belonging to Clavibacter, Curtobacterium and Rhodococcus and Erwinia, Xanthomonas, Ralstonia and Agrobacterium genera, respectively. A reduced effect was observed in the case of the fennel oil. The availability of new active principles such as essential oils appear promising for their possible use in the crop protection from plant bacterial diseases either in the field or, in particular, to eradicate and/or protect seeds from the above pathogens. This is particularly appealing in bio-organic agriculture. Furthermore, the significant antibacterial activity of essential oils toward the bacterial pathogens of mushrooms suggest the possibility to use the substances also on this crop. Of course, other studies are necessary to evaluate the toxicity of the substances of interest toward seeds and/or plants as well as mushrooms and to point out appropriate formulations useful for the purposes.
Mechanisms in biocontrol of Botrytis cinerea on Arabidopsis thaliana and crop plants by various protective bacteria.
Henk-jan Schoonbeek1,2, Anne-Claude Jacquat1, Emmanuel Boutet1, Maarten A. de Waard2 and Jean-Pierre Métraux1.
1 Plant Biology, rue Albert Gockel 3, CH-1700, Fribourg, Switzerland
2 Laboratory for Plant Pathology, Wageningen University, Binnenhaven 5, Wageningen, The Netherlands.
Botrytis cinerea is a widespread plant pathogenic fungus causing grey mould disease on a very broad host range. It causes billions of yield loss on crop plants such as gerberas, roses, strawberries, cucumber, tomato and grapes, and is subject to various disease control measures. Since chemical control is hampered by rapid development of fungicide resistance, biological control has drawn attention over the years. Fungi, yeasts and bacteria have already been found to exert a protective effect against B. cinerea, although they provided more often than not only partial reduction of disease symptoms. We tried to compare the efficacy of various bacteria with a different mode of action in B. cinerea control. Therefore, the role of antibiotics, induction of induced resistance and degradation of oxalate was studied in Pseudomonas chlororaphis, P. fluorescens and Wautersia campinensis. The P. chlororaphis strain PCL1391 has been described as a biocontrol agent working antagonistically against soil born diseases. One of the main factors contributing to protection is the production of antibiotics such as 2,4-DAPG, pyrrolnitrin and phenazines. Application of these bacteria on the surface of tomato plants could also provide some protection against B. cinerea. The in vitro antagonism of these antibiotics against B. cinerea is rather weak, and we found that they induce the expression of ABC transporters in the fungus. BcatrB, an ABC transporter involved in multidrug resistance, can also export phenazines, thus protect the fungus against these antibiotics, and render the plant-protection mechanism of antagonistic bacteria unusable. The plant growth promoting bacterium P. fluorescens CHA0 has been described to provide protection against both root and leaf pathogens when applied to roots, sometimes via induced resistance. They use the ethylene and jasmonic acid dependent pathway to provide Induced Systemic Resistance (ISR) against Hyaloperonospora parasitica in Arabidopsis thaliana. However, ISR was not functional in Arabidopsis when CHA0 was applied to the roots and the leaves were challenged with B. cinerea. In an attempt to deprive the pathogen of one of its virulence factors, we focussed on oxalic acid. B. cinerea and the related white rot fungus Sclerotinia sclerotiorum produce oxalic acid at the onset if infection to chelate Ca2+, disrupt the cell wall structure, lower the pH, and set the conditions for concerted action of cell wall degrading enzymes and other virulence factors. We have performed a screening of bacteria found in Swiss agricultural soil to find bacteria that are able to degrade oxalic acid. Of 42 isolates that could degrade oxalic acid on agar, four were selected that also provided protection of A. thaliana against B. cinerea. The degree of protection provided by W. campinensis Ox-strain B after spraying on leaves of A. thaliana, cucumber, tomato and grapevine is between 35 and 60% reduction of lesion size. Pilot experiments indicate that these bacteria are also able to protect grape berries under field conditions against grey mould. In conclusion, we can say that different mechanisms exerted by biocontrol bacteria only provide partial control of grey mould and that combination of these traits may render a more efficient strategy.
Effect of seed treatment of winter wheat with the biopreparation Supresivit or with the chemical dressing Panoctine 35 on occurrence of fungi of the Fusarium genus in the soil and on plant infestation of differently susceptible cultivars
Research Institute of Crop Production, Drnovská 507, Prague 6 - Ruzyne, Czech Republic
Winter wheat varieties Sida, Siria, Livia and Arina were grown in field trials conducted on fields in RICP Praque-Ruzyně. The variants were founded in four replications and were configured randomly. The biopreparation Supresivit, containing conidia of the mycoparasitic fungus Trichoderma harzianum, was applied onto the seeds of winter wheat before sowing. The doses of biopreparations used in the experiments were recommended by producers in the Checklist of registered plant protection means. The efficacy of biopreparations was compared with standard chemical treatments with Panoctine 35 (quazatine). Monitoring of fungal diseases of the crop in the field was carried out during the entire season from sowing to harvest. Visual monitoring of infection stress and plant infestation was monitored along with collection of samples for laboratory tests. The monitoring of soil mycoflora changes was performed during the entire season using the methods of soil dissemination described by Komada (1976). Samples of a surface layer of the soil were collected from the field for every experimental variant and replication for every month during the growth of the crop. Winter wheat cultivation in the same field led to increased occurrence of Fusarium spp. in the soil during the three years. The seed treatment with the biological preparation Supresivit and the chemical dressing Panoctine 35 reduced this trend. Repeated introduction of T. harzianum conidia into the soil as a seed treatment acted by decreasing Fusarium spp.