bluuebunny/crossref_metadata_2025 huggingface dataset:
Properties and partial purification of infective material from plants containing groundnut rosette virus*
Authors: REDDY D. V. R. , MURANT A. F. , RASCHKÉ J. H. , MAYO M. A. , ANSA O. A.
Published: February 2008

Groundnut plants with chlorotic rosette disease contain a manually transmissible virus, groundnut rosette (GRV), which is also transmitted in the persistent (circulative) manner by aphids (Aphis craccivora), but only from plants that are co‐infected with a manually non‐transmissible luteovirus, groundnut rosette assistor virus (GRAV). Strains of GRV from plants with chlorotic or green forms of rosette are called GRV(C) and GRV(G) respectively. An isolate of GRV(C) from Nigeria remained infective in Nicotiana clevelandii leaf extracts for 1 day at room temperature and for 15 days at 4d̀C, but lost infectivity after 1 day at ‐20d̀C or after dilution to 10‐‐4. Its infectivity and longevity in vitro were not altered by addition of 1 mg/litre bentonite to the extraction buffer. Infectivity in leaf extracts was abolished by treatment with 50% (v/v) ether, 10% (v/v) chloroform or 8% (v/v) n‐butanol, but not by treatment for 30 min with RNase A at up to 100 ng/ml. In attempts to purify GRV(C), nearly all the infectivity from N. clevelandii extracts was found in the pellets from centrifugation at 65 000 g for 1. 5 h; infectivity also occurred in a cell membrane fraction that collected at the top of a 30% sucrose ‘cushion’ containing 4% polyethylene glycol and 0.2 M NaCI. However, no virus‐like particles were found in either type of preparation by electron microscopy.

Nucleic acid preparations made directly from GRV(C)‐infected N. clevelandii leaves were very infective; this infectivity was totally inactivated by treatment for 30 min with RNase A at 10 ng/ml in buffers of both low and high ionic strength and was therefore attributed to ssRNA. When nucleic acid preparations were electrophoresed in gels no virus‐specific bands were visible but the position of the infectivity indicated that the infective ssRNA has an apparent mol. wt of c. 1.55 × 106. A similar mol. wt was indicated by the rate of sedimentation of the infective ssRNA in sucrose gradients. Preparations of dsRNA made from GRV(C)‐infected N. clevelandii leaves contained a species of mol. wt c. 3.0 × 106; in addition some dsRNA preparations contained an abundant component of mol. wt c. 0.6 × 106 together with several other components of intermediate mol. wt. Similar patterns of bands were observed in dsRNA preparations made from Nigerian‐grown groundnut material infected with GRV(C) alone, or with GRV(C) + GRAV, or with GRV(G) + GRAV.

The properties of GRV closely resemble those of two other viruses that depend on luteoviruses for transmission by aphids, carrot mottle virus and lettuce speckles mottle virus.
Observations on the occurrence of Phalaris paradoxa in England and Wales
Authors: THURLEY B. , CHANCELLOR R. J.
Published: February 2008

A study of the occurrence of Phalaris paradoxa in England and Wales was made during summer 1984. Visits were made to 73 farms reported to be infested with this species. The presence of P. paradoxa was confirmed on 68 of them. Three other Phalaris species were also recorded as weeds on five farms. Infested farms were located over a wide area of southern England, with a majority in Essex. Most infestations were apparently less than 10 years old. Many infested fields had P. paradoxa only in the headlands. Varying degrees of control had been achieved with herbicides, hand roguing, cutting down and planting fields to grass. Counts of the densest area in 24 fields gave a median density of 167 and a maximum density of 1289 heads m‐2. With a mean of 96 caryopses per head these densities represent a potential seed production of 16 000 and 120 000 caryopses m‐2 respectively. It is concluded that further spread of the weed could be limited by suitable publicity about its occurrence and the best methods of control.
Anther culture in Brussels sprouts (Brassica oleracea var. gemmifera).
Authors: OCKENDON D. J.
Published: February 2008

Embryo yields from anther culture were determined for seven F1 hybrid genotypes of Brussels sprouts, one of which was known to be highly responsive. At least 1400 anthers were cultured for each genotype and the genotypes were tested in two groups. Although the results were variable, the genotypes were provisionally grouped as follows: two were highly responsive (with up to 180 and 376 embryos per 100 anthers cultured), one was moderately responsive (with up to 53 embryos) and four were virtually non‐responsive. The possible genetic basis for the difference in responsiveness is discussed, together with the implications of the results for the utilisation of anther culture in Brussels sprouts breeding.
Evidence for resistance in wheat cultivars grown in sand culture to the take‐all pathogen, Gaeumannomyces graminis var. tritici
Authors: PENROSE L.
Published: February 2008

A laboratory method to inoculate seedlings uniformly with Gaeumannomyces graminis var. tritici is described. Resistance is defined via the rate of hyphal entry into the vascular tissue of host seedlings, and is measured by direct observation and by early stelar lesion development in seminal roots. The two scores for resistance are compared and evaluated, for infection with an isolate of low virulence. Evidence was obtained for resistance in the roots of wheat seedlings to G. graminis.
Fungi growing on stored soybeans and their significance in lipid breakdown*
Authors: LISKER N. , BEN‐EFRAIM A. , HENIS Y.
Published: February 2008

US Grade 2 soybeans contain about 20% cracked and split seeds, 3% damaged seeds and 2% foreign material. Examination by scanning electron microscopy showed that intact seeds were externally almost free of microorganisms. In cracked seed coats and in damaged areas on broken soybeans, profusely developing fungal mycelia were frequently observed. Fungi penetrated the beans through these cracks and through the micropyle. Penetration through the hilum was observed only in cases where the seed coats showed pronounced signs of damage. No penetration through pore‐like structures in the seed coat could be observed. Light microscope observations of sections of naturally infested soybeans showed little penetration into the underlying cell layers. Sections of soybeans kept at 99% r.h. and 26d̀C for 4 days revealed profusely developing fungi colonising both seed coat tissue and cotyledons. In the cotyledonous tissue hyphae did not penetrate into the cells but developed only in the intercellular spaces.

