bluuebunny/crossref_metadata_2025 huggingface dataset:
Distribution of 14CO2 during ontogeny of chickpea (Cicer arietinum) grown at two moisture levels
Authors: HOODA R.S. , SHEORAN I. S. , SINGH RANDHIR
Published: February 2008

The distribution of assimilates of 14CO2 in ethanol soluble and insoluble fractions was measured at 20‐day intervals from 45–135 days after sowing (DAS) in chickpea (Cicer arietinum) grown at two moisture levels. The contribution of pre‐flowering assimilates to pods, although very low, was higher under the stress conditions. At the time of harvest, the recovery of 14C in pods was 0.4 and 0.9% of the total 14C fed 45 DAS in soluble and 2.5 and 5.1% in insoluble fractions in control and stressed plants, respectively. The %14C received by nodules continuously decreased with increasing age of plants. Stressed plants diverted more 14C to nodules, compared to control, during vegetative and flowering stages. During active seed filling, stressed plants diverted more 14C to reproductive parts and less to nodules, compared to control. Significant amounts of 14C were retgined by the stem and leaves during the seed‐filling period and it appears that there is scope for the remobilisation of pre‐flowering, as well as post‐flowering assimilates for seed‐filling of chickpea.
Quality losses in wheat caused by the orange wheat blossom midge Sitodiplosis mosellana
Authors: HELENIUS J. , KURPPA S.
Published: February 2008

In three sets of data pooled over spring wheat varieties and lines a number of grain quality measurements were related to the levels of infestation by Sitodiplosis mosellana larvae. The Hagberg falling number value was negatively correlated with the proportion of damaged grains. The 1000‐grain weight, protein content and gluten content were not affected. Differences between cultivars in infestation and damage level were found to depend on the development phenology (timing of ear emergence) and on the percentage of damaged grains remaining in the yield after harvest. The falling number values were reduced most when the attainable values remained low in cultivars prone to sprouting damage, and in seasons with unfavourable weather conditions for quality maintenance.

The proportion of damaged grains in relation to the number of larvae was well described by a logit‐transformed regression. Sampling for infestation level and preventive measures against quality loss are discussed.
Forecasting the incidence of virus yellows in sugar beet in England
Authors: HARRINGTON RICHARD , DEWAR ALAN M. , GEORGE BRIAN
Published: February 2008

A new forecasting system for virus yellows incidence in sugar beet in the UK has been devised using multiple regression analyses. The forecast equations include data on (1) the previous year's virus incidence, (2) temperature in January and February and (3) the timing of the spring migration of Mytus persicae. Forecasts using the first two of these variables account for 63% of the variance in virus incidence in the main beet growing area of Eastern England and give growers information in time to decide on whether to apply aphicidal granules at drilling to control the vectors of the disease. Forecasts using all three variables account for 87% of the variance in virus incidence and can forewarn growers and the sugar industry of the likelihood of an epidemic. Forecasts for the northern and western regions of the beet growing area are derived from the forecast for the eastern region.
Biological characteristics of grass geminiviruses from eastern Australia
Authors: GREBER R. S.
Published: February 2008

Two serotypes of chloris striate mosaic virus (CSMV), paspalum striate mosaic virus (PSMV) and geminiviruses infecting Bromus catharticus and Digitaria didactyla were investigated. Their field occurrence and experimental hosts are listed. Serial transmission data for CSMV by single Nesoclutha pallida show a minimum latent period of 12–14 h, and regular transmission with occasional breaks for up to 50 days. Cicadulina bimaculata did not transmit any isolates after plant feeding acquisition, but transmitted CSMV inefficiently after insect injection. The vector of PSMV was found to be a specific biotype of N. pallida which bred only on Paspalum spp. The rate of transmission of CSMV with the Chloris biotype of N. pallida and of PSMV with the Paspalum biotype reached c. 50% with single insects, but only when freshly‐infected source plants were used. Geminate particles were found in thin sections of leaf tissue infected with all four viruses, and partially purified preparations were made of three of these. In gel diffusion tests, the virus from Microlaena stipoides produced a spur reaction with CSMV, when reacted with CSMV antiserum. The B. catharticus and D. didactyla isolates failed to react serologically with CSMV, maize streak or Vanuatu digitaria streak viruses.
Host range, purification and some properties of a new ilarvirus from Humulus japonicus
Authors: ADAMS A. N. , CLARK M. F. , BARBARA D. J.
Published: February 2008

In 1986, during routine quarantine testing, an apparently undescribed virus was isolated from two of 21 plants of Humulus japonicus grown from seed imported into the UK from Beijing, Peoples Republic of China. The virus, for which we propose the name humulus japonicus virus (HJV), was transmitted mechanically to a wide range of herbaceous plants. No symptoms were seen in virus‐infected H. japonicus plants. HJV infected, but did not become systemic, in the cultivated hop (Humulus lupulus) under our conditions although it has been detected serologically in both species of Humulus growing near Beijing. The virus was transmitted through seed of Chenopodium quinoa and was also associated externally with pollen of that species, but no pollen‐transmission tests were conducted. HJV was easily purified. Virus particles comprised a single polypeptide (mol. wt c. 26 350) and four RNA molecules (mol. wts 1.31, 1.05, 0.75 and 0.39×106). The three larger mol. wt RNAs were not infective in the absence of the smallest RNA. The particles were quasi‐isometric and variable in size. Purified preparations of particles formed four bands in sucrose density gradients but (after fixing with formaldehyde) only a single band (with a density of 1.364 g/ml) in caesium chloride isopycnic gradients.

