bluuebunny/crossref_metadata_2025 huggingface dataset:
The incidence of viruses in wild Brassica rapa ssp. sylvestris in southern England
Authors: PALLETT D W , THURSTON M I , CORTINA‐BORJA M , EDWARDS M‐L , ALEXANDER M , MITCHELL E , RAYBOULD A F , COOPER J I
Published: July 2006

Using enzyme‐linked immunosorbent assays, the frequency of occurrence of six viruses was determined in Brassica rapa ssp. sylvestris collected from two Thameside sites (Abingdon and Culham) in Oxfordshire and one near the Avon (Claverton) in Bath & North East Somerset. During 2000–2001, the viruses detected were: Beet western yellows virus (genus Polerovirus) (BWYV), Cauliflower mosaic virus (genus Caulimovirus) (CaMV), Turnip crinkle virus (genus Carmovirus) (TCV), Turnip rosette virus (genus Sobemovirus) (TRoV), and Turnip yellow mosaic virus (genus Tymovirus) (TYMV). BWYV and TYMV were the most frequently detected viruses at the Oxford shire sites, both as single infections (20/1743 and 66/1743 respectively) and as dual infections (7/1743). Turnip mosaic virus (genus Potyvirus) (TuMV) was not detected in the field‐grown plants assayed from any of the sites. There was a highly significant (x2[1]=30.07, P<0.001) difference in the proportion of plants at each Oxfordshire site in which one or more viruses were detected, and essentially the same pattern of virus infection was observed in tests on B. rapa from the site near Claverton. At least one representative isolate of each detected virus was tested for its morphological and serological effects on glasshouse‐grown individuals from different half‐sib families of B. rapa from both Oxfordshire sites. Except for TRoV, where there was a large difference in the frequency of successful infection in B. rapa from the two locations (1/15 vs 11/15), no clear evidence of resistance or immunity to challenge was observed, although tolerance (virus invasion without symptoms) was frequent. Fewer of the plants from Abingdon were infected than those from Culham, when mechanically challenged with TRoV, but the two B. rapa populations were not otherwise consistently different, either in their infectibility by this virus or in their responses to challenge. However, with TCV, viral antigen concentration was closely linked to the severity of disease and the B. rapa from both Oxfordshire sites segregated into two classes: those with symptoms and most viral antigen, and those without symptoms and least viral antigen. These results suggest that generic risk assessments cannot be made due to differences in the way distinct B. rapa populations react to virus challenge.
Stress‐induced changes in the root architecture of white lupin (Lupinus albus) in response to pH, bicarbonate, and calcium in liquid culture
Authors: KERLEY S J , HUYGHE C
Published: July 2006

Current agronomic cultivars of white lupin (Lupinus albus) are intolerant of calcareous or limed soils. In these soils, high pH, bicarbonate (HCO3−), and calcium (Ca) concentrations are the major chemical stresses to the root system. To determine the responses of the root system to these factors, evaluate root architecture, and compare genotypes for tolerance, a series of liquid culture experiments was completed using root chambers that allowed the study of the root system in two dimensions. Each stress condition caused changes in different parts of the root system and there was no generalised stress response. HCO3− (5 mM) had the greatest effect on cultivars intolerant of calcareous soil; it decreased the dry weight of the shoot and caused the highest percentage of tap root deaths. HCO3− also discriminated between short (determinate) and long (indeterminate) roots, as it decreased the number and density of the determinate roots only. Calcium (3 mM) affected all parts of the root system. The tap root was shortened and showed an increased tortuousness in its path compared with 1 mM Ca, although no plants suffered tap root death. The numbers and densities of the two lateral root forms were also decreased, as were the lengths of the indeterminate roots. Stress from alkaline pH (7.5) media caused a lower number and density of determinate lateral roots to be produced than at pH 6.5. The experiments demonstrated that each culture condition elicited a definable stress response. Stress conditions altered the root architecture of genotypes reported to be tolerant of calcareous soil less than in intolerant genotypes. Although soil is more complex than liquid culture, it is possible that in a calcareous or limed soil each stress condition examined may affect the overall stress of the plant, and increased tolerance may result from tolerance to a single stress.
Detection of Banana streak virus in field samples of bananas from Uganda
Authors: HARPER GLYN , HART DARREN , MOULT SARAH , HULL ROGER
Published: July 2006

Banana streak virus (BSV) is one of the major constraints to banana production in Uganda. To develop a diagnostic technique, 59 samples were taken from 30 farms at 14 locations across Uganda; a further three samples were taken from infector plants for BSV epidemiology experiments. BSV was found in 51 of the field samples and in the three infector plants. The possible variation of the virus was assessed by serology (ISEM and ELISA) using a broad‐spectrum antiserum and by PCR. Virus was poorly detected in many of the samples by serological tests even though other techniques showed its presence. Virus was detected in most samples by PCR with a degenerate primer set on extracted viral DNA and on immune‐captured (1C) or directly bound (DB) virus particles. The epidemiology experiment samples did not give a product with these degenerate primers but did with other primer sets. A diagnostic procedure was developed involving concentrating the virus in sap by polyethylene glycol precipitation followed by 1C‐ or DB‐PCR using a degenerate primer set which detected virus in most samples.
Patchouli virus X, a new potexvirus from Pogostemon clabin
Authors: FILHO P E MEISSNER , RESENDE R de O , LIMA M I , KITAJIMA E W
Published: July 2006

