproductive parts of the plant. Foliar fungal diseases also affected nitrogen partitioning, apparently by interfering with the transport of stored nitrogen to the developing grain.

Seasonal influences, especially rainfall during the grain filling period, were found to have profound effects on the pattern of change in ear and grain nitrogen concentration, and hence malting quality. The ability to predict final grain nitrogen concentration from measurements made earlier in the season is not therefore likely to be feasible.
A computer‐based advisory system for cereal aphids‐field‐testing the model
Authors: MANN B. P. , WRATTEN S. D.
Published: February 2008

A previously developed computer‐based interactive model which can aid farmers in the control of summer aphids on winter wheat was tested in field trials carried out from 1985 to 1988. These trials showed that the model performed very well when compared with other popular types of advice available. Economic comparison of the model with current and previous ADAS advice showed that the model performed as well or better. It also had the advantage that it used the economics of the situation, as well as the size of the pest population, in calculating advice.
Disease in wheat genotypes naturally infected with Gaeumannomyces graminis var. tritici
Authors: PENROSE L. D. J.
Published: February 2008

Wheat genotypes consisting of seven homozygous lines and 40 segregate families were studied at two sites naturally infested with the take‐all pathogen, Gaeumannomyces graminis var. tritici. The numbers of seminal and coronal roots infected with G. graminis and other root pathogens were recorded. The genotypes differed in infection with G. graminis, with little evidence of genotype × environment interactions. The incidence of G. graminis and Rhizoctonia solani was negatively associated, but the association did not greatly influence differences between wheats in infection with G. graminis. The distribution of R. solani was negatively associated with the severity of take‐all at only one site. Of symptoms of infection with G. graminis, wheat genotypes differed most in incidence of deadheads, but differences were not consistent over environments, and were associated with earliness of maturity. Wheats differed more in expression of disease than in infection with G. graminis.

The course of disease was deduced from associations between the incidence of pathogens and components of plant growth and yield. G. graminis was the dominant pathogen at both sites, and caused a yield loss of 0–15% at one site, and an average 62% loss at the other. More components of yield were affected where disease was most severe.
A variant of the satellite RNA of groundnut rosette virus that induces brilliant yellow blotch mosaic symptoms in Nicotiana benthamiana
Authors: KUMAR I. K. , MURANT A. F. , ROBINSON D. J.
Published: February 2008

Some Malawian cultures of groundnut rosette virus (GRV) give rise to variants that, although still causing symptoms of the chlorotic type of rosette in groundnut, induce brilliant yellow blotch mosaic symptoms, instead of the usual veinal chlorosis and mild mottle, in Nicotiana benthamiana. One such isolate (YB) induced the formation in infected plants of a 0.9 kbp dsRNA having extensive sequence homology with molecules of similar size in other naturally occurring isolates of GRV. These dsRNA molecules were shown to be double‐stranded forms of single‐stranded satellite RNA molecules. Experiments in which the satellite was removed from and restored to isolate YB, or exchanged with those from other GRV isolates, showed that it carries the determinant for yellow blotch mosaic symptoms. Plants inoculated with the 0.9 kbp dsRNA (denatured or undenatured) developed yellow blotch mosaic even when the satellite‐free GRV helper was not inoculated until 11 days later. The satellite RNA is therefore a very stable molecule. Prior infection of N. benthamiana with a GRV isolate containing a normal form of the satellite protected against expression of yellow blotch mosaic symptoms when the plants were later inoculated with isolate YB, whereas prior infection with satellite‐free isolates did not. This provides a simple method of determining whether a GRV isolate has an associated satellite RNA. The YB satellite seems to be a newly recognised variant additional to those known to cause the chlorotic, green and other forms of groundnut rosette disease.
Purification and some properties of strawberry mottle virus
Authors: YOSHIKAWA N. , CONVERSE R. H.
Published: February 2008

