The fungicidal properties of plant extracts and essential oils The aesthetic, medicinal and antimicrobial properties of plant essential oils have been known since ancient times. Numerous studies on the fungicidal and fungistatic activities of essential oils have indicated that many have the power to inhibit fungal growth. Several studies have been conducted within the university of Hertfordshire on the antimicrobial effects of the essential oils of basil (Ocimum basilicum), Coriander (Corriandum sativum), Lavender (Lavandula angustifolia), Neem (Azadirachta indica) and Thyme (Thymus vulgaris). Both in vitro and in vivo experiments were designed to find out the fungicidal, fungistatic and phytotoxic effects of the oils both as a contact and as a fumigant fungicide. The test organisms were a range of economically significant fungi (Alternaria sp., Aspergillus sp., Botrytis cinerea, Erysiphe graminis). Several techniques were evaluated to find the Minimum Inhibitory Concentration (MIC) of the oil needed to inhibit the growth of the fungi, these included the droplet technique, the borehole method and the disc diffusion method. Vapour chambers were constructed to evaluate the fungicidal properties of the volatile components of the oil. Various degrees of inhibition were observed for all oils examined except Neem
oil, which did not show any fungicidal properties. Thyme oil proved to be
extremely effective as a fumigant as well as a contact fungicide. The findings
emphasise the fungitoxicity of various oils and pave the way for further studies
and for their adoption as effective fungicides in the horticulture and
agriculture industries.
The history of fireblight in England in relation to weather Movement of diseased plant material was an important factor in the spread of
fireblight across England but, the amount of disease in different seasons on
different hosts and cultivars was largely weather dependent. Major outbreaks of
fireblight since 1957 were as follows: pear secondary blossom (1957 - 1960,
1966, 1967); late apple primary blossom (1978, 1982); hawthorn blossom (1960,
1964, 1982); pyracantha and cotoneaster blossom (1960, 1966, 1967 and some later
years). Significant shoot blight on two or more hosts was associated with stroms
(1968, 1969, 1982, 1994). In 1982, disease was widespread and severe on all
hosts except pear. Since then, outbreaks on pear, apple and hawthorn have been
sporadic but rarely severe. Weather patterns associated with outbreaks will be
shown and problems of cross-infection between hosts described. The importance
for risk assessment of good flowering records for each host and of storm records
is emphasised.
Field Resistance of Wheat Varieties to Isolates of Mycosphaerella
graminicola. Field trials of the resistance of 69 wheat varieties to single-pycnidium isolates of Mycosphaerella gramincola were carried out in England, Switzerland and the Netherlands in 1995, 1996 and 1997. These included varieties and breeding lines from the Czech Republic, England, France, Germany, the Netherlands, Portugal, Sweden and Switzerland, varieties from Europe and America which are parents of precise genetic stocks held at the John Innes Centre, and Veranopolis and Kavkaz-K4500, which have been identified as possible sources of resistance. There was great variation among the varieties in their resistance to M. graminicola. A Czech breeding line was the most resistant, followed by Veranopolis, but several varieties which have been grown widely in the UK also had very good resistance. This indicates that there is considerable potential for UK breeders to improve the general level of resistance using well-adapted germplasm but further improvements in resistance may be obtained by introgression from exotic varieties. There was also considerable specificity in interactions between varieties and
isolates. In particular, a number of lines were resistant to IPO323 but
susceptible to other isolates; these include parents of JIC precise stocks from
countries throughout western and eastern Europe and from the United States.
Variety×isolate interaction must therefore be taken into account in wheat
breeding, because the evolution of specifically virulent M. gramincola
populations presents a threat to the durability of varietal resistance. Although
very little is currently known about the frequencies of specific virulences
towards wheat varieties, the trials gave a hint that there may be regional
differentiation between sub-populations of M. graminicola from different parts
of Europe, since varieties which are used as resistant parents in Portuguese
wheat breeding programmes were very susceptible to several Dutch isolates.
