bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of infection by the endophytic fungus Acremonium lolii on growth and nitrogen uptake by perennial ryegrass (Lolium perenne) in flowing solution culture
Authors: LEWIS G C , BAKKEN A K , MACDUFF J H , RAISTRICK N.
Published: February 2008

Clonal tillers of a genotype of perennial ryegrass (Lolium perenne), either with or without the endophytic fungus Acremonium lolii, were grown under natural light in flowing nutrient solutions with mineral N maintained automatically at concentrations of 3 or 30μm NH4NO3 for 28 days. Uptake of N was monitored daily and dry matter production was assessed by sequential harvesting. The presence of endophyte had no significant effect on shoot or root biomass production at either N level, but shoot: root ratios were significantly increased by endophyte infection at both N levels at some harvests. All plants absorbed NH4+ preferentially to NO3‐ and the ratio was not affected by endophyte infection. Also, infection did not affect total N content of plants, which was significantly more in plants at the higher N level than at the lower level. It is concluded that endophyte infection had only minor effects on growth and N economy of the plant, under the conditions imposed in this experiment.
Analysis of the occurrence and distribution of tobacco rattle virus in field soil and disease in a subsequent tulip crop
Authors: PLOEG ANTOON T , ZOON FRANS C , BREE JOOP DE , ASJES CEES J
Published: February 2008

The occurrence and distribution of tobacco rattle virus (TRV) in field plots was determined by soil bait‐testing and disease incidence in tulips subsequently grown on these plots was studied. The virus occurred in patches, calculated as 1.5 m × 3.6 m. The presence of virus was not correlated with numbers of potential vector trichodorid nematodes. Of three trichodorid nematode species present, only Paratrichodorus teres transmitted TRV which, as with virus isolates obtained in bait‐tests and from infected tulips, reacted in serological tests with an antiserum prepared against a Dutch isolate of pea‐early browning virus (PEBV). Virus prevalence in a subsequent tulip crop was 0.8% and in a sample of tulip plants, virus was recovered only from plants showing virus symptoms. Plots from which TRV was recovered in bait‐tests yielded significantly more virus diseased tulips than plots which tested negative for virus. Growing bait‐plants in field‐plots, as compared with greenhouse tests using soil collected as a series of sub‐samples, resulted in an underestimate of the occurrence of TRV.
Resistance of tomato infected with cucumber mosaic virus satellite RNA to potato spindle tuber viroid
Authors: YANG XICAI , KANG LIANGYI , TIEN PO
Published: February 2008

Tomato (Lycopersicon esculentum cvs Rutgers and Lichun) plants were firstly pre‐inoculated either with a cucumber mosaic virus (CMV) isolate containing satellite RNA (CMV‐S52) or with a CMV isolate without satellite RNA, and then challenged 14 days later with a severe strain of potato spindle tuber viroid (PSTVd). Also, tomato plants transformed with CMV satellite cDNA and non‐transgenic control plants were directly inoculated with PSTVd. Protection effects were assessed by the observation of symptoms and by assay of PSTVd accumulation in tomato plants using return polyacrylamide gel electrophoresis and silver staining. The results indicated that the satellite‐transgenic plants and plants pre‐inoculated with CMV‐S52 showed much milder symptoms of PSTVd infection than the respective control plants. The concentration of PSTVd RNA in the satellite‐transgenic plants and CMV‐S52 pre‐inoculated plants was reduced to about 0.02–0.03 of the controls. PSTVd infection did not increase the amount of satellite ds‐RNA in plants. It is concluded that the plant resistance to PSTVd is induced by the presence of satellite RNA rather than the CMV infection. It is suggested that as there is considerable sequence similarity between satellite RNA and PSTVd, base pairings may be a cause of reduction of both symptoms and the accumulation of PSTVd.
The experimental transmission of hop latent viroid and its elimination by low temperature treatment and meristem culture
Authors: ADAMS A N. , BARBARA D J. , MORTON A. , DARBY P.
Published: February 2008

Two aspects of hop latent viroid (HLVd) relevant to control were examined: the production of viroid‐free plants from infected material and transmission of HLVd in the field. Plants free from HLVd were obtained by a combination of storing infected source plants at low temperature (2–4oC in the dark) for several months followed by meristem culture using small explants. A total of 77 plants of six cultivars and male pollinator clones were grown from meristems and 28 of these were free from HLVd. Tests showed that the cutting of stems (mimicking the use of tools) was more effective than abrasion (mimicking natural plant to plant contact) for the mechanical transmission of HLVd between hop plants. When field‐grown test plants were inoculated, infection occurred more commonly in May before plants had grown large enough for significant contact between neighbouring plants than later in the season. The aphid Phorodon humuli could not be shown to transmit HLVd.

