Relative significance of nursery infections and orchard inoculum in the development and spread of apple canker (Nectria galligena) in young orchards

Three nurseries produced apple rootstocks (M9) and budwood (cv. Royal Gala), which they exchanged at the end of the first year. Each nursery then budded its own budwood onto the rootstocks it had produced and that from the other two nurseries. Budded trees were grown on for a further year before being planted at HRI, East Malling in southern England; NIHPBS, Loughgall in Northern Ireland; and ADAS, Rosemaund in the West Midlands of England. Canker development was monitored twice a year. The position of the infected trees within the orchard was recorded, as was the position of the canker on each tree (main-stem or peripheral). Nectria galligena was isolated from representative cankers and analysed using molecular techniques. At the sites in Northern Ireland and HRI there was a strong positional effect, especially of peripheral cankers, indicating that most of the inoculum was external and had been spread from neighbouring orchards. There was little or no positional effect on main-stem cankers at any of the three sites. The proportions of different isolates taken from peripheral cankers was different in Northern Ireland from that in England, suggesting different populations associated with the geographic areas. In contrast, the populations of N. galligena obtained from main-stem cankers were very similar in England and Northern Ireland. It was concluded that a small proportion of trees developing canker were infected during propagation, with no symptom development until after planting. In a second trial it was demonstrated that trees infected during the propagation phase, and particularly at budding and heading back, could develop canker up to 3 years later. While it is clear that some canker developing in the orchard can be associated with the nursery of production, in climatic conditions conducive to the formation and dissemination of conidia, inoculum from surrounding infected orchards is the primary source of the pathogen. Aerial spread is therefore an essential element of the epidemiology of N. galligena, and its control is a crucial part of any canker-control programme.     

Survey of benomyl resistance in Pseudocercosporella herpotrichoides on winter wheat and barley in England and Wales in 1983

Surveys of 528 randomly selected commercial fields in England and Wales in 1983 showed that isolates of Pseudocercosporella herpotrichoides resistant to benomyl were common and widespread on winter wheat and winter barley. During June and July resistant strains were recovered from 16 to 66% of fields and the proportion of resistant isolates was 37–52%. The frequency of occurrence of resistant isolates was positively correlated with the number of applications of carbendazimgenerating (MBC) fungicides during the previous 8 years. Benomyl resistance was found in 21–48% of fields where it was claimed that MBC had never been used, and 7–28% of isolates from those fields, were resistant. Resistance was more frequent in R-type than in W-type isolates of the pathogen. The proportion of R-type isolates decreased as the number of previous winter wheat crops rose and increased with the number of winter barley crops grown and with the number of MBC sprays applied to crops in previous years. The implications of these findings for the control of eyespot in England and Wales are discussed.     

The role of alternative hosts of Polymyxa betae in transmission of beet necrotic yellow vein virus (BNYVV) in England

The host range of beet necrotic yellow vein virus (BNYVV) and Polymyxa betae was determined by growing plants in naturally infested soils from rhizomania outbreaks in England. Apart from Beta vulgaris , plant species infected by BNYVV were included in the families Chenopodiaceae ( Atriplex patula, Chenopodium bonus-henricus, C. hybridum, C. polyspermum and Spinacia oleracea ), Amaranthaceae ( Amaranthus retroflexus ) and Caryophyllaceae ( Silene alba, S. vulgaris, S. noctiflora and Stellaria graminea ). Only P. betae isolates from B. vulgaris, C. polyspermum and S. oleracea were found to be able to transmit BNYVV back to sugar beet. When a range of weed plants from infected fields were tested, none were found to be infected by BNYVV. Therefore, it seems likely that the weed hosts play only a minor role in the spread of rhizomania disease compared to that of sugar beet, other Beta vulgaris crop types or spinach.     