In inoculated, detached seed coats, fungi developed better on the inner than on the outer side. On cotyledons free of seed coats, fungal development was better than in the seed coat itself. In broken soybeans of commercial stock origin, free fatty acids (FFA), mould count and respiration rate increased 3.5‐, 3.5‐and 5.0‐fold, respectively as compared with intact ones. When broken and intact soybeans were mixed there was no increase in the rate of deterioration.

It is concluded that fungi are involved in the increase of FFA in soybeans during storage and that this process is significantly faster in the broken bean fraction.
The effect of anti‐viral thermal treatments on germination of lettuce (Lactuca sativa) seeds and subsequent seedling development
Authors: DREW R. L. K. , BROCKLEHURST P. A.
Published: February 2008

Experiments on the effects of virus‐inactivating high‐temperature (40d̀C) treatments (thermotherapy) of lettuce seeds partially imbibed in polyethylene glycol solution on subsequent germination and seedling development are described. Precise temperature control is shown to be important and subsequent recovery periods at lower temperature (20d̀C) may be beneficial. Fungal contamination which developed on seeds during thermotherapy was controlled, in some seedlots, by treatment in sterile conditions. The fungi were saprophytic on seeds killed by the thermotherapy. Old seed, even with high viability, was more susceptible to heat damage than fresh seed, and even fresh seed may be pushed close to its limits of tolerance by a 10‐day treatment. The techniques described may be suitable for producing small numbers of virus‐free plants for experimental or breeding purposes.
The resistance of genotypes of two species of Phaseolus beans to the leafhopper Empoasca kraemeri
Authors: GALWEYI N. W. , TEMPLE S. R. , SCHOONHOVEN A. VAN
Published: February 2008

To determine whether two species of Phaseolus beans differ in their suitability for reproduction of the leafhopper Empoasca kraemeri, resistant and susceptible genotypes of the two species were exposed to egg laying leafhoppers and the resultant numbers of nymphs on each were compared. Resistant genotypes of P. acutifolius bore fewer nymphs than any genotype of P. vulgaris. Even susceptible P. acutifolius genotypes bore no more nymphs/leaf than resistant P. vulgaris genotypes though they did bear more nymphs/cm2 of leaf area. These results indicate that P. acutifolius may be a useful donor of oviposition non‐preference, increased egg mortality, or possibly nymphal non‐preference, and confirm that counts of nymphs provide a useful screening technique in the selection of parental genotypes for an improvement programme.
Negative cross‐resistance between benomyl and MDPC in British isolates of Botrytis cinerea, Pseudocercosporella herpotrichoides and Verticillium fungicola var. fungicola
Authors: NATHANIELS N. Q. R. , WILSON KATHRYN , FLETCHER J. T.
Published: February 2008

Fifteen isolates of Pseudocercosporella herpotrichoides, four isolates of Botrytis cinerea and four isolates of Verticillium fungicola var. fungicola were examined on potato dextrose agar amended with benomyl or methyl N‐(3, 5‐dichlorophenyl)‐carbamate (MDPC). Negatively correlated cross‐resistance was clearly demonstrated with the isolates of P. herpotrichoides and B. cinerea. There were indications that the same phenomenon might also operate with the isolates of V. fungicola var. fungicola.
Hypersensitivity in apple to feeding by Dysaphis plantaginea: effects on aphid biology
Authors: LYTH M.
Published: February 2008

Effects on rosy apple aphid (Dysaphis plantaginea) of hypersensitivity to aphid feeding in apple were assessed in a series of insectary experiments in 1980–82. Hypersensitive plants rapidly produced tissue necroses at aphid feeding sites. Inoculation with apterae demonstrated that, in comparison with aphids on susceptible plants, aphids on hypersensitive plants showed symptoms characteristic of host antibiosis, including increased mortality, failure to reproduce and slower development. Embryo number indicated that fecundity of surviving adults was lower on hypersensitive plants and mean relative growth rate of aphids was reduced. Hypersensitivity did not prevent colonisation by gynoparae returning from the summer host, nor subsequent egg‐laying. It conferred, however, a strong resistance against colonisation after egg‐hatch the following spring. The potential of hypersensitivity as a field‐resistance is discussed.
The effect of root‐knot nematode on vascular resistance to Fusarium oxysporum f. sp. vasinfectum in the stems of cotton plants
Authors: HILLOCKS R. J.
Published: February 2008

