The Soilborne Plant Diseases Unit of the Agricultural Research Council’s Plant Protection Research Institute hosted the 15th interdisciplinary symposium on soilborne plant diseases on 21 and 22 September 2005 at the Vredenburg Research Centre of the ARC-PPRI in Stellenbosch.
The topic for this year’s symposium was Ecology and Soilborne Plant Diseases and was attended by 65 representatives of Research Councils, National and Provincial Departments of Agriculture, private companies and universities. Participants represented a wide range of disciplines such as agronomy, botany, entomology, horticulture, microbiology, nematology, plant pathology, plant physiology and soil science.
Participants in the Symposium of the Soilborne Plant Diseases Interest Group included: front row, from left, J.C. Janse van Rensburg, A. Botha, A.J. Valentine, B.M. Molope, S.C. Lamprecht, M. Mazzola, P. Cadet, N.W. Mc Laren, L.V. Serage, H. Fourie, S.H. Koch; second row, A. Kleinert , S.G. Storey, A. Steyn, M.B. Von Wechmar, A. Swanepoel, R. Gouws, C.P. Millard, A. Jacobs, E.J. van der Linde, T.A.S. Aveling, M. Truter, E.N. Menzi, F.L. Phalane, C.L. Munro, T. Gevers, Z. Dawood, E.E. Bunting, M.C.E. Kellerman, L. van Schoor, K.J. Cloete; third row, P.T. Khoza, J. Bloem, C.M. Lubbe, A. Mc Leod, E. van Biljon, B. Janse van Rensburg, W.J. Laubscher, I. Tshivhandekano, B.C. Flett, A.H. Mc Donald, C. Mouton, S. Tweer, M. Daneel, H.J. Hugo; fourth row, N. Labuschagne, M.C. Pretorius, F.G.H. van Zyl, M.J. Southwood, R. Knoetze, S.D. Berry, Y.T. Tewoldemedhin, C.F.J. Spies, A. Viljoen, H.F. le Roux, G.J. van Coller, W.F. van Wyk.
The following aspects were introduced and discussed in depth: Root ecology: Interaction of roots with the environment. - Consideration of microbial ecology in the purported “biofumigation” response of Brassica soil amendments.
- Effect of a mixture of sugarcane varieties on nematode community composition and yield of sugarcane.
- The relationship between wilt diseases and nematodes of cotton.
- Nematodes as a factor in arable soil habitats.
- The ecology of the earthworm.
- The ecology of arbuscular mycorrhizal fungi.
- Potential use of soil microorganisms as indicators of soil quality and sustainability.
- The potential of the T-RFLP technique to assess changes in microbial diversity in soil.
- The use of reporter genes in microbial ecological studies.
Speakers at the symposium were: Front row, from left, Dr A.J. Valentine (Cape Peninsula University of Technology), Dr B.M. Molope (Group Executive Officer of Public Support Services, ARC), Dr S.C. Lamprecht (organiser, ARC-Plant Protection Research Institute), Prof. M. Mazzola (USDA-ARS, USA), Dr P. Cadet (Institute of Research for Development, France), Back row, from left, Ms A. Swanepoel (ARC-Institute for Industrial Crops), Ms C.P. Millard (ARC- Roodeplaat Vegetable and Ornamental Plant Institute), Prof. A. Botha (University of Stellenbosch), Prof. A.H. Mc Donald (ARC-Grain Crops Institute), Dr A. Mc Leod (University of Stellenbosch) and Ms J. Bloem (ARC-Plant Protection Research Institute).
Dr Alex Valentine of the Cape Peninsula University of Technology and Prof. Mark Mazzola of the USDA-ARS delivered keynote addresses.
Conclusions reached by the delegates to this symposium can be summarized as follows:
1. The study and understanding of the ecology of roots, i.e. the interaction between the biological, physical and environmental factors, and how they influence the productivity of plants, should be viewed as of crucial importance.
2. Plants live in a dual medium i.e. both aerial and subterranean, and there are interactions between these two environments. A change in the aerial environment can have significant effects on roots and visa versa.
3. Plant pathologists often refer to stress without taking into account the mechanisms or understanding the processes involved in stress and thus many potential disease control strategies could be overlooked.
4. Glucosinolate hydrolysis products can be important in the suppression of specific plant pests through the application of brassicaceous plant residues. However, it is apparent that other functional mechanisms operate in certain systems and that in several instances pest control is achieved irrespective of plant glucosinolate content. Understanding these underlying mechanisms is essential for the effective management of soilborne plant diseases.
5. Soil microorganisms play an important role in the maintenance of soil structure, soil fertility and soil health. Soil quality indicators (physical, chemical and biological) reflect how agricultural management practices influence the health of a particular soil. Applying this information could provide more cost-effective and environmentally acceptable management decisions that support sustainable agriculture.
6. Scaling down on chemical control of nematodes will cause significant increases in nematode-related crop damage. More information is needed to understand the intricate relationships between nematodes, host plants, other co-inhabitants of soils and the environment.
7. The need for biodiversity of nematodes in the control of plant parasitic nematodes was emphasized. It was suggested that pathogenicity is inversely proportional to nematode diversity and while the actual number of nematodes is not reduced, diversity does limit damage.
8. More research is warranted on the interaction of plant parasitic nematodes and other soilborne plant pathogenic organisms.
9. Future in depth research to investigate the ecological function of mycorrhizal symbiosis under ecologically realistic multi-functional conditions of the kind that prevail in nature is expedient.
10. The size and composition of earthworm communities in soils is greatly influenced by environmental and management factors including soil temperature, water content, soil texture, pH, tillage practice, addition of fertilizers and pesticides. Earthworm activity can significantly influence the physical, chemical and microbial properties of soils as well as the distribution of microorganisms within the soil. There is unfortunately a lack of information on the effect of earthworms on soilborne plant diseases.
11. Several methods are available to detect changes in the biological status of soils and these may provide an early warning of negative impacts on soil health and allow timely interventions.
12. Reporter genes are particularly effective in studying the mode of infection of host tissues by pathogenic organisms and have been used to quantify the activity and efficacy of biocontrol agents.
13. The importance of a multidisciplinary approach to soilborne plant diseases was again emphasized. Not only scientists but decision makers and particularly funders must take cognizance.
14. Understanding biological communities, the dynamics of their physical and chemical environments, the underlying interactions between these systems and the mechanisms of the interactions, is critical to develop sustainable disease management strategies against soilborne plant diseases. |
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