These results indicate that all hop varieties and pollinator clones can be made available to the industry free from HLVd and that the chances of infection can be reduced by avoiding early‐season cultural operations that cut into hop shoots.
The effect of temperature and inoculation access period on the transmission of barley yellow dwarf virus byRhopalosiphum padi (L.) and Sitobion avenae (F.)
Authors: LOWLES A J. , TATCHELL G M. , HARRINGTON R. , CLARK S J.
Published: February 2008

Winged individuals of Rhopalosiphum padi and Sitobion avenae transmitted the PAV‐like and MAV‐like isolates of barley yellow dwarf virus respectively. Success of transmission after inoculation access periods of 2, 6, 12, 24, 48 and 72 h were examined and survival, reproduction and movement of the aphid vectors were recorded at these times. The experiment was done at four different temperatures: 6oC, 12oC, 18oC and 23oC. For both isolates the inoculation efficacy did not increase after a 24 h inoculation access period and there was no difference in inoculation efficiency at the three highest temperatures, that at 6oC being significantly lower than at 12oC to 23oC. The results suggest that autumn temperature is a critical factor for BYDV epidemiology in Britain with a small increase in autumn temperature leading to greatly increased infection rates.
Use of polymerase chain reaction (PCR) to study transmission of banana bunchy top virus by the banana aphid (Pentalonia nigronervosa)
Authors: HU J S. , WANG M. , SETHER D. , XIE W. , LEONHARDT K W.
Published: February 2008

Banana bunchy top virus (BBTV) is a ssDNA virus transmitted by the banana aphid, (Pentalonia nigronervosa). A polymerase chain reaction (PCR) assay was used to study BBTV transmission efficiency, to determine the minimum acquisition‐access period, the minimum inoculation‐access period, the retention time, and to examine the possibility of transovarial transmission in this vector. BBTV was acquired by banana aphids within 4 h and was transmitted within 15 min feeding. On average, more than 65% of single viruliferous adult aphids transmitted BBTV. The aphids retained BBTV for their adulthood of 15–20 days. None of the 131 offspring from adult aphids reared on infected bananas were BBTV positive. Aphid transmission experiments were conducted to determine if taro and gingers are hosts of BBTV. None of the 87 taro and ginger plants exposed to aphid inoculation were infected by BBTV. The BBTV‐free status of these plants was verified by PCR assay for 6 months post‐inoculation. In addition, none of the taro and ginger samples collected from fields adjacent to BBTV‐infected banana plants tested positive for BBTV.
Ovule abortion in white clover (Trifolium repens L.)
Authors: MARSHALL A H. , JAMES I R. , POTTER J F.
Published: February 2008

Plants of white clover (Trifolium repens L.) cv. Olwen were grown in an open glasshouse maintained at a mean temperature of 20oC and ovule growth and seed production measured. Differences in the rate of growth of ovules within ovaries were observed as early as 2 days after pollination. Ovules reached a maximum size after 8 days with the smallest only half the size of the largest. After 8 days, the smallest ovules became flaccid and shrivelled. Ovule position within the ovary had little effect on the frequency of seed set and although there was an apparently higher probability that central ovules produced a seed than those nearer the peduncle or style this was not statistically significant. Inflorescence position and floret position on the inflorescence had a significant effect on the number of seeds per floret and seed weight; the first formed inflorescences and the first florets to be pollinated on each inflorescence had more seeds per floret and heavier seeds and fewer florets with no seed than later pollinated florets. There were also differences between florets within the same whorl. The role of a number of factors which may influence floret site utilisation are discussed.
Varietal mixtures: a viable strategy for sustainable productivity in subsistence agriculture
Authors: SMITHSON J B. , LENNÉ J M.
Published: February 2008

Remarkable parallels link the development of varietal mixtures across subsistence farming systems. Mixtures are grown and persist because they prolong harvest and income flow and provide diversity of diet. From our review of research on agronomic and disease aspects of mixtures in modern agriculture, it is also clear that improved stability and decreased disease severity are common features of mixtures relative to their components in monoculture. Such advantages are of value to both modern and subsistence agriculture. However, in the majority of cases, the yield advantage of mixtures is small. Overall, we conclude that varietal mixtures are presently a viable strategy for sustainable productivity in subsistence agriculture, have potential for improvement without sacrifice of diversity, are an important resource for future global food production and may have an expanding role in modern agriculture in situations where qualitative uniformity is not the guiding priority.
Influence of Liriomyza species (Diptera: Agromyzidae) and their host plants, on oviposition by Opius dissitus females (Hymenoptera: Braconidae)
Authors: OLIVERA CAROLINA ROUX , BORDAT DOMINIQUE
Published: February 2008

Two factors, among others, influence the oviposition of Opius dissitus Muesebeck. The first was the host species, the second the plant upon which the pest host larvae develop. O. dissitus females prefer Liriomyza trifolii (Burgess) larvae over those of L. huidobrensis (Blanchard). O. dissitus females were more attracted to the larvae of L. trifolii or L. huidobrensis when these were present on courgette rather than tomato or lettuce.
Development of selective aphicide treatments for integrated control of summer aphids in winter wheat
Authors: OAKLEY J N. , WALTERS K F A. , ELLIS S A. , GREEN D B. , WATLING M. , YOUNG J E B.
Published: February 2008

Field experiments on the use of recommended and reduced application rates of aphicides for control of summer aphid infestations on winter wheat have been done at five sites each year from 1990 to 1992. The experiment compared sprays of pirimicarb at recommended rate (140g a.i. ha‐1) and reduced rate (25 g a.i. ha‐1) and of alphacypermethrin at recommended rate (15 g a.i. ha‐1) and one third recommended rate (5 g a.i. ha‐1), each applied either at flag leaf emergence or at flowering. Aphid infestations were allowed to develop naturally and were measured at critical growth stages. In 1990, overwintered aphid infestations, together with established populations of parasitoids, were detected at four of the five sites when the first assessment was made in April. Parasitoids provided sufficient aphid control to prevent yield loss at two sites, without pesticide applications. At three sites both aphicides gave similar levels of control and yield response at both recommended and reduced application rates. In 1991 and 1992 no overwintered aphids were detected in the crops and aphid infestations developed much later. Aphicide applications gave significant yield responses at four sites in 1992. Recommended rates gave better control of aphids than reduced rates. There was no significant difference in the yield response obtained with different rates of aphicide.
Fungicidal activity of Ranunculus asiaticus and other weeds against Fusarium oxysporum f.sp. lycopersici
Authors: QASEM J R.
Published: February 2008

