bluuebunny/crossref_metadata_2025 huggingface dataset:
Community‐scale seedbank response to less intense rotation and reduced herbicide input at three sites
Authors: SQUIRE G R , RODGER S , WRIGHT G
Published: July 2006

Species diversity and abundance in weed seedbanks were measured at the beginning, and after 3 and 6 yr of the TALISMAN experiment at ADAS Boxworth, Drayton and High Mowthorpe. Fifty species were distinguished in the seedbanks of treatments comprising winter and spring rotations and full and reduced herbicide input. After 6 yr, the number of seedbank species in the main treatments ranged from 11 in the most intense to 26 in the least intense management. Principal co‐ordinate analysis showed that the seedbank community diverged over time between sites and additionally between the two rotation treatments at Boxworth. Only four species were common to all sites but community‐scale descriptors indicated that the change in seedbanks following reduced inputs had common features at the three sites. First, species‐area relations showed a greater relative increase in number of taxa at a plot scale than in the site as a whole, indicating lower inputs encouraged the common weeds more than rare species. Second, both the mean and the standard deviation of the species‐abundance distribution at 6 yr increased in response to reduced inputs. As a result, the number of species slightly more than doubled as herbicide units were reduced from four to one while the total number of seeds increased by two orders of magnitude. Some causes of seedbank change were identified: spring‐germinating species tended to increase when spring cultivation was common in the rotation, while some competitive weeds had a relatively low abundance when they were targeted by herbicide. The results are discussed in relation to optimising the various functions of the seedbank.
Comparison of the changes in mushroom (Agaricus bisporus) compost during windrow and bunker stages of phase I and II
Authors: SHARMA H S S , LYONS G , CHAMBERS J
Published: July 2006

The changes in thermophilic fungi and biochemical characteristics, during windrow and bunker stages of phase I and phase II composts, were compared in this investigation. Composts prepared by the two phase I systems differed in a number of key parameters including mean straw length, population of Scytalidium thermophilum, dry matter, conductivity, nitrogen dry matter, ammonia, fibre content and ash. S. thermophilum populations in phase I composts were significantly higher in windrow compared to bunker‐composted materials as a result of the larger high temperature (65‐80°C) core in bunker treatment, which inhibited microbial activity. Assessment of the composts for loss of matter during composting has revealed that the bunker system can conserve fresh matter better than the windrow production system, possibly due to lower microbial activities during bunker composting. The productivity of the phase II composts prepared from windrow and bunker systems was compared in trials using commercial growers.
A thermal time model for predicting time to aerial shoot elongation in Variegated Solomon's Seal
Authors: YEH D M , LIN Y R , ATHERTON J G
Published: July 2006

Aerial shoot development in Variegated Solomon's Seal (Polygonatum odoratum‘Variegatum’) was studied under warm (mean 18°C) conditions after dormant rhizomes had been stored at a range of temperatures. After chilling at 0.8–5.5°C for 21–77 days, all rhizomes produced elongated aerial shoots, with mean lengths from 33 cm to 44 cm. Exposure of rhizomes to 15°C or 20°C for 21–77 days resulted in 17% to 50% of buds emerging as shoots, but these either aborted or failed to extend beyond a rosette. The earliest aerial shoot elongation was observed after 7–13 days at 18°C in rhizomes that had been chilled at 0.8–2°C treatments for 59–72 days. The base, optimum and maximum temperatures during pre‐planting storage for subsequent aerial shoot elongation were derived respectively as −1.5°C, 1.9°C and 15.8°C. A thermal time of storage was calculated from these cardinal temperatures and the rate of progress to normal aerial shoot clongation was shown to increase linearly with increasing thermal time to c. 150°Cd. The thermal time procedure for predicting time to aerial shoot elongation constructed from growth room/chamber data was validated using rhizomes that had been exposed to varying temperatures in shadehouse conditions during the winter in Taiwan.
The impact of dimethoate on the spatial distribution of beneficial arthropods in winter wheat
Authors: HOLLAND J M , WINDER L , PERRY J N
Published: July 2006

The within‐field spatial distribution of beneficial arthropods was assessed using two‐dimensional grids of pitfall traps and suction sampling across two winter wheat fields of 4 and 16 ha, before and after an application of dimethoate. An unsprayed 6 m wide buffer zone was left around half the edge of the larger field. Arthropod numbers fluctuated to varying extents prior to spraying. Two species of Carabidae (Pterostichus madidusandP. melanarius), Linyphiidae, Lycosidae andAphidiusspp. (Braconidae) all showed their greatest reduction after spraying. For five carabid taxa,Tachyporusspp. (Staphylinidae) and Collembola the decline in numbers following spraying was no greater than any reduction found during the pre‐spraying period. Within field spatial distributions of three arthropod groups were analysed using SADIE.P. madidus, present in patches across the centre of both fields prior to spraying, was removed by dimethoate and by 34 days after spraying had recovered most at the field edges. Linyphiidae were evenly distributed across both fields prior to spraying. Their numbers were reduced considerably by dimethoate and they did not recover to pre‐spray levels. However, where recovery occurred this was across the centre of both fields indicating their potential to reinvade whole fields.Aphidiusspecies were also evenly distributed across both fields prior to spraying, but did not recover after spraying. Some, but not all arthropods survived within the unsprayed buffer zone and there was some indication that reinvasion of the mid‐field was more extensive where this was present. The importance of field margins with respect to insecticide treatments is discussed.
Effectiveness of resistance genes to the large raspberry aphid, Amphorophora idaei Börner, in different raspberry (Rubus idaeus L.) genotypes and under different environmental conditions
Authors: JONES A T , McGAVIN W J , BIRCH A N E
Published: July 2006