The effect of root‐knot nematode (Meloidogyne incognita) on external wilt symptoms and on the cotton plant's vascular response to stem‐inoculation with Fusarium oxysporum f. sp. vasinfectum was investigated. Wilt symptoms were more severe in all plants inoculated with both organisms than with the fungus alone but relative wilt resistance of the cultivars was maintained. Greater symptom severity was associated with greater fungal proliferation in the stele and this was related to the ability of the nematode to reduce the efficiency of vascular occlusion. The nematode had no effect on the accumulation of infection‐induced terpenoid aldehyde compounds.
Yield responses of two ryegrass and two white clover varieties grown in contrasting mixtures with applications of phosphate at different depths and on different soils
Authors: GOODMAN P. J. , COLLISON M.
Published: February 2008

To validate earlier findings using 32P in upland soil and at different depths in lowland soil, ryegrass varieties S.23 or Titania were grown in mixtures with white clover varieties S.184 or Olwen. Unlabelled phosphate (0 or 43 kg P/ha) was applied to the surface or at 30 cm depth in lowland soil, and dry matter yields of grass and clover were measured. In June, on lowland soil, the greatest yield of clover was obtained by surface application. The most productive mixture was S.23/Olwen, although in August Titania outyielded S.23. By October S.23 again outyielded Titania. These results validated the isotopically discovered interactions between phosphate depth and grass/clover mixtures.

On upland peat and mineral soil, 0 or 43 kg P/ha was surface applied to the same varietal mixtures. In May, phosphate application to mineral soil slightly decreased clover presence, while clover was increased by mixture with Titania rather than S.23. In July, no significant phosphate effects were found, but in October phosphate increased clover yield and, at least on mineral soil, S.23/Olwen responded most.
A bioassay for predicting the resistance of wheat leaves to Septoria nodorum
Authors: GRIFFITHS HELEN M. , JONES D. GARETH , AKERS A.
Published: February 2008

Plants of the winter wheat cv. Bounty were inoculated with Septoria nodorum and then assayed for ergosterol. A detached leaf technique was used in which leaf segments were incubated on agar containing benzimidazole. Four levels of a conidial suspension inoculum were applied using a measured droplet technique. Ergosterol in plant extracts was measured using HPLC and its identity confirmed by co‐injection with pure ergosterol as an internal standard. The extracts were also assayed by silica‐gel thin layer chromatography with the sterol being visualised with rhodamine; the presence of ergosterol in the material from the two higher disease level treatments was confirmed by analysing the eluted spots in a spectrophotometer. Additional confirmation of ergosterol was obtained using gas‐liquid chromatography comparing a mixture of known plant sterols with a sample from the diseased leaf tissue.

The ergosterol assay was found to be very sensitive and offers a high level of reproducibility. It would therefore appear that such assays could be of value in breeding programmes when it is necessary to screen wheat cultivars for their reaction to S. nodorum or other fungal pathogens.
Traits associated with virulence to the aphid Macrosiphoniella sanborni in eighteen isolates of Verticillium lecanii
Authors: JACKSON C. W. , HEALE J. B. , HALL R. A.
Published: February 2008

Eighteen isolates of the entomopathogenic fungus Verticillium lecanii from various world‐wide locations, from insect hosts and soil were bioassayed against the aphid Macrosiphoniella sanborni in the laboratory. Virulence ranged from an isolate which achieved 100% mortality and LT 50 value (adults) of 3 days ± 0· 2 at 24 ° C, compared with the least virulent isolates causing less than 10% mortality over 14 days (when treated with an inoculum of 1 × 106 conidiospores/ml). All isolates produced extracellular protease and lipase, irrespective of their virulence. A number of traits were frequently associated with the expression of virulence including fast germination, high sporulation rate, an absence of extracellular amylase activity and high extracellular chitinase activities. Large spore size was not strongly associated with virulence. There were exceptions in each variate studied, suggesting that overall expression of virulence is a result of the total complex of these and other traits still to be determined.
Cereal production, crop protection and plant breeding*
Authors: WILLIAMS WATKIN
Published: February 2008

Trends in British agriculture which have led to the eclipse of rotations, to the concentration of cereal production on wheat and barley, and to a changeover to winter cereals, have increased the vulnerability of cereal crops to disease. Epidemics have been prevented by the deployment of effective resistances and, more recently, of a wide range of crop protection chemicals. Ecological protection by means of variety mixtures and field diversification has now added a new and effective element for the defence of cereals. The problem of durability of resistances and of the continuing effectiveness of chemicals remains, and new problems of susceptibility of crop varieties to herbicides have arisen. It is possible through the combined use of genetical, chemical and ecological defence mechanisms, to maximise the period of effectiveness of resistance genes and of fungicides and insecticides. The experience of the past half‐century has shown that dependence on a single protective mechanism provides only a transient solution to controlling disease.
A quantitative analysis of varietal and moisture status effects on the growth of Vicia faba in relation to radiation absorption
Authors: GREEN C. F. , HEBBLETHWAITE P. D. , ISON DEBORAH A.
Published: February 2008

Growth of two cultivars of Vicia faba, under various conditions of moisture status, was analysed in terms of solar radiation absorbed by their foliage.

The relationship between dry‐matter production and absorbed photosynthetically active radiation was linear throughout the growing season for both cultivars (Minica and Alfred) and for all levels of soil moisture status. A straight line was used, the slope of which represented a constant mean seasonal ‘efficiency’ of conversion of radiation into biomass.

