British Society for Plant Pathology

BSPP Presidential Meeting 1997

Plant Pathology - Global Perspectives of an Applied Science

Session II - Identifying the Problem

The role of extension services -agony and ecstacy
Dr Reuben Ausher
Ministry of Agriculture and Rural Development, Extension Service, P.O.Box 7054, Tel Aviv 61070, Israel

Extension Services are supposed to cover the whole technology development continuum, namely technology generation, diffusion and adoption. Further, they should convert data and information into knowledge and technologies. The classical growers/extension/research triangle is getting much more complex due to a proliferation of actors interacting with growers. Extension services should catalyze the conversion of subsistence farmers into commercial growers and finally into entrepreneurs. Most extension systems are either production, environment or community oriented. Adviser/advised ratios differ widely from 1:325 in Europe to 1:3500 in the Near East. Under intensive cropping systems there is an increased demand for advice to support both managerial and technical decisions. Agricultural extension faces a series of management and professional conflicts and crises. The crises debilitate extension organizations and they could dwindle and even collapse. Extension systems in the developing world are either managed by government (as community-, commodity-, integrated development and Training & Visit systems) or partially privatized and decentralized. In the industrialized world most systems are either government-managed, land-grant, grower-owned or privatized. The debate on the function of privatized extension (consulting) systems and the need for agricultural extension and R&D as public goods is still not resolved. The era of ideology and of rigid extension models adequate for the developing world is over. One central requirement has to be stressed in this context - professionalism.

Fortunately, extension faces new opportunities and is expected to develop leadership in areas such as Integrated Pest Management, computer-supported technologies, distant education. We feel new and clear front-line demand for integrated crop protection extension focusing on disease, pest and weed control; good understanding of crop husbandry, protection and marketing; wide range diagnostic capabilities; understanding of the whole range of chemical control, and application techniques; mastering supervised control, fully-fledged IPM, and biocontrol practices; specialization of crop protection extension by commodities.

Monitoring for disease in seed potato production
Dr Jane M. Chard
Scottish Agricultural Science Agency, East Craigs, Craigs Road, Edinburgh, EH12 8NJ

Monitoring for disease is an integral part of the Seed Potato Classification Scheme administered by the Scottish Office Agriculture, Environment and Fisheries Department in Scotland. The Scheme is based on visual assessment for disease and trueness to variety to meet tolerances specified in national regulations. Visual assessment is also used to monitor infection of stocks in the previous season.

Surveys are done to fulfil legislative requirements to confirm freedom from quarantine pathogens and also to monitor the occurrence of other pathogens in seed stocks. The data from such surveys, when compared with those of previous years, can reflect the impact of changes in technology or cultural practices.
Occasionally it is necessary to implement specific monitoring for diseases or their vectors. In Scotland an aphid monitoring scheme has been in operation since 1992. A reduction in virus incidence in stocks has been recorded following implementation of this measure.

Monitoring for diseases is a vital component of the seed potato production system in Scotland. For successful control of diseases within the Scheme, however, in addition to monitoring disease occurrence, measures and specified tolerances must be based on a sound knowledge of the biology and epidemiology of each pathogen.

Sustainable farming - are we getting there?
Prof. Martin S. Wolfe
Wakelyns Agroforestry, Fressingfield, Suffolk, IP21 5DS, England

A comprehensive concept of sustainable farming must take into account social, economic and environmental aspects of agriculture. However, the current structure of mainstream farming in Europe arose from the post Second World War policy that was directed to secure adequate food supplies at almost any cost. Subsidies and technological developments did secure a vast increase in some agricultural commodities. Unfortunately, this movement was based largely on monocultures supported by high levels of external inputs, often with unforeseen and far-reaching negative consequences. A wide range of technical solutions is now being applied to try to improve existing mainstream systems. However, in terms of long-term sustainability, there are strong arguments to suggest that this may be the wrong approach. Biological, economic and social reasoning indicates that a major alternative direction is to change towards greater diversity within farming systems. The basis for this view, some of the progress made so far and some implications for plant pathology, will be considered, together with some suggestions for further development.