This work describes a potexvirus obtained from patchouli, Pogostemon clabin, collected in São Paulo, Brazil in 1992. The plants showed mosaic and were infected by a potyvirus and a potexvirus. The potexvirus had a host range limited to Amaranthaceae, Solanaceae and Labiatae and was named Patchouli virus X (PatVX). PatVX was not transmitted by scissors pruning, in tobacco seeds or by Myzus nicotinae. The virus was purified and a specific antiserum with a titre great than 1:512 000 in dot‐ELISA was produced. The virus was serologically related to Papaya mosaic virus, Potato virus X, Viola mottle virus, White clover mosaic virus and Lily virus X. It had a coat protein of 21 071 ± 1 010 Mr. as determined by SDS‐PAGE. Immunolabelling tests demonstrated that fibrillar masses in the cytoplasm contain the coat protein. The presence of a dsRNA was detected in PatVX infected plants.
Release and establishment of a biological control agent, Psyllaephagus pilosus for eucalyptus psyllid (Ctenarytaina eucalypti) in Ireland
Authors: CHAUZAT MARIE‐PIERRE , PURVIS GORDON , DUNNE RICHARD
Published: July 2006

An Australian parasitoid wasp, Psyllaephagus pilosus, was collected from a previous release site in France and introduced into a commercial eucalyptus foliage plantation in Co. Kerry in the south west of Ireland to control the eucalyptus (blue gum) psyllid Ctenarytaina eucalypti. The first parasitised psyllid nymphs were observed 26 days after the release was made in late May 1998, and 49 days elapsed before a new generation of adult parasitoids was seen. Visually assessed indices of psyllid parasitism and adult wasp incidence were used to quantify the pattern of adult dispersion and establishment. A second generation of adult wasps emerged in late August, initiating a rapid spread of parasitism throughout the release site during September that culminated in a peak rate of almost 100% parasitism by late October. Subsequently by the end of 1998, an apparently random process of dispersion and successful natural colonisation occurred at eight out of ten monitored plantations at distances up to 70 km from the release point. The first colonisers of the other two sites arrived very late in 1998, and consequently failed to establish viable populations by the following summer. Probably this failure was because the small numbers of colonisers had arrived too late in the growing season to effect population establishment before the onset of winter. Assisted introductions were, therefore, made at these sites in June and August 1999, respectively. Once fully established, the parasitoid had no difficulty in surviving winter conditions at all monitored sites and demonstrated excellent potential as a biological control agent.
Dissection and manipulation of metabolic signalling pathways
Authors: HALFORD N G , HEY SANDRA , JHURREEA D , LAURIE S , MCKIBBIN R S , ZHANG Y , PAUL M J
Published: July 2006

The partitioning of resources between different plant organs and compounds is an important determinant of crop quality. We are attempting to change resource partitioning in crop plants by manipulating the cellular mechanisms involved in metabolite sensing and signalling. One of the proteins involved is SnRK1 (sucrose nonfermenting‐1‐related protein kinase 1), so‐called because of its homology and functional similarity with sucrose non‐fermenting 1 (SNF1) of yeast. SnRK1 is a protein kinase that plays a key role in the global control of plant carbon metabolism. Here we review studies on the characterisation of SnRK1 gene families, SnRK1 regulation and function, and the identification of SnRK1‐interacting proteins. We also describe some potential applications of manipulating SnRK1 activity, including controlling sprouting in stored potato tubers, inducing male sterility in barley and increasing sterol levels in oilseeds.
Economic consequences for UK farmers of growing GM herbicide tolerant sugar beet
Authors: MAY M J
Published: July 2006

Weed control is important and one of the more expensive inputs to sugar beet production. The introduction of genetically modified herbicide tolerant (GMHT) sugar beet would result in a major saving in weed control costs in the crop for growers, including control of problem weeds such as perennial weeds and weed beet. However, there would be other economic consequences of growing GMHT beet, some of which would manifest themselves in other parts of the rotation, such as the previous crop, the cereal stubbles that proceed most beet crops, soil tillage and spray application. The average national saving for UK sugar beet growers if they could use the technology would be in excess of £150 ha−1 yr−1 or £23 million yr−1, which includes reductions in agrochemical use of c. £80 ha,−1 yr−1 or £12 million yr−1. However, for some growers, the gains would be much larger and for a few, less than these figures. The possible cost savings are sufficiently large that they could ensure that sugar beet production, with its regionally important environmental benefits as a spring crop, remains economically viable in the UK post reform of the EU sugar regime.
Growth, radiation use efficiency and yield potential of enset (Ensete ventricosum) at different sites in southern Ethiopia
Authors: TSEGAYE ADMASU , STRUIK P C
Published: July 2006

Knowledge on the physiological parameters that determine the growth of enset (Ensete ventricosum) and on how these parameters develop over time and affect yield under field conditions is scarce. Field experiments were carried out at three sites in southern Ethiopia using suckers of several clones to generate crop physiological parameters and to describe the time course of leaf number, leaf area and plant height. Yield potentials at different sites were estimated using these parameters and weather data, and compared with the actual yield.