These properties are similar to those of ilarviruses, and HJV was very distantly related serologically to prunus necrotic ringspot ilarvirus. We suggest, therefore, that HJV be regarded as a new member of the ilarvirus group.

All known infected plants of H. japonicus at the site of introduction have been destroyed and the virus has probably been eliminated from there. Testing is continuing to confirm this.
Effects of increasing weed‐beet density on sugar‐beet yield and quality
Authors: LONGDEN P. C.
Published: February 2008

Weed beets are an increasing problem in many sugar‐beet crops in many countries. At present about one sugar‐beet field in four in England is infested with weed‐beet seed. Control in other crops can be achieved using selective herbicides but in sugar beet the weed beets, many of which are of annual habit, are not easily controlled and often compete with the crop. Experiments were done to quantify the yield loss caused by weed beet in sugar‐beet crops. Transects were laid out across three fields in 1985 and 1986 and plots located thereon to include the range of weed‐beet densities found in the field. Weed beet did not affect the concentration of sugar (sucrose), potassium, sodium, α amino nitrogen or invert sugar in the crop beets. Root and sugar yields were progressively reduced by increasing densities of weed beet. A rectangular hyperbola described the data slightly better than an asymptotic model. There was no indication of a threshold density of weed beet below which there was no yield loss, which averaged 11.7% for each weed beet plant/m2. This corresponds to an average 0.6% sugar yield loss for each 1% of bolted weed beet in the root crop up to 100%, which is similar to the reported losses resulting from bolters in the root crop.
Viability of rape (Brassica napus L.) seeds following selection on the basis of newly‐emerged radicles then subsequent drying and storage
Authors: FINCH‐SAVAGE W. E. , McKEE J. M. T.
Published: February 2008

Germinating rape seeds selected on the basis of newly‐emerged radicles (1 ± 0.5 mm) were dried to an equilibrium moisture content (c. 11%) in air at 20°C and 80% relative humidity without loss of viability. Storage life of these low‐moisture‐content germinating (LMCG) seeds at 15°C was limited to 7 days before viability was significantly reduced. However, viability of LMCG seeds was maintained for 84 days in storage at ‐20°C. Longer periods in store reduced viability, but 96% of seeds still remained viable after 336 days at ‐ 20°C. Increasing periods of storage at ‐20°C reduced the subsequent seed longevity at 15°C, indicating a reduction in vigour during storage. Storage under reduced pressure or in a nitrogen atmosphere had little significant effect on seed longevity. Reduction of moisture content below 11% using vacuum drying at a range of temperatures reduced seed vigour.
An analysis of rain‐mediated dispersal of Drechslera teres conidia in field plots of spring barley
Authors: DEADMAN M. L. , COOKE B. M.
Published: February 2008

In two separate trials rain‐mediated dispersal of Drechslera teres conidia was observed in field plots of cv. Beatrice spring barley. Within the crop spore number was greater towards the base reflecting both the downward movement of conidia and the greater availability of spores on older leaves. From the edge of the crop half as many conidia were trapped at 100 cm as at 25 cm. In both trials the cumulative spore catch total lagged behind the increase in net blotch infection levels on the top two leaves. The number of spores sampled appeared closely related to rainfall intensity.
Use of three screening techniques for the evaluation of fungicides to control rhizoctonia root rot of wheat
Authors: COTTERILL P. J. , BALLINGER D. J. , KOLLMORGEN J. F.
Published: February 2008

Twenty fungicides were screened for their abilities to reduce the saprophytic growth of Rhizoctonia solani on agar and in soil, and to control root rot of wheat (Triticum aestivum) in pots of soil. Thirteen showed some activity against the in vitro growth of R. solani, the most promising being Sandoz 619F and flutolanil, although none of these reduced saprophytic growth of the fungus in soil. Only benomyl and thiabendazole, which were ineffective on agar and against disease in pots, reduced saprophytic growth in soil. None of the fungicides reduced the number of plants infected in the pot experiments and only six (flutriafol, diniconazole, Schering 539865, propiconazole, Bayer HWG1608 and flutolanil) of the thirteen active on agar (+ triadimefon which was not) reduced root rot severity. The results of this study indicate the differing reactions towards R. solani of chemicals in the three screening tests and confirm the potential for chemical control of rhizoctonia root rot of wheat.
The effects of fungicide‐coated seeds on the establishment of VA mycorrhizal infection
Authors: SPOKES J. R. , HAYMAN D. S. , KANDASAMY D.
Published: February 2008

Commercial fungicide‐coated seed of five plant species was tested to determine whether the fungicides used affected seedling infection by VA mycorrhizal fungi. All the plants became mycorrhizal, with no differences between those emerging from fungicide‐coated or non‐fungicide‐coated seed. However, when the same fungicides were applied as soil drenches, mycorrhizal infection was greatly inhibited, and in some instances was absent throughout the duration of the experiment.
Seed‐borne alfalfa mosaic virus infecting annual medics (Medicago spp.) in Western Australia
Authors: JONES R. A. C. , PATHIPANAWAT W.
Published: February 2008