The effects of aqueous extracts of some common weed species against Fusarium oxysporum Schlecht f.sp. lycopersici (the causal agent of tomato wilt disease) were investigated under laboratory conditions. Anagallis foemina L., Cerastium dicotomum L., Falcaria vulgaris L., Ranunculus asiaticus L., Scorpiurus mur‐icatus L. and Solanum nigrum L. extracts were the most toxic to the fungus. Further studies on buttercup (Ranunculus asiaticus L.) showed that fresh shoot extract of this species prevented growth of F. oxysporum when incorporated into agar medium. Extracts of different parts of the plant inhibited fungus growth and sporulation, but the fungitoxicity decreased with incubation period with only slight changes in the toxicity of fresh shoot extract. The shoot and fresh parts extracts were more toxic than root and dried tissue extracts. Addition of 0.5 ml fresh shoot or 1 ml fresh root extract to the growing medium significantly reduced fungal colony growth, and the effect was extract concentration dependent. Fresh shoot extract of R. asiaticus added to a liquid medium significantly reduced mycelial dry weight compared with the control, and incorporation of 0.1 g dried shoot or 0.2 g dried roots in the media strongly inhibited fungus growth. Results of a pot experiment showed no harmful effects of R. asiaticus extracts on tomato growth.
Variation in pathogenicity of isolates of Cercospora spp. attacking Heliotropium spp.
Authors: BRUN L. , SHEPPARD A W. , LOPES V.
Published: February 2008

The pathogenicity of a set of 13 Cercospora samples collected in France, Turkey and Australia from four Heliotropium species has been evaluated with a detached leaf technique. All of five Euro‐Asian Heliotropium species tested were susceptible to all Cercospora species isolates. However, variation in the degree of partial resistance to different isolates was observed and showed some similarity for isolates from the same region of origin. Further studies are required to clarify the taxonomy of Cercospora blight strains, but the consequences of the noted differences in pathogenicity are discussed in relation to the biological control ofH. europaeum L. in Australia.
Cavity spot of carrots: II. Cell‐wall‐degrading enzymes secreted by Pythium and pathogen‐related proteins produced by the root cells
Authors: ZAMSKI E. , PERETZ I.
Published: February 2008

This study investigates the biochemical relationships between carrot roots and Pythium violae, the pathogen responsible for cavity spot (CS) disease. P. violae isolates obtained from CS lesions, cultured in Petri dishes on agar were used for inoculation of uninfected mature carrots. The fungus secreted a wide spectrum of enzymes that degraded the cellulose and pectic substances of the carrot cell walls. Cellulase and polygalacuronase (pg) showed the highest activity during the first day post‐inoculation, subsequently declining. Pectin lyase (PnL), pectate lyase (PeL) and pectin methylesterase (PME) gradually increased to their highest levels of activity 14 to 30 days post‐inoculation. This pattern of activity enables the penetration of the fungus through the walls of the host cells and the establishment of the hyphae. Several plant pathogen‐related substances such as peroxidase, chitinase, glucanase and polyphenol oxidase were produced in the infected tissue. Peroxidase activity rose in the inoculated roots from day 1 post‐inoculation. Chitinase, glucanase and polyphenol oxidase activities first appeared 3–4 days post‐inoculation. At this time, two bands corresponding to chitinase at about 26 and 33 KDa and one band corresponding to glucanase at about 24 KDa could be resolved by SDS‐PAGE.
Variation in pathogenicity among isolates of Elsinoe phaseoli from Phaseolus species
Authors: PHILLIPS A J L
Published: February 2008

Expanding primary leaves of 11 cultivars of Phaseolus vulgaris, and one each of Phaseolus coccineus, Phaseolus lunatus and Vigna unguiculata were inoculated with 23 isolates of Elsinoe phaseoli from Phaseolus spp. and one from Vigna unguiculata. On the basis of the macroscopic and microscopic appearance of the lesions, symptoms were placed into five classes. Spore yields from the lesions in each class were used to classify the types of lesions as representing resistance or susceptibility to each isolate. There was a differential response of cultivars to isolates. According to the reaction of five cultivars of P. vulgaris to infection, isolates were placed in four pathogenicity groups.