The introduction into commerce of raspberry cultivars with major gene resistance to the large raspberry aphid, Amphorophora idaei, an important pest and virus vector on red raspberry in Europe, has been very effective both in decreasing pest numbers and greatly restricting infection with the viruses it transmits. However, biotypes of the aphid able to overcome these genes have developed in the field in recent years. Additionally, in field and laboratory tests, the response to aphid biotypes and recognised aphid strains of certain raspberry cultivars, such as Glen Prosen and Delight, differ markedly despite the fact that they are reputed to contain the same A. idaei‐resistance gene, A1. In attempts to understand the reasons for this difference in response, analysis was made of the segregation of progeny seedlings from crosses between A. idaei‐resistant and ‐susceptible cultivars to two recognised strains of the aphid. These studies showed that, as expected, cv. Autumn Bliss contained the A. idaei‐resistance gene, A10, and cvs Delight and Glen Prosen each contained the A. idaei‐resistance gene, A1. When progeny seedlings were assayed in a heated glasshouse as young plants and in an unheated Tygan house as 1 m tall plants, the segregation ratios for resistance and susceptibility to A. idaei were largely unchanged. However, when the resistance of individual progeny plants was assessed, c. 37% of the putative gene A1‐containing progeny and 9–23% of the putative gene A10‐containing progeny, behaved differently in these two environments. Experiments involving an A. idaei‐resistant and ‐susceptible parent cultivar showed that shading plants increased their susceptibility to A. idaei colonisation. Whilst this shading effect has implications for experimentally detecting A. idaei‐resistant progeny in segregating raspberry seedlings, it does not explain the difference in field resistance to A. idaei of cvs Delight and Glen Prosen. Such differences in the field seem best explained by the presence in these cultivars of ‘minor’ genes for A. idaei resistance and/or susceptibility that influences the effectiveness of gene A1.
Spectral filters for the control of Botrytis cinerea
Authors: WEST J S , PEARSON S , HADLEY P , WHELDON A E , DAVIS F J , GILBERT A , HENBEST R G C
Published: July 2006

Experiments performed in vitro examined the sporulation of Botrytis cinerea (grey mould) under different spectral distributions. Eighty‐three isolates, taken from plants of primula (Primula vulgaris) at different locations throughout the UK, were incubated in the dark, with visible light only and visible plus near‐ultraviolet (nUV) light. On average, compared to isolates not exposed to nUV, sporulation was increased 54‐fold following illumination with nUV light. No isolates showed complete insensitivity to near ultraviolet. New polyethylene materials with different optical properties were then tested on two typical isolates. A film which removed nUV up to 405 nm, compared to a film with nUV absorption up to 384 nm, resulted in the lowest production of conidia (by 5‐fold). The former film was used to clad horticultural polyethylene tunnels in which crops of P. vulgaris and strawberry were grown for two seasons and the incidence of B. cinerea assessed throughout the growth of the crops. The incidence of infection on the P. vulgaris and strawberries was reduced by c. 50% and c. 26% respectively with the nUV blocking film compared to a standard film. The results are discussed in terms of the potential of spectral filters as a novel means of grey mould control in greenhouse‐produced crops.
Elderberry latent virus: its relationship to Pelargonium ringspot virus and its identification as a distinct member of the genus Carmovirus, family Tombusviridae
Authors: JONES A T , McGAVIN W J , BRUNT A A , PHILLIPS S
Published: July 2006

The properties of Elderberry latent virus (ELV) and Pelargonium ringspot virus (PelRSV) were compared. The viruses were largely indistinguishable in herbaceous host range and symptomatology, particle morphology, sedimentation coefficient and RNA profiles and size. They were also very closely related serologically with SDI differences in agarose gel double‐diffusion tests of 1 to 3. Purified virus particle preparations of each virus contained isometric particles c. 30 nm in diameter that sedimented as a major component with an sO20W of 112–115S. Purified virus particle preparations contained a major and a minor ssRNA species that in polyacrylamide gel electrophoresis (PAGE) had estimated sizes of c. 3.8 kb and c. 1.6 kb respectively. Plants of Chenopodium quinoa infected with ELV or PelRSV each contained three dsRNA species of c. 3.8, 2.6 and 1.8 kbp, although the smallest of these species was not evident in all preparations. Protein from purified virus particle preparations contained a major polypeptide that, in SDS‐PAGE, had an estimated Mr of 40 000 (40K). However, after storage of purified virus particles for 7–10 days, protein preparations from PelRSV particles also contained an additional major polypeptide of estimated Mr of 37 000 that is probably derived by degradation of the 40K protein; this additional component was not observed in freshly prepared preparations of ELV. Neither virus was found to be related serologically to 16 other viruses with isometric particles and similar properties. These data, together with the recent finding by other researchers that the smallest RNA species is a sub‐genomic RNA, suggests that both viruses are members of the genus Carmovirus, and that PelRSV is a minor variant of ELV. However, the taxonomic status of these two viruses is discussed in relation to recent brief reports comparing the nucleotide and amino acid sequences of these two viruses.
Insecticidal activity, mammalian cytotoxicity and mutagenicity of an ethanolic extract from Nerium oleander (Apocynaceae)
Authors: EL‐SHAZLY M M , EL‐ZAYAT E M , HERMERSDÖRFER H
Published: July 2006