Effects of meteorological conditions, sclerotial position and cropping
practice on Sclerotinia in field-grown lettuce Five sequential crops of lettuce were planted in 1996 and 1997, on a
naturally infected site and a disease free site, in both Cheshire and East
Anglia. Plots of single (normal) spaced plants and double spaced plants were
artificially infested with sclerotia placed at specific positions relative to
the plants. Meteorological stations were set up in 1995 to measure rainfall, air
and soil temperatures in the winter months and, in addition, soil moisture, soil
moisture tension, surface wetness, wind speed and solar radiation during the
growing seasons. The maximum sclerotial germination observed per plot in 1996
and 1997, respectively, was 100% and 52% in Cheshire, and 34% and 16% in East
Anglia. There was considerable variation in the timing and quantity of
apothecial development between plantings and particularly between sites. Disease
only occurred at the Cheshire site with maximum disease incidence per inoculated
plot of 66% and 22% plants affected in 1996 and 1997, respectively. Disease was
not related to the presence of apothecia directly beneath plants, which suggests
that airborne ascospores may be responsible for infection. A qualitative
examination of the meteorological data suggested that temperatures between 10
and 18oC and an increase in soil tension, i.e. a period of drying
following a rain event appeared to stimulate the formation of apothecia in the
field. Laboratory and glasshouse studies under controlled conditions are
underway to confirm field observations of the key factors controlling apothecial
production and lettuce infection.
The effect of the spore concentration of Verticillium albo-atrum and salt
treatment on infection and disease progression in tomato plants The pathogenic effects of virulence of Verticillium diseases on tomato plants was increased when they were inoculated with high spore concentration of the fungus in early stages of growth (for-week old seedlings). When plants were inoculated in later stages (five-week old) with a lower spore concentration the effect of pathogen on tomato plants was decreased (although it was still pathogenic to tomato). The severity of the disease was higher in tomato plants treated with the
fungus and salt solution, than in plants given either treatment separately.
Pathogenicity of lucerne (V1) and tomato (V2) isolates of Verticillium
albo-atrum to salt-tolerant lucerne strains The pathogenicity of lucerne V1 isolate and tomato V2 isolate to
salt-tolerant lucerne strains (150, 200, 250 and 300 mol/m3) was
investigated both under greenhouse and field conditions. Six week old
salt-tolerant lucerne seedlings (Medicago media) were inoculated by the method
of root dipping and wound inoculation. Height and symptom index were assessed
one week after inoculation for a period of ten weeks. Isolate V2 caused mild
symptoms under greenhouse conditions but did not cause any symptoms or height
reduction under field conditions on salt-tolerant strains, while isolate V1
caused severe symptoms on the salt-tolerant plants both in the greenhouse and
under field conditions. Susceptibility of salt-tolerant plants to the disease
increased in both conditions when their level of tolerance to salt increased. Assessing the Greening Effect of New Fungicide Chemistry on Winter Wheat Two new groups of plant protection chemicals, Strobilurin fungicides and plant activators, have been reported to have, apart from disease control, a 'greening' effect on treated plants, the leaves having a more intense green colour and staying green longer than controls. The main aim of this study was to test if the claimed greening effect was measurable on winter wheat (Triticum aestivum L.) with methods currently used to assess leaf colour. A secondary aim was to compare the performance of the available methods of detecting possible differences in greenness. Chlorophyll content of the leaves was assessed by extraction in acetone and
with a portable SPAD-502 chlorophyll meter. Spectral transmittance and
reflectance were measured with a LI-COR LI-1800 spectroradiometer with an
integrating sphere attachment. A high correlation was obtained for the
calibration curve (R2 = 0.97) between SPAD readings and extractable
chlorophyll. The relation between SPAD readings and the NIR/R ratio calculated
from LI-COR measurements was also highly correlated (R2 = 0.92). both
the SPAD meter and the LI-COR detected differences in greenness (P<0.01)
between leaf layers, with the second leaf being the greenest in all treatments.