Plant height and LAI increased faster at Awassa and Areka than at Hagereselam because of a higher leaf appearance rate associated with temperatures being closer to the optimum. The trend in plant height was best described by a logistic function, whereas the trend in LAI was best described by a logistic function only at Awassa and Areka.

A high leaf appearance rate (0.18 leaves day−1) during early growth at Awassa and Areka made it possible that leaves that were senesced during unfavourable climatic conditions could be rapidly replaced without strong fluctuation in leaf area index. At Hagereselam, however, the rate of leaf appearance (0.09 leaves day−1) was too small to compensate for the decline in the number of green leaves per plant during adverse conditions and thus LAI fluctuated over the whole growing period.

The trend in fraction of PAR intercepted was best described by a generalised logistic function. At 300 days after transplanting the suckers, LAI reached a value of 4.5 and enset clones intercepted 92–97% of incoming PAR. The mean extinction coefficient was between 0.56–0.91 and radiation use efficiency (RUE) ranged from 1.43–2.67 g MJ−1. Dry matter kocho yield potentials of 17.1 to 33.9 t ha‐1 yr‐1 were estimated for enset clones. Important yield potential differences existed between clones mainly because of differences in radiation use efficiency that was probably partly associated with viral infection. The average ratio of actual yield:yield potential (0.24) was low mainly because of large losses associated with traditional fermentation techniques, yield reducing cultivation methods such as repetitive transplanting and leaf pruning, presence of diseases, lack of adequate fertilisation and shortage and uneven distribution of rainfall.
Resistance to crown rot (Phytophthora cactorum) in strawberry cultivars and in offspring from crosses between cultivars differing in susceptibility to the disease
Authors: EIKEMO H , STENSVAND A , DAVIK J , TRONSMO A M
Published: July 2006

During a period of five years (1998‐2002), 26 strawberry cultivars and five selections were tested for resistance to crown rot. Cold stored plants inoculated with zoospores of Phytophthora cactorum were used in all experiments. The results showed that resistance to P. cactorum varies greatly between cultivars, and the most resistant ones were Senga Sengana, Induka, Melody, Glima and Bogota, while the most susceptible were Tamella, Inga, Evita and Jonsok. The results were compared to those obtained by other authors, and there were clear indications that the genetic background affects the degree of susceptibility to P. cactorum. Many of the most resistant cultivars descend from Senga Sengana (e.g. Bounty, Glima, Induka and Melody), and several of the most susceptible cultivars have common parentage (e.g. Inga, Tamella, Elsanta and Evita). In a resistance test of the progeny from two separate crosses between a resistant and a susceptible cultivar 61% and 65% of the offspring were intermediately to very susceptible, and 17% and 13% were resistant at the level of Senga Sengana. Hence, there is a high risk of losing offspring with high levels of resistance if selection for resistance to crown rot is not performed at an early stage in a breeding programme.
Genetic basis of yield as viewed from a crop physiologist's perspective
Authors: SLAFER G A
Published: July 2006

The final yield of a crop is the product of growth during the growing season and a number of developmental processes occurring throughout the life cycle of a crop, with most genes influencing the final outcome to a degree. However, recent advances in molecular biology have developed the potential to identify and map many genes or QTLs related to various important traits, including yield, plant adaptation and tolerance to stresses. Significant G×E interactions for yield have been identified, as have interactions associated with QTLs for yield. However, there is little evidence available to confirm that a QTL for yield from a parental line in one mapping population may improve yield when transferred into an adapted, high‐yielding line of another population. In order to narrow the apparent gap between the genotype and the phenotype with regard to yield, it is important to identify key traits related to yield and then attempt to identify and locate the genes controlling them. The partitioning of the developmental time to anthesis into different phases: from sowing to the onset of stem elongation and from then to anthesis, as a relatively simple physiological attribute putatively related to yield, is discussed. If the relationship holds in a wider range of conditions and the genetic factors responsible are located then the genetic basis of yield should be identified. There has also been significant progress in crop simulation modelling. Using knowledge of crop physiology and empirical relationships these models can simulate the performance of crops, including the G×E interactions. Such models require information regarding the genetic basis of yield, which are included in the form of genetic coefficients. Essentially models are constructed as decision‐making tools for management but may be of use in detecting prospective traits for selection within a breeding programme. Problems associated with this approach are discussed. This review discusses the need to use crop physiology approaches to analyse components of yield in order to reliably identify the genetic basis of yield.
Geminivirus classification and nomenclature: progress and problems
Authors: FAUQUET CLAUDE M , STANLEY JOHN
Published: July 2006