In addition to the differential reaction of cultivars, there was some evidence of host specificity among the isolates. Thus, P. lunatus was susceptible to most of the P. vulgaris isolates but resistant to the ones from P. coccineus. Vigna unguiculata was susceptible only to the V. unguiculata isolate and was resistant to all the isolates from Phaseolus spp. The isolate from V. unguiculata failed to infect any of the bean cultivars or the other Phaseolus spp. The need to select suitable isolates for challenging cultivars in a breeding programme is stressed.
Host range, vector relations and serological relationships of cotton leaf curl virus from southern India
Authors: NATESHAN H M , MUNIYAPPA V. , SWANSON M M , HARRISON B D
Published: February 2008

In 1989 to 1991, leaf curl disease was observed in cotton (Gossypium bar‐badense cv. Local) grown in kitchen gardens in five districts in Karnataka State, India, and in 1994 it was recorded in G. hirsutum cv. Sharada in two districts. Symptoms consist of leaf curling, vein thickening, leaf enations, and stunting and distortion of plants. The disease is caused by cotton leaf curl virus (CLCuV‐K), which was transmitted by the whitefly Bemisia tabaci to 24 plant species in six families. Hosts include bean (Phaseolus vulgaris), pepper, tobacco, tomato and several weeds, almost all of which developed leaf curl, with or without vein thickening. CLCuV‐K was transmitted from cotton to cotton by adult B. tabaci after an acquisition access period of 1 h, could be inoculated in 5 min, had a minimum latent period of 8 h and was retained by viruliferous insects for up to 9 days. Female B. tabaci transmitted more frequently than males. CLCuV‐K is a whitefly‐transmitted geminivirus. It reacted with two out of 17 monoclonal antibodies (MAbs) raised to African cassava mosaic virus and five out of 10 MAbs raised to Indian cassava mosaic virus. CLCuV‐K isolates from different locations in Karnataka had similar epitope profiles. As judged by these profiles, CLCuV‐K is closely related to Indian tomato leaf curl virus from Karnataka, is distinguishable from several other whitefly‐transmitted geminiviruses found in India and is still more distantly related to those, including cotton leaf crumple virus from the USA, found in other continents.

CLCuV‐K infected all cultivars tested of G. barbadense and one of six cultivars of G. hirsutum but none of G. arboreum or G. herbaceum.
Serological studies on the accumulation and localisation of three tomato leaf curl geminiviruses in resistant and susceptible Lycopersicon species and tomato cultivars
Authors: FARGETTE D. , LESLIE M. , HARRISON B D
Published: February 2008

Accessions of wild Lycopersicon spp. and selected Fl hybrid tomato cultivars were compared for their resistance to three whitefly‐transmissible geminiviruses: Indian tomato leaf curl virus (ITmLCV) and tomato yellow leaf curl viruses from Sardinia (TYLCV‐Sar) and Senegal (TYLCV‐Sen). The resistance of different plant lines was expressed in different ways but in most instances a given line reacted similarly to graft inoculation with the three viruses. L. pimpinellifolium LA1478 produced as much virus antigen, assessed by triple antibody sandwich‐ELISA, as the susceptible cv. Moneymaker but developed only very mild symptoms and is therefore tolerant of infection. In L. hirsutum LA1777 and L. peruvianum CMV‐INRA, very mild or no symptoms developed but antigen concentrations were substantially less than in Moneymaker. L. chilense LA1969 remained symptomless and its antigen concentration was < 1% of that in Moneymaker. Symptoms were mild or barely evident in the Fl hybrid cultivars. Cultivars Tyking and Fiona had antigen concentrations about 5–10% of those of Moneymaker, whereas TY20, Top 21 and Tyger had intermediate antigen concentrations. In a few instances, the extent to which virus accumulation was restricted depended on the challenge virus. Accumulation of TYLCV‐Sen in TY20, Top 21 and Tyger was less affected than that of the other two viruses, and accumulation of TYLCV‐Sar in accessions LA1777 and CMV‐INRA was less affected than that of TYLCV‐Sen or ITmLCV.

Tissue‐printing tests showed that ITmLCV and TYLCV‐Sen antigens were confined to phloem tissue. In Tyking, the number of virus antigen‐containing phloem traces and the antigen content of individual traces were less than in Moneymaker but the partitioning of antigen between internal and external phloem was unaffected.
Effects of sub‐lethal cold stress on the Western Flower Thrips, Frankliniella occidentalis
Authors: McDONALD J R , BALE J S , WALTERS K F A
Published: February 2008

In order to establish in a new geographical area, introduced insects must be able to survive any period of adverse conditions such as a temperate winter and be capable of subsequent development to adulthood and/or reproduction. However, this aspect of insect overwintering and cold tolerance has been poorly studied. At high latitudes, Frankliniella occidentalis is typically associated with artificially heated glasshouses, but has some ability to tolerate low temperatures and may survive winter field conditions for short periods, or for longer periods of time during mild winters. The effects of overwintering on the viability of survivors are, however, unknown. In this study, acute and chronic cold exposure regimes were imposed on first instar larvae and adult female Western Flower Thrips, after which the longevity, development and reproductive capacity of the survivors were monitored and compared to those of non‐stressed individuals. Survival of cold exposure did not affect subsequent survivorship of immature or adult insects, though cold treated larvae took approximately two days longer to reach adulthood than untreated individuals (at 20°C, 18L:6D). Chill treatment of adult females significantly reduced their rate of reproduction (from 1.45 to 0.93 larvae day‐1), reproductive lifespan (from 13.3 to 9.2 days) and as a result, total reproductive output (from 20.4 to 10.8 larvae), compared to control females. Acute exposure resulted in non‐significant decreases of the same parameters. The relevance of the above effects to overwintering of F. occidentalis is discussed.
Effects of cover crops, weeds and plant debris on development ofMycocentrospora acerinain caraway
Authors: EVENHUIS A. , VERDAM B.
Published: February 2008

