bluuebunny/crossref_metadata_2025 huggingface dataset:
An assessment of genetic variability in somacloned lettuce plants (Lactuca sativa) and their offspring
Authors: BROWN C. , LUCAS J. A. , CRUTE I. R. , WALKEY D. G. A. , POWER J. B.
Published: February 2008

Plants were regenerated from callus derived from cotyledons and first true‐leaves of the lettuce cultivars Salad Bowl, Lobjoits Cos and Pennlake. Sexual progeny of these regenerants were assessed under glasshouse and field conditions for variation including reaction to lettuce mosaic virus (LMV) and downy mildew (Bremia lactucae). All three cultivars exhibited somaclonal variation. Mutations detected at the seedling stage included reduced vigour, albinism and changes in chlorophyll content, with most being recessive. Variation for leaf shape and vigour was detected in mature plants. One line exhibited increased yield and chlorophyll content together with early flowering. Enhanced and reduced susceptibility to both LMV and B. lactucae were observed. Reduced susceptibility to B. lactucae was indicated by an extended latent period following inoculation in two lines. Reduced susceptibility to LMV in glasshouse trials could not be confirmed in the field although one such line exhibited an improved yield and a second line segregated 1:1 in glasshouse tests for plants which were obviously infected and those without symptoms. All variable lines were diploid.
The effects of nitrogen application on growth and nitrogen distribution within the potato canopy
Authors: MILLARD P. , MACKERRON D. K. L.
Published: February 2008

The effect of applying nitrogen (N) fertiliser on the growth and distribution of N within the potato canopy was studied in 1983 and 1984. In both years N was applied either in excess of that required to produce maximum tuber yields, or not at all. The large application of N changed the pattern of canopy growth ‐ stimulating growth of leaves at the top of the stem, particularly lateral branches, for longer during the season, and accelerating the death of (shaded) leaves at the base of the canopy. The pattern of canopy senescence was, therefore, changed from a synchronous to a progressive type.

Application of nitrogen fertiliser at supra‐optimal rates increased the N contents of leaves, stems and tubers. The extra N in the leaves of these plants was present as reduced N in all leaf positions, and as nitrate (NO‐3) in the lowermost leaves. In addition, substantial quantities of NO‐3 were also stored in the stems. Part of this extra N in the canopy was redistributed during subsequent growth, especially to the lateral branches as crop N uptake slowed towards the end of the season. In addition, substantial quantities of N were also potentially available for redistribution to the growing tubers. There was little redistribution of N from the leaves of N‐deficient plants.

It is suggested that redistribution of N in the canopy of N‐replete plants allowed the growth of lateral branches towards the end of the season, thereby maintaining photosynthetically active leaves for longer than N‐deficient plants.
Field studies on the effects of peanut stunt virus on growth, nodulation and yield of Viciafaba in the Sudan
Authors: AHMED A. H.
Published: February 2008

The effects of the Sudanese isolate of peanut stunt virus on the growth, nodulation and yield of two cultivars of broad bean (Viciafaba) were assessed in field trials in the Sudan for two consecutive years. Virus infection reduced both the fresh and dry weights of shoots and roots, reduced nodulation by up to 78% and significantly reduced the number and weight of seed per plant. Seed yield per area was reduced by up to 91% and 93% in the cultivars Silaim and Tarbia respectively. These adverse effects were attributed to the virulence of the virus strain, the time of infection and the susceptibility of the cultivars tested.
Control of cereal aphids in winter wheat by natural enemies: aphid‐specific predators, parasitoids and pathogenic fungi
Authors: CHAMBERS R. J. , SUNDERLAND K. D. , STACEY D. L. , WYATT I. J.
Published: February 2008

Winter wheat fields on two farms in West Sussex were sampled in 1980 and 1981 for cereal aphids and their natural enemies. The grain aphid, Sitobion avenae was present in all 19 fields examined, but in no case did the populations increase to densities liable to cause economic damage. The observations strongly suggest that aphid population growth was stopped by aphid‐specific predators, hymenopterous parasitoids and fungal pathogens. In two fields in 1980, S. avenae population densities approximately equalled five aphids per ear at flowering, the threshold at which insecticide application is recommended in the UK, but numbers were then reduced by natural enemies, mainly aphid‐specific predators. In three fields in 1981, S. avenae would probably have exceeded the spray threshold had natural enemies not intervened in late May.
Characterisation of the distribution of individual response times in bacterial infection of plants
Authors: ERCOLANI G. L. , VANNELLA S.
Published: February 2008

The distribution of time of visible response to infection was followed after inoculation of Pseudomonas syringae pv. syringae onto the flowers of pear cv. Williams, Pseudomonas syringae pv. phaseolicola into the leaves of bean cvs Borlotto di Vigevano and Saluggia, Corynebacterium michiganense subsp. michiganense into the stem of tomato cvs Fiorentina and C 1402 and Agrobacterium sp. biovar 3 into the stem of sunflower cv. Egnazia at a dosage of either 0.5–32 times the median effective dose (ED50) or 1–64 ED50. The distribution contracted and the median response time decreased as the dose of inoculum was increased for each host‐pathogen combination. Modified Weibull regressions with shape parameter 1< c < 2.5 gave a highly significant fit to the observed distributions of individual response times in all dose groups and host‐pathogen combinations.
Melon rugose mosaic virus, the cause of a disease of watermelon and sweet melon
Authors: JONES PHILIP , ANGOOD SAEED BA , CARPENTER JOHN M.
Published: February 2008