Differences were also found (P<0.01) between untreated and fungicide treated
plants. The top three leaf layers of the Strobilurin treated plants were shown
to be significantly greener (P<0.05) than corresponding leaves of all other
treatments, with a suggestion of a stronger effect on older leaves. This
suggestion was further supported by the lower percentage (P = 0.017) of dead or
very senesced fourth layer leaves found in this treatment. Transmittance spectra
provided an indication that there was also an effect of the Strobilurin
fungicide on internal leaf structure. No significant greening effect was found
for the plant activator.
Foliar fertilisers can suppress Septoria tritici Septoria tritici is a widespread and damaging disease of winter wheat in he UK. It has been suggested that fertiliser application, particularly potassium chloride, to the foliage of wheat will suppress S. tritici. A field experiment was set up to investigate the efficacy of potassium chloride compared to a conventional fungicide. Potassium chloride or epoxyconazole (opus, BASF) was applied tot the leaves of winter wheat, cultivar Consort, either at growth stage (GS) 31, or 39, or at both growth stages, or according to a disease threshold. The percentage leaf area infected with S. tritici was assessed visually at GS 71. Although not significant between timings, applications of potassium chloride were shown to significantly reduce the percentage area of leaf 2 affected with S. tritici, from 18.4% in unsprayed controls to between 10.3% and 12.3% in treated plots. A similar situation was observed following epoxyconazole applications, where between 2.1% and 9.5% of leaf area 2 was affected, depending on timing, compared to 18.4% in control plots. On leaf 3 two applications of potassium chloride or epoxyconazole proved most effective, reducing the severity of S. tritici from 28.6% in control plots to 22% for potassium chloride and 9.7% for epoxyconazole treated plots. This may be because leaf 3 was more severely infected. Therefore foliar applied potassium chloride can suppress S. tritici, although to a lesser degree than epoxiconazole. In vitro experiments were undertaken to investigate whether the potassium or
the chloride ion was the most active against S. tritici mycelial growth and
spore germination. Potassium chloride, sodium chloride and potassium nitrate
were used. All three salts significantly reduced mycelial growth and spore
germination. Both potassium chloride and sodium chloride caused an almost linear
reduction in mycelial growth up to 2 M concentration. potassium nitrate caused
an greater reduction of mycelial growth up to 1 M concentration compared with
the chloride salts. Concentrations of potassium nitrate greater than 1 M did not
cause a further reduction in growth. Spore germination was significantly reduced
from 98% to approximately 2% by all three salts at concentrations of 1.5 M and
2.0 M. Since all three salts were effective, it cannot be only the potassium ion
or only the sodium ion which is responsible for reducing mycelial growth and
spore germination. It is possible that this reduction is caused by adverse
osmotic conditions.
Survival of Phytophthora infestans sporangia exposed to solar radiation Sporangia of Phytophthora infestans of the US-1 and US-8 clonal lineages were
collected from lesions and exposed to direct solar radiation (SR) and viability
assessed by germination. Exposures during a three-hour period from 800 to 1100,
from 1100 to 1400 or from 1400 to 1700 on sunny days (SR> 600 W/m2)
resulted in practically complete inhibition of germination after each exposure
period regardless of the time of the day. Sporangia were then exposed on sunny
or cloudy days (< 400 W/m2) from 1100 to 1400 with samples taken
at hourly intervals. In sunny days after one hour of exposure sporangia had low
germination levels. On overcast (SR < 300 W/m2) days survival
after three hours was only slightly reduced. On cloudy days the average ED95
of solar radiation was 7.7 MJ/m2 and the effective time (ET95)
necessary to inactivate 95% of the sporangia was 7.9h. On sunny days, one hour
exposure periods from 1100 to noon with samples taken at every 15 min confirmed
the previous results of reduced viability after one hour. Overall, on sunny days
the average ED95 was 2.8 MJ/m2 and ET95
was 1.1h. The ET95 of non-exposed sporangia was on average 16.8h.