A bioassay procedures utilising the western‐banded blow fly, Chrysomya albiceps (Diptera‐Calliphoridae) has been used to guide the fractionation of an ethanolic extract from the leaves of Nerium oleander (Apocynaceae). The cardiotonic glycoside, neriifolin: (3‐[(6‐deoxy‐3‐0‐methyl‐α‐L glucopyranosyl) oxy]‐14‐hydroxy‐5 β Card‐20 [22]‐endolide) was crystallised from the insecticidal active fraction of the ethanolic extract. The values of LC50 of the ethanolic extract, active fraction, isolated crystals and authentic neriifolin were 164 ppm, 57 ppm, 35 ppm and 36 ppm, respectively when incorporated into the blow fly diet. A primary test on the cytotoxicity and mutagenicity of the crude extract against non‐target organisms was achieved by determining the cytotoxicity and mutagenicity on a mammalian cell line using different concentrations of the extract (in vitro) through a radioactive thymidine incorporation technique and hypoxanthine phosphoribosyl transferase (HPRT) test, using the Chinese hamster lung fibroblasts (V79‐MZ cell line). Cytotoxicity tests revealed that the LC50 was approximately 200 ppm, and the mutagenicity was very low compared to the standard active mutagen.
Bruising of sugar beet roots and consequential sugar loss: current understanding and research needs
Authors: WILTSHIRE J J J , COBB A H
Published: July 2006

Bruising of sugar beet roots and the consequential sugar loss do not receive the attention they deserve within the sugar beet industry. Recent harvester tests have indicated that current levels of bruising damage could be decreased with existing technology. There is, however, little understanding of biological factors affecting susceptibility to bruising of sugar beet roots. This paper examines the available information on causes of bruising, the significance of some tissue characteristics, the processes of sugar loss following bruising and agronomic, physiological and biochemical considerations relevant to bruising and the sugar loss that follows. Some research needs are identified in conclusion.
Marker gene expression driven by the maize ubiquitin promoter in transgenic wheat
Authors: ROOKE L , BYRNE D , SALGUEIRO S
Published: July 2006

Selecting a promoter for driving transgene expression is one of the most important factors to consider in a transformation project. Information about the native regulation of the promoter activity is important, but it is also necessary to consider how that activity will be affected when integrated into the genome of the transformed plants. Study of a promoter performance in individually transformed lines provides useful information in this area. The maize ubiquitin 1 (Ubi‐1) promoter has been widely used to drive constitutive transgene expression in monocotyledonous plants. However, lack of data on its activity in individual transformed wheat lines constitutes a gap in the understanding and predictability of this promoter's performance. In this paper, we began addressing this problem by examining the expression of the marker gene uidA, coding for β‐glucuronidase (GUS), under the control of the maize Ubi‐1 promoter in individual transgenic wheat (Triticum aestivum L.) lines from different wheat varieties. The expression of uidA driven by this promoter depended to a great extent on the specific transformation event. Whilst expression was strong and constitutive in all tissues in some of the lines analysed, there were also transgenic lines in which GUS activity was restricted to only a few tissues. In general the maize Ubi‐1 promoter had strong activity in young, metabolically active tissues and in pollen grains.
Cyclamen (Cyclamen persicum L.): a dead‐end host species for 16Sr‐IB and ‐IC subgroup phytoplasmas
Authors: ALMA A , MARZACHÌ C , D'AQUILIO M , BOSCO D
Published: July 2006

Phytoplasmas belonging to the 16S rDNA subgroups IB and IC were found in five cyclamen (Cyclamen persicum L.) plants showing virescence and yellow stunted leaves and one plant showing phyllody, rolled and thickened leaves, respectively. Two cyclamens, representing the two syndromes, were chosen as source plants for transmission trials in which three leafhopper species, known as vectors of IB and IC subgroup phytoplasmas, were used to inoculate cyclamen and periwinkle [Catharanthus roseus (L.) G. Don] test plants. Out of 366 tested plants only one periwinkle exposed to Euscelis incisus was found harbouring a 16Sr‐IB phytoplasma. Out of 60 tested vector insects, only one adult of Macrosteles quadripunctulatus and two of E. incisus fed on 16Sr‐IB source cyclamen gave a positive amplification signal in nested PCR. This extremely low level of transmission to both cyclamen and the very susceptible periwinkle strongly suggests that cyclamen, commonly found infected in crops, is an unsuitable species for phytoplasma acquisition and can be regarded as a dead‐end host plant for phytoplasmas belonging to both IB and IC subgroups. Indications for glasshouse management are drawn from these findings. Among the leafhoppers investigated E. incisus falls most under suspicion since it feeds better than the others on cyclamen, was able to transmit the disease to one periwinkle plant, and IB phytoplasmas were detected in two individuals.
Effects of diseases on the growth and yield of spring linseed (Linum usitatissimum), 1988–1998
Authors: PERRYMAN S A M , FITT B D L
Published: July 2006

