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SESSION 1 - Discovery - New horizons in plant pathology - page 24 / 65





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respected. Too often the growers trusting the efficacy of chemical control wait until the appearance of the first symptoms to start disease control. The most common approach to biological control consists in selecting effective antagonistic micro-organisms, studying the modes of action of these micro-organisms and then developing a biological control product. Despite progress made in the knowledge of the modes of action of these biological control agents, practical application of these BCAs fails to control disease in the field. One of the reason explaining this failure is that the bio-control product is used the same way as a chemical product. Being biological these products have to be applied in accordance to their ecological requirements. There is generally not enough research effort dealing with the environmental conditions required for the BCAs to establish on the plant organ to be protected and to express their antagonistic capacities. One may question the rightness of such an approach which is biological but not ecological and sustainable. Another approach, very fashionable today, is to utilize the induction of plant defence reactions. This can be done by application of natural substances produced by or extracted from either micro-organisms, plants, algae. Since they do not aim at killing the pathogens, these methods of disease control are totally different from chemical control, but, as the plant physiology is fundamentally involved, the environmental conditions required for full efficacy must be well defined. Today, most often the efficacy observed under laboratory conditions is not observed in nature. A third approach, much more difficult, consists in choosing cultural practices that might decrease the incidence or severity of diseases. These methods include the choice of the most adapted variety, the respect of a well balanced fertilisation, the choice of an appropriate crop rotation with management of the crop residues, application of organic amendments and the use of new technology such as the biological disinfestations of soils. Biological control practices need an integrative approach, as suggested by IOBC guidelines for integrated production. However, this integrated approach needs more knowledge, and more practice than chemical control.

Profiling and characterisation of microbial populations in peat samples considered suppressive and conducive for Pythium sylvaticum- induced damping-off.

Paul J. Hunter, Leo A. Calvo-Bado, Alun Morgan, Geoff Petch, Tim Pettit, John Whipps.

Warwick HRI, Wellesbourne, Warwick CV35 9EF, UK.

A cress seedling bioassay was used to classify a range of peats from different countries as either suppressive or conducive for damping-off induced by Pythium sylvaticum. An inverse correlation between microbial activity in the raw (unamended) peats and levels of P. sylvaticum was identified and peats which were designated as suppressive were found to generally have high levels of microbial activity. Molecular characterisation of peat samples representing the suppressive and conducive groups was carried out by DGGE profiling and cloning of regions of the bacterial 16S and fungal 18S rRNA genes. Bacterial population structures were similar in suppressive and conducive peats as were the fungal populations. However, considerable changes in the bacterial population profiles were detected during the process of conditioning the raw peat (a standard commercial practice) prior to use in the bioassay. In contrast, the fungal population profiles were similar at all stages of peat conditioning. Two DGGE bands from the fungal 18S amplification were, however, present in the suppressive peats but not detected in the conducive samples. These two bands were investigated further by sequencing, and comparison to sequence databases used to determine if similar species had any known properties as fungal inhibitors.

Isolation of Bacillus amyloliquefaciens from the infection court of tomato plants and its use alone and in combination with Bacillus brevis for biocontrol of Grey Mould.

Eunice Allan, Eftihia Tsomlexoglou, Ioanna Lazaraki and Barrie Seddon.

School of Biological Sciences, College of Medical and Life Sciences, Hilton Campus, University of Aberdeen, Aberdeen, AB24 4FA , Scotland, UK.

Three Bacillus isolates were selected from a broad ranging screening programme, based on in vitro and in planta assays, for antagonism against the grey mould pathogen Botrytis cinerea in a tomato glasshouse trial. A randomised block experimental design was used, with four replicates and five treatments (3 biocontrol agents and two controls), using 192 tomato plants. All the treatments were applied at 7-d intervals with sprayers. Disease assessment was carried out every 7 d in terms of percentage of infected leaves per plant, length of infected stems, number of infected flowers and rotten fruits as well as number of fruits showing ghost spot. Two isolates effectively reduced incidence of grey mould disease in all aerial parts of the tomato plants throughout the glasshouse trial while the third only gave control for the first five weeks. Incidence of ghost spot symptoms on tomato fruits was also reduced significantly by these two isolates. One isolate, identified as Bacillus amyloliquefaciens, showed better control of leaf infection. Bacillus brevis strain Nagano

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