During the last few years there has been some confusion among geminivirologists about how to determine the taxonomic status of a geminivirus and provide appropriate names for newly discovered viruses. The Seventh Report of the International Committee on Taxonomy of Viruses (ICTV) published in 2000, that provides guidelines for classification within the family Geminiviridae, is rapidly becoming obsolete, due mainly to the large number of complete genomic sequences that have become available. These sequences have provided a wealth of information with which to establish a coherent and durable taxonomic system, although the realisation that frequent inter‐species recombination events occur has introduced an additional level of complexity. This has resulted in a number of individual initiatives that were not fully compatible with current classification. The Geminiviridae Study Group of the ICTV exploited the last two International Geminivirus Workshops, held in Puerto Rico (1998) and Norwich, UK (2001), to debate some of the issues arising, allowing taxonomic proposals to be formulated that are in the process of being accepted by the ICTV for publication in the Eighth Report due in 2004. The present paper reviews these established principles and provides a reference with which to name and classify geminiviruses appropriately.
The theoretical basis and practical application of relationships between different disease intensity measurements in plants
Authors: MCROBERTS N , HUGHES G , MADDEN L V
Published: July 2006

The literature concerning relationships among different measures of plant disease intensity is reviewed. Some previous confusion over the definition of the terms “incidence” and “severity” is noted and clarified. The review highlights the common features of relationships between incidence and severity, incidence and disease density, and incidence at pairs of scales in a spatial hierarchy. These relationships often show a similar saturation curve form that can frequently be described empirically using the complementary log‐log transformation. A catalogue of alternative functional forms is provided. Practical applications in varietal evaluation are discussed.
Agrobacterium tumefaciens‐mediated transformation and regeneration of herbicide resistant onion (Allium cepa) plants
Authors: EADY COLIN , DAVIS SHEREE , FARRANT JULIE , READER JILL , KENEL FERNAND
Published: July 2006

Transgenic onion plants (Allium cepa) tolerant to herbicides containing active ingredients glyphosate and phosphinothricin were recovered from immature embryos of open pollinated and hybrid parent onion lines at a maximum transformation frequency of 0.9%. Transformants of different onion cultivars, grown on different selective agents and confirmed by Southern analysis, thrived with no apparent ill effects when sprayed with the respective herbicides at double the recommended field dosage for weed eradication. This study demonstrates that the transformation process described previously can be used with different selective agents and is cultivar independent.
Efficacy and phytotoxicity of lime sulphur in organic apple production
Authors: HOLB I J , DE JONG P F , HEIJNE B
Published: July 2006

Curative and preventive efficacy and phytotoxicity of lime sulphur spray schedules, based on a warning system, were evaluated in the Netherlands during two growing seasons under field conditions. In most cases, lime sulphur treatments applied either curatively or preventively resulted in significantly lower scab damage on both the leaves and fruits compared to wettable sulphur treatments. However, all lime sulphur treatments showed high phytotoxicity values, reduced leaf size and had a tendency to a reduced yield quality compared to all other treatments. For curative schedules of lime sulphur on scab control, phytotoxicity and yield did not differ significantly from preventive schedules of lime sulphur. However, the use of a warning system combined with curative schedules of lime sulphur saved one and two lime sulphur sprays in 2000 and 2001, respectively, compared to the preventive treatments of lime sulphur. Our results demonstrated that a curative spray programme with lime sulphur at 0.75–2%, applied 35–45 h after predicted infection periods, can provide effective primary apple scab control, but no benefit in either yield or fruit quality was reached under organic growing conditions. Moreover, research herein clearly showed that organic growers are forced to find a balance between good efficacy and phytotoxic effects of lime sulphur.
Selection, biological properties and fitness of resistance‐breaking strains of Tomato spotted wilt virus in pepper
Authors: THOMAS‐CARROLL M L , JONES R A C
Published: July 2006

In glasshouse tests, infective sap from plants infected with 17 different isolates of Tomato spotted wilt virus (TSWV) from four Australian states was inoculated to three Capsicum chinense accessions (PI 152225, PI 159236 and C00943) carrying single genes that confer hypersensitive resistance to TSWV. The normal response to inoculation was development of necrotic (hypersensitive) local lesions in inoculated leaves without systemic invasion, but 3/1386 infected plants also developed systemic susceptible reactions in addition to hypersensitive ones. Similarly when two isolates were inoculated to C. chinense backcross progeny plants, 1/72 developed systemic susceptible reactions in addition to localised hypersensitive ones. Using cultures from the four plants with susceptible reactions and following three to five further cycles of serial subculture in TSWV‐resistant C. chinense plants, four isolates were obtained that gave systemic susceptible type reactions in the three TSWV‐resistant accessions, and in TSWV‐resistant cultivated pepper (C. annuum). When three of these isolates were inoculated to tomato (Lycopersicon esculentum) breeding lines with single gene resistance to TSWV, resistance was not overcome. Similarly, none of the four isolates overcame partial resistance to TSWV in Lactuca virosa. When TSWV isolates were inoculated to tomato breeding lines carrying partial resistance from L. chilense, systemic infection developed which was sometimes followed by ‘recovery’. After four successive cycles of serial passage in susceptible cultivated pepper of a mixed culture of a resistance‐breaking isolate with the non resistance‐breaking isolate from which it came, the resistance‐breaking isolate remained competitive as both were still found. However, when the same resistance‐ breaking isolate was cultured alone, evidence of partial reversion to wild‐type behaviour was eventually obtained after five but not four cycles of long term serial subculture in susceptible pepper, as by then the culture had become a mixture of both types of strain. This work suggests that resistance‐breaking strains of TSWV that overcome single gene hypersensitive resistance in pepper are relatively stable. The findings have important implications for situations where resistant pepper cultivars are deployed widely in the field without taking other control measures as part of an integrated TSWV management strategy.
Blockage of stylet tips as the mechanism of resistance to virus transmission by Aphis gossypii in melon lines bearing the Vat gene
Authors: MARTIN B , RAHBÉ Y , FERERES A
Published: July 2006