Phytophthora ramorum and Phytophthora kernoviae: the woodland perspective

Phytophthora ramorum and P. kernoviae were first identified in Great Britain (GB) in 2002 and 2003 respectively, although both are believed to have been present for perhaps 10–20 years. Public gardens have been badly affected by these pathogens, but British woodlands are also considered at risk as a number of tree species have been found to be susceptible to the pathogens. The principal host of both Phytophthoras in GB is Rhododendron ponticum , which is arguably our most invasive weed species. It is found extensively in GB, especially along the west coast which has ideal climatic conditions for its growth and spread. In 2004 the Forestry Commission surveyed 1479 woodlands where R. ponticum was present, and in 2008 both infected and non-infected R. ponticum were cleared from approximately 1200 ha of woodlands in England and Wales where P. ramorum had been found. No clearance to date has taken place in Scotland. In the case of a positive finding in a garden or woodland, all woodlands with rhododendron within a 3 km radius of such a finding are to be surveyed. As both pathogens are notifiable any positives must be eradicated or contained through the serving of an official phytosanitary notice. Ministerial approval has now been given to a joint Defra and Forestry Commission initiative to undertake inter alia the removal of host plants (primarily rhododendrons) infected with these sporulating pathogens in woodlands and the wider environment in England and Wales. A similar programme will be effected in Scotland where the Forestry Commission is working with the Scottish Government's Rural Payments and Inspections Directorate.     

Population Dynamics of Small Rodents in Farm Buildings and on Arable Land1

Live-capture/recapture data on house mice caught in buildings on a single farm in England over a 1-year period showed that the populations were essentially unstable, being characterized by constant changes in size and composition. Less than 50% of the mice were recovered 8 weeks after they had been first captured. Although there was considerable individual variation in the movements of male and of female mice within particular buildings, movement between isolated populations was rare (6/439 animals; 1.4%). The house mouse was also found to be present in hedgerows near and distant to the farm buildings, albeit in low number. Movements of out-door living mice into farm buildings were not extensive, but could be important in relation to the re-invasion of cleared premises. The most abundant small rodent in the hedgerows was found to be Apodemus sylvaticus (L.).     

Tracing the origins of White Tip disease of Cirsium arvense and its causal agent,Phoma macrostoma

Cirsium arvense (Asteraceae) is known as creeping thistle in its native range in the UK and Canada thistle in its invasive North American range. Recently, the fungus Phoma macrostoma was registered in Canada as a bioherbicide in turfgrass, where it causes severe chlorosis (White Tip disease) and death of C. arvense and other broadleaved weeds. It was hypothesised that the disease originated in the UK on its thistle host and, therefore, that fungal isolates from both countries should be biologically and genetically similar. Twenty‐six strains in the genus Phoma– isolated during surveys in the UK – were compared morphologically with the type culture of P. macrostoma, tested for bioherbicidal activity using the inoculum mat bioassay and genetically screened with bioherbicide‐specific primers. White tip disease was found to be restricted to the eastern and southern counties of England. Phoma macrostoma was isolated consistently from diseased bleached tissues. Bioherbicidal isolates of P. macrostoma occupy a unique clade, which is phylogenetically distinct but morphologically indistinguishable from the type culture. Most isolates from the UK had the same bioherbicidal activity and similar genetic make‐up as strain SRC 94‐44B, the active ingredient in the registered Canadian product. The origin of all bioherbicidal strains found to date has a clear presence in both Canada and the UK, with strong genetic similarities, supporting the view of a common ancestry. Thus, on the evidence presented, the ‘white tip’ clade of P. macrostoma evolved in southern England. Therefore, the bioherbicide based on strain SRC 94‐44B should also be eligible for registration in the UK, based on the pest risk assessment data already available.     

Occurrence and distribution of Raspberry bushy dwarf virus in commercial Rubus plantations in England and Wales

