Download Executive Summary of Final Report from final report as of December

Executive Summary of Final Report from final report as of December
1998:
1)
Epidemiology and forecasting of diseases on winter oilseed rape:
In field experiments, severe epidemics of light leaf spot or stem canker were
associated with autumn infection of leaves by the pathogens and could be
controlled only by autumn fungicide applications. Criteria for infection by
spores of light leaf spot or dark leaf/pod spot were established and
mathematical models of effects of temperature and leaf wetness duration
were made. A provisional scheme for forecasting, in the autumn, the risk of
severe light leaf sport epidemics the following spring included seasonal risk
indices on a regional basis and crop risk indices. A protocol was developed
for sampling crops to assess light leaf sport incidence so as to modify crop
risk indices from October to March.
2)
Detection of diseases in winter oilseed rape:
A method developed for diagnosis of light leaf spot on leaves without clear
symptoms involved incubation of suspect leaves in polyethylene bags at 1015oC for 3-4 days to produce diagnostic white pustules. Early in the season
the % plants with light leaf spot gave an adequate measurement of epidemic
progress. A molecular method for detection of light leaf spot is being
developed and molecular methods were used to show that stem canker
isolates from the UK were predominately aggressive. A prototype spore
sampler has been developed using monoclonal antibodies to detect spores of
grey mould or dark leaf sport collected from the air. These methods offer the
potential for developing novel techniques for early detection of the pathogen
as part of a disease forecasting scheme.
3)
Effects of disease: modelling disease severity/yield loss relationships.
In field experiments, yield responses were related to control of light leaf spot
or stem canker and descriptive yield loss models were derived to relate yield
loss to disease incidence on stems in June/July. A predictive yield loss model
was developed to forecast the yield loss from light leaf spot for use at early
stem extension, a time when fungicide spray can still be applied to decrease
the incidence of the disease. Data from field experiments on oilseed rape
since 1975 are being collated in the Electronic Rothamsted Archive for use to
improve the yield loss models.
4)
Biology and effects of diseases of linseed and minor oilseed crops:
The main disease problems on spring linseed were identified as grey mould
and leaf blight in seasons when weather between flowering and harvest was
wet. Powdery mildew and the soil-borne Verticillum were favoured when
weather was hot and dry at this time. Grey mould and leaf blight survived
between crops on infected debris and infected seeds. Spores of both
pathogens were dispersed by wind. Flowers and senescent capsules were
more susceptible to infection by grey mould than leaves or young capsules.
Amounts of head and stem rot in sunflower crops were related to
concentrations of air-borne Sclerotina ascospores during infection periods
several weeks earlier. Isolates of Verticillium from three different hosts (lupins,
linseed, sunflowers) were shown to be pathogenic to other hosts.
Future research priorities:
Further strategic work is needed on the biology and epidemiology of light leaf
spot and, especially stem canker on winter oilseed rape:-
1)
Factors influencing disease attacks early in autumn (which produce
several epidemics)
To define factors (temperature, wetness, light etc.) influencing the maturation
and release of ascospores of the two pathogens; To improve detection of airborne ascospores, perhaps using immunological or molecular diagnostic
methods, as part of an early warning scheme; To establish criteria
(temperature, wetness duration) for infection of oilseed rape leaves by
ascospores; To study the influence of temperature on spread of the stem
canker pathogen from leaf to stem (where it can no longer be controlled).
2)
Yield loss estimation (e.g. from autumn to summer)
To describe accurately disease severity/yield loss relationship (especially
between stem canker severity and yield loss); to improve prediction of stem
canker severity and yield loss by determining relationships between Phoma
leaf spot in autumn and stem canker in summer; to improve prediction of yield
loss from light leaf spot by estimating effects of leaf and plant death from light
leaf spot in winter; to construct models to predict the combined effects of stem
canker and light leaf spot on yield, in areas where both diseases occur, to
determine threshold amounts of disease (at the times when spray decisions
are made) which will result in economic damage.
3)
Forecasting and integrated disease management:
To improve the provisional scheme for forecasting the severity of light leaf
spot by incorporation of weather and disease severity factors in revising the
methods for calculating seasonal and crop risk indices, to develop a scheme
for forecasting the severity of stem canker epidemics, including seasonal and
crop risk indices. Ultimately, to construct an integrated scheme for
management of diseases on winter oilseed rape in the UK.