In spring linseed field experiments with fungicides at Rothamsted from 1988 to 1998, substantial yield losses assoeiated with diseases occurred in three years and slight losses could be associated with diseases in other years. These yield losses were related to decreases in yield components (thousand grain weights and number of capsules). Leaf browning was observed each year and percentage leaf area with browning was the disease factor most consistently related to yield losses (in five years). Yield loss relationships for these five years suggested that for each 10% increase in percentage leaf area with browning there was a yield loss of 0.10 to 0.18 t ha−1. Stem browning, lesions on capsules and powdery mildew were associated with yield losses in two years, three years and one year, respectively. Yield losses were greatest in years when the period of flowering and early capsule development in June and July was wetter than average; the predominant disease was grey mould (Botrytis cinerea) in wet years up to 1996, whereas pasmo (Mycosphaerella linicola) was most important in 1997 and 1998. Observed yield losses were small in hot, dry years when powdery mildew (Sphaerotheca lini) and verticillium (Verticillium dahliae) were the predominant diseases.
Oligogenic inheritance for resistance to Zucchini yellow mosaic virus in Cucurbita pepo
Authors: PARIS H S , COHEN S
Published: July 2006

‘True French’ is an open‐pollinated cultivar of the Zucchini (Courgette) Group of Cucurbita pepo and is susceptible to Zucchini yellow mosaic virus (ZYMV). Using C. moschata‘Menina’ as the source of ZYMV resistance and following six generations of backcrossing, a true‐breeding line nearly isogenic to ‘True French’, designated 381e, was recovered that carried ZYMV resistance, albeit not at as high a level as in ‘Menina’. ‘True French’ and accession 381e were crossed, and their reciprocal F1, F2, and backcross progenies were grown in a chamber and inoculated with a highly virulent, non‐aphid‐transmissible strain of ZYMV. Nearly all F1 plants and all plants of the backcross to 381e were classified as resistant. Segregation to resistant and susceptible individuals occurred in the backcross to the susceptible parent, in accordance with a 3:5 three‐gene ratio of resistant: susceptible. The F2 segregated in accordance with a ratio of 45 resistant : 19 susceptible, which would be obtained if there was one major gene for resistance, Zym‐1 (Zym), and two other genes, herein designated Zym‐2 and Zym‐3, both of which for complementary to Zym‐1. The presence of Zym‐1 and either Zym‐2 or Zym‐3 is necessary for resistance to be expressed in young plants, but the presence of all three might be necessary for resistance to continue to be expressed during subsequent development of the plants. Evidently, Zym‐2 and Zym‐3 are ubiquitous in C. moschata but their susceptible alleles are much more common in C. pepo. As the level of resistance of 381e to ZYMV is not as high as that of C. moschata‘Menina’, additional, as yet unidentified, genes must be involved in conferring high resistance to this virus.
Effect of potato used as a trap crop on potato cyst nematodes and other soil pathogens and on the growth of a subsequent main potato crop
Authors: SCHOLTE K
Published: July 2006

A field experiment in which main‐crop potatoes were grown every other year was conducted on a sandy soil from 1994 to 1999. The aim of the experiment was to control soil‐borne pathogens of potato with ecologically sound methods. Potato grown as a trap crop from the end of April to the end of June (8 wk) was used to control potato cyst nematodes (PCN) (Globodera pallida), and its effects on other important soil pathogens and on the growth of a subsequent potato crop were also assessed. Additional experimental treatments were a potato crop from which the haulm was removed and a green manure crop. Three potato cultivars with different degrees of resistance to PCN were grown as the main crop. Duplicate sets of the experiment were run concurrently.

The PCN were effectively controlled by the potato trap crop. When a highly resistant potato cultivar was grown as a main crop after the trap crop, the post‐harvest soil infestation was very low. When a moderately resistant cultivar was grown after the trap crop the soil infestation also remained low. When the trap crop was alternated with a susceptible potato cultivar as a main crop, soil infestation increased slightly, but the degree of control when compared with no trap crop averaged 96%.

Soil infestation with root‐knot nematodes (mainly Meloidogyne hapla) increased when potato was grown as a trap crop, but soil infestation with the root‐lesion nematode Pratylenchus crenatus was not affected. Stem canker caused by Rhizoctonia solani was not affected by the trap crop but black scurf (sclerotia of R. solani) on tubers was reduced. Soil infestation with Verticillium dahliae declined in one of the duplicate sets of the experiment but not in the other. However, stem infections by V. dahliae were significantly decreased in both sets, although the effect depended on the PCN‐resistance level of the potato cultivar. When a highly resistant potato cultivar was grown Verticillium stem infections were not significantly affected, they were decreased with a moderately resistant cultivar but the decrease was most pronounced with a PCN‐susceptible cultivar.

Senescence of a following potato crop was not influenced by the trap crop when a highly PCN‐resistant cultivar was grown, but it was delayed in the case of a moderately resistant or a susceptible cultivar, resulting in higher tuber yields for those cultivars.