Aphis gossypii is the main virus vector in muskmelon crops. The melon gene Vat confers resistance to non‐persistent virus transmission by this aphid. The mechanism of this resistance is not well understood, but no relationship has been detected between resistance and the probing behaviour of aphids on resistant plants. Results presented here suggest that temporary blockage of aphid stylet tips preventing virus particle release may explain the resistance conferred by Vat gene. We performed experiments in which viruliferous aphids were allowed to probe different sequences of resistant (Vat‐bearing) and/or susceptible melon plants. The results demonstrated that A. gossypii inoculates Cucumber mosaic virus (CMV) efficiently in susceptible plants having previously probed resistant plants, showing that the resistance mechanism is reversible. Furthermore, the infection rate obtained for susceptible plants was the same (25%) regardless of whether the transmitting aphid had come directly from the CMV source or had subsequently probed on resistant plants. This result suggests that virus is not lost from stylet to plant during probing of resistant plants, supporting the temporary blockage hypothesis. We also found that the ability of Myzus persicae to transmit CMV is noticeably reduced after probing on resistant plants, providing evidence that this aphid species also responds to the presence of the Vat gene. Finally, we also found that in probes immediately after virus acquisition M. persicae inoculates resistant plants with CMV more efficiently than susceptible plants, perhaps because the Vat gene product induces increased salivation by this aphid.
Wild flower seed predation byPterostichus madidus(Carabidae: Coleoptera)
Authors: HURST C , DOBERSKI J
Published: July 2006

The objective of the study was to investigate the ability ofPterostichus madidus, one of the most abundant carabid beetles in the United Kingdom, to consume wildflower seeds. The plant species chosen are commonly included in wildflower seed mixes sown to enhance the biodiversity of arable field margins, and hence any seed predation could potentially reduce successful seedling establishment. The study combined cafeteria style laboratory feeding experiments with predation studies in an established field margin.

In laboratory studies thePterostichus madidusconsumed both unimbibed and imbibed seeds ofCentaurea scabiosa, Galium verum, Leucanthemum vulgareandPrimula veris. Seed consumption was still evident whenDrosophilapupae were also supplied, although there was significant preference for the pupae. Placement of seeds in the field showed high levels of seed consumption, although part of this was attributed to slugs. Carabid beetles may have a significant role as wild flower seed predators and thus may affect establishment of re‐seeded flower‐rich meadows.
The coincidence of thrips and dispersed pollen in PNRSV‐infected stonefruit orchards – a precondition for thrips‐mediated transmission via infected pollen
Authors: MILNE J R , WALTER G H
Published: July 2006

Recent laboratory studies have demonstrated that Prunus necrotic ringspot virus (PNRSV) (family Bromoviridae) can be readily transmitted when thrips and virus‐bearing pollen are placed together on to test plants. For this transmission mechanism to result in stonefruit tree infection in the field, PNRSVbearing pollen must be deposited onto surfaces of stonefruit trees on which thrips also occur. In a previous paper, we demonstrated that almost all pollen in a PNRSV‐infected Japanese plum orchard in southeastern Queensland was deposited onto flowers, whereas few grains occurred on leaves and none on stems. Here, we present results of our investigation of thrips species composition, distribution and abundance on stonefruit trees in the same study area as our previous pollen deposition study. We collected a total of 2010 adult thrips from 13 orchards during the 1989, 1991 and 1992 flowering seasons of which all but 14 were in the suborder Terebrantia. Most (97.4%) terebrantian thrips were of three species, Thrips imaginis, Thrips australis and Thrips tabaci. Thrips tabaci as well as species mixtures that included T. imaginis, T. australis and T. tabaci have been shown to transmit PNRSV via infected pollen in laboratory tests. Adult thrips were frequently collected from flowers but rarely from leaves and never from stems. Large and significant differences in numbers of T. imaginis, T. australis and T. tabaci adults in flowers occurred among orchards and between seasons. No factor was conclusively related to thrips numbers but flowers of late‐flowering stonefruit varieties tended to hold more thrips than those of early‐flowering varieties. Our results indicate that the common thrips species present on stonefruit trees in the Granite Belt are also ones previously shown to transmit PNRSV via infected pollen in the laboratory and that these thrips are concentrated in tonefruit flowers where most stonefruit pollen is deposited. These results contribute to mounting circumstantial evidence that stonefruit flowers may be inoculated with PNRSV via an interaction of thrips with virus‐bearing pollen and that this transmission mechanism may be an important cause of new tree infections in the field
The development of a model to assess the effects of rabbit grazing on grass
Authors: DENDY JULIE , MCKILLOP GORDON , FOX SUE , WESTERN GAVIN , LANGTON STEVE
Published: July 2006

Grass for use as silage is widely grown in the UK. However there is little information on the effects of rabbit grazing on crop yield. In a three‐year trial, grass was grown in six enclosures following current agronomic procedures and was subjected to grazing by two population densities of rabbits. The annual yield loss at the end of the trial was found to be 1% per rabbit ha−1. The yield loss per rabbit was calculated to be around 200 kg and the financial loss was calculated as £3.40 per rabbit at 1998 prices (approx. £17 t−1).