A mechanically transmissible virus with isometric particles c. 32 nm in diameter, was isolated from infected watermelons and sweet melons in the People's Democratic Republic of Yemen. Purified virus preparations contained two major sedimenting components with sedimentation coefficients of 61S and 117S. In isopycn ic centrifugation in CsCl the particles formed a single band of buoyant density 1.39 g cm‐3. Preparations of virus particles comprised of a single polypeptide of mol. wt c. 22 000 and ssRNA of mol. wt 2.1 × 106. The virus was serologically related to three of six subgroups of tymoviruses tested. The name melon rugose mosaic virus is proposed for this newly described virus.
Effect of ethofumesate on the epicuticular waxes of onion leaves, and on the response of plants to foliage‐applied herbicides
Authors: RUBIN B. , ADLER U. , VARSANO RINA , RABINOWITCH H. D.
Published: February 2008

The herbicide ethofumesate is commonly used in onion fields in Israel. Experiments with four onion cultivars have shown the combination of a pre‐emergence treatment with ethofumesate and foliar application of a variety of herbicides to cause a marked decrease in plant fresh weight. This effect of ethofumesate was still evident when post‐emergence herbicides were applied as late as the third leaf stage of development. Significantly lower amounts of waxes were extracted with chloroform from the leaves of onion plants treated pre‐emergence with ethofumesate, at the rates of 0.2–0.8 kg/ha. SEM micrographs showed considerable changes in the onion epicuticular fine structure following these ethofumesate treatments. Furthermore, a significant increase in the penetration of 14C‐labelled compounds into the onion leaves was measured. The possible implications of ethofumesate effects on onion leaf surface fine structure, are discussed.
Introducing Erynia neoaphidis into a field population of Aphis fabae: form of the inoculum and effect of irrigation
Authors: WILDING N. , MARDELL SUSAN K. , BROBYN PATRICIA J.
Published: February 2008

The effect of treating field populations of Aphis fabae on spring‐sown field beans with different preparations of the entomogenous fungus Erynia neoaphidis, with and without irrigation of the crop, was examined at Rothamsted in 1979. The fungus applied on 21 June as the triturated cadavers of fungus‐killed aphids established infection in the host population as effectively as by distributing living laboratory‐infected aphids. Although the introduced fungus, together with other species present naturally, killed more than 70% of aphids in late July, it failed to multiply fast enough to protect the crop adequately. An application of an homogenate of the fungus grown on agar plates failed to establish infection.

From 25 June to 28 July there was little rain and irrigation greatly increased the proportion of aphids killed by E. neoaphidis during late July confirming that the spread of this fungus can be limited by dry conditions.
Effects of changing temperature regimes on resistance to races of Melampsora medusae in a cultivar of poplar
Authors: PRAKASH C. S. , HEATHER W. A.
Published: February 2008

Leaf discs of Populus deltoides cv. W‐79/307 inoculated with race 4–C of Melampsora medusae, give a compatible reaction when incubated at 16°C (LT), but an incompatible reaction at 26°C (HT). When, over a 12–day period, sets of inoculated leaf discs were reciprocally transferred between the temperature regimes (LT to HT, or HT to LT), incubation for as short as 15 h at HT resulted in incompatibility which was not reversed by subsequent incubation at LT. In contrast, incubation of the inoculated discs at LT for at least 4 days was necessary for the development of a compatible reaction following transfer to HT. Further, incompatibility induced in discs by inoculation with race 4–C and incubation at HT is epistatic to expected compatibility following subsequent inoculation with race 4–M, a temperature non‐sensitive biotype. The rapidity, irreversibility and epistatic nature of the temperature‐induced incompatibility suggests that initial recognition in this pathosystem may be for incompatibility. The significance of these results in this host/pathogen system is discussed.
Genetic studies on resistance to clubroot in Brassica napus
Authors: GUSTAFSSON MATS , FALT ANN‐SOFIE
Published: February 2008

Ten lines of Brassica napus have been tested against four Scandinavian races of clubroot (Plasmodiophora brassicae). The host‐parasite interaction is mainly differential. The genetics of resistance in the host have been investigated. Several major dominant genes have been localised and their distribution in the cultivars is discussed.
Damage to cereal crops by larks in north‐western Iraq
Authors: HALSE S. A. , TREVENEN H. J.
Published: February 2008

Two types of lark‐caused damage occurred in cereal crops in north‐western Iraq: grazing by skylarks and digging by calandra larks. The level of damage in large‐scale cereal plantings was low but extensive damage, resulting in lowered grain yields, occurred in some experimental trials and made evaluation of cereal cultivars difficult. The amount of grazing varied amongst cultivars, differences being more pronounced with grazing than digging.
The effects of fluid drilling and seed covering medium on early carrot production under polyethylene mulch
Authors: FINCH‐SAVAGE W. E.
Published: February 2008