This paper reports on the search for inoculum sources ofMycocentrospora acerinaon caraway (Carum carviL.). Obvious suspects are cover crops of biennial caraway and preceding crops of annual caraway. Other suspects are weeds in or alongside the field. Finally, survival structures of the fungus, chlamydospore chains, packed in plant debris or naked, are suspected.M. acerinais able to infect many plant species, including cover crops of caraway such as spinach for seed production and peas. However, the agronomical suitability of a crop to serve as a cover crop of biennial caraway proved to be a more important factor in determining caraway yield than the susceptibility of the cover crop toM. acerina.This finding was corroborated by the fact that spinach and peas as preceding crops had no significant effects onM. acerinadevelopment in spring caraway sown the next year. Dill, barley and four weed species were found as new hosts ofM. acerina.The role of weed hosts, susceptible crops and plant debris in the survival of the fungus in years without caraway is discussed. Caraway sown on soil containing infested caraway straw, infested debris of other plant species or chlamydospores grown in pure culture, became infected byM. acerina.Only high inoculum densities of chlamydospores in the soil caused severe damping‐off of caraway seedlings. The opportunity for disease management by agronomical means is quite limited.
Ipomoea crinkle leaf curl caused by a whitefly‐transmitted gemini‐like virus
Authors: COHEN J. , MILGRAM M. , ANTIGNUS Y. , PEARLSMAN M. , LACHMAN O. , LOEBENSTEIN G.
Published: February 2008

A whitefly‐transmitted infectious agent, associated with geminate particles, induced distinct symptoms on several Ipomoea species, but not on I. batatas cv. Georgia Jet. The virus was transmitted by Bemisia argentifolii in a persistent manner and by grafting, but not mechanically. No transmission to species outside Ipomoea was obtained. Extracts from infected Ipomoea plants hybridised with a bean yellow mosaic virus riboprobe and a tomato yellow leaf curl virus riboprobe, although not so strongly as hybridisation of these riboprobes with extracts from plants infected with the homologous viruses. Based on host range, we consider this virus to be distinct from sweet potato leaf curl virus reported from the Far East, and propose it be named “Ipomoea crinkle leaf curl virus” (ICLCV).
Quantifying the impact of polyphagous invertebrate predators in controlling cereal aphids and in preventing wheat yield and quality reductions
Authors: HOLLAND JOHN M , THOMAS S R
Published: February 2008

Exclusion barriers were used to manipulate numbers of polyphagous invertebrate predators so that their impact on cereal aphids and consequently wheat yield and quality could be examined. Experiments were conducted within the framework of the LINK Integrated Farming Systems Project which allowed comparisons to be made between the integrated and conventional farming systems under examination on a study farm in Hampshire, UK. Only in 1995 were the numbers of aphids per tiller, the aphid peak and rate of increase to the peak significantly greater in the exclusion areas where the density of polyphagous predators had been reduced. The maximum increase in aphids as a result of excluding polyphagous predators was 31%, which was equivalent to 130 aphid days. However, the polyphagous predators did not reduce the number of tillers infested. The relatively low impact of polyphagous predators was attributed to the aphid population phenology and greater effects may have been found had aphids infested the crops earlier in their development. Sowing date was shown to govern the time over which a crop may be susceptible to yield loss from aphids, with later‐drilled crops being more susceptible to late‐summer aphid infestations.

Aphid numbers rarely affected grain yield but were found to be related to some grain quality parameters, but reducing polyphagous predators had no direct impact on grain yield or quality even where the aphid burden increased.

The peak period of activity and density differed between the species of Carabidae, Staphylinidae and Araneae consequently influencing their relationship with the aphids. Some negative correlations were found between these groups of polyphagous predators and aphids. Species composition and abundance differed between fields thereby influencing the level of aphid predation. The exclusion barriers were most effective at reducing numbers of Carabidae although numbers of Staphylinidae and Araneae were also reduced. The consequences for Integrated Crop Management are discussed.
Inheritance of components of partial resistance of barley to Rhynchosporium secalis with particular reference to race specificity
Authors: KARI ANDREAS G. , GRIFFITHS ELLIS
Published: February 2008

Six spring barley cultivars with no known genes for resistance to specific virulences but varying in partial resistance to Rhynchosporium secalis, were crossed in all combinations (6 × 6 diallel including reciprocals). In addition to seeds from naturally selfed plants, seeds of all parent cultivars were also produced by artificial selfing (emasculation followed by pollination using pollen from the same cultivar). This ensured comparability between seeds of parents and F1. Both sets of parents, F1 and F2 families were grown in the field as single spaced plants and inoculated at Zadoks growth stage 49 with spore suspensions (2 × 106 spores ml‐1) of three races (pathotypes) of R. secalis (Zadoks, Chang & Konzak, 1974). Components of partial resistance, incubation period (ICP), infection frequency (IF) and spore production per lesion (SP/L) were assessed on each plant.

There were highly significant differences for all three components of partial resistance in both sets of parent cultivars but rank order in both sets was similar as evidenced by correlation coefficients, r= 0.96 for ICP and IF and r= 0.87 for SP/L. All three components of partial resistance were strongly correlated with NIAB (National Institute of Agricultural Botany, Cambridge, UK) resistance ratings.