Serological surveys for Raspberry bushy dwarf virus (RBDV) made between 1995 and 1997 and covering ≈ 10% of the commercial farms growing Rubus (red raspberry and hybrid berries) in England and Wales showed that this virus was present on approximately one-quarter of all farms and in approximately one-sixth of all plots tested. RBDV was found in all of the four main raspberry cultivars being grown at that time (Autumn Bliss, Glen Moy, Glen Prosen and Leo), in Loganberry and in Tayberry. Fifteen RBDV genotypes (including two that appeared to be mixed) were identified using RT-PCR/RFLPs, but the majority of genotypes were found only rarely. Of the RBDV isolates tested, two genotypes each comprised 12·5% and another 46·4%. None of the three most common genotypes was associated solely with single Rubus cultivars and vice versa . It is suggested that two separate outbreaks of RBDV are occurring in England and Wales. One outbreak comprises the most frequent genotype combined with one of the moderately frequent genotypes; this outbreak is largely confined to the main growing areas and is either spreading between farms or coming from multiple local sources. Circumstantial evidence suggests that these isolates (and hence this first outbreak) are of the RB pathotype. The second outbreak consists of the other moderately frequent genotype and those genotypes which are less common. These genotypes appear to be more scattered across England and Wales and seem more likely to be coming from local sources and not to be spreading naturally between commercial farms.     

Serotypes of beet soil-borne furovirus from FRG and Sweden1

Four virus isolates were obtained in FRG and Sweden from sugarbeet roots which had become infected via the soil. All isolates had rod-shaped particles of four or five different lengths. Serologically they were unrelated to beet necrotic yellow vein furovirus and several other viruses of a similar morphology including two serologically distinct sugarbeet isolates from California (US). Our isolates were, however, serologically related to beet soil-borne furovirus which has been described in England. They could be subdivided into two serotypes.     

大麦品种对白粉病抗病性鉴定及抗源筛选

通过田间初筛和病圃复筛,对6515份国内外大麦品种进行了白粉病抗性鉴定。重点材料结合苗期、分蘖期鉴定和异地鉴定,筛选出免疫或高抗材料52份,慢白粉病抗性材料59份,并发现具有Mla、Mla6单基因和Mla Mlat、Mla Mlh Mlp多基因组合的国外已知抗病基因品种,在浙江舟山和福建莆田表现抗病。统计分析表明,二棱大麦抗病性较多棱大麦强;抗病品种发病较感病品种迟;抗性材料大多来自国外,英、德、瑞典、叙利亚、澳大利亚、墨西哥等国品种,筛出率较高。     

The occurrence of beet pseudo-yellows virus in England

Beet pseudo-yellows virus (BPYV) has been identified in England for the first titne, in lettuce, following transmission by the greenhouse whitefly ( Trialeurodes vaporariorum ) to healthy plants. Infected plants had leaves with severe interveinal chlorosis and slight downward curling, and were gerterally smaller than healthy plants. Indirect ELISAs with an antiserum raised against the Californian isolate of BPYV were positive with extracts produced from infected plants. Infected but not healthy plants contained a single species of double-stranded RNA of about 7.5 × lO⁶Da, a size similar to that found with beet yellows virus, the type member of the closterovirus group.     

Biological control of two-spotted spider mite (Tetranychus urticae) by Phytoseiulus persimilis on strawberries grown in walk-in' plastic tunnels, and a simplified method of spider mite population assessment

During 1980 and 1981, a large-scale trial of the biological control of two-spotted spider mite ( Tetranychus urticae Koch) on protected strawbenies, using the predatory'mite Phytoseiulus persimilis Athias-Henriot, was done in 52 'walk-in' plastic tunnels on a commercial nursery in southern England. Introductions of predatory mites in March or early April at a rate of one per plant were consistently successful. In 1980, when predators had not been introduced the previous year (so enabling large numbers of spider mites to overwinter) peak mite populations were large, causing slight foliar damage in some tunnels before control was achieved. In 1981, only a small residual population of spider mites had survived from the previous year and peak numbers were small; the crop appeared healthy and there was no visible damage by mites. For jdequate control, reintroduction of predators was found to be necessary when CTops were replanted in the summer following soil cultivation and sterilization with methyl bromide.
A population assessment method for two-spotted spider mite based on counting aggregations of the mites was devised. The mean number of spider mites (all stages) per leaf was found to be approximately the same as the number of leaves with five or more mites present in a 25-leaf sample.     