Ungerminated seeds, fluid‐drilled germinating seeds and fluid‐drilled uniformly‐germinated seeds were sown in furrows that were either uncovered or covered by soil and left unmulch ed or mulched with polyethylene sheet. The effects of these treatments on the emergence and growth of carrots for early harvest were examined. Leaving seeds uncovered or mulching them with polyethylene advanced seedling emergence and increased the percentage that emerged; leaving seeds uncovered also reduced the spread of emergence times and produced seedlings with larger cotyledons. Uniformly‐germinated seeds emerged before germinating seeds and both emerged before ungerminated seeds. The best combination of treatments (i.e. mulched, uncovered uniformly‐germinated seeds) reduced the mean number of days for emergence from the 52 required by traditionally sown seeds to 29. There was a more variable effect of seed treatments on the spread of emergence times and the percentage emergence. Earlier emergence generally led to roots reaching a marketable size earlier and more uniform emergence led to less variation in root weights at harvest.
A study of the relationship between seedling characters and rate of germination within a seed lot
Authors: FINCH‐SAVAGE W. E.
Published: February 2008

The relationship between seedling characters and germination rate within a seed lot was studied in cauliflower, leek and onion seeds. Newly germinated seeds were selected after successive days of imbibition at 20°C and placed on slope tests to assess early seedling growth. In all three species seedling length decreased and the coefficient of variation of those seedling lengths increased with increasing number of days of imbibition required for germination. Slow germinating seeds in all three species produced fewer normal healthy seedlings than faster germinating seeds. The relevance of these results to pre‐germinated seed sowing techniques is discussed.
The effect of previously infested spruce needles on the growth of the green spruce aphid, Elatobium abietinum, and the effect of the aphid on the amino acid balance of the host plant
Authors: FISHER MARTIN
Published: February 2008

The effect of chlorosis induced in needles of Sitka and Norway spruce by the green spruce aphid on growth of the aphid is investigated, and the effect of infestation of the aphid on amino acid levels in Sitka spruce foliage is reported.

On both Sitka and Norway spruce green spruce aphids were heavier when reared on chlorotic (previously infested) needles than when reared on green (previously uninfested) needles. The effect was more pronounced on Sitka than on Norway spruce. Infestation of the aphid altered the amino acid balance of Sitka spruce foliage but not the concentration of total amino acids. Possible causes of chlorosis, the influence of individual amino acids on aphid growth, the potential effect of chlorosis on outbreaks of the aphid and the differences in susceptibility of Sitka and Norway spruce to damage by the aphid are discussed.
Grasshopper feeding rates, preferences, and growth on safflower
Authors: JOHNSON DANIEL L. , MÜNDEL H.‐HENNING
Published: February 2008

Laboratory experiments were conducted to measure the feeding rates, preferences, survival rates, maturation times, and weight gain of four common species of grasshoppers (Orthoptera: Acrididae) on four lines of safflower (Carthamus tinctorius). When safflower lines were presented individually, all were readily consumed although consumption differed significantly according to grasshopper species, age and sex, and to safflower line. Consumption was greatest on a safflower line devoid of spines. However, grasshoppers also fed readily on spiny lines, and results of experiments in which all safflower lines were presented together indicated preferences that did not necessarily correspond to the results of the single‐line feeding trials. Camnula pellucida, a graminivorous species, did feed on safflower, but restricted feeding almost exclusively to stem cambium, whereas Melanoplus bivittatus, M. packardii and M. sanguinipes fed mainly on the heads, flowers and leaves.

Highly significant differences in grasshopper maturation time and weight gain were apparent among grasshopper species, and among safflower lines. Seedtec‐5, the line which was least digestible, least consumed and least preferred nevertheless yielded rapid development and the greatest body weights of grasshoppers. All species of Melanoplus developed more quickly and gained more weight on safflower than on wheat. One species, M. packardii, was more able to utilise safflower than its congeners, and may gain competitive advantage if safflower becomes widely grown.
Bacterial wilt, a new disease of custard apple: symptoms and etiology
Authors: MAYERS P. E. , HUTTON D. G.
Published: February 2008

Pseudomonas solanacearum biovar 3 was identified as the causal agent of two disease syndromes in custard apples (Annona spp.), namely sudden death of young trees and the decline of mature trees. Cross inoculation tests using cultures of P. solanacearum from custard apple and tomato on A. squamosa, A. squamosa×A. cherimola hybrids, Capsicum annuum, three cultivars of Lycopersicon esculentum and Solanum tuberosum failed to distinguish differences in virulence among these isolates. Bacterial wilt resistant rootstock clones, particularly of A. cherimola, constitute the most effective control measure available.
Satellite RNA for the control of plant diseases caused by cucumber mosaic virus
Authors: TIEN PO , ZHANG XIUHUA , QIU BINGSHENG , QIN BINGYI , WU GUSUI
Published: February 2008

Two virus‐protecting strains, S51 and S52, were obtained for the control of cucumber mosaic virus (CMV) by local lesion selection after adding satellite RNA to the RNA genome of CMV. Both were found to protect pepper plants against a virulent strain of CMV under greenhouse and field conditions. Results from 14 localities in China indicated that the use of protective strains decreased the disease index by 21.6% to 82.8% and increased fruit yields by 10.8% to 55.6%. The host reactions and safety of S51 and S52 were tested, and the effects of the strains on plant growth were also investigated. Possible mechanisms of control of CMV‐caused plant diseases by mild strains are discussed.
Safflower susceptibility and response to feeding by grasshoppers
Authors: MÜNDEL H.‐HENNING , JOHNSON DANIEL L.
Published: February 2008

Feeding by three grasshopper species, Camnula pellucida, Melanoplus packardii and Melanoplus sanguinipes, on three safflower (Carthamus tinctorius) lines for a 6‐wk period from anthesis was monitored under field conditions. Ratings of feeding damage to different plant parts (leaves, floral parts, capitula, and peduncles) and measurements after termination of feeding (dry weight, seed yield, seed weight, seeds per capitulum, and capitula per row) were compared among grasshopper species and safflower lines.