Means of F1 and F2 families were correlated with mid‐parent values for ICP and IF but not SP/L. No difference in aggressiveness was found between races but for each component of partial resistance there was a significant interaction between race and parent cultivar (artificial selfs) and, for IF and ICP, a significant interaction between race and F1 family. There was no evidence of interaction between parent (natural selfs) and race nor between race and F2 family.

Examination of genetic control of resistance showed evidence of strong additive effects (combining ability) in both F1 and F2 for ICP and IF but not for SP/L. There was no evidence for maternal or reciprocal differences, but there was evidence for dominance effects although their nature differed between components of partial resistance and between F1 and F2 generations. In the F1, but not the F2 generation, several elements of dominance (direction, distribution of dominant genes between parent cultivars, specific combining ability) showed for ICP or IF (but not SP/L) significant interaction with race.
The morphology of bracken (Pteridium aquilinum (L.) Kuhn) in the North York Moors—a comparison of the mature stand and the interface with heather (Calluna vulgaris (L.) Hull) 1. The fronds
Authors: WHITEHEAD S J. , DIGBY J.
Published: February 2008

The encroachment of bracken (Pteridium aquilinum (L.) Kuhn) into areas previously dominated by heather represents a threat to the ecology, agricultural economy and landscape value of many UK upland areas, including the moorland of the North York Moors National Park.

The morphology of bracken, within a mature stand and at several bracken‐heather interfaces, has been studied at a number of sites within the National Park. Differences have been found in the frond growth of bracken in a mature stand, at stationary stand margins, and at advancing stand margins where bracken is encroaching into heather.

Frequency of fronds present on bracken rhizome growing at a stationary stand margin close to the interface with heather (1–2 m behind the boundary) are approximately the same as those found within a mature stand. At advancing margins (again 1–2 m behind the boundary), maximum frond densities were often found to exceed those present in either a mature stand or at a stationary margin. Frond numbers decline rapidly at the stand margins as distance from the stand increases. This is especially true where the front is stationary and bracken is not encroaching into heather at a significant rate. Maximum frond heights in a mature stand consistently exceed those at stand margins (even 1–2 m into the stand) and are greater at stationary margins than at advancing margins.

Outlying fronds at the edges of bracken stands are generally present in greater numbers, and further into the area dominated by heather, where the margin is advancing. Heights of outlying fronds fall as distance from the bracken stand increases, as does stipe length. Fronds at the edges of bracken stands emerge each spring before those further into the stand and are therefore particularly vulnerable to frost damage. Outlying fronds are not, however, the first to emerge. Early emerging fronds reach their maximum height and eventually become senescent before later emerging fronds. Whilst most fronds emerge before the end of June a few fronds continue to emerge throughout the summer.

Frond densities close to the edges of bracken stands (1–2 m into the stand) are comparable to those in a mature stand. At advancing stand margins frond densities generally exceed those in a mature stand, suggesting that a large number of potential entry points for foliage‐applied herbicides are available for bracken control at the stand margins. The ratio of potential uptake points to biomass of rhizome is also greatest at the edges of the stand, and the canopy 1–2 m into the stand is usually almost completely closed. It is possible therefore, the efficacy of herbicides could be improved by the use of small scale applications, using tractors or hand‐held sprayers, close to the margins of bracken stands.
The influence of nitrogen fertiliser on the population development of the cereal aphids Sitobion avenae (F.) and Metopolophium dirhodum (Wlk.) on field grown winter wheat
Authors: DUFFIELD S J , BRYSON R J , YOUNG J E B , SYLVESTER‐BRADLEY R. , SCOTT R K
Published: February 2008

The effect of nitrogen fertiliser on populations of the cereal aphidsSitobion avenaeandMetopolophium dirhodumon winter wheat was investigated in a three year field experiment. Naturally occurring aphid populations were monitored on three nitrogen treatments; none, nitrogen application using Canopy Management guidelines (130–210 kg ha‐1) and conventional practice (190 kg ha‐1). Inoculations of laboratory rearedS. avenaewere used to enhance field populations on half the plots.

Natural populations ofM. dirhodumremained below the current UK spray threshold level of two‐thirds of shoots infested at the start of flowering, or five aphids per shoot in all years, whilst populations ofS. avenaeexceeded the threshold in all years.

The response of the two species to nitrogen differed. Significantly higher populations ofM. dirhodumwere recorded in both treatments which received nitrogen in all years, whilst the response ofS. avenaevaried between years. In 1994 and 1995 when environmental conditions favoured aphid development, higher populations were recorded in the two treatments which received nitrogen. In 1993 when high rainfall created unfavourable conditions, higher populations were recorded in the plots receiving no nitrogen.

Differences in peak density and cumulative aphid index ofS. avenaeresulted from differences in the rate of population increase between ear emergence and peak density on the different treatments. Populations prior to ear emergence were higher in the plots which received nitrogen but the differences were not statistically significant. There was no evidence of a difference in the timing of population decline in the different treatments.

In 1993 higher levels of infection by entomopathogenic fungi were observed in all treatments. Significantly higher levels of infection were recorded in the treatments receiving nitrogen, which may have accounted for the lowerS. avenaepopulations recorded. It is possible that the larger canopies recorded in these treatments produced conditions which favoured infection by fungi, thereby limiting aphid population growth.