Infection with alfalfa mosaic virus (AMV) was widespread in introduction, evaluation and seed increase plots of cultivars and numbered selections of annual medics (Medicago spp.) in Western Australia; the virus was detected in plots of seven species. When seed stocks from the West Australian annual medic collection harvested in 1984–1986 were sown and seedlings tested, seed‐borne AMV was found in all 12 cultivars and in 44/50 numbered selections, belonging to 10 species. Seed transmission rates to seedlings ranged from 0.3–74% and exceeded 5% in 33 seed lots. By contrast, when seedlings of four species grown from seed harvested in 1971–1978 were tested, no AMV was detected; the oldest infected seed stock found was from 1980. In commercial seed stocks of two cultivars released in 1987, the levels of seedling infection with AMV found were 0–0.2% for M. polymorpha cv. Santiago and 526% for M. murex cv. Zodiac. In commercial 1986 seed of M. polymorpha cvs Serena and Circle Valley, AMV was detected in 3/13 and 6/9 stocks respectively; transmission rates to seedlings in infected stocks were 0.1–0.7%. In a survey of 47 annual medic pastures in medium and low rainfall zones of the Western Australian wheat belt in 1987, the virus was detected in leaf samples from only three sites.

When inoculated mechanically, AMV systemically infected 11 cultivars and 12 selections belonging to 13 species, but did not infect one selection each of M. aculeata and M. orbicularis. Infected plants in ten species developed only faint mosaics or were symptomlessly infected, but M. littoralis, M. polymorpha and M. tornata developed distinct mottling, reduction in leaf size and, in some instances, leaf deformation and dwarfing. In pot tests, AMV infection decreased herbage and root production (dry wts) of M. polymorpha cvs Serena and Circle Valley by about 30% and 50–60% respectively, but did not decrease herbage production in M. murexcv. Zodiac. In spaced plants growing outside, AMV decreased herbage, root (dry wts) and seed production of M. polymorpha cvs Circle Valley and Santiago by about 60%.
Some properties of a previously undescribed virus from cassava: Cassava American Latent Virus
Authors: WALTER B. , LADEVEZE ISABELLE , ETIENNE L. , FUCHS M.
Published: February 2008

A virus with spherical particles c. 28 nm in diameter was sap‐transmitted from different cassava (Manihot esculenta) cultivars to a limited range of species in the families Chenopodiaceae and Solanaceae. Cassava seedlings infected by inoculation with sap or with purified virus preparations did not show any symptom, although the virus was readily detected by ELISA or by further inoculations. Leaf extracts from infected Nicotiana benthamiana were infective after dilution of 10‐‐3but not 10‐‐4, and after heating for 10 min at 70°C, but not at 72°C. The virus was purified from N. benthamiana, N. clevelandii or from cassava. On sucrose gradients, the virus particles sediment as three components all containing a protein of mol. wt c. 57000. The genome of the virus is composed of two RNAs of mol. wt c. 2.54 times 106(RNA‐1) and 1.44 times 106(RNA‐2). RNA‐2 was detected in the middle and the bottom nucleoprotein components, and RNA‐1 only in the bottom component. An antiserum prepared to purified virus particles was used to readily detect the virus in cassava and other host plants by ELISA and by ISEM. No serological relationship was shown between this virus and eight nepoviruses, including the recently described cassava green mottle nepovirus infecting cassava in the Solomon Islands (Lennon, Aiton & Harrison, 1987). The virus described here is the first nepovirus isolated from cassava in South America, and is named cassava American latent virus.
Temperature effects on the life history of the eulophid wasp Diglyphus isaea, an ectoparasitoid of leafminers (Liriomyza spp.), on tomatoes
Authors: MINKENBERG OSCAR P. J. M.
Published: February 2008

The effect of constant and alternating temperatures on the life‐history of Diglyphus isaea, as an ectoparasitoid of Liriomyza leafminers on tomato plants, was examined in the laboratory.

Parasitoid development and size were significantly affected by temperature and sex. Males showed a shorter development time and pupal size than female parasitoids. Both development time and pupil size in D. isaea differed according to the host species. Pupal size showed no consistent relationship with temperature. The lower thermal threshold for development and oviposition was determined. Fecundity with L. byroniae as host did not differ significantly between temperature regimes. Furthermore, larger females did not produce larger numbers of offspring. Development and reproduction under the alternating temperature regime did not differ from those at the comparable constant temperature, suggesting a rapid response to changes in temperature.