Moisture stress reduced both the amount of radiation intercepted, by limiting the size of the canopy, and the efficiency of its conversion into dry matter. Efficiency of both cultivars grown under optimal water regimes was similar, however, drought had a more drastic effect on conversion efficiency of Minica.

Mean crop growth rates were highly dependent upon both absorption and efficiency, as were maximum crop growth rates during the linear portion of growth.

Reductions in seed yield were similar to trends in total biomass production. Harvest index was reduced by moisture stress in Minica, and increased to compensate for dry‐matter loss in Alfred.
An analysis of leaf growth in sugar beet.
Authors: MILFORD G. F. J. , POCOCK T. O. , RILEY JANET
Published: February 2008

The responses of leaf appearance and expansion to temperature in sugar beet were measured under controlled conditions, using ruler and auxanometers, to establish a basis for a subsequent analysis of leaf growth in field crops. The studies showed that leaf appearance rate responded linearly to temperature above 1°C, that leaf expansion rate responded likewise above 3°C and that both rates were zero below these base temperatures. Auxanometer measurements of leaf extension showed that daily rates of expansion of leaf area increased linearly with the daily integral of temperature. However, hourly rates of extension in length alternated with those in width during each 24 h cycle in patterns that were not clearly related to hourly changes of temperature or to the day/night sequence.
Factors affecting the cold hardiness of the peach‐potato aphid Myzus persicae
Authors: O'DOHERTY ROSE , BALE J. S.
Published: February 2008

Supercooling point studies were used to investigate the factors influencing the cold hardiness of the peach‐potato aphid Myzus persicae, a freezing‐susceptible insect. Overwintering adults lost cold hardiness as winter progressed, with a variable proportion showing a marked reduction in supercooling ability. Cold hardiness increased in spring so that all individuals demonstrated extensive supercooling ability typical of aphids reared in the laboratory at 20°C with a long photoperiod; these levels of cold hardiness were maintained in the field during summer and early autumn. First instar nymphs demonstrated considerable cold hardiness all year.

Surface moisture caused inoculative freezing in some first instar nymphs and adults when supercooled, but the majority were unaffected.

In the laboratory, adults starved for 7 days at 5°C showed distinct losses of supercooling potential equivalent to those observed in the field during mid to late winter. No loss of cold hardiness was found in first instar nymphs starved under the same conditions.

The results demonstrate that the cold hardiness characteristics of M. persicae are atypical of those observed in other freezing‐susceptible insects and it is suggested that continued feeding during mild winter conditions allows maintenance of cold hardiness particularly in adult aphids, and provides a possible explanation for the successful anholocyclic overwintering of M. persicae during such winters.
Effects of pirimicarb, dimethoate and benomyl on natural enemies of cereal aphids in winter wheat
Authors: POWELL W. , DEAN G. J. , BARDNER R.
Published: February 2008

The insecticides, pirimicarb and dimethoate are commonly applied to cereal crops in the UK and when this study was begun the fungicide benomyl was also regularly used. The effects of these chemicals on natural enemies of cereal aphids were examined in replicated plots of winter wheat.

Benomyl did not affect any of the groups examined but it was applied early in the season (April/May) when most natural enemies were few or absent from the crop. Numbers of carabid beetles, staphylinid beetles and spiders, sampled using pitfall traps and a vacuum net sampler, were all reduced by dimethoate but not by pirimicarb, although these effects were only detected by pitfall traps when the small plots were surrounded by polyethylene barriers to prevent inter‐plot movements. Parasitic Hymenoptera were decreased by both insecticides, partly due to direct toxicity and partly to host removal. Data on the aphid predators, Coccinellidae, Syrphidae and Chrysopidae were inconclusive because there were very few in the crop due to the scarcity of aphids.

Ways in which pesticides can affect natural enemy populations other than by direct mortality and the dangers associated with routine, prophylactic pesticide applications are discussed.
Predicting pathogen‐induced mortality in Hakea sericea (Proteaceae), an aggressive alien plant invader in South Africa
Authors: RICHARDSON D. M. , MANDERS P. T.
Published: February 2008

The woody shrub Hakea sericea is an aggressive invader of natural vegetation in South Africa. Large‐scale die‐back in H. sericea is attributed to a form of the fungus Colletotrichum gloeosporioides. The progression of symptoms of the disease was monitored over 21 months. Results were used to construct a transition matrix model to predict further progression of the disease. Eighty‐two percent mortality is predicted after 10 years. Pathogen‐induced seed release occurred mainly between October and January. No regeneration was observed beneath or near infected stands of H. sericea. The model will be useful to managers when identifying priority areas for weed control operations.
Factors affecting the survival of sclerotia of Sclerotium cepivorum in the Fraser Valley of British Columbia
Authors: LEGGETT M. E. , RAHE J. E.
Published: February 2008

Sclerotia of Sclerotium cepivorum buried in muck soil in the Fraser Valley decayed with time. The rate of decay of sclerotia was influenced by local environmental conditions. A mixture of soil with sclerotia increased their survival but there was no difference in the rates of decay in three different soils. The decay was greatest during winter when Fraser Valley fields are often flooded. Sclerotial decay was also affected by pretreatment of the sclerotia. Dried sclerotia decayed significantly (P < 0.05) faster than sclerotia which had not been dried, a phenomenon which is apparently due to changes in micro‐organisms on the sclerotia. Dried sclerotia which had been incubated in moist soil had fewer bacteria and more fungi than sclerotia which had been incubated in soil without being dried. The increase in fungi on the dried sclerotia was due to a dramatic increase in Trichoderma spp.
Persistence and phytotoxicity of napropamide residues in soil
Authors: WALKER A. , BROWN PAULINE A. , MATHEWS P. R.
Published: February 2008