These results suggest a differential effect of SR on cloudy days compared to
sunny days. Apparently sporangia of both clonal lineages were similarly
sensitive to solar radiation.
A Multiplex PCR method for the simultaneous detection of Tomato Yellow Leaf
Curl and Tomato Mottle geminiviruses
Protecting Brassica plants from Plasmodiophora brassicae CIH1, A biotrophy-related gene expressed specifically at the intracellular
interface formed between Colletotrichum lindemuthianum and French bean The rapid detection of Colletotrichum gloeosporioides in yam tubers by ELISA References
Experiences with blight forecasting The Smith period is the major late blight forecasting scheme available to UK
growers and provides recommendations, based on specific weather conditions, on
when to begin a protective fungicide spray programme. Warnings of impending
blight attack are issued by ADAS, using weather data from a selected set of the
Meteorological Office's synoptic network of weather stations. The stations are
widely separated and often located many miles from the major potato growing
areas which means that one station has to cover a large geographical area.
Within such an area the conditions experienced in many potato fields may be
quite different from those at the meteorological station leading either to false
alarms or, more seriously, a failure to warn sufficiently ahead of an outbreak
to allow sprays to be applied. Using frequently recorded in-crop weather data from each of five widely
dispersed locations during 1996-1997, the Blitecast, NEGFRY, Sparks, Ullrich
& Schrödter and Smith Period forecasting systems were evaluated with
respect to time of first blight warning, the first occurrence of blight and the
number of sprays recommended. No single system proved effective at all sites in
all years. The schemes varied widely in their ability to predict blight
infection particularly in the drier year of 1996. Furthermore the number of
applications recommended could be doubled or halved depending which scheme was
used despite being challenged with the same meteorological data.
Using disease survey data to develop schemes for predictinG epidemics of
light leaf spot (Pyrenopeziza brassicae) on winter oilseed rape in England and
Wales Data on incidence and severity of light leaf spot (Pyrenopeziza brassicae) of winter oilseed rape has been collected as part of the MAFF Winter Oilseed Rape Pest and Disease Survey since 1987. Light leaf spot is a serious disease of oilseed rape in the UK but the disease incidence and severity differ between regions and between seasons. During the last ten years the incidence of light leaf spot at pod ripening has varied between 5% and 46% plants affected with highest levels occurring in 1987, 1988 and 1994. Based on these data, annual yield losses, after fungicide application to control the disease, were estimated to range between £13M and £49M. Fungicide inputs to control diseases of oilseed rape have increased substantially since 1992 with costs exceeding £8M in 1996 when disease risk was relatively low. The extent of the losses during epidemics and the high costs of inputs clearly indicate the need for a forecasting scheme for this disease, not only to reduce yield losses but to reduce fungicide inputs in years with low disease risk. Analyses of the survey data indicated a strong link between the incidence of plants affected with light leaf spot on the pods and the subsequent incidence of plants with leaf infection at stem extension in the following spring. Disease levels in surveyed crops were greatly influenced by the timing of sprays to control light leaf spot. Sprays applied during mid-November proved most effective. The data were further analysed to identify additional seasonal and crop risk factors involved in outbreaks of light leaf spot. Analyses identified agronomic factors such as sowing date, cultivar and geographical location as important crop risk factors. These risk factors have been integrated into a predictive model to forecast epidemics of light leaf spot which can be used at a time when spray decisions need to be made. Meteorological factors have been recently included to improve accuracy of the model. Regional predictions made during 1996 for the 1997 growing season indicated that accurate forecasts were possible.
Dispersal of the mycoparasite Coniothyrium minitans by soil mesofauna
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