The intrinsic rate of increase (rm) and net reproduction (Ro) of D. isaea nearly doubled from 15°C to 25°C and 20°C, respectively, and generation time at 25°C was less than half that at 15°C. Because the parasitoid's population growth is higher than that of these pest insects at all temperatures, D. isaea is a promising candidate for seasonal inoculative biological control of Liriomyza on tomato crops in Scandinavian and western European glasshouses. Possible constraints to its effectiveness are discussed.
Estimation and validation of a function describing the rate at which Mycosphaerella graminicola causes yield loss in winter wheat
Authors: SHAW M. W. , ROYLE D. J.
Published: February 2008

An experiment designed to generate a wide variety of epidemics of Mycosphaerella graminicola without deliberate replication was done in two years. Disease severity was estimated at frequent intervals during the life of the crop and yields measured at harvest. Absolute estimates of disease severity were derived by regression of visual estimates on subsamples of leaves on which severity was estimated objectively using an image analysis system. Yield was predicted best by the integral of the square root of M. graminicola severity over the normal lifetime of each leaf, measured in thermal time. Only the top two leaves contributed to yield loss; no influence of the third leaf on yield was detected. Thousand grain weight was best predicted by the integral of the square root of M. graminicola severity on the flag leaf alone. Parameter estimates were similar in the two years. The prediction equations were consistent with yields observed in an experiment done in a third year using two sowing dates and two rates of nitrogen fertilisation, despite a much greater range of disease severity. Although critical point models could describe each year's results adequately, neither parameter estimates nor the growth stage at which the best relation occurred were consistent across years. The equations to predict loss may be useful for farmers in decision‐support systems which are based on prediction.
A hydathode inoculation technique for the simulation of natural black rot infection of cabbage by Xanthomonas campestris pv. campestris
Authors: ROBESON D. J. , BRETSCHNEIDER KARIN E. , GONELLA M. P.
Published: February 2008

A technique was developed for the reliable inoculation of Xanthomonas campestris pv. campestris into the cabbage host, in a manner which simulates a natural process of penetration. By introducing the inoculum into guttation droplets on the leaf margin, the bacteria are taken into the plant via the hydathodes, thereby avoiding mechanical injury to the plant and the possibility of producing artefacts. This technique, while being highly efficient, possesses several advantages over commonly used methods of inoculation.
Host plant preference and the influence of different cabbage cultivars on the toxicity of abamectin and cypermethrin against Plutella xylostella Lepidoptera: Plutellidae
Authors: ABRO G. H. , WRIGHT D. J.
Published: February 2008

The toxicity of avermectin B, (abamectin) and cypermethrin was determined against fourth instar larvae of Plutella xylostella L. reared on three cabbage cultivars which differed in their suitability as host plants. Cabbage cultivars were assessed as hosts for P. xylostella on the basis of larval and pupal weight and adult fecundity. Larvae reared on the best host, the cabbage cv. Offenham Flower of Spring were significantly (P > 0.01) less sensitive to topically‐applied abamectin (4.7‐fold at LD50) or cypermethrin (2.3‐fold) when compared with larvae reared on the intermediate host, the Savoy cabbage cv. Aquarius F1. Larvae reared on Offenham Flower of Spring were also significantly (P > 0.01) less sensitive (4.5‐fold) to topically‐applied abamectin compared with larvae reared on the poorest host tested, the cabbage cv. Minicole Fl. In contrast, the residual/ingestion toxicity of abamectin against fourth instars was significantly (P > 0.01) greater (2.5‐fold at LC50) on Offenham Flower of Spring than on Minicole F1. The results are discussed in terms of larval weight and larval feeding rates on the different cabbage cultivars.
Resistance in lettuce to the leaf aphids Macrosiphum euphorbiae and Uroleucon sonchi
Authors: REININK K. , DIELEMAN F. L.
Published: February 2008

Screening of 90 lettuce genotypes revealed great variation in resistance to the leaf aphids Macrosiphum euphorbiae and Uroleucon sonchi. Butterhead genotypes were usually, but not always, moderately to highly resistant to both aphid species. On the other hand mcjst crisphead genotypes had little or no resistance to both species. The results for the modern crisphead cultivar Marbello showed that it is possible to transfer resistance to M. euphorbiae from the butterhead to the crisphead type. Breeding programmes should benefit from the fact that in many cases resistance to M. euphorbiae and to U. sonchi, and in some cases also to other aphid species, was found in the same genotype. However, correlations between resistance scores for M. euphorbiae and U. sonchi were rather low, indicating that some components of resistance are specific to only one of the aphid species. Also within three groups of genotypes with resistance to Nasonovia ribisnigri, Myzus persicae and Pemphigus bursarius, respectively, large differences in resistance to M, euphorbiae and U. sonchi were found. The accumulation in one genotype of various resistance components to create cultivars with broad aphid resistance is a challenging and difficult task for practical plant breeding.
Further studies on breeding for resistance to Botrytis cinerea in red raspberry canes
Authors: JENNINGS D. L. , BRYDON E.
Published: February 2008

A high level of resistance to cane botrytis caused by Botrytis cinerea was transferred from Rubus pileatus to the red raspberry through three generations of backcrossing. The strength of the resistance showed little diminution through these generations and it was therefore thought that a major gene for resistance had been transferred. But discontinuity in the resistance levels observed was detected in plants of only one group of the progenies and so evidence for a major gene is lacking. The results showed the considerable influence of gene H, which confers pubescence, and emphasised that resistance must be separately assessed for pubescent and non‐pubescent segregates.
Segregation of a viroid complex from a graft‐transmissible dwarfing agent source for grapefruit trees
Authors: HADAS RIVKA , BAR‐JOSEPH M. , SEMANCIK J. S.
Published: February 2008

A marked variation in tree size occurred in grapefruit trees budded in trifoliate orange rootstock and inoculated with a graft‐transmissible dwarfing agent (GTD) from grapefruit. Etrog citron (Citrus medico) inoculated with budwood collected from two GTD sub‐types displaying very mild (VM) and mild (M) dwarfing effects showed only mild leaf epinasty, whereas the severe (S) subtype induced severe epinasty and stunting typical of infection by the original GTD source 225‐T. The characteristic symptoms of the three sub‐types were persistent following three serial transfers to ‘Etrog’ indicators.