The experiment proved that a trap crop can be an alternative to chemical soil disinfection but, for several reasons, the potato itself is not an ideal crop for this purpose; a trap crop other than potato must be developed.
Genotypic variation in ‘early warning signals’ from roots in drying soil: intrinsic differences in ABA synthesising capacity rather than root density determines total ABA ‘message’ in cowpea (Vigna unguiculata L.)
Authors: KULKARNI M J , PRASAD T G , SASHIDHAR V R
Published: July 2006

In a comparison of six cowpea cultivars, we determined the variation in abscisic acid (ABA) production as an ‘early warning signal’ produced in response to drought stress. By imposing drought only to the upper 20 cm rooting zone, we compared the rates of ABA synthesis relative to (i) total root mass and (ii) inherent variation per unit root mass. We were able to relate the intensity of the stress response to these two factors, and determine which is quantitatively more important as the primary signal indicating responsiveness to drought stress. Plants were grown in 1.2 m long columns and a soil drying treatment imposed in such a way that that upper roots were in dry soil and deep roots in soil at field capacity. Relative water contents (RWC) of stressed plants were similar and not significantly different from those of well watered controls. However, roots accumulated ABA in the dehydrated zone, where root water content ranged from 10–12 g g−1 DW. The soil moisture contents and root ‐water contents in the dry zone were similar for each of the different varieties. However, the ABA contents were significantly different in drought‐stressed (upper) roots and ranged from 7.82 nmol g−1 DW in cv. APC 689 to 16.02 nmol g−1 DW in cv. APC 370, such that for varieties with similar overall root weights (e.g. APC 580 and APC 540) the different ABA contents were related to the capacity for ABA synthesis. The relationship between stomatal conductance and total root ABA was assessed, with a negative relation (r= 0.90, n= 24, P= 0.05) suggesting that the intrinsic capacity of cowpea varieties for ABA synthesis could play an important role in regulating stomatal conductance in a drying soil and provide useful selection criteria for tolerance to drought stress.
Effect of soil type, salinity, and allelochemicals on germination and seedling growth of a medicinal plant Lepidium sativum L.
Authors: EL‐DARIER S M , YOUSSEF R S
Published: July 2006

The present work was conducted to elucidate the effect of soil type, salinity stress and allelochemicals from alfalfa on the germination efficiency, seedling growth and photosynthetic pigments of Medicago sativa L. The highest germination rate (69.9%) was recorded for seeds cultivated in sandy soil followed by that of clay soil (42%) and then loamy soil (19%).

The maximum germination rate was attained at 50 mM NaCl concentration level, after that the values were decreased as the salinity levels increased. The maximum lengths (cm) of plumule and radicle and their growth rates (cm/day) were obtained at control level and found to decline significantly as the salinity increased.

Aqueous extracts of alfalfa reduced the germination rate, radicle and plumule growth and seedling dry weight of L. sativum. However, chlorophyll and carotenoid content was increased, their maxima were recorded at 50% concentration level. The chlorophyll a/b ratio attained its maximum at the full strength concentration level.
Effects of potassium carbonate as an alternative de‐icer on ground vegetation and soil
Authors: ERHART E , HARTL W
Published: July 2006

The effects of the new de‐icer potassium carbonate on the growth and species composition of a mixed sward and on the pH and electrical conductivity of the soil were examined in a four‐year field trial and compared with sodium chloride. There were small positive effects of K2CO3 on the biomass yield of the sward at application rates up to 200 g m−2 yr−1, while effects were less negative than those of NaCl at annual application rates of 200 – 400 g m−2 yr−1. The species composition of the sward changed considerably with K2CO3 application, Agropyron repens becoming the dominant species. The pH was elevated slightly more by K2CO3 than by NaCl application. Electrical conductivity as an index of soil salinity was increased by both de‐icers. K2CO3 was more adsorbed to soil colloids than NaCl, so that the rise in E.C. resulting from application of the former was restricted to the uppermost 10 cm of soil.
Impact of a disease and a defoliating insect on houndstongue (Cynoglossum officinale) growth: implications for weed biological control
Authors: CONNER R L , DECLERCK‐FLOATE R A , LEGGETT F L , BISSETT J D , KOZUB G C
Published: July 2006

The noxious weed houndstongue (Cynoglossum officinale) has become a major problem on the forested rangelands in the interior of British Columbia. However, recently the fungus Phoma pomorum and the ranchman's tigermoth (Platyprepia virginalis) were identified as potential biocontrol agents of this biennial weed. Infection by the fungus Ph. pomorum resulted in the formation of large brown lesions on leaves of houndstongue. In culture, the fungus readily produced pycnidia with pycnidiospores measuring 5.7 μm × 1.7 μm. The effect of Ph. pomorum and P. virginalis on the growth of houndstongue was examined over a six week period. Leaf age strongly influenced the intra plant distribution of insect feeding and lesion formation with Ph. pomorum primarily attacking the older leaves, while P. virginalis larvae preferred feeding on young leaves. Infection of leaves by Ph. pomorum resulted in their premature death. The effect of infection by Ph. pomorum on plant weight varied among tests, but the disease usually increased the number or percentage of dead leaves and reduced root biomass. A study of the effect of plant age and disease on houndstongue showed that younger plants infected with Ph. pomorum had a slightly higher percentage of dead leaves than older plants, but that reductions in live leaf weight and root weight were similar for different age groups. Six weeks after exposure to feeding damage by P. virginalis, there was no significant effect of P. virginalis on plant weight either acting alone or in combination with Ph. pomorum.
Responses of the sweetpotato whitefly, Bemisia tabaci, to the chinaberry tree (Melia azedarach L.) and its extracts
Authors: HAMMAD E M ABOU‐FAKHR , NEMER N M , HAWI Z K , HANNA L T
Published: July 2006