The time for 50% loss of napropamide following incorporation into a sandy loam soil in the field varied from about 130 days when applied in spring or early summer to over 200 days when applied later in the year. When left on the soil surface, up to 75% of the applied dose was lost during the first 28 days after application in June or July, whereas losses following application in November, December or January represented less than 25% of the amounts applied. These losses following surface application were closely correlated with the amounts of incoming solar radiation. First‐order half‐lives for degradation in nine soils incubated moist at 20°C in the laboratory varied from 72 to 150 days. They were positively correlated with the extent of herbicide adsorption by the soils and with their clay content, and negatively correlated with soil pH. Phytotoxicity to wheat and barley in the same soils in glasshouse experiments was inversely related to their organic matter content and to the extent of herbicide adsorption. Wheat was more tolerant of the herbicide than was barley. The results are discussed in terms of possible carryover problems with napropamide in some crop rotations.
Loss of genetic diversity in pea germplasm by the elimination of individuals infected by pea seedborne mosaic virus
Authors: ALCONERO R. , WEEDEN N. F. , GONSALVES D. , FOX D. T.
Published: February 2008

Significant reduction of genetic diversity was observed in seed coat colour and electrosphoretic isozyme genotypes when infected plants were eliminated in genetically heterogeneous pea populations. Some accessions where genetic homogeneity was expected were apparently mixtures. Detection of latent infections by pea seedborne mosaic virus by the ELISA method was more effective on single‐plant samples than on bulked samples of four to five plants, and from older plants rather than young seedlings. The implication of these findings in relation to a virus eradication programme in plant germplasm collections are discussed.
Some species of Atherigona (Diptera: Muscidae) reared from Gramineae in Senegal
Authors: GAHUKAR R. T.
Published: February 2008

The sorghum shoot fly, Atherigona soccata is a pest of economic importance, on late‐sown local sorghums in Senegal. Rearing of shoot flies on five sorghum cultivars (Congossane, 51–69, Naga white, CE 90 and Swarna) showed no antibiosis effect on pest biology. Seven species of the sub‐genus Atherigona were reared from sorghum, five from pearl millet and one species from grasses in the laboratory. Atherigona soccata preferred sorghum and developed satisfactorily on Brachiaria grasses during the off seasons. The sub‐genus Acritochaeta was presented by A. orientalis.
Plant pathogenicity and transmission tests with Acholeplasma spp. isolated from coconut palms in Jamaica
Authors: EDEN‐GREEN S. J. , MARKHAM P. G. , TOWNSEND R. , ARCHER D. B. , CLARK M. F. , TULLYH J. G.
Published: February 2008

Isolates of Acholeplasma spp. cultured from lethal yellowing‐diseased coconut palms were characterised by polyacrylamide gel electrophoresis (PAGE) of cell proteins and by serological tests. Analysis of PAGE profiles placed 23 of the isolates in either of two related subgroups, (1A) or (IB), which show similarities to A. axanthum; 11 isolates were placed in group (2) which show similarities to A. oculi; and a single isolate formed a unique category (3). Serological relationships determined by fluorescent antibody and growth inhibition tests were in broad agreement with the PAGE classification. There was no evidence of transmission to plant hosts following injection of representative isolates into the cicadellids, Chlorotettix spp., Dalbulus maidis, Euscelidius variegatus or the cixid, Myndus crudus. Some isolates consistenty multiplied in E. variegatus following injection but were not acquired or transmitted during feeding through membranes. Antiserum to A. axanthum did not react with diseased or healthy palm tissues in enzyme‐linked immunosorbent assay and the recovery of further acholeplasma isolates from palms affected by bud‐rot disease demonstrated that these organisms were not specifically associated with lethal yellowing. The results suggested that these acholeplasmas are epiphytes or saprophytes on coconut palms.
The role of flying aphid vectors in the transmission of cucumber mosaic virus and potato virus Y to peppers in Israel
Authors: RACCAH B. , GAL‐ON A. , EASTOP V. F.
Published: February 2008

More than 44 species of aphids were trapped by suction during the spring seasons of 1981, 1982 and 1983 over a pepper field at Bet Dagan, Israel. Nineteen species transmitted cucumber mosaic virus (CMV), while seven transmitted potato virus Y (PVY) at least once. Over 80% of the CMV and of the PVY infection among test plants (Capsicum annuum cv. Weindale) exposed to trapped aphids was caused by Aphis citricola and two or three other Aphis species, Myzus persicae and Macrosiphum euphorbiae.

Landing rate was determined by comparing the proportion of each species found on green tiles or pepper plants with that found in suction traps. A. citricola was the most common but was found in a much lower proportion on plants than either in flight or on green tiles. Aphis spp. and M. persicae were more than 2–5 times more frequent (relative to other species) on green tiles than in flight. M. persicae and M. euphorbiae, which colonise peppers, were found on peppers at a proportion several times higher than either on green tiles or in the air.