The Melanoplus species fed preferentially on leaves, floral parts, and capitula, while C. pellucida exhibited only peduncle feeding, which resulted in head clipping. Defoliation of 20 to 30% was associated with significant increases in total dry matter, seed yield, and number of capitula. Further defoliation resulted in decreases.

The safflower lines differed in response to grasshopper feeding. S‐208 was most susceptible to defoliation by grasshopper feeding, exhibiting decreased dry weight, seed yield, and capitula number. Lesaf 34C‐00 was most tolerant and only M. packardii caused significant dry weight and seed yield reductions. Feeding by C. pellucida on this line resulted in an overall seed yield increase. Feeding by M. sanguinipes on Seedtec‐5 resulted in yield increases of up to 16%. It appears that certain grasshopper species can increase seed yield in some safflower lines by stimulating the production of additional capitula. Therefore, moderate populations of such grasshoppers in fields of appropriate safflower cultivars do not necessarily require control.
A key for stages of development of the pea (Pisum sativum)
Authors: KNOTT C. M.
Published: February 2008

A key is presented to described stages of development of the pea (Pisum sativum). The aim was to produce a simple system to aid accuracy in communicating instructions for timing of field operations. The coded description is divided into four principal stages: germination and emergence, vegetative, reproductive and senescence. These are sub‐divided into secondary stages. The practical use of the key is discussed with particular reference to the timing of application of agrochemicals.
Effects of sustained immobilisation on aphids
Authors: BERGER P. H. , ZEYEN R. J.
Published: February 2008

Immobilisation of aphids of three species, Schizaphis graminum, Myzus persicae and Dactynotus ambrosiae, was accomplished using low temperature (6 ± 1°C; or nitrogen (N2), argon (Ar), or carbon dioxide (CO2) gases at 25°C for 1,3,6, or 24 h. Mortality was recorded and also times until treated aphids first walked or probed. Cold immobilisation caused least mortality and allowed rapid recovery of walking and probing abilities. CO2 treatment, even when accompanied by cyclic administration of bottled air, caused excessive mortality when used beyond 6 h, and long recovery times. After 24 h immobilisation with CO2 aphids seldom walked or probed. N2 or Ar gases, when administered with alternating cycles of bottled air, produced a nontoxic, hypoxic immobilisation from which aphids recovered fairly rapidly to walk and probe, apparently normally.
Predation of Rhopalosiphum padi (Homoptera: Aphididae) by polyphagous predatory arthropods during the aphids' pre‐peak period in spring barley
Authors: CHIVERTON PHILIP A.
Published: February 2008

Polyphagous predators (e.g. Araneae, Carabidae and Staphylinidae), collected from spring barley fields during 1981‐85, were examined by either gut dissection or a R. padi‐specific antiserum in enzyme linked immunosorbent assay (ELISA) in order to detect predation of Rhopalosiphum padi during the aphids' establishment and exponential growth phases.

Overall 18% of c. 3000 carabids dissected were shown to feed on R. padi during the aphids' pre‐peak period. No overall relationship was found between percentage carabids with R. padi in the diet and peak R. padi densities. Relatively high proportions of Bembidion spp. (particularly B. lampros) and Pterostichus cupreus fed on R. padi during the aphids' establishment phase, and proportions of those predator taxa containing R. padi increased with increasing R. padi densities in both high and low aphid density years. P. melanarius and Harpalus rufipes mainly fed on R. padi during the aphids' exponential growth phase.

Overall 11% of c. 1350 predators examined in ELISA gave positive reactions to the R. padi antiserum. Relatively high proportions of linyphiid and lycosid spiders were positive throughout the aphid pre‐peak period. Several Acari, Opiliones, Trechus spp. (Carabidae), Philonthus spp. (Staphylinidae), Cantharidae and Chilopoda were positive mainly during the aphids' exponential growth phase. Sample sizes were small, however.

Very few of the Bembidion spp. tested in ELISA were positive compared with those examined by gut dissection. The maximum period of R. padi protein (antigen) detection in B. lampros was related to temperature, i.e. 8.5 h at 30°C, 20.5 h at 20°C and 34.5 h at 10°C, respectively. It is suggested that the rate of R. padi protein digestion in B. lampros is faster at higher temperatures than the rate of elimination of prey solids from the guts.

Several key predators (in this case B. lampros, P. cupreus and linyphiid spiders) which are abundant in spring cereal fields at a time when R. padi emigrants arrive in the crop and which feed on R. padi during the aphids' establishment phase, are identified. The results are compared with those from similar investigations elsewhere with predators of Sitobion avenae and Metopolophium dirhodum.
Flight periodicity and infestation size of Sitona lineatus
Authors: HAMON N. , BARDNER R. , ALLEN‐WILLIAMS L. , LEE J. B.
Published: February 2008

Sitona lineatus displays two distinct flight periods; a post‐teneral flight in the late summer and a post‐diapausal flight in the spring. The late summer flight begins as soon as adults start to emerge from pupal cells during late July and continues until mid‐October. Maximum aerial density is observed in late August. Less than 10% of newly emerged adults leave the crop by flight, the rest remain in the soil or move to overwintering sites by walking. Spring flight begins in late March if temperatures are above the 12.5°C flight threshold and reaches a peak in mid‐April.