Strawberry mottle virus (SMoV) (three isolates: HJ, 3E and N) were transmitted to Chenopodium quinoa plants by sap inoculation. All three isolates induced very similar symptoms consisting of chlorotic spots and ringspots in inoculated leaves, and vein chlorosis, mottling, and dwarfing of the upper leaves. SMoV isolate HJ was purified from infected C. quinoa by homogenisation with 10 mM phosphate buffer, pH 7.2 containing 5% Triton X‐100, followed by differential, sucrose density‐gradient and CsCl equilibrium density‐gradient centrifugations. A fraction with a buoyant density of 1.42g‐ cm‐3 after CsCl density‐gradient centrifugation was highly infectious to C. quinoa and contained many isometric virus‐like particles c. 37 nm in diameter. These virus‐like particles were never found in fractions from uninfected preparations. Electrophoretic analysis of a fraction containing virus‐like particles revealed that these particles might have a single coat protein subunit with the apparent molecular mass of 26 K daltons and one nucleic acid of 6.6 kilobases. Double‐stranded RNA analysis of isolate HJ‐infected or uninfected C. quinoa and Fragaria vesca var. semperflorens seedling line ‘Alpine’ plants showed that both infected plants had two infection‐specific dsRNA bands of mol. wts 4.5 and 3.9 × 106.
Transmission of prunus necrotic ringspot virus using plum pollen and thrips
Authors: GREBER R. S. , KLOSE M. J. , MILNE J. R. , TEAKLE D. S.
Published: February 2008

Prunus necrotic ringspot virus (PNRSV) was transmitted to cucumber but not to peach seedlings after they were dusted with infective plum pollen and caged with 8–10 thrips per seedling for 24 h. When the pollen was taken from three plum trees shown by mechanical inoculation tests to have highly infective flower buds and pollen, the transmission rates to cucumber seedlings were 56% with Thrips tabaci and 66% with a mixture of five thrips species collected from Ageratum houstonianum flowers. However, the transmission rate averaged only 7% when pollen was taken from five other plum trees which had flowers with less infectivity in sap transmission tests. In 1990 T. imaginis, T. tabaci and T. australis, which were present in the mixture of thrips from A. houstonianum, also formed the major part of the thrips population in flowers of the plum trees used as the pollen source.
Comparison of eight isolates of beet yellows virus by filter hybridisation and enzyme‐linked immunosorbent assay
Authors: MOSELEY J. , HULL R.
Published: February 2008

An improved method of virus purification was developed for beet yellows virus (BYV), which resulted in higher virus yields and fewer broken particles than from other methods.

Double antibody sandwich enzyme‐linked immunosorbent assay (ELISA) was not able to differentiate eight isolates of BYV, but filter hybridisation analyses, using cloned cDNA from one of the isolates as the probe was successful in distinguishing some of these isolates.

The degree of hybridisation did not correlate with the severity of the symptoms associated with infection by isolates. Therefore, hybridisation cannot be used as a means of predicting symptom severity. The hybridisation data also indicated that the isolates consisted of stable mixtures of strains.

Cross‐hybridisation of clones derived from one isolate indicated that certain areas of the BYV genome cloned preferentially to other areas.
Control of potato pale cyst‐nematode, Globodera pallida, with a granular nematicide and partially resistant potatoes
Authors: WHITEHEAD A. G. , NICHOLS A. J. F. , SENIOR J. C.
Published: February 2008

The effects of oxamyl applied to the seedbed and growing partially resistant potatoes in controlling potato pale cyst‐nematode, Globodera pallida, were assessed in eleven field experiments on sandy, peaty and silty loam soils in England from 1986 to 1988. Standardised procedures allowed valid comparisons to be made between data from the three experiments in 1987 and from the seven experiments in 1988.

In soil moderately or heavily infested with G. pallida, oxamyl frequently increased tuber yields of susceptible cv. Désirée and of partially resistant potatoes and lessened crude nematode increase (Pf/Pi) significantly at some sites but not at others. Although 2.8 kg oxamyl ha“1 often increased tuber yields significantly, it was significantly less effective than 5.6 kg in controlling G. pallida at one site and at another site G. pallida increased more than in untreated plots.

Potatoes partially resistant to G. pallida were more effective that oxamyl in controlling nematode increase at some sites but not at others. Combined use of oxamyl and partially resistant potatoes was generally more effective in controlling G. pallida than either measure alone. As measured by a ‘control coefficient’ (weight of tubers over 40mm diameter (t ha“1) 4‐crude nematode increase (Pf/Pi)), the most effective integrated control of G. pallida was obtained by growing cvs Glenna, Morag or Santé in soil treated with 5.6 kg oxamyl ha‐1.
Agro‐ecology of onion couch (Arrhenathemm elatius var. bulbosum).
Authors: KHAN AMIN U.
Published: February 2008