The results indicate that application of nitrogen increases natural populations ofM. dirhodum, and under favourable conditions, populations ofS. avenae.However, in suboptimal climatic conditions, the application of nitrogen fertiliser can lead to lower populations of 5.avenae.The data also suggest that there is no consistent difference between a conventional and Canopy Managed approach to nitrogen fertiliser use in terms of the risk of infestation by cereal aphids.
Detection and relationships of cotton leaf curl virus and allied whitefly‐transmitted geminiviruses occurring in Pakistan
Authors: HARRISON B D , LIU Y L , KHALID S. , HAMEED S. , OTIM‐NAPE G W , ROBINSON D J
Published: February 2008

A stock culture of cotton leaf curl virus from Pakistan (CLCuV‐PK), was transmitted by whiteflies (Bemisia tabaci) to seven plant species, including French bean, okra, tobacco and tomato, and caused vein thickening and leaf curl symptoms. It was readily detected in triple antibody sandwich ELISA (TAS‐ELIS A) by 11 out of 31 monoclonal antibodies raised against the particles of three other geminiviruses: African cassava mosaic, Indian cassava mosaic and okra leaf curl viruses. Reaction strength was enhanced when the tissue extraction fluid contained sodium sulphite. Minor variations in epitope profile were found among virus isolates from cotton (Gossypium hirsutum) collected from different districts in Pakistan over a 5‐year period. These epitope profiles were distinguishable from that of cotton leaf curl virus from G. barbadense in southern India but indistinguishable from the profiles of viruses causing yellow vein disease of okra in India or Pakistan, or leaf curl of okra {Abelmoschus esculentus), Hibiscus tiliaceus, radish or sunflower in Pakistan, suggesting that these plants are putative natural hosts of CLCuV‐PK. The viruses in cotton, and in okra with leaf curl or yellow vein symptoms, were also detected by PCR with three pairs of CLCuV‐PK‐specific primers.

Five additional whitefly‐transmitted geminiviruses were found among isolates from 11 other naturally‐infected species in Pakistan, and were distinguished by their epitope profiles. These viruses were associated, respectively, with tobacco leaf curl, squash yellow blotch, tomato yellow leaf curl, watermelon leaf crinkle and soybean yellow mosaic diseases. The first four of these viruses were detected readily by PCR with geminivirus general primers but only weakly, if at all, with two pairs of CLCuV‐PK‐specific primers. Pakistani crops are infected with a range of distinguishable but relatively closely related whitefly‐transmitted geminiviruses, some of which resemble those found in India.
Novel resistances to four potyviruses in tuber‐bearing potato species, and temperature‐sensitive expression of hypersensitive resistance to potato virus Y
Authors: VALKONEN J P T
Published: February 2008

Novel potyvirus resistance specificities were found in eight tested wild potato species (clones): hypersensitive resistance (HR) to potato Y potyvirus (PVY) strain groups PVYO in Solanum megistacrolobum and S. polyadenium and PVYN in S. stoloniferum; HR to potato V potyvirus (PW) in S. maglia, S. polyadenium, S. stoloniferum, S. sparsipilum and S. sucrense, HR to potato A potyvirus (PVA) strain group 1 in S. sucrense, and extreme resistance (ER) to PVA in S. polyadenium. S. commersonii and S. stoloniferum expressed HR to tobacco etch potyvirus (TEV) which has not been reported previously in potato species. The studied clone of S. stoloniferum expressed HR to all potyviruses and potyvirus strains tested. The clone of S. stoloniferum (2n = 48; nuclear DNA content (2C) = 3.6 pg) and S. chacoense (2n = 24; 2C=1.9 pg) were crossed and one hybrid (2n = 36; 2C = 2.9 pg) was obtained. The hybrid expressed HR to all tested potyviruses except PVA, which indicated that HR to PVA was controlled by a gene which is different from the genes (or gene) controlling HR to PVYO, PVYN, PVV and TEV in S. stoloniferum. On the other hand, S. chacoense and the hybrid expressed ER to cucumber mosaic cucumovirus (CMV), whereas S. stoloniferum was susceptible to CMV. All tested wild species and the six tested potato cultivars (S. tuberosum subsp. tuberosum) expressed HR to PVV. Expression of HR following infection with PVYN induced systemic acquired resistance (SAR) in S. chacoense. HR to PVYN in S. sparsipilum and S. sucrense and to PVYO in potato cv. Pito was efficiently expressed at lower temperatures (16/18°C) indicated by the development of distinct necrotic lesions and/or vein necrosis in inoculated leaves, whereas the HR was rendered less effective at higher temperatures (19/24°C) which was indicated by the development of systemic infection with leaf‐drop and mosaic symptoms.
Classification as a first step in the interpretation of temporal and spatial variation of crop yield
Authors: LARK R M , STAFFORD J V
Published: February 2008

Automated pattern recognition by multivariate clustering is proposed as a tool for interpreting the temporal and spatial variation of crop yield. A trial showed that some general patterns of season‐to‐season variation could be identified and related to soil variability. Such a procedure would be a useful first step in the investigation of sources of yield variation, leading to interpretation and (possibly) spatial variation of inputs.
A morphological study of flower initiation and development in strawberry (Fragaria x ananassa) using cryo‐scanning electron microscopy
Authors: TAYLOR D R , ATKEY P T , WICKENDEN M F , CRISP C M
Published: February 2008