Extracts from ‘Etrog’ citron containing either the 225‐T or its derivative S displayed a profile of five viroid bands when analysed by the sequential PAGE system for detection of circular RNAs. The profile obtained included the well characterised 371 nucleotide citrus exocortis viroid (CEV) and four additional viroids of approximately 330, 300, 295 and 275 nucleotides. Sub‐types M and VM lacked the CEV band and each contained a complement of only three viroids of 330, 295, 275 and 300, 295, 275 nucleotides, respectively. These results indicate that a segregation of the viroid complex in grapefruit budwood was a major factor in the variation seen among trees inoculated from the GTD source 225‐T.
Distribution of 14C‐sucrose applied to leaves at different nodes of okra (Abelmoschus esculentum) during flowering and early pod growth
Authors: RAO N. K. SRINIVASA , BHATT R. M.
Published: February 2008

The distribution pattern of 14C‐sucrose from 14C‐sucrose applied to vegetative okra plants and leaves 1–9 on separate plants during the green pod development stage were investigated in relation to duration and leaf position. Results indicated bi‐directional transport of assimilates to both apical and basal portions of the stem. Within 48 h 14C moved to all plant parts; stem and leaves appeared to be strong sinks. In plants fed at the vegetative stage, 48 h after feeding, 66% of the fed activity was exported from the fed leaf. At the pod development stage, about 35% of the activity exported from the fed leaf was present in green pods and 65% in vegetative parts. In plants where leaf 1–9 was fed, irrespective of the position of the fed leaf, the subtending fruit was the strongest sink among the reproductive parts. Leaves and stems were the principal sinks.
Competition between maize and Echinochloa crus‐galli analysed by a hyperbolic regression model
Authors: SPITTERS C. J. T. , KROPFF M. J. , de GROOT W.
Published: February 2008

Yield reduction of maize in relation to naturally established populations of Echinochloa crus‐galli and Chenopodium album was studied in field experiments over 2 years in which the maize was grown at a wide range of weed densities. Both the crop and the weeds were harvested at intervals during the season. The competitive relations were described accurately by a model based on a hyperbolic relation between yield and plant density. The model can be linearised by considering the reciprocals of the average weight per plant. However, estimating the regression coefficients by linear regression introduced a severe bias due to heterogeneity of variances. Estimation was improved by applying non‐linear regression, using a logarithmic transform of the yield equation. Fitted regressions were used to interpolate the yield data to standard weed densities. At a density of 100 Echinochloa plants m‐2, maize yields were reduced by 8% and 82% in 1982 and 1983, respectively, illustrating the problems in generalising the results of one competition experiment to the other. Three possible fields of application of the competition model are discussed, i.e. adjustment of experimental plot yield for variation in weed population, prediction of expected crop yield losses, and prediction of long‐term changes in weed seed populations.
The effect of pod growth stages in cowpea on aphid reproduction and damage by the cowpea aphid, Aphis craccivora (Homoptera: Aphididae)
Authors: OFUYA T. I.
Published: February 2008

Cowpea, Vigna unguiculata was infested at the young, mid‐fill and mature pod growth stages with, respectively, one, two and three pre‐reproductive adult apterae of Aphis craccivora per pod in a screen house. A. craccivora caused pod shrivelling at the young and mid‐fill pod stages, on which the aphid was more fecund. All levels of infestation caused significant reduction in seed yield irrespective of age of pod.
Cross‐protection between arabis mosaic virus and grapevine fan leaf virus isolates in Chenopodium quinoa
Authors: HUSS B. , WALTER B. , FUCHS M.
Published: February 2008

Cross‐protection experiments were performed in Chenopodium quinoa using arabis mosaic virus (ArMV) and grapevine fanleaf virus (GFLV) isolates.

Two factors were specially studied, namely the time interval and the distance between the two inoculations, respectively, with the hypovirulent isolate and with the hyper virulent challenge isolale.

ArMV‐S clearly protected C. quinoa from a super infection with GFLV‐F13 as shown by a diminution, or even suppression, of the synthesis of the coat protein and the nucleic acids of the GFLV‐F13 isolate. In the homologous interaction between GFLV isolates (GH and F13), protection was also observed. In the interaction between GFLV‐GH and ArMV‐862, by contrast, symptoms were typical of the hyper virulent ArMV‐862 and the amount of coat protein of ArMV‐862 was normal.
Aspects of herbicide activity and persistence under low level polyethylene covers
Authors: BOND W. , WALKER A.
Published: February 2008