The relative importance of the different vector species was calculated by multiplying abundance by the proportion of transmitters and the landing rate. A. citricola and Aphis spp. were responsible for more than 50% of the total transmission of either CMV in 1981 and 1982 and of PVY in 1981. Peaks of CMV infection of bait plants coincided with peaks of transmitters of A. citricola and Aphis spp. caught in suction traps. The significance of these findings in primary infection of peppers with CMV and PVY is discussed.
Inapparent infection of honey bee pupae by Kashmir and sacbrood bee viruses in Australia
Authors: DALL D. J.
Published: February 2008

Inapparent infection of pupae of Apis mellifera by Kashmir bee virus (KBV) and sacbrood virus (SBV) was detected by two different methods, in three consecutive summers, from two widely separated locations in Australia. The prevalence of inapparent KBV infections varied from year to year, in contrast to the more consistent levels of inapparent SBV infection. The implications of inapparent infection for the epizootiology of the viruses in Australia are discussed.
Weed‐crop competition studies in swedes.
Authors: FORBES J. C.
Published: February 2008

Hand‐weeding experiments were conducted over a three‐year period in field‐grown crops of swedes in north‐east Scotland. When weeds were left to grow all season they reduced the dry matter yield of swede roots by 62% in 1980 and 79% in 1981 but by only 42% in the dry year 1982, in comparison with a weed‐free crop.

In all three years there was at least one time when a single removal of all weeds was sufficient to prevent yield loss by weed competition. In 1980 this was 6 wk after crop sowing, but the intervals between weed removal times were too great to reveal how critical this timing was. With shorter intervals in 1981 the timing of a single removal of weeds to achieve maximum crop yield was found to be highly critical at 6 wk after sowing, but in 1982 when weed biomass was much lower a single weeding any time from 4–7 wk after sowing gave as high a yield as a crop kept weed‐free all season.

Earlier weeding allowed subsequently emerging weeds to become competitive and reduce crop yield, while delaying weeding until after the optimum time allowed early competition from weeds emerging with the crop to depress final yield. In all years if weed removal was delayed until 12 wk after sowing, the crop yield was only slightly or no higher than if weeds were left to grow all season. It is concluded that swedes, unlike red beet or sugar beet, are incapable of recovery from the severe restriction to growth caused by weeds competing with the crop from 6–12 wk after sowing.
Weed‐crop competition studies in swedes.
Authors: FORBES J. C.
Published: February 2008

In each of three hand‐weeding experiments in 1980, 1981 and 1982 the biomass of field‐grown crops of swedes was unaffected by weed competition up to 6 wk after sowing but by 9 wk unweeded plots had much reduced crop biomass compared with weed‐free plots. Propachlor, applied to half the plots in 1980 only, had little effect on the severity of weed competition but caused an early check to swede growth from which the crop fully recovered by 12 wk after sowing. In 1981 there was no significant biomass reduction due to weed competition until 9 wk after sowing, yet if weeds were removed 7 or 8 wk after sowing the crop biomass at harvest was substantially lower than if weeds were removed 6 wk after sowing. In 1980 and 1981 swedes made no late compensation for early growth restriction due to weed competition, but in 1982, when weed competition was less severe, late‐weeded or unweeded swedes made partial recovery at the very end of the season.

Growth analysis of the 1981 and 1982 crops showed that weed competition reduced leaf area index (LAI) more markedly than net assimilation rate (NAR), though in 1982 weed removal 9 or 12 wk after sowing was immediately followed by a short‐lived increase in NAR. The failure of swedes to recover from weed competition was shown to result from an inability to generate new leaf area rapidly when the weeds were removed. It is suggested that competition between swedes and weeds may be primarily for soil nutrients, especially nitrogen.
Weed‐crop competition studies in swedes.
Authors: FORBES J. C.
Published: February 2008

The developmental morphology and anatomy of swede cv. Ruta Øtofte from seedling emergence to vegetative maturity is described, with particular emphasis on development of leaves at the shoot apex and of storage tissue in the hypocotyl and root. Most of the growth of the storage organ takes place by proliferation of parenchyma from secondary cambia scattered throughout the inner secondary xylem.

The effects of weed competition on these processes were studied by means of hand‐weeding experiments in field‐grown swede crops in 1981 and 1982. Weed competition greatly reduced leaf area per plant from about 9 wk after sowing onwards, through restriction of both number and size of leaves. Only leaves which had not fully emerged by the onset of weed competition 6 wk after sowing were reduced in area. Weed removal at 9 wk allowed some recovery of leaf number but not of leaf size; weed removal at 12 wk was similar in effect to leaving the crop unweeded all season. Effects of weed competition on storage organ growth were later to appear than effects on leaf area. Weed competition reduced both the number of cambia initiated and the proliferation of parenchyma from these cambia; again if weed removal was delayed until 12 wk the effect was similar to leaving the crop unweeded but some recovery took place if weeds were removed at 9 wk.

Artificial shading had similar effects on swede growth to weed competition, except that leaf number was more strongly affected than leaf size and no recovery in cambial initiation took place if shading was removed at 9 wk. Growth analysis showed that shading affected net assimilation rate to a greater extent than leaf area, at least in the early stages, whereas weed competition had previously been found primarily to affect leaf area.