Host preference bioassays for adults of the sweetpotato whitefly were performed with leaves of the chinaberry tree Melia azedarach L., tomato, cucumber and bean. Fruit and leaf extracts of the chinaberry tree were tested against adults of the sweetpotato whitefly. Fruit extracts were tested against eggs, first and second instar nymphs, and pupae of the insect. Treatments included aqueous, methanol, and acetone fruit extracts of 200 mg ml−1 and serial dilutions of 20.0 and 2.00 mg ml−1, ether extract, the botanical insecticides Azatin® and Margosan® ‐O and the control, water or water with Triton®. Mortality data was collected at 6, 7, and 8 days after treatment of the eggs, nymphs and pupae, respectively. Results of the host preference bioassays indicated a significantly lower number of live insects on leaves of the chinaberry tree vs leaves of bean, cucumber, and tomato after 24 h. This indicates that M. azedarach is not a good host for the sweetpotato whitefly. Adults of the insect were significantly more repelled from tomato plants treated with the undiluted extracts when compared to the control after 72 h. There were significant differences in percent mortality of nymphal instars when exposed to the undiluted extracts compared to other extracts and the control. However, there was no significant effect of the fruit extracts on the egg and pupa instars. Thus M. azedarach extracts were found to be repellent to the whitefly adults, while the fruit extracts have shown a significant detrimental effect against early nymphal instars. In general, the methanol extracts were more active against B. tabaci than extracts with other solvents.
Effects of foliar sprays of azoxystrobin on take‐all in wheat
Authors: JENKYN J F , BATEMAN G L , GUTTERIDGE R J , EDWARDS S G
Published: July 2006

Average percentages of winter wheat plants with severe take‐all were decreased by up to half by azoxystrobin applied as foliar sprays in four field experiments. Decreased take‐all in three of the experiments was associated with increased grain yield but effects on other diseases may have contributed to these responses. Standard fungicide sprays were ineffective. The effects differed, but not consistently, among different cultivars that were tested in three of the experiments. One, two or three sprays of azoxystrobin or kresoxim‐methyl, in autumn, spring or summer, were tested in the fourth experiment. Unlike azoxystrobin, kresoxim‐methyl had no consistent effects but a smaller amount was applied. Two or three sprays of azoxystrobin were more effective than a single spray but their timing was unimportant. Such control of a root disease by a foliar‐applied fungicide is unusual but may help to explain some of the unexpectedly large yield responses to azoxystrobin that have been reported. This relatively broad‐spectrum fungicide may have the potential to contribute to the practical management of take‐all but further research is needed to determine how best to exploit its effects consistently.
Relationships between phoma leaf spot and development of stem canker (Leptosphaeria maculans) on winter oilseed rape (Brassica napus) in southern England
Authors: SUN P , FITT B D L , GLADDERS P , WELHAM S J
Published: July 2006

Models were constructed to describe the relationships between incidence of phoma leaf spot at different growth stages in autumn/winter or early spring and incidence of stem canker (basal canker or stem lesions) in summer on winter oilseed rape in southern England. Model 1, describing the phoma leaf spot/basal canker relationship, wasy1=β0+β1x1+β2(x2‐x1) ifx2>x1, andy1=β0+β1x1ifx2≤x1, in whichy1was the incidence (% plants affected) of basal canker at harvest,x1was the maximum incidence of phoma leaf spot during the period from sowing to growth stage (G.S.) 1,6‐1,7 (about 100 days after sowing) andx2was the maximum incidence of phoma leaf spot between G.S. 1,7 and G.S. 2,0 (start of stem extension). Model 2, describing the phoma leaf spot/stem lesion relationship, wasy2=α0+α1x3+α2x4, in whichy2was the incidence of stem lesions at harvest,x3was the incidence of phoma leaf spot at G.S. 3,3–3,5 (flower buds visible) andx4was the incidence of phoma leaf spot at G.S. 4,5–5,5 (flower buds opening). Data from field experiments with four winter oilseed rape cultivars at Boxworth or Rothamsted in the 1992/93, 1993/94, 1996/97, 1997/98 or 1998/99 seasons were used to test the models. The values ofR2for the regression equations testing model 1 for the phoma leaf spot/basal canker relationship were 0.75, 0.93, 0.91 and 0.89 for cvs Apex, Bristol, Capitol and Envol, respectively. The values ofR2for the regression equations testing model 2 for the phoma leaf spot/stem lesion relationship were 0.58, 0.57, 0.54 and 0.71 for cvs Apex, Bristol, Capitol and Envol, respectively. The phoma leaf spot/basal canker relationship (model 1) could also be fitted to the combined data set for all four cultivars (R2= 0.65), whereas the phoma leaf spot/stem lesion relationship (model 2) could not to be fitted to the combined data set for the four cultivars. The relationships between incidence and severity of stem canker were examined and the values ofR2for the regressions of severity on incidence were 0.91 for basal canker and 0.89 for stem lesions.
Identification of resistance to Peanut bud necrosis virus (PBNV) in wild Arachis germplasm
Authors: REDDY A S , REDDY L J , MALLIKARJUNA NALINI , ABDURAHMAN M D , REDDY Y V , BRAMEL P J , REDDY D V R
Published: July 2006