In an experiment prepared in autumn, weed numbers were not affected by covering the soil with clear perforated polyethylene. Weed growth was enhanced, however, and the fresh weight at the time of polyethylene removal in spring was more than three times greater on the covered compared with the uncovered areas. In a similar experiment prepared in spring, covering with perforated polyethylene increased weed numbers by a factor of two and weed fresh weight by a factor of seven. The performance of a number of herbicides used in carrots, in terms of percentage reduction in weed number and weed fresh weight, was similar under covers and in the open. The most effective weed control was achieved with broad‐spectrum herbicide treatments, particularly under the polyethylene, since surviving weed seedlings grew rapidly in the protected environment. When weed control was good, covering enhanced carrot yield. Measurement of the distribution of herbicide residues in the soil demonstrated that persistence was increased and movement in the soil decreased by covering with polyethylene.
Photosynthetic assimilation of 14CO2 and fate of 14C‐labelled photosynthate in winter wheat (Triticum aestivum) near‐isoclines differing in alleles at the Rht1 and Rht2 reduced‐height loci*
Authors: KIYOMOTO R. K. , GENT M. P. N.
Published: February 2008

The mechanism by which reduced‐height genes, Rht1 and Rht2 influence yield and harvest index (HI) were investigated in dwarf (D, Rht1Rht2), semidwarf (SD‐1 and SD‐2, Rht1rht2 and rht1Rht2, respectively), and tall (T, rht1rht2) near‐isogenic lines (isolines) derived from winter wheat cv. Burt. Dry matter accumulation, yield, and assimilation, distribution, and retention of 14C label from photosynthetic assimilation of 14CO2, was followed in field‐grown plants in Connecticut, USA. The relationships among the isolines were similar over the two years of study. The tall isoline ranked highest in grain yield and biomass, but had a small HI; SD‐1 was similar to T in yield and biomass, but had the largest HI; SD‐2 was similar to SD‐1 in HI, but its yield and biomass were less than SD‐1 and T; and D yielded the least grain and biomass and had a small HI similar to T.

Following photosynthetic assimilation of 14CO2 during grain filling, the distribution of 14C in ears at maturity was similar for SD‐1, SD‐2, and T. When labelled shortly after anthesis or late in grain filling, the distribution of 14C to the mature ear of D was less than that for other isolines. At maturity D also retained the smallest amount of the radioactivity initially assimilated. The low yield and HI of D may be related to its inability to retain photosynthate and distribute it to the grain. The SD‐1, SD‐2, and T isolines did not differ in retention at maturity of 14C in the whole plant. When labelled shortly after anthesis, stems of T retained more 14C, which may represent a tendency to sequester more photosynthate in its stems that would reduce its HI at maturity. In contrast, the yield of SD‐2 was limited by photosynthetic capacity.
The response of apples cv. Cox's Orange Pippin to different concentrations of oxygen in the storage atmosphere
Authors: STOW J.
Published: February 2008

The response of apples cv. Cox's Orange Pippin to storage in flowing streams of air and nitrogen mixed to generate atmospheres ranging from 0.5% to 2% oxygen was examined in two seasons. The benefits of reducing store oxygen concentrations below 1.25% were small but storage in 0.75% may be advantageous for Cox's Orange Pippin apples in seasons when flesh firmness is low at harvest. Ethanol‐induced flesh breakdown was recorded in samples stored in 0.5% O2 in one season and the risk of low temperature breakdown was increased in oxygen levels below 1.25%. Ethylene production was reduced by lowering the oxygen concentration.
The effects of temperature and host quality on the rate of increase of the grain aphid (Sitobion avenae) on wheat
Authors: ACREMAN S. J. , DIXON A. F. G.
Published: February 2008

From 10°C to 25°C Sitobion avenae reared on wheat developed faster, had a higher mean relative growth rate and a higher intrinsic rate of increase on ears than on the flag leaves. At temperatures above 25°C there is a marked decline in the performance of the aphid. The intrinsic rate of increase is strongly correlated with the mean relative growth rate during development for both aphids reared on ears and flag leaves from 10°C to 25°C.
Genetic control of immunity to turnip mosaic virus in winter oilseed rape (Brassica napus ssp. oleifera) and the effect of foreign isolates of the virus
Authors: WALSH J. A.
Published: February 2008

Immunity to a UK isolate (UK 1) of turnip mosaic virus (TuMV) was studied in eight lines of oilseed rape selected from cv Rafal. Six of these lines were uniformly immune and two segregated. Segregation ratios in the F2 generation of reciprocal crosses between two uniformly immune lines and two uniformly susceptible cultivars (Mikado and Yeoman) showed that immunity was controlled by a dominant nuclear allele. The immunity was confirmed by the inability to detect virus particles in mechanically inoculated plants by back inoculations, ELISA and ISEM tests. Plants were immune to repeated inoculations and aphid transmissions.

The immunity was effective against one other UK isolate and two German isolates of TuMV. Another UK isolate (UK 3) and a Greek isolate partially overcame the immunity causing local infection and a Canadian and a Danish isolate overcame it completely causing systemic mosaic‐type symptoms. When these immunity‐breaking strains were tested against swede line 165 which is also immune to UK 1 TuMV, the Canadian isolate overcame the immunity whereas the Danish isolate did not. Using this swede line, one susceptible and one immune line of oilseed rape as differentials, four distinct groups of TuMV isolates could be identified. Selections of oilseed rape immune to UK TuMV isolates were more severely affected by the Canadian TuMV than UK TuMV susceptible selections. The gene determining immunity to TuMV had no pleiotropic effect on susceptibility to cauliflower mosaic virus.