枸杞叶片净光合速率与其它生理参数及环境微气象因子的关系

采用英国PPS国际有限公司生产的CIRAS-1型光合作用综合测定仪测定了3a生枸杞6月下旬净光合速率、蒸腾速率、气孔阻力等植物生理因子的逐时变化,并同时测定了照度、光合有效辐射、叶温、气温、湿度和田间微风。通过枸杞诸因子与外界环境气象因子的模拟,研究了枸杞叶片净光合速率与外界光、温、水、气和风的关系。结果表明,枸杞净光合速率除受蒸腾速率、气孔导度等因子的影响外,与辐射、温度等环境因素和气象因素的关系非常密切,可以用某些环境气象因子推测植物生理因子的变化。     

Genetic variation among field isolates of Pyrenopeziza brassicae

Amplified fragment length polymorphism (AFLP) markers were used to determine genetic diversity and population structure of Pyrenopeziza brassicae , the causal agent of light leaf spot of Brassica spp. Fungal isolates were sampled from six regions in the UK, one region in Germany and one region in France. A high level of genetic diversity was found ( H _T = 58%), with most variation attributed to within regions ( H _S = 43%), which suggests that sexual reproduction is frequent. F _ST values suggested significant population differentiation between England and the continent, but not between Scotland and England and Scotland and the continent. Overall, a moderate but significant level of regional differentiation was found ( F _ST = 16 ± 4.0). There was no correlation between F _ST values and distance, indicating that long-distance dispersal by natural factors does not occur at high frequencies. However, the lack of differentiation among populations from Aberdeen, Winchester and Cambridge suggests that seed transmission or other artificial methods of dispersal may be important.     

Relationships between populations of Pseudomonas syringae pv. persicae determined by restriction fragment analysis

Pseudomonas syringae pv. persicae , the pathogen causing bacterial decline of stone-fruit, was first noted almost simultaneously in France and in New Zealand, together with a closely related pathogen from myrobalan plum in England. The relative similarity of 31 strains from these three countries was examined by comparing DNA restriction endonuclease fragment patterns. Fragment patterns produced from digested DNA samples which were electrophoresed on polyacrylamide gels and visualized by silver-staining, were analysed using the software package Gelcompar. The fragment patterns produced by strains from France and England formed homogeneous but separate groups, while those from New Zealand were relatively heterogeneous. This finding suggests that the New Zealand population of P.s. persicae is older than those found in Europe. Problems in explaining the distribution of the pathogen are discussed.     

A comparison of fungicide seed treatments to improve sugar beet seedling establishment

In a series of field trials from 1977 to 1979, steeping sugar beet seed in thiram gave slightly better plant establishment than the ethyl mercury phosphate (EMP) steep currently applied to all sugar beet seed used in England. Steeping in a phenyl mercury acetate solution gave establishment close enough to EMP steep to show that it could be used as a replacement for EMP if the latter were unavailable for agricultural use. TCMTB steep and maneb slurry were clearly inferior to EMP steep, particularly when the incidence of seed-borne Phoma betae was high.     

A selective survey of potato cyst-nematode pathotypes in Great Britain

One hundred and forty-four samples of potato cyst-nematodes, the majority chosen to contain G. pallida , from England, Wales and Scotland were identified to pathotype. Where G. rostochiensis was present it proved to be pathotype Rol, there being no indication of other pathotypes of this species. Of G. pallida , a minority of samples incorporated pathotype Pa 1; many were pathotype Pa3 but distinction between Pa2 and Pa3 was unsatisfactory in many more. It is concluded that recognition of these latter two pathotypes is of little value. The proposed pathotype New Leake could not be recognized.     

Variation in the pathogenicity of two Turnip mosaic virus isolates in wild UK Brassica rapa provenances

Brassica rapa can be infected with Turnip mosaic virus (TuMV) as a result of manual inoculation or aphid transmission, but infected plants have not been found in the field. In this study, B. rapa plants grown from seed collected from two field sites in southern England were mechanically inoculated with one of two distinct isolates (pathotypes) of TuMV under glasshouse conditions. These had either been isolated from Brassica oleracea growing wild in Wales, (GBR 83, pathotype 3) or Dorset (GBR 98, pathotype 1). Use of ELISA as an index of infection in manually inoculated B. rapa showed that although seed provenance had a small effect on the proportion of plants infected, the biggest factor was the virus isolate. Both virus isolates infected both lines of B. rapa , but invaded at different rates, although both resulted in easily discernible symptoms. The severity of symptoms was not related to amounts of virus in the infected plants. A significantly greater proportion of plants were infected with GBR 83 at 45 days post-inoculation (d.p.i.) than GBR 98. but GBR 98 caused significantly more severe and obvious symptoms as well as greater mortality at 119 d.p.i., in plants from both sites than GBR 83.     