Eighty three wild Arachis germplasm accessions, belonging to 24 species of five sections and one natural hybrid derivative of a cross between the cultivated and a wild Arachis species, were evaluated along with a susceptible groundnut cultivar for resistance to Peanut bud necrosis virus (PBNV) in a replicated field trial at ICRISAT, Patancheru, India. Thirty days after sowing, the percentage of infected plants were recorded for all the accessions and subsequently young leaflets from all these accessions were tested for the presence of the virus by enzyme linked immunosorbent assay (ELISA). One accession each of A. benensis and A. cardenasii, and two accessions of A. villosa, in the section Arachis, two accessions of A. appressipila in the section Procumbentes, and one accession of A. triseminata under section Triseminatae were not infected by PBNV. These seven field‐resistant accessions were tested under glasshouse conditions for virus resistance by mechanical sap inoculations. One accession of A. cardenasii and two accessions of A. villosa did not show systemic infection. Similarly, in another glasshouse test, where 13 A. cardenasii accessions of section Arachis were evaluated, two accessions did not show systemic infection. In all these resistant accessions, the inoculated leaves showed infection, but the systemic leaves did not show the presence of virus in spite of repeated mechanical sap inoculations. So, the resistance in these accessions appears to be due to a block in systemic movement of the virus. To our knowledge this is the first report on the identification of resistance to PBNV in wild Arachis species. Since both A. cardenasii and A. villosa are the progenitors of cultivated groundnut and can be hybridised with the latter, the resistant accessions are being utilised in conventional breeding programmes to transfer PBNV resistance to widely adapted groundnut cultivars.
Pathogenicity of fungi associated with melon vine decline and selection strategies for breeding resistant cultivars
Authors: IGLESIAS A , PICÓ B , NUEZ F
Published: July 2006

Melone Vine Decline is a severe rot root disease of increasing world‐wide importance. In Eastern Spain it is related to the presence ofAcremonium cucurbitacearumandMonosporascus cannonballus. The strong influence of environmental conditions on the progress of this disease has made its study difficult. A field screening ofCucumis meloaccessions has been conducted over four years. Simultaneously, the pathogenicity of isolates of the two fungi recovered from the screening field was studied. These were more aggressive than other Spanish and American isolates. Percentage of vine decay was scored, togeter with root damage, the latter being evaluated by using four scoring systems based on root characteristics and disease severity. Root inspection alowed the selection of resistance sources, even when aboveground symptoms did not appear, due to the lack of environmental stresses at time of fruit maturity. The root damage scoring if environmental stresses occur during fruit maturity.

The accessionC. melovar.agrestisPat 81 consistently exhibited high field resistance level, expressed as a higher percentage of symptomeless plants, together with a significant delay in symptoms appearance. The F1hybrids derived from the cross Pat 81 ×C. melosusceptible varienties showed an intermediate level of resistance between the parents, suggesting a partial dominance gene action. The high resistance level found in Pat 81, and also in its derived hybrids, against the aggressive isolates found in this area, makes it promissing for breeding melon verieties resistant to melon vine decline.
The physiological response of winter wheat to reductions in plant density
Authors: WHALEY J M , SPARKES D L , FOULKES M J , SPINK J H , SEMERE T , SCOTT R K
Published: July 2006

The effects of reducing the plant density of winter wheat (cv. Haven) on canopy formation, radiation absorption and dry matter production and partitioning were investigated in field experiments in 1996/97 and 1997/98. Crop densities established ranged from 19 to 338 plants m−2. Grain yield was maintained with large reductions in plant density. At low plant densities the relative growth rate of the crop increased allowing a maintenance of crop dry matter production. An 18 fold reduction in plant density led only to a six fold reduction in green area index at the beginning of stem extension and by anthesis the difference was less than two fold. Crops grown at low plant densities increased green area per plant through increased duration of tiller production, green area per shoot and shoot survival. Main stem leaf number, phyllochron and tiller production rate were not significantly affected by plant density. Radiation use efficiency was greater at the low plant densities. We propose that better radiation distribution through the canopy and increased canopy nitrogen ratio were the causative mechanisms for this increase in RUE. As a result of increased green area per shoot and a decrease in ear production, more radiation was absorbed per shoot at the low plant densities, allowing an increase in grain number per ear from 32 to 48.
Potato yellow vein virus: its host range, distribution in South America and identification as a crinivirus transmitted by Trialeurodes vaporariorum
Authors: SALAZAR L F , MÜLLER G , QUERCI M , ZAPATA J L , OWENS R A
Published: July 2006