The implications on these findings in relation to breeding for virus resistance are discussed.
The pattern of frost‐hardening of leaves of winter cauliflower (Brassica oleracea var. botrytis cv. Clause 30)
Authors: FULLER M. P. , GROUT B. W. W. , TAPSELL C. R.
Published: February 2008

The suitability of an electrical conductivity assay of leaf material for determining frost hardiness in winter cauliflower was established. The assay was used to monitor the changes in hardiness of field‐grown plants during two seasons at two sites.

Levels of frost hardiness were related to mean air temperature over the 7‐day period prior to sampling (r = 0.6008, P< 0.001). There was no clear disjunction of any temperature to indicate a threshold temperature of hardening. Dehardening occurred in spring and during mild spells in winter. In the mild regions where this crop is grown commercially it is likely that plants are not fully hardened for much of the winter. This may facilitate curd growth but may put the crop at risk from frost damage.
Establishing the large scale osmotic priming of onion seeds by using enriched air
Authors: BUJALSKI W. , NIENOW A. W. , GRAY D.
Published: February 2008

Onion seeds were primed in polyethylene glycol solutions (PEG) (‐1.5 MPa) for 14 days at 15°C on filter paper and in bubble columns containing 50 g seed litre‐1 PEG using air or enriched air (75% O2/25% N2) to aerate and suspend the seeds. Compared with untreated seeds, priming seeds in bubble columns using enriched air increased the percentage seed germination but it did not when air was used, or when seeds were primed on filter paper. Mean germination times (tm) were significantly reduced in all cases but the reduction was greatest using enriched air and least using air. The spread of germination times was significantly reduced only for seeds primed in enriched air.

Drying seeds following priming reduced the percentage germination compared with untreated seeds, but only significantly for those primed in bubble columns using air. Drying also increased the mean germination times by 1.5 to 1.8 days (relative to primed seed which had not been dried). Seeds primed in enriched air were least affected. This increased time is that typically required for water re‐imbibition after drying.

Priming with enriched air followed by drying gave the same number of normal seedlings as untreated seeds.
A ribosomal DNA probe to distinguish populations of Rhopalosiphum maidis (Homoptera: Aphididae)
Authors: LUPOLI R. , IRWIN M. E. , VOSSBRINCK C. R.
Published: February 2008

Total DNA from clones of Rhopalosiphum maidis was digested with restriction endonucleases and hybridised with a heterospecific ribosomal DNA probe. DNA banding patterns exhibited sufficient differences to distinguish five different clones, and provided greater resolving power than gel electrophoresis of allozymes. The mechanisms and applications of this marking technique are discussed.
Forecasting of peak population density of the rose grain aphid Metopolophium dirhodum on wheat
Authors: HOWARD M. T. , DIXON A. F. G.
Published: February 2008

Suction trap catches for the period 1969 to 1984 were used to develop a forecasting system for M. dirhodum. This was achieved by using the strong relationships that exist between: a) suction trap catches of Metopolophium dirhodum at Broom's Barn and populations of the aphid in fields near Norwich, and b) winter and spring temperatures and the time when the crop became unsuitable for this aphid.

This forecasting system was tested in 1985, 1986, 1987 and 1988 and successfully forecast early in the season that it would not be necessary to apply aphicides in 1987 and 1988. The use of this forecasting system would have correctly indicated that aphicide application against this aphid was unnecessary in 9 out of the 16 seasons from 1969 to 1984.
Double‐stranded RNA analysis of strawberry plants affected by June yellows
Authors: WATKINS C. A. , JONES A. T. , MAYO M. A. , MITCHELL M. J.
Published: February 2008

Using an improved method for extraction of dsRNA from strawberry leaf tissue, small quantities of several dsRNA species with mol. wt greater than 1.0 × 106were detected in strawberry plants free from known strawberry viruses but affected by June yellows (JY). No such dsRNA species were detected in plants of Fragaria vesca or seven strawberry cultivars known to be free from JY. Neither JY symptoms nor these dsRNA species were detected in healthy strawberry and F. vesca plants graft‐inoculated with tissue from JY‐affected plants. It is not known whether the JY‐associated dsRNA species are those of a causal agent of JY or are a consequence of the JY condition. Nevertheless, the detection of such dsRNA species in plants affected by JY may offer a possible objective method for detecting the incipient condition in symptomless strawberry plants. However, the concentrations of dsRNA in JY‐affected plants are very low and dsRNA analysis is thought not to be sufficiently reliable for routine testing of plants. The occurrence of anomalous dsRNA species in extracts from some strawberry plants was caused by dsRNA from two‐spotted spider mites (Tetranychus urticae) infesting the plants.
Different variants of the satellite RNA of groundnut rosette virus are responsible for the chlorotic and green forms of groundnut rosette disease*
Authors: MURANT A. F. , KUMAR The late I. K.
Published: February 2008