The failure of swedes to make any recovery from weed competition if this was removed at 12 wk was primarily due not to depletion by weeds of soil nutrient resources nor to restricted sink capacity in the storage organ, but to limitation of source capacity. Swedes, unlike sugar beet, apparently cannot rapidly generate new leaves in mid‐season to take advantage of weed removal, though there is a large reserve of leaf primordia at the shoot apex. This difference between swedes and sugar beet is discussed in terms of relative sink strength of shoot apex and storage organ.
Components of partial resistance to Septoria nodorum in winter wheat
Authors: LANCASHIRE PETER D. , JONES D. GARETH.
Published: February 2008

Components of partial resistance to Septoria nodorum were investigated in 10 cultivars of winter wheat having similar field resistances. The components measured were infection frequency, latent period, size, shape and rate of growth of lesions, spore production and its rate of increase. Latent period was found to be lognormally distributed. Some of the components of resistance were found to be significantly different between cultivars. Cluster analysis also showed that cultivars could be distinguished on the basis of their components of resistance. Principal components analysis indicated that resistance could be broken down into four underlying factors, three of which could be readily interpreted. The measurements of the components of resistance were combined in a model, the r‐index, based on Van der Plank's r. The amount of variation between cultivars cast some doubt on the predictive value of the index but all the cultivar values were well within the range bounded by two ‘synthetic’ cultivars made up of combinations of either the most resistant or the most susceptible components. It is considered that the r‐index has potential in screening for field resistance. The possibility of incorporating the most resistant‐type components into one cultivar is discussed. The use of cultivar mixtures containing cultivars having similar field resistances is also discussed in the light of the variability found in this study.
Race specific resistance to lettuce downy mildew (Bremia lactucae) in the lettuce cultivar Bourguignonne Grosse Blonde d'Hiver
Authors: NORWOOD JUDITH M. , CRUTE I. R.
Published: February 2008

A stock of lettuce cv. Bourguignonne Grosse Blonde d'Hiver used in previous studies was shown to carry the race specific resistance factor R1 and not R9 as originally thought. Investigations into a commercial stock of cv. Bourguignonne which exhibited a heterogeneous reaction to some B. lactucae isolates showed that it was a mixture of two lines. Each line carried one of two R‐factors (referred to as R9A and R9B) in a homozygous condition, although their identification was made difficult by the presence of R5/8. No plants were found which carried both R9A and R9B.
The effect of insecticides and a plant barrier row on aphid populations and the spread of bean yellow mosaic potyvirus and subterranean clover red leaf luteovirus in Vicia faba in South Australia
Authors: JAYASENA K. W. , RANDLES J. W.
Published: February 2008

The effect of the insecticides malathion, demeton‐S‐methyl and disulfoton, and a barley barrier row on the rate and pattern of spread of bean yellow mosaic potyvirus (BYMV) and subterranean clover red leaf luteovirus (SCRLV) in Vicia faba was investigated in field plots with artificially introduced sources of viruses and vectors.

The systemic insecticide treatments reduced aphid populations in the plots and this was associated with reduced spread of SCRLV, but not of BYMV. The barley barrier did not affect aphid populations in plots; however, it reduced the spread of BYMV to rows 1 · 1 m from the source but had only a minor effect on the spread of SCRLV.

Apterae rather than alates of Aulacorthum solani were implicated in the spread of SCRLV. Spread of BYMV was attributed mainly to alate migrants of Myzus persicae and Macrosiphum euphorbiae, but other aphid species and morphs which occurred in high populations at the times of most rapid virus spread may also have had an active role as vectors of BYMV.
Effects of delaying fungicide treatment of wounded potatoes on the incidence of Fusarium dry rot in store
Authors: HIDE G. A. , CAYLEY G. R.
Published: February 2008

Potato tubers artificially inoculated with Fusarium solani var. coeruleum or F. sulphureum 3 months after harvest were uniformly wounded and held at 5, 10 or 15°C for up to 21 days before immersion in fungicide suspensions. Holding tubers for 14 days at 15°C (curing conditions) or at 5°C did not alter the incidence of dry rot subsequently developing on tubers stored at 10°C, and holding tubers for up to 21 days at 15°C slightly increased disease caused by both pathogens. Thiabendazole, imazalil and prochloraz applied to tubers immediately after wounding almost completely prevented dry rot. Treatment after 3 days was less effective and the amount of disease increased with further delay; fungicides were more effective on tubers held at 5°C than at 10 or 15°C before treatment and storage, and efficacy of the fungicide was decreased by increasing the amount of inoculum on tubers.

Wounds became less susceptible to infection by F. solani var. coeruleum and F. sulphureum when tubers were held at 15°C before inoculation, and the incidence of rots was decreased by 70–80% by delaying inoculation for 7 days. Treating tubers with dichlorophen immediately after wounding slightly increased the disease. The effects of fungicide treatment, curing conditions and wound healing are discussed.
Studies on beet western yellows virus in oilseed rape (Brassica napus ssp. oleifera) and sugar beet (Beta vulgaris)
Authors: SMITH HELEN G. , HINCKES JENNIFER A.
Published: February 2008

Oilseed rape (Brassica napus L. ssp. oleifera) was studied as a potential overwintering host for the sugar‐beet yellowing viruses, beet yellows virus (BYV) and beet mild yellowing virus (BMYV), and their principal vector, Myzus persicae. In spring 1982, plants infected with a virus which reacted positively in enzyme‐linked immunosorbent assay (ELISA) with BMYV antibody globulin were found in oilseed‐rape crops; none of the plants contained virus which reacted with BYV antibody globulin. This virus was subsequently identified as beet western yellows virus (BWYV). No leaf symptoms could be consistently associated with infection of oilseed rape, but the virus was reliably detected by sampling any leaf on an infected oilseed‐rape plant. Some isolates from oilseed rape did infect sugar beet in glasshouse tests, but the proportions of inoculated plants which became infected were low. Apparently there is therefore little danger of much direct transmission of BWYV by M. persicae from oilseed rape to sugar beet in spring.