Variation in the pine stem rust fungus Peridermium pini in the United Kingdom

Peridermium pini aeciospores from lesions on Scots pine ( Pinus sylvestris ) in Scotland and in Thetford Forest, East Anglia, differed in terms of germ tube morphology and cytology. The former produced long aseptate germ tubes containing a pair of nuclei. The latter produced short septate germ tubes, each cell containing a single nucleus. One third of the 'Scottish' germ tubes ended in a vesicle. Nuclei could be counted in only a small proportion of ungerminated aeciospores. On average 83% of Scottish spores had two nuclei and 4% had one. The equivalent figures for Thetford spores were 66 and 20%. A small number of aeciospore samples from other parts of England resembled Scottish spores rather than Thetford spores in germ tube morphology and cytology.
Both Scottish and Thetford spores proved capable of causing infection of wounded Scots pine shoots. In addition, some Thetford spores caused infection on leaf discs taken from certain Paeonia cultivars. From these results it is concluded that two distinct forms of Peridermium pini exist in the UK. The implications of this finding are discussed in relation to the history of pine stem rust in the country and the genetics and taxonomy of P. pini.     

ISSR markers detect high genetic variation among <Emphasis Type="Italic">Fusarium poae</Emphasis> isolates from Argentina and England

Fusarium poae is one of the Fusarium species isolated from cereal grains infected by Fusarium head blight (FHB), and in recent years it has been identified as a major FHB component. In this study, 97 F. poae isolates from Argentina (n = 62) and England (n = 35) were analysed by inter-simple sequence repeats (ISSR) to examine the genetic diversity and to determine whether intraspecific variation could be correlated with geographic and/or host origin. The molecular analysis showed high intraspecific variability within F. poae isolates, but did not reveal a clear relationship between variability and the host/geographic origin. Fusarium poae isolates from the same geographic region or host appeared in different subclusters. Conversely, isolates with the same haplotype were also collected from different geographic regions. However, we did observe subclusters consisting of isolates from Argentina only or from England only. Furthermore, a single seed sample was found to host different haplotypes. Analysis of molecular variance (AMOVA) indicated a high genetic variability in F. poae, with most of the genetic variability explained by differences within, rather than between Argentinean and English populations. This is the first report on genetic diversity of F. poae using ISSR markers. Moreover, ISSR fingerprinting generates highly polymorphic markers for F. poae and proved to be a useful and reliable assay for genetic variability studies.     

Potential impacts of climate change on the threat of potato cyst nematode species in Great Britain

Potato cyst nematode (PCN) species have different temperature optima for various life cycle stages, therefore a risk assessment of the threat of PCN species under future climates is essential to guide adaptation strategies. Data defining the spatial coverage of potato crops in Great Britain were combined with probabilistic climate change data and a newly developed PCN life cycle model to project the future risk to potato crops from PCN. The model was based on the results of controlled environment experiments to investigate the effect of temperature on survival to female maturity using three PCN populations: Globodera pallida (Lindley) and G. rostochiensis from the James Hutton Institute PCN collection, and a field population of G. pallida (S‐Fife). It was found that projected increases in soil temperature could result in increased survival to female maturity for all three PCN populations, with greater increases expected for Scotland, followed by Wales then England. The largest projected increases in Scotland were for G. pallida, whereas G. rostochiensis showed the largest increases in Wales and England. The potential impact of several agronomic adaptation strategies on projected PCN risk were also investigated. The results from the model suggest that soil infestation levels would have to be reduced by up to 40% in order to negate projected increases in PCN risk, and that advancing the start date of the growing season or modifying planting patterns could be successful strategies to reduce future PCN risk.