The closed environment - a challenge to horticulture
Dr G Martin McPherson
Horticulture Research International, Cawood, Selby, North Yorkshire, YO8 0TZ, UK


Salad crops have been grown intensively under protection for many decades and production has increasingly relied heavily on fungicides to maintain control of both foliar and root infecting pathogens. The occurrence of persistent soil-borne root pathogens, e.g. Pyrenochaeta lycopersici, Phomopsis sclerotioides, largely uncontrolled by fungicides, stimulated the move into soil-less or hydroponic production systems. Partly as a consequence of this move into inert substrates, e.g. rockwool, the marketable yield and quality of tomato and cucumber crops improved dramatically.

In the last few years environmental issues have predominated and attention has been focused on the increased occurrence of pesticide residues in harvested produce and the threat of ground-water contamination by both fertilisers and pesticides in the run-off from these crops. The hydroponics industry, particularly in developed countries, are now looking to respond to retailer and consumer needs by developing 'closed' production systems to minimise both environmental pollution and pesticide inputs into salad crops.

Fungicides are used prophylactically in both the aerial and root environment of salad crops. The challenge for horticulture, as we move towards the next millennium, will be to develop sustainable production techniques which reduce pesticide use, minimise residues in food and which safeguard the environment for future generations. This must be achieved within a framework of continued economic production to deliver the quality of produce that the consumer has become accustomed.

The aerial environment

Significant advances have been made in the area of pest control in UK-grown protected salad crops and it is now unusual for any insecticides to be applied. Instead, natural enemies (predators) are routinely introduced to suppress pest populations. Yet, in these same crops, fungicides continue to be used routinely for the control of powdery mildew (Sphaerotheca fuliginea, Erysiphe sp.), grey mould (Botrytis cinerea) and stem rots (Didymella [Mycosphaerella] spp.) These fungicides potentially disrupt not only the predator-prey balance but also the epiphytic microflora and prevent the establishment of myco-parasites. We should, as pathologists, perhaps be a little disappointed that further progress has not been made to improve our understanding of the role, and possible antagonism, of the epiphytic microflora on leaf surfaces and at the same time established myco-parasites, e.g. Ampelomyces quisqualis 'AQ10', Sporothrix flocculosus, for use in this controlled environment. It should be acknowledged that, in the UK at least, one of the primary hurdles hindering progress in this area is the registration or authorisation process for 'bio-pesticides'.

The root environment. Currently, in most hydroponic crops, excess nutrient solution and the nitrates, phosphates, pesticides and any pathogen propagules it might contain, is discarded. This approach minimises the risk of disseminating pathogen spores though is perceived to be environmentally unfavourable. As production costs rise, the inefficient use of both water and fertiliser is encouraging growers to consider recirculation or 'closed' hydroponics technology.

It has been demonstrated that various root pathogens are disseminated widely in re-used hydroponic solution, although this can be effectively countered by adopting a strategy of solution disinfection, e.g. heat, UV, ozone, albeit at a significant cost. Interestingly, the rate of disease development in 'closed' hydroponic crops has been observed to be much slower than in equivalent 'open' culture systems. This has led to a series of hypotheses to account for the observed disease suppression. Collaborative studies are now paving the way towards a better understanding of the various plant-microbe interactions in the hydroponic root environment. The hope is that the observed suppressive mechanisms may be harnessed and utilised more fully to maintain disease control in these crops without resorting to prophylactic use of fungicides in the future.

Satellite imagery - avoiding muddy boots?
Dr Mike D Steven
University of Nottingham, Department of Geography, University Park, Nottingham NG7 2RD

Satellite imagery offers the opportunity to monitor the health of crops over a wide region, but to be useful for monitoring plant disease, it must satisfy certain preconditions:

  • The satellite observation must be significantly affected by the disease
  • Satellite data must be available at the critical times required.

Remote sensing systems operate from optical wavelengths, through the region of thermal emissions to microwave wavelengths. The best prospects for disease monitoring lie in detecting changes in leaf area or leaf pigmentation, which are susceptible to optical techniques, or in stomatal responses which can sometimes be detected thermally, or in canopy structural responses which may be detectable by radar. However, a difficulty with current orbiting systems is that the spatial resolution is not fine enough to measure the spatial patterns traditionally associated with crop disease monitoring from a Landsat image acquired six weeks earlier, suggesting that satellite imaging might offer a feasible approach in a less demanding climate.