This new information provides farmers with a better understanding of the economics of damage caused by rabbits enabling them to make more informed decisions as to whether their rabbit population needs to be managed, or whether their crop needs to be protected by some other means.
Characterisation of pumpkin yellow vein mosaic virus from India
Authors: MUNIYAPPA V , MARUTHI M N , BABITHA C R , COLVIN J , BRIDDON R W , RANGASWAMY K T
Published: July 2006

Yellow vein mosaic disease symptoms occur frequently in pumpkin in India. Diseased plants show vein yellowing, which sometimes coalesces to form chlorotic patches. Infected plants are stunted and flowers drop prematurely, greatly reducing yields. Diseased plants are infected by a begomovirus, designated pumpkin yellow vein mosaic virus (PYVMV), which is transmitted readily and in a persistent manner by the whitefly, Bemisia tabaci. Transmission of PYVMV requires minimum acquisition and inoculation access periods of 30 min and 10 min, respectively. The minimum latent period in the insect is 6 h and the virus persists in the vector for at least 8 days. PYVMV has a narrow host range consisting of a small number of cucurbit species and some tobacco cultivars. It was detected serologically in diseased plants and in viruliferous B. tabaci using polyclonal antibodies in a double‐antibody sandwich enzyme‐linked immunosorbent assay. Reactions with monoclonal antibodies in a triple‐antibody sandwich ELISA showed that PYVMV has an epitope profile distinct from those of other begomoviruses from the Indian sub‐continent. Polymerase chain reaction amplified fragments from the putative viral coat and movement protein genes. Based on comparative phylogeny of complete coat protein gene sequences, PYVMV was most similar to the bipartite Tomato leaf curl New Delhi virus from India and appears to be a new strain of this virus.
Daily variation in the number of slugs under refuge traps
Authors: HOMMAY G , KIENLEN J C , JACKY F , GERTZ C
Published: July 2006

Daily variation in the number of slugs under and around 25 cm × 25 cm pad‐traps was recorded in plots of crop cultures. Grey field slugs Deroceras reticulatum and garden slugs (Arion distinctus and Arion hortensis) left traps at dusk and came back at the end of the night. The time of day at which the number of trapped slugs was maximal did not occur in the middle of the day, when slugs were inactive, but in the early morning and in the evening, a few hours before dusk. This was due to a rise in temperature under the traps in the middle of the day. However, the grey field slugs stayed under traps throughout the morning, when temperatures under the traps reached values more favourable for rest.
Spatial dispersion patterns of potential leafhopper and planthopper (Homoptera) vectors of phytoplasma in wine vineyards
Authors: ORENSTEIN S , ZAHAVI T , NESTEL D , SHARON R , BARKALIFA M , WEINTRAUB P G
Published: July 2006

Species from three subfamilies of Cicadellidae and one species of Cixiidae, all potential vectors of phytoplasmas, were trapped in vineyards over the course of two years. These insects were caught on yellow sticky traps during the spring; virtually none were trapped during the summer months. Molecular analysis (PCR) of selected samples of the leafhoppers and planthoppers for presence of phytoplasma DNA was conducted on most species. Neoaliturus fenestratus was the most abundant known vector species and was positive for stolbur (Stol) and aster yellows (AY) phytoplasma. Circulifer haematoceps complex, which were also positive for Stol and AY, were about 10‐fold fewer than N. fenestratus. Hyalesthes obsoletus, also a known phytoplasma vector, occurred in substantial numbers only late in the season when the vines and leaves were dehiscing and turning brown, but was positive for Stol and AY. A species whose vector status is unknown (Megophthalmus scabripennis) was also caught in large numbers and was shown, by PCR analysis, to be positive for AY. Other known vector species trapped included: Anaceratagallia laevis (positive for AY), Austroagallia sinuata, Dryodurades sp. (dlabolai?) (positive for AY), Macrosteles quadripunctulatus (positive for Stol), and Orosius orientalis. The spatial dispersion pattern of the four most abundant species were investigated by using Moran's spatial statistic; N. fenestratus and M. scabripennis showed significant spatial patterns, whereas C. haematoceps and H. obsoletus did not.
A new phytoplasma detected in the South Australian native perennial shrub, Allocasuarina muelleriana
Authors: GIBB K S , TRAN‐NGUYEN L T T , RANDLES J W
Published: July 2006

Allocasuarina muelleriana shrubs growing in natural sclerophyll roadside vegetation near Willalooka in the upper south‐east of South Australia have a high incidence of a yellowing disorder in either all or part of the foliage, combined in some cases with a shortening and curling of the leaf‐bearing stems. Samples from symptomatic and adjacent asymptomatic plants were tested for phytoplasmas by the polymerase chain reaction (PCR) assay. All but one asymptomatic plant were negative for phytoplasmas, whereas about half of the symptomatic plants were positive. Restriction fragment polymorphism analysis of PCR products indicated that the phytoplasma was related to the buckthorn witches.‐broom (BWB) and apple proliferation (AP) groups of phytoplasmas, members of which have not been previously reported in Australia. Further evidence from the sequence of the 16S rRNA gene and the use of PCR primers specific to the AP and pear decline (PD) phytoplasmas confirmed the close relationship to the BWB and AP group phytoplasmas.
Plants as a source of anti‐cancer and anti‐HIV agents
Authors: CRAGG G M , NEWMAN D J
Published: July 2006