Most migratory flight is downwind. Little trivial flight occurs and once individuals have located a crop, redistribution is by walking. Laboratory studies indicate that adults fly most often during the day, particularly at noon.

The size of infestations appeared to be independent of the area of legumes grown in a locality with large differences occurring even between neighbouring fields.

Examination of the yields of field experiments at Rothamsted demonstrate an unexpected trend for higher yields in later sown spring bean crops. This may be because late sowing avoids infestation by spring migrants.
Stimulation of germination in teliospores of Urocystis agropyri by volatiles from plant tissues
Authors: GOEL R. K. , JHOOTY J. S.
Published: February 2008

In tests using pre‐soaked teliospores of Urocystis agropyri, germination was stimulated by tissues from all parts of the host plant (wheat) irrespective of cultivar or resistance to flag smut. Seedling tissues of some non‐hosts (maize, rice, sorghum, cotton, mungbean and groundnut) also stimulated germination. Similar stimulatory effects were achieved by brief exposure to volatiles from wheat seedling tissues, and from the known sources of ethylene, ripening bananas, lemon fruit and ethephon (2‐chloroethyl phosphonic acid) solution. The possibility that ethylene may have a direct triggering effect on teliospore germination is discussed.
Development of appressoria of Erysiphe graminis f.sp. hordei in response to host plant age and water stress
Authors: WOOLACOTT B. , AYRES P. G.
Published: February 2008

Appressoria were observed to develop in sequence up to three lobes, each of which may establish a penetration of the underlying host cell and, ultimately, give rise to a haustorium and elongating secondary hyphae (ESH). Upon fully susceptible, well‐watered seedling plants increased appressorium development in terms of lobe number led to reduced penetration success, as judged by ESH formation. A concomitant reduction in the initiation of further penetration attempts at lobes newly formed after earlier unsuccessful penetration attempts was also observed. The effects of increased plant age and water stress upon this interaction were examined.
Aphid retention of maize dwarf mosaic virus (potyvirus): epidemiological implications
Authors: BERGER P. H. , ZEYEN R. J. , GROTH J. V.
Published: February 2008

In total, 17 589 aphids were assayed for rate of loss of inoculativity and maximum retention times of maize dwarf mosaic (MDMV). The Standard‐treatment, involved acquisition access to MDMV‐infected tissue followed by confinement of active aphids in Petri dishes. In addition various aphid immobilisation treatments were used to prevent probing on solid surfaces after acquisition access to simulate conditions experienced by wind‐borne aphids when aloft. Immobilisation treatments, using nitrogen or argon gases at 25°C, or cold treatments at 6°C after acquisition access greatly increased the efficiency of MDMV transmission by greenbugs, Schizaphis graminum, in an experimental design where insects were individually assayed for transmission over a 7 h period.

Further tests in which groups of greenbugs were assayed for MDMV transmission revealed that MDMV strains may be retained for over 21 h, regardless of post‐acquisition access treatment. Experiments with other aphid vectors of MDMV (Dactynotus ambrosiae, Macrosiphum euphorbiae, Rhopalosiphum maidis and Myzus persicae) also demonstrated MDMV retention times exceeding 18 h.

These results show that the rate at which aphids lose MDMV inoculativity is lower when solid surface probing behaviour is denied, and that MDMV retention times are longer than those previously published. The findings are discussed in relation to the epidemiology of nonpersistent viruses and their dispersal over great distances.
Effect of cocksfoot mottle virus on resistant and susceptible cocksfoot cultivars grown alone or in combination with healthy or ryegrass mosaic virus‐infected Italian ryegrass
Authors: CATHERALL P. L. , POTTER L. R.
Published: February 2008

Cocksfoot mottle virus (CfMV) was readily transmitted on cutting implements. However, after six harvests, only a quarter as many plants of the resistant cv. Cambria as of the susceptible cv. S.37 became infected. In addition to resistance to becoming infected, cv. Cambria also possessed some resistance once infected, and suffered less mortality than S.37. More CfMV‐infected plants died when competing with healthy plants than when competing with other infected plants.

Both CfMV and ryegrass mosaic virus (RMV) caused greater reductions in the yield of their respective hosts in mixed stands of cocksfoot and Italian ryegrass than in single species stands. CfMV reduced the proportion of cocksfoot in the mixture and RMV the proportion of ryegrass. However, CfMV‐infected cv. Cambria competed better than CfMV‐infected cv. S.37 with healthy or with RMV‐infected ryegrass.