BWYV was introduced to and spread within oilseed‐rape crops in autumn by M. persicae, and autumn‐sown oilseed rape proved to be a potentially important overwintering host for M. persicae. In a survey of 80 autumn‐sown crops of oilseed rape in East Anglia, northern England and Scotland in spring 1983, 78 were shown to be extensively infected with BWYV.

Experimental plots of oilseed rape with 100% BWYV‐infection yielded approximately 13.4% less oil than plots with 18% virus infection, the result of a decrease in both seed yield and oil content.
Effects of dalapon and TCA on the growth and yield of oilseed rape (Brassica napus)
Authors: LUTMAN P. J. W.
Published: February 2008

The tolerance of oilseed rape (Brassica napus cv. Jet Neuf) to the herbicides dalapon and TCA was studied in two series of 10 experiments over four years. TCA (7.6–30.4 kg a.i./ha) was applied pre‐emergence and dalapon (2.9–11.6 kg a.i./ha) was sprayed post‐emergence between September and November at two growth stages (2–5, 4–7 leaves). Dalapon at all doses caused the leaves to appear yellow‐green in colour and at the higher rates (5.8–11.6 kg a.i./ha), especially when applied at the later of the two growth stages, scorched the leaf margins and stunted the plants. TCA also caused the leaves to appear yellow‐green and was noted to affect the retention of water by the leaf surfaces. In general the visible effects of treatment with dalapon were more severe than those of TCA.

The effects of these two herbicides on rape seed yields were variable, with some trials showing statistically significant reductions and others none. However by combining the results of trials with similar treatments some underlying trends were identified. In the overall analyses dalapon at 11.6 kg a.i./ha, applied at both growth stages and at 5.8 kg a.i./ha, applied at the later one, reduced yields significantly. TCA at 15.2, 22.8 and 30.4 kg a.i./ha also caused significant yield reductions in the combined analyses. Further statistical analysis questioned the safety of the lower rates of both herbicides, which were similar to those recommended by the manufacturers. The severity of the foliar damage caused by dalapon was well correlated with the risk of significant yield reductions but not with the actual percentage loss of yield. No such correlations were possible with TCA as the visual symptoms were similar on all sites and were unaffected by dose.

Recent changes in agricultural practices and in crop cultivar do not appear to have altered the sensitivity of rape to dalapon and TCA appreciably.
Parsnip (Pastinaca sativa) seed production: effects of seed crop plant density, seed position on the mother plant, harvest date and method, and seed grading on embryo and seed size and seedling performance
Authors: GRAY D. , STECKEL JOYCE R. A.
Published: February 2008

Parsnip seeds from four years of seed production (1980–83) were used to examine the effects of position of the seed on the parent plant and several cultural factors on seed and embryo growth and seedling performance. Maximum seed dry weight was reached c. 50 days after flowering (DAF) but embryos continued to grow for a further 7–15 days. The coefficient of variation (C.V.) of seed weight fell from c. 35–40% at 40 DAF, to about 20–25% at maturity. The corresponding figures for C.V. of embryo length were 25–35% at the early harvest and 12–15% at maturity. The effects of seed position, plant density, harvest method, seed grading after harvest on seedling emergence and weight characters were small. Harvesting seeds c. 60 DAF gave, on average, 3.3 days earlier emergence, c. 3.6 days lower ‘spread’ of emergence time and c. 9% higher seedling emergence than harvesting 2 wk earlier. Late harvesting of the seed crop reduced the C.V. of seedling weight from 53 to 46%, on average, but there were variations in response from year to year. Seedling emergence and seedling weight characters were more closely related to embryo length than to seed weight characters.
Reduction of cabbage root fly (Delia radicum) damage by protective discs
Authors: SKINNER G. , FINCH S.
Published: February 2008

Foam‐rubber, carpet‐underlay discs placed in position around the base of the stem directly after transplanting were as effective as certain recommended insecticides in protecting brassica plants from damage by cabbage root fly (Delia radicum). The three factors that contributed to the overall effectiveness of the discs were that only half as many eggs were laid around plants protected with discs as around unprotected plants, that predatory ground beetles preferred to aggregate in the humid microhabitat beneath the discs and consequently ate proportionally more fly eggs/larvae and that the discs acted as a mulch, conserving water around the roots of the plants, and thereby permitting them to tolerate greater amounts of damage.

Application of the repellent benzyl benzoate to the discs improved effectiveness but 12 other insect repellents and two sticky compounds gave no improvement and most were phytotoxic. Root drenches of the insecticide chlorfenvinphos were repellent, reducing oviposition by approximately 25%. The costs of protecting brassica transplants with either discs or insecticide were similar and discs thus appear to be a reasonable method of cabbage root fly control for small‐scale use.