The morphological changes in the apex of strawberry (Fragaria x ananassa) cv. Elsanta during flower initiation and early development were studied by means of apical dissections and cryo‐scanning electron microscopy. Characteristic stages of development were recorded from the earliest discernible evidence of floral initiation until anthesis. The results are discussed in relation to previous studies of floral development in strawberry.
Modelling the predicted geographic and economic response of UK cropping systems to climate change scenarios: the case of potatoes
Authors: DAVIES A. , JENKINS T. , PIKE A. , SHAO J. , CARSON I. , POLLOCK C J , PARRY M L
Published: February 2008

Geographical changes in suitability in England and Wales for the cultivation of potatoes under a climate change scenario were predicted for the years 2023 and 2065 by integrating a climate database (1951‐80) with climate‐driven crop growth models. Initially, model outputs were produced as point values (meteorological site locations) of predicted potential yields for current crop production. The model outputs were validated statistically using actual crop yield figures collated from bibliographic analysis. The most suitable model was run again incorporating projected temperature and precipitation changes for 2023 and 2065. These outputs were then used to predict possible economic changes to farm profitability and general market trends. Results indicated that, although yields may rise, gross margins for maincrop and especially early potatoes may also rise due to shifts in production, to a fall in overall potato output and to price increases.
Counting by weighing and its effect on seed testing procedures
Authors: RIDOUT M S , SUNTHERALINGAM NALYNI
Published: February 2008

Counting by weighing is an approximate procedure for obtaining a given number of items based on an estimate of how much the items will weigh. The procedure can be considerably faster than exact counting. We show how the effects of counting by weighing can be assessed, using a particular problem in seed testing for illustration. We find that using counting by weighing in place of exact counting has little effect on the outcome of the seed test provided that the coefficient of variation of the individual seed weights is not too large, and provided a sufficiently large initial sample is used to estimate mean seed weight.
Neem seed oil inhibits aphid transmission of potato virus Y to pepper*
Authors: LOWERY D T , EASTWELL K C , SMIRLE M J
Published: February 2008

Transmission of potato vims Y to sweet pepper by the green peach aphid, Myzus persicae (Sulzer), was inhibited by foliar applications of 1.0% or 2.0% neem seed oil to infected source plants or to uninfected recipient plants. Neem seed oil interfered with virus acquisition and inoculation in a manner comparable to that of a commercial horticultural oil, while an oil‐free neem seed extract did not reduce rates of transmission compared with controls. The finding that neem seed oil inhibits virus transmission, while oil‐free neem seed extract does not, suggests that the presence of the oil rather than biologically active limonoids such as azadirachtin interfere with virus transmission. None of the treatments affected rates of infection when potato virus Y was transmitted mechanically, or the resulting virus titre and symptom expression. In addition to direct control of insect pests, formulated neem oils may help reduce or delay the spread of non‐persistent plant viruses.
Effects of temperature, cultivar and isolate on the incubation period of white leaf spot (Mycosphaerella capsellae) on oilseed rape {Brassica napus)
Authors: INMAN A J , FITT B D L , WELHAM S J , EVANS R L , MURRAY D A
Published: February 2008

When leaves of oilseed rape (cv. Cobra) were inoculated with conidial suspensions of Mycosphaerella capsellae (white leaf spot) and incubated in controlled environments, the lag period from inoculation to the appearance of the first lesions decreased, and the total number of lesions produced increased, as temperature increased from 5oC to 20oC, although differences between 15oC and 20oC were small. With incubation period estimated as the time from inoculation until 5%, 50% or 95% of the lesions were produced, there was a linear relationship between l/(incubation period in days) and temperature over the range 5oC to 20oC, from which values at intermediate temperatures could be estimated. Summed mean daily temperatures from inoculation to the production of 5% of the lesions were estimated as 115–130 degree‐days in the controlled environment experiments at 5oC to 20oC. When pods or leaves of plants in oilseed rape crops (cv. Cobra or cv. Libravo) were inoculated with conidial suspensions of M. capsellae on five occasions from January to October, with variable temperatures during the incubation period, degree‐days until the first appearance of lesions were in the range 115–230. The numbers of white leaf spot lesions cm‐2 which developed on inoculated leaves differed greatly between nine oilseed rape cultivars, with most on cv. Tapidor and fewest on cv. Libravo, but the incubation period differed little between cultivars. Similarly, the number of lesions which developed differed between four M. capsellae isolates from different regions but the incubation period did not.
Evaluation of a bracken (Pteridium aquilinum (L.) Kuhn) growth model in predicting the effects of control strategies across a range of climatic zones in Great Britain
Authors: PATERSON S. , PAKEMAN R J , MARRS R H
Published: February 2008

A nationwide bracken control experiment provided data over a three‐year period for testing the accuracy of a bracken growth model (BRACON). Objective assessments of model validity identified the model as a reasonably accurate predictor of bracken stand dynamics given the range of environmental conditions currently prevailing in Great Britain, in relation to (1) cutting regimes and (2) spraying asulam. Ranking of treatment efficacy at individual sites was closely reflected in model predictions. Predicted response of the rhizome system to cutting treatments underestimated bracken resilience. Failure to consider the consequences of frond regrowth in the latter portion of the growing season as a means to offsetting energy loss was identified as a potential explanation for this discrepancy. The role of the model as a practical management tool is discussed with particular reference to relating model predictions, based upon generalised environmental data (40 km plusmn; 40 km grid cells), to bracken management at individual sites.