It is concluded that grass cultivars selected for resistance to virus infection will slow down the rate of disease spread within the sward, and selecting for postinfection resistance will help maintain the aggressiveness and competitive ability of plants once they become infected.
The etiology of hop chlorotic disease
Authors: ADAMS A. N. , BARBARA D. J. , VIES D. L. DA
Published: February 2008

Hop chlorotic disease was first described in England in 1930, but it has since been seldom seen and its etiology has remained unknown. In 1983 a patch of plants with the disease occurred in a large area of hops (Humulus lupulus) cv. Bramling Cross planted at Yalding, Kent in 1967. All plants in a rectangular area enclosing the disease outbreak were infected with hop mosaic, hop latent and prunus necrotic ringspot viruses; the diseased plants were additionally infected with arabis mosaic virus (AMV). The disease was also associated with seed‐transmitted AMV, and was induced in hop seedlings inoculated with partially purified preparations of AMV originating from chlorotic disease‐affected hops prepared from Chenopodium quinoa. The disease appears to be caused by AMV, but AMV isolates from hops with chlorotic disease were serologically indistinguishable from AMV isolates from hops with symptoms of bare‐bine and/or nettlehead and showed similar pathogenicity in diagnostic hosts. The basis of the difference between isolates in their pathogenicity in hop remains unknown.
Physiological and ultrastructural changes in Stellaria media following treatment with fluroxypyr
Authors: SANDERS G. E. , PALLETT K. E.
Published: February 2008

The physiological and ultrastructural changes induced by fluroxypyr (4‐amino‐3, 5‐dichloro–6–fluoro–2–pyridyloxyacetic acid) are investigated in a susceptible weed species, Stellaria media. The sequence of symptoms was an initial petiole curvature followed by stem elongation and thickening prior to leaf senescence, stem and petiole necrosis and plant death. Light and electron microscopy revealed leaf tissue containing cells with disrupted and swollen chloroplasts and a disrupted tonoplast. Within the stem tissue there was extensive meristematic differentiation and adventitious root development prior to stem tissue necrosis. Increased levels of reducing sugars and amino acids in treated foliar tissue indicated reserve mobilisation during the initial stages of symptom development.

Fluroxypyr induced oat coleoptile elongation with an optimum concentration at 5 × 10‐5 m compared to 10‐4 m for auxin (IAA). A S. media shoot explant system revealed similar elongation which was maximal during the first 24 h of treatment. Uptake and incorporation of 14C‐leucine was stimulated by 96 h after treatment. It is concluded that fluroxypyr activity against S. media is characterised by an initial cell elongation and reserve mobilisation, followed by extensive cell proliferation, increased RNA and protein synthesis, and ultimately plant death.
The complementary effects of plant resistance and the choice of sowing and harvest times in reducing carrot fly (Psila rosae) damage to carrots
Authors: ELLIS P. R. , HARDMAN J. A. , COLE ROSEMARY A. , PHELPS KATHLEEN
Published: February 2008

The benefits of combining a partially‐resistant carrot cultivar with different sowing and lifting dates to reduce carrot fly, Psila rosae, damage were investigated at Wellesbourne in 1983 and 1984‐85. The partially‐resistant cv. Sytan was less damaged and supported fewer insects than the susceptible cv. Danvers on all lifting dates. The estimated reduction of carrot fly larvae on Sytan compared with Danvers ranged from 33 to 95%. Nine combinations of sowing and lifting dates provided more than 75% marketable roots of Sytan compared with only three combinations of dates for Danvers. An early June sowing of both cultivars provided roots of a marketable size with the least attack. More than 90% of Sytan roots were still marketable in December and fewer insects were produced by the end of the season on these roots than on those sown earlier. In addition, sowing in June decreased the number of pupae produced on cv. Danvers by 10 times compared with earlier sowings. Combining partial resistance with specific sowing and lifting times enabled satisfactory yields of marketable carrots to be obtained in a field infested by high populations of carrot fly.
Genetic control of resistance to cucumber mosaic virus in Cucurbita pepo
Authors: PINK D. A. C.
Published: February 2008

Segregation ratios in the F2s of crosses between courgette cultivars and the pumpkin cv. Cinderella indicated that the resistance of the latter to cucumber mosaic virus (CMV), expressed as a failure to develop systemic symptoms, was controlled by two unlinked recessive genes. However, data from the backcross generations were not consistent with this. Biometrical analysis showed significant gene interactions, possibly between the genes for CMV resistance and the background genotype determining plant vigour and a gene dosage effect for resistance.

The resistance has been successfully backcrossed into courgette breeding material.
The laboratory germination of crisp lettuce seeds under moisture stress
Authors: WURR D. C. E. , FELLOWS JANE R.
Published: February 2008

Seeds of the crisp lettuce cultivar Pennlake were germinated using all combinations of six ‘initial’ solutions of polyethylene glycol 6000 (PEG) with osmotic potentials ranging from 0 to ‐8 bars and seven ‘secondary’ solutions of PEG with osmotic potentials ranging from 0 to ‐10 bars, to which seeds were moved after 24 or 48 h in the ‘initial’ solution. The number of seeds germinating decreased at more negative osmotic potentials of both ‘initial’ and ‘secondary’ solutions but there was an interaction between germination temperature and the osmotic potential of the ‘initial’ solution. At an ‘initial’ solution osmotic potential of 0 bars germination at 20°C exceeded that at 10°C. As the osmotic potential of the ‘initial’ solution decreased germination at 20°C decreased more than at 10°C so that at the more negative osmotic potentials germination at 10°C exceeded that at 20°C. However seeds ungerminated after 14 days germinated normally when transferred back to water, so that the average final germination was 99.5%.