Plant‐derived compounds have played an important role in the development of several clinically useful anti‐cancer agents. These include vinblastine, vincristine, the camptothecin derivatives, topotecan and irinotecan, etoposide, and paclitaxel (Taxol®). Several promising new agents are in clinical development based on selective activity against cancer‐related molecular targets, including flavopiridol and Combretastatin A4 phosphate. Recently, plants have yielded several agents showing anti‐AIDS activity, and one of these, (+)‐calanolide A, is in clinical development.
Antimalarial activities of gedunin and 7‐methoxygedunin and synergistic activity with dillapiol
Authors: OMAR S , GODARD K , INGHAM A , HUSSAIN H , WONGPANICH V , PEZZUTO J , DURST T , EKLU C , GBEASSOR M , SANCHEZ‐VINDAS P , POVEDA L , PHILOGENE B J R , ARNASON J T
Published: July 2006

Gedunin from Cedrela odorata (Meliaceae), a potent in vitro antimalarial agent, was investigated for its in vivo efficacy in CD‐1 mice infected with Plasmodium berghei. When orally administered at 50 mg kg‐1 day‐1 for 4 days, gedunin was able to suppress the parasitaemia level by 44%. However, no clear dose‐response effects were observed in the 0–100 mg kg‐1 day‐1 dose range. Preliminary pharmacokinetics in Sprague‐Dawley rats showed poor absorption. However, a binary treatment of 50 mg kg‐1 day‐1 gedunin with 25 mg kg‐1 day‐1 dillapiol, a cytochrome P450 inhibitor, increased parasitaemia clearance in mice to 75%. A clear dose‐response was observed in the 0–50 mg kg‐1 day‐1 gedunin dose range when administration was combined with 25 mg kg‐1 day‐1 dillapiol. In addition, 7‐methoxygedunin, a semi‐synthetic derivative which is more stable to degradation than gedunin, suppressed the level in mice by 67% at 50 mg kg‐1 day‐1. When administered at this dose in combination with 25 mg kg‐1 day‐1 dillapiol, clearance increased to 80%. These results demonstrate the potentialefficacy of antimalarial drugs and phytomedicines based on gedunin and the value of the combination therapy.
Cerebroside as an elicitor for induced resistance against the downy mildew pathogen in pearl millet
Authors: DEEPAK S A , RAJ S NIRANJAN , UMEMURA K , KONO T , SHETTY H SHEKAR
Published: July 2006

Innate defence mechanisms in plants can be triggered and enhanced by certain agents, which are referred to as inducers. Inducing resistance against a broad spectrum of pathogens in otherwise susceptible plants is seen as a potentially safer alternative to other methods of chemical control of plant diseases. Cerebrosides, which are glycosphingolipids extracted from various plant pathogens, have been reported as resistance elicitors in the rice‐pathogen system. In the present study, cerebroside elicited resistance against downy mildew disease (caused by Sclerospora graminicola) of pearl millet (Pennisetum glaucum) that was highly significant. The resistance was of systemic nature and the time required for the resistance to build up was from 2 days onwards. There was a significant yield enhancement due to disease suppression by cerebroside treatment. Promising results were obtained in a preliminary field trial.
Effects ofMelia azedarach, (Meliaceae) fruit extracts on the leafminerLiriomyza huidobrensis, (Diptera, Agromyzidae): Assessment in laboratory and field experiments
Authors: BANCHIO E , VALLADARES G , DEFAGÓ M , PALACIOS S , CARPINELLA C
Published: July 2006

Control of the widely distributed pestLiriomyza huidobrensis, is complicated due to the protected habit of the leafmining larvae, and their resistance to insecticides. The effects ofMelia azedarach, (Meliaceae) fruit extracts against adults and larvae ofL. huidobrensis, were investigated. In the laboratory, leaves ofCucurbita, sp. infested with first and third instar larvae were treated with different extract solutions. Larval and pupal survival, as well as wing‐spread of adults, were ssessed. Female adult behaviour towards the extract was also analysed in terms of number of feeding punctures and number of offspring left on treated/untreated leaves. In the field, an infestedVicia faba, crop was sprayed four times at weekly intervals with plant extract, water, and a blank solution. The number of adult leafminers and parasitoids emerging from sampled leaves from each treatment were compared. The laboratory tests showed translaminar action of the extracts, which negatively affected leafminer pupal survival, while body size was not affected. The extracts also deterred feeding by adult females and may also have caused reduction in oviposition rates. All solutions and concentrations tested had similar effects. In the field, extract effects were consistent with those from laboratory trials, number of pupae and pupal survival being lower on treated plants. Percentage parasitism was not affected by plant extract treatment, suggesting a selective activity.
Toxicity of parathion‐methyl to cells, akinetes and heterocysts of the cyanobacterium Cylindrospermum, sp. and the probit analysis of toxicity
Authors: PANIGRAHI SIBANANDA , PADHY SACHIDANANDA , PADHY RABINDRA N
Published: July 2006