Sporadic outbreaks of potato yellow vein disease (PYVD) were first observed in the early 1940's by potato growers in Antioquia, Colombia. Long known to be transmitted by the greenhouse whitefly (Trialeurodes vaporariorum), the precise identity of its causal agent (presumably viral in nature) has remained obscure. Here, we present evidence that a closterovirus with a bipartite genome, potato yellow vein virus (PYVV), is associated with PYVD. Electrophoretic analysis revealed that diseased tissue contains 4–5 disease‐specific dsRNAs ranging in size from c. 9 000–1 800 bp. RT‐PCR reactions containing pairs of degenerate primers directed against conserved motifs in the closterovirus heat‐shock protein homologue produced products of the expected sizes. Comparison of the corresponding amino acid sequences revealed striking similarities between PYVV and two bipartite, whitefly‐transmitted criniviruses, Cucurbit yellow stunting disorder and Tomato chlorosis viruses. Epidemiological surveys carried out in Rionegro, Colombia identified Polygonum mepalense, Polygonum spp., Rumex obtusifolium, Tagetes spp., and Catharanthus roseus as potential viral reservoirs. PYVV is transmitted through tubers, and visual symptoms alone cannot be used to determine infection status. A sensitive hybridisation‐based assay for PYVV has been developed for use in seed certification programmes.
Growth and development of plants with potential for use as trap crops for potato cyst nematodes and their effects on the numbers of juveniles in cysts
Authors: SCHOLTE K
Published: July 2006

Growth and development of three plant accessions with potential for use as trap crops for potato cyst nematodes (PCN), Solanum sisymbriifolium and two varieties of S. nigrum, were studied under 12 h and 17 h photoperiods. In pot experiments, rate of plant emergence, plant height, and shoot and root mass were greater for the S. nigrum varieties ‘90‐4750‐188’ and ‘88‐4750‐061’ than for S. sisymbriifolium and markedly greater than for a S. nigrum variety found as a weed of arable fields in The Netherlands. However, the last mentioned S. nigrum variety produced the most berries. Plant height and shoot weight of all the S. nigrum varieties were greater under the longer photoperiod, whereas the root mass was hardly affected. Plant height and shoot weight of S. sisymbriifolium also were greater under the longer photoperiod but the root weight was less. Under field conditions, with sowing dates from the end of March to mid August, S. sisymbriifolium and S. nigrum‘90‐4750‐188’ grew better than S. nigrum‘88‐4750‐061’. In contrast to S. nigrum, S. sisymbriifolium appeared resistant to night frosts in autumn. The stubbles of both S. sisymbriifolium and S. nigrum showed good regrowth after cutting the plants 5 or 10 cm above the soil surface 11 wk after sowing. In a pot experiment, all the plant accessions strongly reduced the numbers of juveniles in cysts compared with flax. Tolerance to Globodera rostochiensis of S. sisymbriifolium and S. nigrum‘90‐4750‐188’ was investigated in pot experiments under glasshouse conditions in sandy soil at pH 4.8 and 6.0. At soil infestation levels ranging from 0 to 56 juveniles ml−1 soil, S. sisymbriifolium appeared much more tolerant than S. nigrum‘90‐4750‐188’. Shoot yield of S. nigrum decreased markedly with increasing soil infestation and root weight also decreased, except at pH 4.8 and light infestation levels. Both S. sisymbriifolium and S. nigrum grew better at soil pH 4.8 than 6.0. The proportion of lateral roots in the total root mass increased in both species with increasing PCN infestation and soil pH. However, although the proportion of lateral roots in plants grown at soil pH 6.0 was greater at PCN infestations up to 14 juveniles ml−1 soil, the proportion of laterals in S. nigrum was considerably less at PCN infestations of 56 juveniles ml−1 soil. The proportion of PCN juveniles hatching was similar for the two species and decreased slightly with increasing initial nematode population densities.
Effects of post‐chilling temperature on growth and variegation in Solomon's Seal
Authors: YEH D M , LIN Y R , ATHERTON J G
Published: July 2006

Effects of temperature were studied on the current and following season's growth of shoots from chilled rhizomes of Variegated Solomon's Seal. The rate of progress to completed elongation of the aerial shoot in chilled plants increased linearly with increasing temperature up to 28°C (24 h mean). A post‐chilling thermal time of 658 ± 47°Cd (> ‐1.3°C) was required for aerial shoots to become fully extended. Temperatures of 28°C and 33°C accelerated aerial shoot senescence and decreased rhizome and root dry weights, as compared with 18°C and 23°C treatments. Leaf number and variegation were not affected by temperature treatments during current growth season and all plants produced 12–13 leaves with between 7% and 9% leaf area variegated. Leaf variegation, however, was significantly increased in plants that had been grown after chilling at 28°C during the preceding growing season. Proteins of approximately 26, 32 and 62 kDa were present in the green parts of leaves but not in the white parts.
Temperature and relative humidity effects on egg and nymphal development of Aceria tulipae (K.) (Acari: Eriophyidae) on garlic leaves (Allium sativum L.)
Authors: COURTIN OLIVIER , FAUVEL GUY , LECLANT FRANÇOIS
Published: July 2006

Aceria tulipae (K.) is responsible for important crop losses of garlic in all production areas around the world. However, very little is known about its development in relation to temperature and relative humidity (r.h). Laboratory rearings from egg to adult stage were done on pieces of the apical part of young garlic leaves. These leaf pieces were placed in aluminium dishes floating on water or put on a solid hygroscopic salt in closed plastic trays. Rearing done in dark incubators at constant temperatures (10°C to 45°C) and with different r.h (25% to 75%) at 15°C and 25°C showed that: i) the shortest development time occurs at about 25°C; ii) the upper lethal temperature and the development threshold for the eggs are respectively estimated about 45°C and 6°C; iii) a r.h close to 100% is required for a high percentage of egg hatching, but water condensation on leaves is harmful. Host transpiration has an important regulatory effect on humidity conditions favouring mite survival.