The results suggest that major fluctuations in soil water potential in a seedbed are unlikely to influence seed germination per se provided that a period of 24 to 48 h at 0 bars tension is available at some time. The timing of such a period relative to sowing will have a considerable effect on the time of germination and hence the time of emergence. It is concluded that factors other than the direct effect of soil moisture content on germination are involved in reducing seedling emergence under fluctuating soil moisture conditions in the field.
Photoperiodic response and heritability of the pre‐flowering interval of two red clover (Trifolium pratense) populations
Authors: BOWLEY S. R. , TAYLOR N. L. , DOUGHERTY C. T.
Published: February 2008

The reaction to 12, 14, and 16 h photoperiods of two medium‐maturing red clover (Trifolium pratense) populations (cv. Kenland and Cycle 6 of a selection for long stems) under controlled environment conditions was studied. Under both 14 and 16 h photoperiods, Kenland flowered sooner and had shorter stems, more stems per plant, and greater herbage yield per plant but had a similar number of internodes compared to the long stem Cycle 6 population.

A daylength between 12 and 14 h was critical for flower initiation in both populations. The critical daylength to induce stem initiation was shorter than the daylength to induce flowering in some genotypes.

From half‐sib analyses, the narrow–sense heritability of the pre‐flowering interval in Kenland ranged from 15 to 23%. The expected response to one cycle of selection (5% selection intensity) for lengthening or shortening the pre‐flower interval was 2.3 to 2.4 days at the 16 h photoperiod and 3.0 days at the 14 h photoperiod. Low correlation between pre‐flowering interval, stem length, and stem number indicated that it may be possible to change one character without affecting the other two. The need for further studies of the genetic nature of the control of flowering in red clover was indicated.
The seasonal response of Italian and hybrid ryegrasses to the control of frit fly, Oscinella frit
Authors: MOWAT D. J. , JESS S.
Published: February 2008

In years of relatively high frit fly activity the control of all generations produced increases averaging 0×44 t d.m. ha‐1 in annual yield of Italian and hybrid ryegrass. A cutting programme designed to make the sward especially vulnerable to frit fly attack did not increase the total annual effect of pesticide treatment but accentuated the periods at which damage occurred. The annual yield increase was almost entirely obtainable by controlling the second and third frit fly generations, but even one treatment for this purpose was of doubtful economic justification. The prospect of augmenting the response to control of later‐occurring pests, such as leatherjackets or eriophyid mites, by including the part of the frit fly response which is recoverable by the same treatment, was a more probable justification for pesticide usage.

There was some evidence that a Westerwold and a hybrid cultivar suffered more damage than an Italian ryegrass cultivar, but pesticide treatment did not improve the persistence of any cultivar.
Influence of microclimate on Drechslera leaf spot of young coconuts: effect of desiccation on spore survival and of moisture and shade on infection and disease development
Authors: FAGAN H. J.
Published: February 2008

Culture‐produced conidia of Drechslera incurvata from coconut failed to germinate on the leaves of coconut seedlings incubating under the dry conditions of a greenhouse. Viability and rate of appressorium formation of artificially‐dispersed, culture‐produced conidia fell significantly during extended incubation of inoculated seedlings in the greenhouse, when 43% of conidia germinated after 90 days incubation compared with 62% at 59 days and 90% at 24 days. Field‐produced conidia on excised leaves also lost viability upon storage in situ on the laboratory bench; germination fell from 60% at 3 months storage to 0×5% at 5 months and no germination at 6 months.

Shading of seedlings in the field with saran cloth producing 30% shade or 50% shade depressed the amount of dew forming on leaves of young coconuts and significantly reduced both the number of infections from artificial inoculations and the severity of leaf spot disease developing subsequently.
The influence of cultivar and isolate on the development of gangrene (Phoma exigua var. foveata) in potato tubers
Authors: BAIN R. A. , LENNARD J. H. , WASTIE R. L.
Published: February 2008

In studies on the infection of potato cultivars with different field isolates of Phoma exigua var. foveata, cultivar × isolate interactions, although sufficiently large to influence the relative pathogenicities of isolates on different cultivars, were not substantial enough to affect cultivar ranking order. Cultivar rank was markedly influenced by pathogen isolate only when both field and culture collection isolates were compared. This suggests that the complications of cultivar × isolate interactions can be avoided in cultivar screening tests by the use of recent field isolates of high pathogenicity. It was found that cultivar was considerably more important than isolate in determining gangrene lesion size. The need to consider both lesion diameter and depth when estimating rot size following point inoculation of different cultivars was confirmed.
The acquisition of a caulimovirus by different aphid species: comparison with a potyvirus
Authors: MARKHAM P. G. , PINNER M. S. , RACCAH B. , HULL R.
Published: February 2008

The acquisition and transmission of cauliflower mosaic virus (CaMV) by six aphid species and three clones of aphids was studied and compared with that of turnip mosaic virus (TuMV) with Myzus persicae. Two clones of Aphis fabae were unable to transmit CaMV, but the other species, Acyrthosiphon pisum, Brevicoryne brassicae, Megoura viciae, M. persicae and Rhopalosiphum padi transmitted in a bior multi‐phasic manner. There was no statistical evidence of a bimodal transmission pattern. R. padi is recorded as a vector of CaMV for the first time.