The toxicity of a commercial formulation of the insecticide parathion‐methyl to the N2‐fixing filamentous cyanobacterium (blue‐green alga) Cylindrospermum, sp. was studied. A concentration of parathion‐methyl of 0.5 ppm caused growth increase in liquid growth media. The minimum inhibitory concentration of parathion‐methyl for both types (N2, fixing and nitrate supplemented) of liquid and solid media was 1.0 ppm. LC50 values were: 4.4 ppm (liquid, N2, fixing), 5.5 ppm (liquid, nitrate supplemented), 3.3 ppm (agar, N2‐fixing) and 4.0 ppm (agar, nitrate supplemented). LC100 values for N2‐fixing liquid and both types of agar media were 10.0 ppm, while for the liquid nitrate supplemented medium the LC100 was 12.0 ppm. Both akinete (spore) formation and germination were inhibited below the highest permissive concentration of 8.0 ppm, with the insecticide incorporated in the agar media. In soil, the LC50 and LC100 values for parathion‐methyl were 13.6 and 30 ppm, respectively. Both the dehydrogenase activity of heterocysts (monitored by 2,3,5‐triphenyl tetrazolium chloride reduction) and the nitrogen concentration of cultures (estimated by the micro‐Kjeldahl method) were affected by the insecticide, but the latter (N2‐fixation) was more sensitive. The Kruskal‐Wallis H test on the numbers of vegetative cells in the filaments revealed that the insecticide significantly affected the division of vegetative cells. The cyanobacterium could detoxify the growth medium containing high levels (30 and 40 ppm) of the insecticide in short‐term exposures at the expense of cell viability.
Dry matter production and partitioning in potato plants subjected to combined deficiencies of nitrogen, phosphorus and potassium
Authors: JENKINS P D , MAHMOOD S
Published: July 2006

Three experiments examined effects on growth, dry matter partitioning and nutrient uptake in potato plants grown in large pots under different combinations of adequate and deficient levels of nitrogen, phosphorus and potassium. N supply affected the growth of all leaves, with low N reducing both the size of individual leaves and the extent of branch growth. P and K availability affected the growth of later formed leaves and only when both were deficient was branch growth substantially reduced. At later stages of growth, total green leaf area was significantly reduced by deficiency of each of the nutrients. Partitioning of dry matter to tubers was markedly reduced by K deficiency and increased in one experiment by P deficiency. When both P and K were deficient, partitioning approximated that under non‐limiting conditions. Leaf weight ratio (LWR) was higher under K deficiency, but not when P was also deficient, and was consistently higher when the ratio of K : P in dry matter was less than approximately five. In these experiments, LWR was not consistently related to shoot N% and N supply had relatively little effect on partitioning. There were large treatment effects on tuber dry matter percentage, characterised by significant interactions especially between N and K. Deficiency of one nutrient increased the concentration of others but uptake was highly regulated as crop content of all three nutrients was reduced when the supply of any one was deficient. The results show that the response of potatoes to single deficiencies may be influenced greatly by the levels of other nutrients.
Cybrids and tetrad sterility for developing true potato seed hybrids
Authors: GOLMIRZAIE ALI M , TENORIO JORGE , SERQUÉN FELIX , ORTIZ RODOMIRO
Published: July 2006

Potato cybrids result from the fusion between cytoplasm and nuclear gene donors. Such genetic materials are an alternative means to broaden the breeding pool by non‐sexual gene transfer. Tetrad pollen sterility provides also another source of male sterility with some potential for true potato seed breeding. The objective of this research was to investigate cybrid‐derived offspring for both agronomic and reproductive characteristics in two contrasting Peruvian locations, and to examine new exotic germplasm for tetrad sterility, with the aim of broadening the breeding pool available at the Centro Internacional de la Papa (CIP). The cybrids were derived from fusions between Y‐245.7, a clone with tetrad sterility, and Atzimba. These cybrids were crossed with selected male parents from the CIP breeding population, and their hybrid offspring were tested in La Molina (coastal desert) and Huancayo (cool highlands). In addition, other clones with tetrad sterility were also crossed with selected testers to determine their breeding value. There were significant differences for tuber yield, style length, and berry number among the hybrid offspring, and the genotype by environment interaction was significant for tuber yield and berry number. The top 25% highest yielding cybrid‐derived offspring across both locations showed the same tuber yield although they were significantly different for some of the reproductive characteristics. With the exception of one cybrid, the others did not exhibit segregation for tetrad sterility in their hybrid offspring, which were male fertile. However, the offspring derived from crosses between other sources of tetrad sterility and the same testers all showed tetrad sterility, and some of them had outstanding tuber yield at La Molina. The lack of segregation for tetrad sterility in these new crosses suggests that the non‐cybrid, male sterile, female parents are triplex or quadriplex for the Tr nuclear locus, which interacts with a sensitive cytoplasm (e.g. Trs from S. verrucosum or S. stoloniferum) to produce tetrad sterility in potato.