Groundnut plants with symptoms of rosette disease contain groundnut rosette virus (GRV), but GRV is transmitted by Aphis craccivora only from plants that also contain groundnut rosette assistor virus (GRAV). Two main forms of rosette disease are recognised, ‘chlorotic rosette’ and ‘green rosette’. GRV cultures invariably possess a satellite RNA and this is the major cause of rosette symptoms: satellite‐free isolates derived from GRV cultures from Nigerian plants with chlorotic or green rosette, or from Malawian plants with chlorotic rosette, induced no symptoms, or only transient mild mottle or interveinal yellowing, in groundnut. When the satellite RNA species from GRV cultures from Nigerian green or Malawian chlorotic rosette were reintroduced into the three satellite‐free isolates in homologous and heterologous combinations, the ability to induce rosette symptoms was restored and the type of rosette induced was that of the cultures from which the satellite RNA was derived. Thus different forms of the satellite are responsible for the different forms of rosette disease. Other forms of the satellite induce only mild chlorosis or mottle symptoms in groundnut. Individual plants may contain more than one form of the satellite, and variations in their relative predominance are suggested to account for the variable symptoms (ranging from overall yellowing to mosaic) seen in some plants graft‐inoculated with chlorotic rosette.
The interaction between lodging and plant population in combining peas
Authors: PULLAN M. R. , HEBBLETHWAITE P. D.
Published: February 2008

The effects of preventing lodging in three varieties of combining peas with contrasting standing ability were studied over a range of plant populations and in two growing seasons.

Maximal yield losses resulted when lodging occurred prior to the end of the flowering period. The likelihood of this event occurring was increased by high populations and was maximised when such populations were used in conjunction with conditions suitable for vigorous plant growth. In such seasons, optimum plant populations (30 plants m‐2) were seen to be very much below those currently recommended.

When conditions were less favourable to plant growth, lodging tended to occur after flowering had ceased. Little yield loss due to population effects were then recorded. Under such conditions, yields were maximised by high plant populations. Under all growing conditions, little yield loss due to interplant competition was noted with increasing plant populations.

It was concluded from these results that if combining pea production is to be successfully expanded out of traditional production areas, plant population recommendations should be lowered to compensate for increased plant vigour.
Inhibition of degreening in the peel of bananas ripened at tropical temperatures.
Authors: BLACKBOURN H. D. , JEGER M. J. , JOHN P. , TELFER A. , BARBER J.
Published: February 2008

Functional and structural changes in peel tissue have been followed by analysing fluorescence induction curves and the lipid composition during the ripening of bananas (Musa AAA, Subgroup Cavendish) at 20°C and 35°C. Changes in the fluorescence induction curves indicated that electron transport capacity was lost more rapidly at 35°C than at 20°C, thus revealing that the chlorophyll retained by bananas ripened at 35°C soon becomes non‐functional photosynthetically, probably because of serious disturbances in thylakoid organisation during ripening at tropical temperatures. By contrast, in plantains (Musa Group AAB, Plantain Subgroup), where degreening is complete at both 20°C and 35°C, the loss of electron‐transport capacity closely corresponds to the loss of chlorophyll. The lipid composition of unripe banana peel resembled other photosynthetic tissue in possessing a high proportion of mono‐ and digalactosyl diacylglycerols, containing predominantly polyunsaturated fatty acids, particularly linolenic acid. Following ripening for four days at 20°C, when degreening was complete, some 50% of the galactolipids had broken down, and the polyunsaturated fatty acids were recovered in the neutral lipid fraction. By comparison, after ripening at 35°C there was a greater loss of galactolipids, and a lower overall recovery of linolenic acid. The significance of these findings for the stability of the chlorophyll‐protein complexes during the incomplete degreening of bananas at tropical temperatures is discussed.
Inhibition of degreening in the peel of bananas ripened at tropical temperatures.
Authors: BLACKBOURN H. D. , JEGER M. J. , JOHN P.
Published: February 2008

A linolenate‐dependent chlorophyll oxidase activity resembling the activity considered responsible for chlorophyll bleaching in senescing leaves has been studied in thylakoids isolated from the peel of bananas (Musa AAA, Subgroup Cavendish). While the degreening of bananas is inhibited as the temperature was raised above 24°C, chlorophyll oxidase activity increased linearly as the temperature was raised from 20°C to 40°C. Cyanide inhibits the chlorophyll oxidase activity in vitro, but the increased amounts of cyanide produced by banana peel ripened at high temperatures do not accumulate, despite the fact that β‐cyanoalanine synthase activity, which effectively traps the cyanide, remains relatively unaffected by the increased temperature. The association of chlorophyll oxidase activity with the functional and structural organisation of the light‐harvesting complexes and photosystems is discussed in relation to the inhibition of degreening in the peel of Cavendish bananas ripened at tropical temperatures.
Biological control of Dutch elm disease: Larvicidal activity of Trichoderma harzianum, T. polysporum and Scytalidium lignicola in Scolytus scolytus and S. multistriatus reared in artificial culture
Authors: JASSIM H. K. , FOSTER H. A. , FAIRHURST C. P.
Published: February 2008

A method is described for the culture of larvae of Scolytus multistriatus and Scolytus scolytus on an artificial medium following exposure to cultures of microorganisms. In control cultures, a natural mortality rate of 21.2% was found for S. multistriatus and 17.6% for S. scolytus. The effects of Trichoderma harzianum, T. polysporum and Scytalidium lignicola on fifth instar larvae of S. scolytus and S. multistriatus reared on the artificial medium were studied. The fungi were larvicidal and larval mortality was increased to more than 80% by inoculation of the larvae with the fungi. Another fungus, Phomopsis oblonga, had little effect on larvae of S. scolytus. The results are discussed in relation to mechanism of pathogenicity of the fungi and their potential use in the control of Dutch elm disease. It is proposed that with modifications, the method is applicable to other bark beetle pests.