The transmission efficiency of CaMV varied with time of acquisition and suggested that accumulation of the virus occurred with two peaks of efficiency within the anterior region of the insect gut. The time at which these two peaks occurred varied between the species, but the basic pattern was common to all transmitting aphid species in this study. This pattern contrasted with that of TuMV. The transmission data are discussed in terms of bimodal transmission, the influence of feeding behaviour, the role of a helper protein associated with both TuMV and CaMV and the evidence for site specific attachment of CaMV.
Relationship between root respiration and seedling age in tomato cultivars infested by Meloidogyne incognita
Authors: ZACHEO GIUSEPPE , MOLINARI SERGIO
Published: February 2008

Measurements were made of respiration in the roots of tomato cultivars susceptible and resistant to Meloidogyne incognita. Nematode infestation of the susceptible cv. Roma VF caused an initial stimulation of the total respiration with an increase in the CN‐sensitivity; the effect decreased and then disappeared as the seedlings aged. In the resistant cv. Rossol nematode infestation initially caused an inhibition of total respiration and a decrease in the CN‐sensitivity; respiration and CN‐sensitivity increased with seedling age. The activity of the alternative respiration pathway (m‐chlorobenzhydroxamic acid‐sensitive) was unchanged by nematode infestation in the resistant cultivar and increased markedly in the susceptible cultivar during the early stages of infestation.
Observations on the control of potato cyst‐nematodes, Globodera rostochiensis and G. pallida in 35 English potato soils in pots by oxamyl and resistant potatoes
Authors: WHITEHEAD A. G. , FRASER JANET E. , PETERS C. G. , NICHOLS A. J. F.
Published: February 2008

The increase of 35 English field populations of potato cyst‐nematodes (Globodera rostochiensis and/or G. pallida) was measured on Désirée, Maris Piper, Caxton (A25/11), Cromwell (A27/20) and clone 11233 ab 22 in pots of sandy, silty or peaty loam soil. Désirée was susceptible to all populations tested and, as in field soils, the final population (Pf) was inversely related to the initial population of potato cyst‐nematode eggs (Pi) in the soil. Maris Piper and Cromwell were resistant to all G. rostochiensis populations, with one possible exception. Maris Piper was susceptible to all G. pallida populations. Caxton was susceptible to some and fairly resistant to other populations of G. rostochiensis, indicating the existence either of two biotypes within the one pathotype (Rol) as yet encountered in Britain, or the existence of an additional pathotype. Caxton and Cromwell were fairly resistant to G. pallida. Clone 11233 ab 22 was only moderately resistant to both species. Resistance to potato cyst‐nematode increase varied considerably, especially in Caxton (to G. rostochiensis) and in 11233 ab 22 (to both species).

Oxamyl greatly reduced the increase of G. rostochiensis populations on Désirée potatoes, with the notable exception of one population but it generally had much less effect on G. pallida populations, regardless of soil type. The difference in effect on the two species may be due to a longer period of hatching in G. pallida than in G. rostochiensis and also perhaps to a second generation in G. pallida.
The effects of cutting pre‐treatments on the performance of asulam on bracken (Pteridium aquilinum)
Authors: LOWDAY J. E. , LAKHANI K. H.
Published: February 2008

The performance of asulam was assessed from a field experiment in which bracken (Pteridium aquilinum) was subjected to a variety of cutting pre‐treatments prior to spraying with the herbicide. Both cutting bracken twice in the year prior to asulam application, and spraying frond regrowth 10 wk after a single mid‐June cut, improved the performance of asulam. Summer cutting removes nutrients and dry matter from the system and reduces frond height, but increases frond density and the number of active buds on the rhizome system. The enhanced efficiency of asulam on pre‐cut plots may be due to any one of these factors, or a complex interaction between some (or all) of them. In areas of tall bracken a cutting pre‐treatment has the important practical advantage of reducing the height of the canopy, making the subsequent use of ground spraying equipment easier.
Intensity of radicle fluorescence as related to the resistance of seedlings of lettuce to the lettuce root aphid and carrot to the carrot fly
Authors: COLE ROSEMARY A.
Published: February 2008

A technique is described which indicates by u.v. fluorescence the concentration of caffeoylquinic, chlorogenic and isochlorogenic acids in roots of germinating lettuce and carrot. The surface fluorescence of radicles from lettuce root aphid (Pemphigus bursarius) resistant seedlings was more intense than for susceptible seedlings, attributable to the higher concentration of isochlorogenic acid. In contrast, radicles of carrot seedlings resistant to carrot fly (Psila rosae) were less fluorescent than susceptible seedlings, corresponding to the lower concentration of chlorogenic acid in resistant seedlings. The technique is non‐destructive and has been developed to distinguish between cultivars or breeding lines potentially resistant to these insect pests.
Multiple components of the resistance of potatoes to potato leafroll virus
Authors: BARKER H.
Published: February 2008

In glasshouse experiments the ranking of potato genotypes for resistance to infection with potato leafroll virus (PLRV) using three concentrations of aphid‐borne inoculum was the same as their field resistance ratings. In field‐grown plants this resistance to infection increased in all genotypes as the plants aged but its rate of increase differed between genotypes. In tests on field‐grown plants infected by aphid‐ or graft‐inoculation, the proportion of virus‐free progeny tubers increased the later the date of inoculation but was greater in resistant than in susceptible genotypes. This trend was most pronounced in the resistant clone G7445(1), in which the virus failed to move from the foliage to the tubers of some plants infected in glasshouse tests.

The spread of PLRV will thus be minimised in crops of resistant compared with susceptible genotypes for three reasons: plants have greater resistance to infection, systemic spread of virus from their foliage to tubers is less likely and, as shown previously, the low concentration of virus particles in leaf tissue makes infected plants less potent sources of inoculum for aphids.