The agro‐ecology of onion couch (Arrhenatherum elatius var. bulbosum), a well known weed of arable land is studied. Contribution of seeds from onion couch and a more widespread variety of Arrhenatherum elatius: tall oat‐grass, towards future ingress of onion couch in arable fields has indicated that the tall oat‐grass variety is not a potential weed of arable land. It appears that vegetative propagules rather than the seeds are the effective means of propagation of the onion couch variety in arable fields. An experiment performed to test any modifying effect of the soil texture indicated that onion couch is restricted to loamy soils and there is a complete absence from heavy clays and sandy soils. This could be due to the moist and protective micro‐environment provided by the texture of the soils to partially buried vegetative propagules of onion couch, which are susceptible to drought.
Agro‐ecology of onion couch (Arrhenathemm elatius var. bulbosum (Willd.)).
Authors: KHAN AMIN U. , MORTON ALAN J.
Published: February 2008

This study investigates the performance of vegetative propagules of onion couch (Arrhenatherum elatius var. bulbosum) of varying sizes during the crop growth cycle; especially trends in tiller and bulb production and crop yield loss. The results suggest that the earlier the crop canopy closes the more suppression it will exert on the bulb formation stage of onion couch and hence its future reproductive potential. The closed canopy provided by a dense crop cut short the bulb formation phase and forced onion couch to invest more in aerial tillers in order to compete and coexist with the taller tillers of the crop. An additive experimental design used here to predict the crop losses indicated that natural infestation of onion couch caused greater crop yield loss compared to artificially planted plots. It was found that, although the regrowth from large aggregates with densely packed bulb chains is reduced by correlative dominance and density dependent mortality, presence of such large aggregates can affect crop yield by interfering with the establishment of crop. The competitiveness and development pattern of onion couch suggests that the recent spread of the weed and the reported variable results of control measures is due to the recent shift in agricultural practices.
Optimum plant densities for three semi‐leafless combining pea (Pisum sativum) cultivars under contrasting field conditions
Authors: HEATH M. C. , KNOTT C. M. , DYER C. J. , ROGERS‐LEWIS D.
Published: February 2008

Yield and yield components of three semi‐leafless pea (Pisum sativum) cultivars, of contrasting seed type/growth habit, were assessed at target planting densities of 40–140 plants/m2 on nine sites over three years. Flat‐topped parabolic/asymptotic yield/density relationships were obtained. The plant density required to maximise (p max) and optimise (p opt) yield differed between cultivars: Helka, small blue, p max 126 plants/m2, p opt 101 plants/m2; Solara, large blue, p max 124 plants/m2, p opt 94 plants/m2; and Countess, white‐seeded, p max 104 plants/m2, p opt 71 plants/m2. Near‐maximum yields were maintained between 70 and 140 plants/m2 due to the ability of the pea crop to make compensatory increases in the number of pods per plant as density declined. Yield/density responses were influenced by site (e.g. soil type) more than by seasonal factors. The risk of yield reductions occurring at densities below 70 plants/m2 was greater on a mineral soil than on a fertile organic soil. On the basis of agronomic and economic considerations, there was no evidence that target plant densities required to optimise yield should necessarily be higher for semi‐leafless cultivars studied than for conventional leafed peas.
Symbiotic nitrogen fixation — exploitation and unachieved potential
Authors: JONES D. GARETH
Published: February 2008

The accompanying papers and posters at this conference provide ample testimony that there is much potential in the exploitation of micro‐organisms. The classical use of microorganisms in fermentation processes is well established and will not be discussed here but, in an age when research without a molecular input is likely to be judged as unfashionable, it is well worth emphasising that the microbiological aspects of brewing, dairy products and many industrial processes have been widely exploited, in many instances from before the earliest written histories.
A cotyledon double inoculation technique for evaluating resistance to anthracnose (Colletotrichum orbiculare) and scab (Cladosporium cucumerinum) in cucumber
Authors: VAKALOUNAKIS D. J. , WILLIAMS P. H.
Published: February 2008

A technique for simultaneous inoculation of cucumber cotyledons with Colletotrichum orbiculare race 1 and Cladosporium cucumerinum has been developed. The procedure permitted both resistant and susceptible plants to be recovered. Seedlings were grown at 20°C and inoculated 24 h after emergence with Colletotrichum orbiculare (200 spores in 2 μ1 of water) and Cladosporium cucumerinum (1000 spores in 5 μ1 of water) followed by 48 h of incubation in the dark at 20°C and 100% r.h., and 48 h in a 20°C lighted growth chamber. Seedlings were then moved to a growth chamber at 21°C at night and at 26°C during the day for 4 days and plants were rated as resistant or susceptible 8 days after inoculation. No interference in the expression of resistance or susceptibility of cultivars to either pathogen was detected in simultaneous inoculations.